Development and characterization of ductile polylactic acid blends with plasticized zein for injection molding applications

Development and characterization of ductile polylactic acid blends with plasticized zein for injection molding applications | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Development and characterization of ductile polylactic acid blends with plasticized zein for injection molding applications Carlos Lazaro-Hdez, Mario Miranda-Pinzon, Maria del Puig Vicente-Vinas, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7869492/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 27 Mar, 2026 Read the published version in Journal of Polymers and the Environment → Version 1 posted 18 You are reading this latest preprint version Abstract This study explores the development of polylactic acid (PLA) blends incorporating plasticized zein, a corn-derived protein, and dipropylene glycol (DPG) as a biobased plasticizer to enhance compatibility and processability. Blends were produced via twin-screw extrusion and injection molding, with plasticized zein content ranging from 10 to 50 wt%. Mechanical testing showed a significant increase in ductility, with elongation at break rising from 6.3% (neat PLA) to 56.3% (50 wt% zein), accompanied by reduced tensile strength (58.4 MPa to 22.7 MPa) and impact resistance (42.2 kJ/m 2 to 11.5 kJ/m 2 ), due to phase separation and limited compatibility. Shore D hardness slightly declined (from 82.9 to 77.4). Thermal analysis revealed a single glass transition temperature (T g ) in all blends, indicating partial miscibility, with T g decreasing from 59.5°C to 39.9°C as zein content increased. Thermogravimetric analysis showed reduced thermal stability with zein addition, dropping the initial degradation temperature from 360.0°C to 188.2°C. Morphological analysis indicated greater heterogeneity at higher zein levels due to partial miscibility. Colorimetric data showed visible changes, and FTIR spectra confirmed physical interactions and partial miscibility between PLA and zein. Polylactic acid Zein Dipropylene glycol Blend Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1 Introduction The widespread reliance on non-renewable, petroleum-based polymers has raised critical concerns regarding environmental sustainability [ 1 ]. Once polymer-based products are discarded, they can remain in the environment for extended periods, significantly contributing to waste accumulation and ecosystem degradation [ 2 ]. This issue is especially pronounced in industries such as food packaging, where single-use items are commonly produced. Due to the high consumption of these products, substantial volumes of waste are generated. Often these products have a very short life cycles and limited opportunities for effective management [ 3 ]. In response to growing awareness of the ecological impact of petroleum-derived plastics, considerable efforts have been devoted to the development and implementation of more sustainable, bio-based alternatives [ 4 ]. Biopolymers, derived from renewable resources, are being explored as promising candidates to replace conventional plastics [ 5 ]. These materials are valued for their biodegradability, renewability, and, in many cases, their biocompatibility. Among the most studied are polylactic acid (PLA), polyhydroxyalkanoates (PHA), thermoplastic starch (TPS), and polymers derived from other starch-based sources [ 6 , 7 ]. Protein-based biopolymers, obtained from crops such as soy and maize, are also gaining attention due to their potential in creating environmentally friendly materials [ 8 , 9 ]. One of the most widely used bio-based polymers globally is PLA, a thermoplastic synthesized from lactic acid, typically obtained by means of fermentation of starch-rich feedstocks such as corn or sugarcane [ 10 , 11 ]. PLA is known for its good mechanical strength, ease of processing, and non-toxic degradation, making it suitable for use in sectors such as packaging, automotive components, and biomedical applications [ 12 – 14 ]. However, despite these advantages, PLA exhibits certain limitations, including brittleness and low impact resistance [ 15 ]. Various strategies have been employed to overcome these drawbacks, such as the addition of fillers, polymer blending, and the incorporation of plasticizers [ 16 , 17 ]. Among these, polymer blending stands out for its ability to combine properties from different materials. However, challenges related to miscibility can arise, leading to suboptimal performance in the final material [ 18 ]. Protein-based biopolymers, such as those derived from soy or zein, have shown potential for blending with PLA [ 19 – 21 ]. These materials are particularly appealing to the food industry due to their ability to disintegrate through biodegradation, as well as their biocompatibility, which allows for safe contact with the human body. Nevertheless, they also present issues, including poor mechanical strength, low thermal stability, and limited processability. In efforts to enhance their performance, blending with more robust bio-based polymers like PLA is being explored [ 19 , 20 ]. Zein, a protein extracted as a byproduct from the corn industry, has emerged as a promising candidate for such blends [ 22 , 23 ]. Despite its potential, zein is inherently rigid and brittle and poses difficulties during processing, especially under extrusion or injection molding conditions [ 24 ]. To address these challenges, the use of plasticizers is essential. Plasticizers help reduce intermolecular forces within the polymer structure, increasing flexibility and enhancing processability [ 25 ]. Selecting an appropriate plasticizer is critical to achieving effective plasticization. Commonly used plasticizers for zein include glycerol (GLY) [ 26 ], oleic acid (OA) [ 27 ], polyethylene glycol (PEG) [ 28 ], and dipropylene glycol (DPG) [ 29 ], among others. DPG belongs to the glycol family and contains two hydroxyl groups (–OH), which can interact with the hydrophilic groups in zein, thereby improving its flexibility [ 30 ]. Furthermore, in PLA-zein blends, the plasticizer plays a crucial role not only in softening zein but also in promoting compatibility between the two phases. This study focuses on the development and comprehensive characterization of plasticized PLA-zein blends. Zein, derived from maize, was incorporated into PLA matrices at varying concentrations, with dipropylene glycol (DPG) used as a plasticizer to improve both the compatibility and processability of the system. The materials were compounded using twin-screw extrusion and shaped through injection molding to produce the test specimens. A broad range of characterization techniques was applied to evaluate properties such as the mechanical, thermomechanical, morphological, and colorimetric properties of the prepared blends. Particular attention was given to the influence of DPG on the dispersion of zein within the PLA matrix and its role in modifying the structural and functional behavior of the resulting materials. The findings from this investigation provide meaningful insights into the performance of DPG plasticized PLA-zein systems and support their potential application in environmentally responsible packaging solutions and other biodegradable material markets. 2 Experimental 2.1 Materials The biopolymer was employed in this study was polylactic acid (PLA), acquired from Ercros (Barcelona, Spain), specifically ErcrosBio LL 712. This grade of PLA exhibits a mass flow rate of 4 g/10 min (ISO 1133-A 190 ºC and 2.16 kg). Zein was obtained in powder form from Sigma-Aldrich (CAS No.: 9010-66-6), with a moisture content below 8%. Prior to processing, both materials underwent drying for 8 hours at 80°C employing an MDEO dehumidifier manufactured by Industrial Marsé (Barcelona, Spain). The plasticizer utilized was dipropylene glycol (DPG), with 134.18 g/mol molecular weight and a purification level exceeded 95%, and was procured from Tokyo Chemical Industry Co., LTD (TCI EUROPE) (Zwijndrecht, Belgium). 2.2 Compounding of multiple formulations The materials were compounded employing a twin-screw extruder, in a Xplore Micro Compounder MC-40 (Sittard, The Netherlands). The initial step involved processing the zein + DPG (coded as Z) mixture at 130°C for 1 min. This blend was then pelletized using an air-cutting unit. Subsequently, neat PLA was processed independently at 180°C for 1 min. Finally, the formulations containing PLA and plasticized zein (Z) were extruded at 170°C for 1 min. In all cases, the screw speed was controlled at 100 rpm with a maximum torque of 40 N m. The nomenclature and the specific quantities used in the preparation of these formulations are presented in the following table. Table 1 Composition and coding of the PLA blends with plasticized zein. Code PLA (wt%) zein + DPG (wt%) zein (wt%) DPG (wt%) Z (zein + DPG) - - 75 25 PLA 100 - - - 90P-10Z 90 10 - - 80P-20Z 80 20 - - 70P-30Z 70 30 - - 60P-40Z 60 40 - - 50P-50Z 50 50 - - 2.3 Sample injection Normalized injection-molded specimens were produced using an Xplore Injection Moulder IM12 (Sittard, The Netherlands). Different injection conditions were applied depending on the formulation. For PLA, a nozzle temperature of 180°C, a mold temperature of 35°C, and an injection pressure of 8 bar were used for 7 s, followed by a packing time of 3 s. For the formulations containing plasticized zein, the nozzle temperature was set to 170°C, with the mold maintained at 35°C, an injection pressure of 6 bar was applied for 7 s, and 3 s of packing. 2.4 Mechanical behavior analysis Three separate tests were performed for the assessment of the mechanical properties. Tensile properties were evaluated using a universal testing machine, the IBERTEST ELIB-50 from S.A.E. Ibertest (Madrid, Spain), with a 10 kN load cell and operated at a crosshead speed of 10 mm/min. Specimens were prepared according to ISO 527-2:2012 using type 1BA geometry. Charpy impact resistance was assessed following ISO 179-1:2010, using specimens measuring 80×10×4 mm³ and tested with a 6 J pendulum impact tester from Metrotec S.A. (San Sebastian, Spain). Shore D hardness was measured using a 637-D durometer from Instruments J. Bot S.A. (Barcelona, Spain), in compliance with ISO 868, allowing a stabilization period of 30 s before reading. All reported values represent the average of five replicates. 2.5 Thermal behavior analysis Differential scanning calorimetry (DSC) was employed to analyze the thermal behavior of the samples, on a DSC 25 unit from TA Instruments (Delaware, DE, USA). The analysis included multiple thermal cycles: an initial heating from − 50°C to 200°C at a rate of 10°C/min to eliminate any residual thermal history, followed by a cooling cycle from 200°C to -50°C at -10°C/min. A second heating cycle from − 50°C to 200°C at 10°C/min was then conducted to identify all relevant thermal transitions. A nitrogen atmosphere at 50 mL/min was used throughout the tests to inhibit oxidative degradation. The degree of crystallinity (X c ) was determined using Eq. 1: ΔH m and ΔH cc (J/g) represent the melting enthalpy and cold crystallization enthalpy, respectively. The theoretical value of \(\:{\varDelta\:\text{H}}_{\text{m}}^{0}\) (J/g), corresponding to 100% crystalline PLA, was taken as 93.0 J/g according to the literature [ 31 ]. The variable w denotes the weight fraction of total additives present in the PLA blends. Thermogravimetric analysis (TGA) was employed to assess the thermal stability of the samples, using a TG-DSC2, by Mettler-Toledo (Columbus, OH, USA). The thermal behavior was examined by heating the specimens from 30°C to 700°C at a constant rate of 20°C/min under an oxygen flow of 50 mL/min. To ensure reproducibility and accuracy, all formulations were tested in triplicate. 2.6 Thermomechanical behavior analysis Dynamic mechanical thermal analysis (DMTA) was carried out to evaluate the mechanical behavior of the samples under thermal and dynamic conditions, the equipment used was Mettler-Toledo DTMT1 (Columbus, OH, USA). Specimens measuring 20×4×2 mm³ were subjected to a heating cycle from − 100°C to 100°C at increments of 2°C/min. The tests were conducted under dynamic loading at a frequency of 1 Hz, with a maximum displacement amplitude of 10 µm. Thermomechanical analysis (TMA) was employed to evaluate the dimensional stability of the materials using a Q400 instrument from TA Instruments (New Castle, DE, USA). Samples with dimensions of 10×10×4 mm³ were heated from − 70°C to 70°C at a rate of 2°C/min was applied in an air atmosphere, under a constant load of 0.02 N. 2.7 Color characterization Colorimetric properties were evaluated using a KONICA CM-3600d Colorflex-DIFF2 spectrophotometer from Hunter Associates Laboratory (Reston, VA, USA), based on the CIELab color scale [ 32 ]. Ten measurements were taken to determine the L *, a *, and b * coordinates, where L * represents lightness, a * corresponds to the red-green axis, and b * indicates the yellow-blue axis. The total color difference, \(\:{\varDelta\:E}_{ab}^{*}\) , was calculated using Eq. 2. Where Δ L *, Δ a *, and Δ b * represent the differences between the color coordinates of the samples and those of the reference. Color variation was evaluated according to the following criteria: unnoticeable difference ( \(\:{\varDelta\:E}_{ab}^{*}\) < 1), perceptible only to a trained observer ( \(\:{\varDelta\:E}_{ab}^{*}\) ≥ 1 and < 2), noticeable by an untrained observer ( \(\:{\varDelta\:E}_{ab}^{*}\) ≥ 2 and < 3.5), and clearly noticeable by all observers ( \(\:{\varDelta\:E}_{ab}^{*}\) ≥ 3.5 and < 5) [ 33 ]. 2.8 Fracture surface analysis Fractured surface morphology of the charpy test specimens was examined using a ZEISS ULTRA 55 microscope from Oxford Instruments (Abingdon, UK) operating at an acceleration voltage of 3 kV. Prior to imaging, a gold–palladium coating was applied using a SC7620 sputter coater from Quorum Technologies Ltd. (East Sussex, UK). 2.9 Chemical characterization of the processed formulations FTIR analysis was carried out using a Vector 22 spectrometer from Bruker S.A. (Madrid, Spain), equipped with a PIKE MIRacle single-reflection diamond ATR accessory from PIKE Technologies (Madison, USA). Each sample was scanned 10 times with a spectral resolution of 4 cm⁻¹ over a wavelength range of 4000 to 600 cm⁻¹. 3 Results and discussion 3.1 Mechanical behavior of PLA–zein blends. The mechanical behavior of the processed samples containing different percentages of plasticized zein was evaluated using tensile testing, Charpy impact testing, and Shore D hardness measurements, as summarized in Fig. 1 . Figure 1 a-c presents the results obtained from the tensile test. The results for PLA samples are consistent with those reported in numerous studies involving injection-molded samples [ 34 ]. The material exhibited a high maximum tensile strength and a high elastic modulus, along with low elongation at break, this behavior is characteristic of rigid materials. Regarding the mechanical properties of the PLA-zein blends, it is important to consider that their behavior is strongly influenced by their morphology, which will be discussed later. Figure 1 a-c illustrates a clear trend, as the amount of plasticized zein increases, both tensile strength and elastic modulus decrease while elongation at break increases. Similar behavior was observed in the study conducted by Bo Liu et.al. [ 35 ], where blends of PLA with plasticized soy protein (SP) showed a reduction in mechanical strength and a partial improvement in elongation with increasing soy content. The highest elongation at break values were recorded for the 60P–40Z and 50P–50Z blends, reaching 25.5% and 56.2%, respectively. These samples also exhibited tensile strengths around 33 MPa and an elastic modulus of approximately 2100 MPa, indicating a reduction in both stiffness and strength. This effect is attributed to the increased amount of plasticizer in the final formulations. As more zein is incorporated into the PLA matrix, the overall plasticizer content also rises. The plasticizer molecules intercalate between PLA chains, enhancing chain mobility and facilitating their displacement. This plasticizing effect has been widely reported in the literature [ 34 , 36 , 37 ] . In terms of impact testing, it can be observed that the incorporation of plasticized zein leads to embrittlement of the samples. As the percentage increases, the impact strength decreases, as shown in Fig. 1 d. A similar trend was reported in the study by Rui Zhu et.al [ 38 ], where increasing amounts of SP in PLA resulted in reduced impact resistance. This embrittlement may be attributed to the higher concentration of particles formed by the agglomeration of plasticized zein within the PLA matrix, as noted in the research by Bo Liu et.al. [ 35 ]. Finally, the hardness test results show similar values across the samples, indicating that the addition of plasticized zein does not significantly affect hardness. However, a slight decrease in hardness can be observed as the plasticized zein content increases. This reduction may be attributed to the presence of the plasticizer, as discussed earlier, which contributes to improved ductile behavior. 3.2 Thermal behavior of PLA–zein blends. The thermal behavior of the PLA–zein blends was analyzed through a dynamic DSC test. Three different stages were scheduled and the analysis emphasized the intermediate cooling stage and the second heating cycle. Figure 2 displays the corresponding DSC thermograms, and the main thermal parameters are represented in Table 2 . TGA was utilized to examine the thermal stability and decomposition profile of the materials by subjecting them to a single controlled heating cycle. The results of this analysis are presented in Fig. 3 . DSC analysis was used to obtain the characteristic thermal transitions of the processed formulations. One of the most relevant transitions is the glass transition temperature (T g ), which marks the point at which the material shifts from a rigid solid to a rubbery state. In this case, neat PLA exhibited a T g of 59.5°C, a value consistent with those reported in the literature. However, the incorporation of zein + DPG led to a noticeable decrease in T g , reaching 39.9°C for the 50P–50Z blend. This trend indicates that increasing the zein + DPG content results in a progressive reduction of T g , bringing it closer to room temperature, which justifies the improvement in ductility. A similar effect was reported by Shengzhe Yang et.al. [ 39 ], who observed a reduction in T g with higher amounts of SP in PLA based blends. They also noted that the presence of a single T g in each formulation suggests partial miscibility between components, since immiscible systems would typically exhibit two separate glass transitions. In the present study, each formulation displayed only one T g , supporting the conclusion of partial miscibility. This reduction can be explained by the inherently low T g values of plasticized zein. According to Rojas-Lema et al. [ 21 ], zein plasticized with 25 wt% glycerol exhibited a T g of 38.3°C. Therefore, the combination of PLA with increasing amounts of plasticized zein significantly lowers the overall T g of the blends. Additionally, the plasticizer contributes to this effect by inserting itself between polymer chains, reducing intermolecular forces and facilitating chain mobility. This mechanism, often described as a lubricating effect, has been widely reported in the literature [ 21 , 40 , 41 ]. Another relevant thermal transition is the cold crystallization temperature (T cc ), which is shown in Fig. 2 b. A decrease in T cc is observed, promoted by the addition of plasticized zein [ 42 ]. Additionally, the area under the curve, which corresponds to the enthalpy of crystallization (ΔH cc ), also decreases. This reduction is attributed to the increasing zein content, as zein is an amorphous material that does not undergo crystallization. Therefore, only the PLA phase contributes to the crystallization process. Regarding the melting temperature (T m ), Table 2 shows that T m decreases as the plasticized zein content increases. Additionally, the appearance of two melting peaks is observed. The appearance of multiple melting peaks is associated with the formation of various types of crystals of PLA; fewer perfect crystals melt at lower temperatures, while crystals with greater structural order tend to melt at elevated temperatures. The incorporation of plasticized zein promotes the formation of these crystal types in the matrix of PLA. A similar behavior was reported by Wen Zhang et al. [ 20 ], who observed dual melting peaks in PLA–SP blends at various ratios and noted that the addition of SP induces the formation of distinct crystalline structures. At this temperature, as in the previous case, only PLA contributes to the melting behavior, making it solely responsible for the observed melting peak. Consequently, Table 3 shows a reduction in the melting enthalpy (ΔH m ), which corresponds to the decreasing PLA content in the formulations. Regarding the degree of crystallinity (X c ) of the blends, an increase is observed as the content of zein + DPG rises. This is attributed to the fact that although the amount of PLA, the phase capable of reorganizing to crystallize, decreases, the proportion of plasticizer used to plasticize the zein increases. As the plasticizer is incorporated between PLA chains, it enhances chain mobility and facilitates tighter packing, leading to a higher degree of crystallinity. Garcia-Garcia et al. [ 43 ] reported similar findings, demonstrating that increasing the plasticizer content in PLA improves chain rearrangement and consequently enhances crystallinity. Table 2 Thermal properties of the PLA–zein blends obtained from the second heating cycle of the DSC test include: glass transition temperature (T g ), cold crystallization temperature peak (T cc ), first melting temperature peak (T m1 ), second melting temperature peak (T m2 ), cold crystallization enthalpy (ΔH cc ), melt enthalpy (ΔH m ), and degree of crystallinity (X c ). Code T g (°C) T cc (°C) T m1 (°C) T m2 (°C) ΔH cc (J/g) ΔH m (J/g) X c (%) PLA 59.5 ± 0.3 114.4 ± 0.2 - 151.4 ± 0.4 25.5 ± 0.5 29.9 ± 0.4 4.7 ± 0.4 90P-10Z 55.4 ± 0.3 106.4 ± 0.3 148.1 ± 0.2 156.0 ± 0.5 26.8 ± 0.4 32.6 ± 0.3 6.9 ± 0.2 80P-20Z 51.0 ± 0.2 105.9 ± 0.3 148.3 ± 0.2 155.2 ± 0.2 23.4 ± 0.3 30.6 ± 0.3 9.7 ± 0.3 70P-30Z 45.3 ± 0.4 110.8 ± 0.4 143.9 ± 0.4 150.9 ± 0.4 18.7 ± 0.2 25.5 ± 0.4 10.5 ± 0.2 60P-40Z 43.4 ± 0.3 102.9 ± 0.2 141.3 ± 0.3 150.8 ± 0.3 15.3 ± 0.1 22.3 ± 0.3 12.5 ± 0.4 50Z-50P 39.9 ± 0.5 92.9 ± 0.3 135.3 ± 0.3 147.6 ± 0.5 14.3 ± 0.3 23.1 ± 0.5 18.9 ± 0.3 In TGA analysis, the onset of thermal degradation is commonly defined in the literature as the temperature at which a 5% mass reduction occurs [ 44 ]. Table 3 presents the onset degradation temperature (T₅ % ) for the different formulations. Figure 3 a displays the TGA curves of the processed materials. For neat PLA, a single degradation slope is observed. However, when plasticized zein is added, up to three distinct slopes appear, corresponding to the degradation of both zein and the plasticizer, due to their limited thermal stability. In the 90P–10Z and 80P–20Z blends, only two slopes are visible, as the degradation of DPG and zein overlaps due to their low concentrations. In contrast, the remaining formulations show three distinguishable slopes, which can be interpreted as follows. First slope, occurring in the range of 150°C and 220°C, is associated with the degradation of the plasticizer, which is known for its high volatility and low thermal stability [ 45 ]. Second slope corresponds to the degradation of zein, which is more thermally stable than DPG but less than PLA, and occurs between 220°C and 350°C [ 21 ]; the final slope corresponds to the thermal degradation of PLA. The highest T₅% value is observed for neat PLA, indicating its superior thermal stability compared to the blends. As the proportion of plasticized zein increases, the T₅% decreases, reaching 188.2°C for the 50P–50Z blend. This demonstrates that the addition of zein + DPG reduces the overall thermal stability and significantly lowers the degradation temperature. Figure 3 b shows the first derivative of the TGA curves, which identifies the temperature at which the degradation rate is at its maximum. These curves confirm the observations from the T₅ % data, with multiple peaks corresponding to the degradation of the individual components. Neat PLA shows only one main degradation peak, while the formulations containing plasticized zein exhibit several. A similar trend was reported by Gonzalez et al. [ 46 ], who studied PLA blends with SP plasticized with glycerol and observed multiple degradation events due to the different thermal stabilities of the components. Finally, Table 3 shows that the residual mass at the end of the test increases with higher zein + DPG content. Similar behavior has been reported in the literature [ 47 , 48 ]. Table 3 Thermogravimetric properties derived from the TGA test include: onset of degradation temperature (T 5% ), maximum degradation rate temperature (T max ), and residual mass (%). Code T 5% (ᵒC) T max (ᵒC) % Residual mass PLA 360.0 ± 1.3 389.3 ± 0.8 4.6 ± 0.3 90P-10Z 325.2 ± 1.0 362.3 ± 0.7 9.6 ± 0.6 80P-20Z 286.2 ± 0.9 345.5 ± 0.5 11.1 ± 0.8 70P-30Z 245.0 ± 1.2 336.1 ± 0.6 13.0 ± 1.0 60P-40Z 189.9 ± 1.0 335.8 ± 0.5 13.0 ± 0.9 50Z-50P 188.2 ± 1.1 335.1 ± 0.8 15.1 ± 1.1 3.3 Dynamic-mechanical thermal analysis of PLA–zein blends. The samples were evaluated through DMTA t for a range of temperatures to determine their dynamic mechanical behavior. TMA was conducted to evaluate the influence of temperature on the dimensional stability of the samples. Table 4 presents the storage modulus (E') at 0°C and 25°C, obtained from the DMTA test. Also, the coefficient of linear thermal expansion (CTLE) measured by means of TMA is studied. Table 4 Thermomechanical properties obtained from the DMTA test E' at 0°C and 25°C and CTLE by means of TMA. Code E' at 0°C (MPa) E' at 25°C (MPa) CTLE below Tg (mm/m·°C) CTLE above Tg (mm/m·°C) PLA 2059 ± 31 1970 ± 26 85 ± 5 1440 ± 15 90P-10Z 2021 ± 32 1904 ± 24 54 ± 6 924 ± 16 80P-20Z 2064 ± 23 1851 ± 17 93 ± 10 506 ± 12 70P-30Z 2058 ± 34 1768 ± 21 109 ± 14 369 ± 8 60P-40Z 1869 ± 34 1502 ± 18 100 ± 15 603 ± 9 50Z-50P 1779 ± 30 1283 ± 23 119 ± 12 2455 ± 13 The DMTA is especially effective in identifying variations in mechanical properties relative to temperature changes. Temperature plays a critical role in determining the behavior of polymeric materials. Above the T g , the material undergoes a shift from a rigid solid to a solid rubbery. As shown in Fig. 4 , a clear change in behavior is observed in the samples above this transition. Regarding the E’, its values approach 0 MPa as the material nears T g , reflecting the pronounced transition from a solid to a rubber-like phase at this temperature [ 49 ]. As shown in Fig. 4 a, increasing the plasticized zein content has a significant effect on the E'. High concentrations, such as in the 60P–40Z and 50P–50Z blends, exhibit values nearing 0 MPa even before reaching their T g . This behavior is likely due to increased polymer chain mobility caused by the presence of the plasticizer, which increases the free volume and facilitates molecular movement. Additionally, the higher plasticized zein content contributes to this effect, as zein is an entirely amorphous material, and amorphous components require less energy to initiate molecular motion [ 50 ]. A similar phenomenon was reported by Shengzhe Yang et al. [ 39 ], who observed a decrease in E' values with increasing SP content in PLA–SP blends. Moreover, a noticeable change in thermal stability is observed across the formulations. As the proportion of plasticized zein increases, the plateau region before the transition becomes shorter, indicating a gradual and less abrupt change in material behavior. This trend suggests reduced thermal stability, which is also evident in Table 4 , where samples with higher plasticized zein content exhibit a greater reduction in E' between 0°C and 25°C. Regarding the damping factor (tan δ), the peak values shift toward lower temperatures as the plasticized zein content increases. This shift confirms the reduction in T g with higher plasticizer and zein content, as previously observed in the DSC analysis. The decrease in T g is a result of the combined effect of the plasticizer, which enhances molecular mobility, and the amorphous nature of zein. The temperatures obtained in this test were consistent with those measured by DSC, supporting the validity of the results. Furthermore, only one peak was observed for each formulation, indicating a certain degree of miscibility between the components, Fig. 4 b. Dimensional stability was evaluated using TMA, which enables the assessment of dimensional changes in the processed blends as a function of temperature. As shown in Fig. 5 , two distinct regions can be identified: the first extends from the beginning of the test to approximately 45°C, where a linear relationship is observed between temperature increase and dimensional stability. The second region begins at around 45°C, corresponding to the T g of the materials, and is characterized by a pronounced change in slope due to the transition from a rigid solid to a rubbery state, where significant dimensional expansion occurs. To analyze the effect of zein + DPG incorporation, the CTLE was examined both below and above the T g to quantify the thermal response of each formulation. Neat PLA exhibited CTLE values of 85 µm/m·°C below T g and 1440 µm/m·°C above T g , which are consistent with previously reported data [ 34 ]. The addition of zein + DPG increased the free volume and enhanced chain mobility, as supported by earlier mechanical tests showing more ductile behavior in these formulations. This dimensional change is attributed to the reduced PLA content and the plasticizing effect of DPG, which acts as a lubricant between PLA chains, lowering the matrix rigidity [ 51 ]. As a result, formulations with higher zein + DPG content exhibit an earlier transition to a rubbery state and a more pronounced thermal expansion. For instance, the 50P–50Z blend reached CTLE values of 119 µm/m·°C below T g and 2455 µm/m·°C above T g . Overall, these findings confirm that higher concentrations of zein + DPG promote earlier and more significant dimensional expansion in response to temperature. 3.4 Color characterization of PLA–zein blends. A clear visual distinction was observed between the virgin PLA samples and those containing PLA-zein. Table 5 presents the color coordinate values, while Fig. 6 offers a visual comparison that highlights the differences among the various formulations. Table 5 Colorimetric properties of the PLA-zein samples. Code L * a * b * \(\:{\varDelta\:E}_{ab}^{*}\) PLA 37.3 ± 0.1 -0.3 ± 0.2 2.2 ± 0.2 - 90P-10Z 49.9 ± 0.7 5.8 ± 0.6 30.3 ± 0.7 31.4 80P-20Z 59.8 ± 0.6 8.3 ± 0.3 37.2 ± 0.6 42.5 70P-30Z 58.9 ± 1.4 8.9 ± 0.7 38.6 ± 0.6 43.3 60P-40Z 56.0 ± 2.5 11.0 ± 1.3 38.2 ± 0.8 42.1 50Z-50P 56.4 ± 1.2 9.3 ± 0.7 30.7 ± 1.3 35.7 The L* parameter, which indicates sample luminance, increased significantly with the addition of zein, suggesting a lightening effect as the zein content increased. Neat PLA exhibited the lowest luminance value (37.3), while blends 80P-20Z and 70P-30Z showed the highest values (59.8 and 58.9, respectively), reflecting a shift toward brighter and whiter tones. The low L* value in neat PLA is attributed to its high transparency, which allows significant light transmission and thus results in low diffuse reflectance. Consequently, a reduced L* value in this context does not indicate opacity, but rather the material’s limited light reflection due to its transparent nature. The a* parameter, representing the red-green axis, showed a near-neutral tone for PLA (-0.3). However, all zein samples displayed a marked shift toward the red region, with values ranging from 5.8 (90P-10Z) to 11.0 (60P-40Z), indicating the presence of red tones introduced by zein. Regarding the b* parameter represents the yellow-blue axis, changed notably with zein incorporation. While neat PLA showed a slightly yellow hue (2.2), zein formulations reached b* values as high as 38.6 (70P-30Z), indicating a pronounced yellowish appearance, as shown in Fig. 6 . The total color difference ( \(\:{\varDelta\:E}_{ab}^{*}\) ) supports these observations, with values exceeding 30 for all zein-based formulations, confirming significant visual differences compared to neat PLA. The most substantial change was recorded in 70P-30Z (43.3), indicating a clearly perceptible color deviation, also illustrated in Fig. 6 . These shifts are consistent with modifications in surface morphology and polymer interactions induced by zein, resulting in altered optical behavior. Even when comparing only zein-containing materials among themselves, \(\:{\varDelta\:E}_{ab}^{*}\) values exceeded 5, implying that noticeable visual distinctions persist across different plasticized zein concentrations. 3.5 Morphological characterization of PLA–zein blends. The images obtained from the optical analysis reveal the fracture surface morphology of each formulation. Distinct morphological differences are evident among the various samples, as illustrated in Fig. 7 . The PLA sample (Fig. 7 a) exhibited characteristic features of brittle fracture, with a smooth, laminar surface and no visible signs of plastic deformation [ 52 ]. This brittle nature aligns with the mechanical behavior previously discussed. In contrast, the PLA-zein blends (Fig. 7 b–f) showed progressively more heterogeneous morphologies as the zein content increased. The 90P–10Z and 80P–20Z samples (Fig. 7 b–c) displayed dispersed spherical domains, indicative of phase separation between the PLA matrix and plasticized zein rich regions, suggesting partial miscibility and the presence of protein aggregates. As the zein proportion increased further (Fig. 7 d–f), the fracture surfaces became increasingly rough, porous, and irregular, with noticeable cavities and voids. The 50P–50Z blend (Fig. 7 f) exhibited the highest porosity and most pronounced phase separation, reflecting poor interfacial adhesion between the components. Similar findings were reported by Kun Fang et al. [ 53 ], who observed aggregate formation in PLA- SP blends. As the plasticized zein content increased in the formulations, the polymer chain mobility was enhanced due to the higher plasticizer concentration within the PLA matrix [ 54 ]. However, this also promoted zein aggregation and phase separation at higher concentrations, as clearly observed in Fig. 7 . 3.6 Analysis of the chemical structure of PLA–zein blends. FTIR analysis was conducted to identify the main functional groups present in the PLA-zein blends and to detect possible molecular interactions among their components. All spectra exhibited a strong absorption band around 1745 cm⁻¹, corresponding to the stretching vibration of the carbonyl (C = O) group typical of PLA [ 55 ]. This band remained present in the zein blends, although slight changes in intensity and shape were observed, suggesting interactions between the ester groups of PLA and the functional groups of zein or the plasticizer. As the plasticized zein content increased, new bands appeared or existing signals intensified in the 1650–1530 cm⁻¹ region, which are associated with amide I and II vibrations characteristic of zein. These signals confirm the incorporation of the protein into the polymer matrix [ 56 ]. In the 3200–3400 cm⁻¹ range, a progressive broadening of the O–H and N–H stretching band was observed, indicating a higher presence of hydroxyl groups and the potential formation of hydrogen bonds between PLA and zein + DPG [ 46 ]. Additionally, variations were detected in the 2800–3000 cm⁻¹ region, corresponding to aliphatic C–H stretching, suggesting structural changes related to the dispersion of the components and the effect of the plasticizer [ 57 ]. Overall, the spectra indicate partial miscibility between the components, with the presence of physical interactions particularly hydrogen bonding, but no clear evidence of chemical reactions between the phases. These findings are consistent with the morphological results. 4 Conclusions This study evaluates the development of PLA-zein blends. To this effect a corn-derived protein was plasticized with DPG as a natural plasticizer. Plasticized protein help modify the properties of PLA, in this case making it more ductile. The materials were processed through twin-screw extrusion and injection molding. Various concentrations of plasticized zein with DPG were integrated into the PLA matrix to assess their combined influence on processability and overall performance. Mechanical testing reveals that increasing the plasticized zein content enhances the ductility of the material. In contrast, as the concentration of plasticized zein rises, tensile strength and elastic modulus decrease. This effect is related to the plasticizer’s ability to disrupt the polymer chains, allowing greater mobility and improved flexibility. Notably, the 60P-40Z and 50P-50Z blends achieved elongation values of 25.5% and 56.25%, respectively. In contrast, Charpy impact resistance declines with higher plasticized zein content, likely due to the increased aggregation and heterogeneity between the PLA and zein phases, which leads to greater brittleness. For instance, the impact strength drops from 42.2 kJ/m² for neat PLA to 11.5 kJ/m² for the 50P-50Z blend. Shore D hardness remains relatively stable, though a slight reduction is observed at higher plasticizer concentrations, decreasing from 82.9 for neat PLA to 77.4 for 50P-50Z, indicating a softening effect due to the plasticizer. Thermal analysis using DSC shows that all blends exhibit a single T g , suggesting partial miscibility between the components. T g decreases as the plasticized zein content increases, from 59.5°C for neat PLA to 39.9°C for the 50P-50Z sample, consistent with the expected plasticizing effect. TGA demonstrates that the thermal stability of the materials declines with higher zein + DPG content. The T 5% drops significantly, from 360.0°C for PLA to 188.2°C for 50P-50Z. Additionally, residual mass at the end of the TGA test increases with greater plasticized zein loading, reflecting the contribution of non-volatile protein and plasticizer residues. Thermomechanical analysis via DMTA supports the previous findings. The results confirm that samples with higher plasticized zein content exhibit more ductile behavior and lower T g values, consistent with a more flexible molecular structure. TMA analysis revealed that the incorporation of zein + DPG into PLA-based blends significantly affected their dimensional stability. Colorimetric evaluation indicates a notable change in the visual appearance of the material. The lightness parameter ( L* ) increases, while the color shifts toward red ( a* ) and yellow ( b* ) hues. The total color difference ( \(\:{\varDelta\:E}_{ab}^{*}\) ) exceeds a value of 5, indicating visibly distinguishable samples. Morphological analysis corroborates the mechanical findings. As the zein + DPG content increases, more surface inclusions appear, highlighting the partial miscibility and limited compatibility between phases. The fracture surfaces become rougher, consistent with enhanced ductility, compared to the smooth fracture of neat PLA. Finally, FTIR analysis confirms the presence of physical interactions and some degree of miscibility between PLA and zein, further supporting the interpretation of the mechanical and thermal results. Overall, the incorporation of zein and DPG into the PLA matrix results in a more ductile material, while simultaneously enhancing the mechanical performance and processability of the zein–DPG phase. This combination of materials presents an interesting alternative due to its natural origin that helps to reduce petroleum dependency. In addition, biocompatibility, and biodegradability, making it interesting for various industries, including food packaging and biomedical applications. Declarations Acknowledgements This research is a part of the grant PID2023-152869OB-C22, and the grant TED2021-131762A-I00, funded by MCIN/AEI/10.13039/501100011033 and by the European Union “NextGenerationEU”/PRTR. The authors also thank Generalitat Valenciana - GVA, grant number CIGE/2023/46 and CIAICO/2023/253, for supporting this work. C. Lazaro-Hdez thanks Generalitat Valenciana - GVA for funding a predoc position through the CIACIF program co-funded by ESF Investing in your future, grant number CIACIF/2023/244. M. Miranda-Pinzon thanks Vice-rectorate for Research of the Universitat Politècnica de València (UPV) for funding a predoctoral contract in the PAID-01-24 program. J. Ivorra-Martinez thanks Generalitat Valenciana - GVA for funding a postdoc position through the CIAPOS program co-funded by ESF Investing in your future, grant number CIAPOS/2023/362. Microscopy services at UPV are also acknowledged for their help in collecting and analyzing FESEM images. Funding for open access charge: CRUE-Universitat Politècnica de València. Author contributions Carlos Lazaro-Hdez : Investigation, Data curation, Validation, Writing original draft, Writing – review & editing, Visualization, Methodology. Mario Miranda-Pinzon : Investigation, Resources, Methodology, Formal analysis, Data curation, Visualization. Maria del Puig Vicente-Vinas : Investigation, Formal analysis, Validation, Data curation. Teodomiro Boronat : Conceptualization, Supervision, Validation, Project administration, Writing – review & editing, Funding acquisition. 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14:02:17","extension":"png","order_by":16,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":71676,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7869492/v1/586fa12b30750a597dac7e20.png"},{"id":95391092,"identity":"4d914ed3-9896-4ecb-ad4d-0a3bb664c6da","added_by":"auto","created_at":"2025-11-07 14:02:17","extension":"png","order_by":17,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":204757,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-7869492/v1/ab85160746f968676ad734d7.png"},{"id":95391093,"identity":"ef7c6b52-6211-4a27-bc28-6584339511d5","added_by":"auto","created_at":"2025-11-07 14:02:17","extension":"png","order_by":18,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":23791,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-7869492/v1/35d65602e4792287f2619c45.png"},{"id":95391095,"identity":"252139d1-2108-465e-a357-52acd7ab8ed9","added_by":"auto","created_at":"2025-11-07 14:02:17","extension":"xml","order_by":19,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":144306,"visible":true,"origin":"","legend":"","description":"","filename":"e54273e046434fd08a987860587c1ef71structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7869492/v1/2e59c4f512079663b6cfc0d2.xml"},{"id":95391094,"identity":"5b06252d-0fa7-407d-90bc-d092d9eefa64","added_by":"auto","created_at":"2025-11-07 14:02:17","extension":"html","order_by":20,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":153025,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7869492/v1/199bfe5d03c21ca409e6eceb.html"},{"id":95391067,"identity":"c996074e-979f-470a-bac6-8cfe7c0c718f","added_by":"auto","created_at":"2025-11-07 14:02:16","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":88627,"visible":true,"origin":"","legend":"\u003cp\u003eMechanical results for the PLA–zein blends evaluated in terms of: a) ultimate tensile strength (σ\u003csub\u003em\u003c/sub\u003e), b) elongation at break (ε\u003csub\u003eb\u003c/sub\u003e), c) tensile modulus (E\u003csub\u003et\u003c/sub\u003e), d) Charpy impact resistance of unnotched specimens (a\u003csub\u003ecU\u003c/sub\u003e), e) Shore D hardness, and f) tensile test curves.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7869492/v1/0f6eda0da8ef8c0f7aed8f15.png"},{"id":95391068,"identity":"33eb0ed1-9326-44b4-8574-a8999da90218","added_by":"auto","created_at":"2025-11-07 14:02:17","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":46176,"visible":true,"origin":"","legend":"\u003cp\u003eDSC thermograms of the various processed samples are presented as follows: a) cooling process and b) second heating cycle.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7869492/v1/07d845e29cd66e1189677ce4.png"},{"id":95526366,"identity":"ffb98a62-5a52-4492-aae2-3275bce36c07","added_by":"auto","created_at":"2025-11-10 10:06:50","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":57871,"visible":true,"origin":"","legend":"\u003cp\u003eThermogravimetric curves of the different samples are shown as follows: a) sample weight \u003cem\u003evs\u003c/em\u003etemperature and b) first derivative \u003cem\u003evs\u003c/em\u003e temperature.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7869492/v1/d2aa2b59e36be32df58e4dce.png"},{"id":95391072,"identity":"aa256e59-aa28-44bb-bafc-c7c6437f9656","added_by":"auto","created_at":"2025-11-07 14:02:17","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":50370,"visible":true,"origin":"","legend":"\u003cp\u003eDMTA curves of the different samples are shown, highlighting: a) storage modulus (E') and b) damping factor (Tan (d)).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7869492/v1/f11f0259e1a3f4a67874836a.png"},{"id":95525503,"identity":"f2e87c22-4023-4ce7-a50a-0effada55e7e","added_by":"auto","created_at":"2025-11-10 10:05:09","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":36989,"visible":true,"origin":"","legend":"\u003cp\u003eTMA curves of the various processed samples are presented, emphasizing the dimensional change.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7869492/v1/f009212304c50f862f6de30a.png"},{"id":95526781,"identity":"cc04bfb9-3276-470d-a190-02b6dc9bc52e","added_by":"auto","created_at":"2025-11-10 10:07:51","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":175108,"visible":true,"origin":"","legend":"\u003cp\u003eVisual appearance of the PLA-zein samples is shown as follows: a) PLA, b) 90P-10Z, c) 80P-20Z, d) 70P-30Z, e) 60P-40Z, and f) 50P-50Z.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7869492/v1/85fea5e2c9278c63a88c0879.png"},{"id":95526907,"identity":"84c50892-1f77-4e3d-807d-84bd25c7c010","added_by":"auto","created_at":"2025-11-10 10:08:34","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":379974,"visible":true,"origin":"","legend":"\u003cp\u003eFESEM images at 500× magnification of the different samples are presented as follows: a) PLA, b) 90P-10Z, c) 80P-20Z, d) 70P-30Z, e) 60P-40Z, and f) 50P-50Z.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7869492/v1/d58ae4752a416d3c2a3bbbb3.png"},{"id":95391076,"identity":"6b462ece-32ba-4312-a8e7-fc575832c1d6","added_by":"auto","created_at":"2025-11-07 14:02:17","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":92714,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of the PLA-zein samples processed.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-7869492/v1/2d1dc1435f877bb1d9cb0ac8.png"},{"id":105755599,"identity":"9cd0f935-3224-42bb-b4e7-46eb58b5eede","added_by":"auto","created_at":"2026-03-30 16:28:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2063318,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7869492/v1/c30e1f42-3339-43ce-84d5-9f534d4306d6.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Development and characterization of ductile polylactic acid blends with plasticized zein for injection molding applications","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe widespread reliance on non-renewable, petroleum-based polymers has raised critical concerns regarding environmental sustainability [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Once polymer-based products are discarded, they can remain in the environment for extended periods, significantly contributing to waste accumulation and ecosystem degradation [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. This issue is especially pronounced in industries such as food packaging, where single-use items are commonly produced. Due to the high consumption of these products, substantial volumes of waste are generated. Often these products have a very short life cycles and limited opportunities for effective management [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. In response to growing awareness of the ecological impact of petroleum-derived plastics, considerable efforts have been devoted to the development and implementation of more sustainable, bio-based alternatives [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eBiopolymers, derived from renewable resources, are being explored as promising candidates to replace conventional plastics [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. These materials are valued for their biodegradability, renewability, and, in many cases, their biocompatibility. Among the most studied are polylactic acid (PLA), polyhydroxyalkanoates (PHA), thermoplastic starch (TPS), and polymers derived from other starch-based sources [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Protein-based biopolymers, obtained from crops such as soy and maize, are also gaining attention due to their potential in creating environmentally friendly materials [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. One of the most widely used bio-based polymers globally is PLA, a thermoplastic synthesized from lactic acid, typically obtained by means of fermentation of starch-rich feedstocks such as corn or sugarcane [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e\u003cp\u003ePLA is known for its good mechanical strength, ease of processing, and non-toxic degradation, making it suitable for use in sectors such as packaging, automotive components, and biomedical applications [\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. However, despite these advantages, PLA exhibits certain limitations, including brittleness and low impact resistance [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Various strategies have been employed to overcome these drawbacks, such as the addition of fillers, polymer blending, and the incorporation of plasticizers [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Among these, polymer blending stands out for its ability to combine properties from different materials. However, challenges related to miscibility can arise, leading to suboptimal performance in the final material [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eProtein-based biopolymers, such as those derived from soy or zein, have shown potential for blending with PLA [\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. These materials are particularly appealing to the food industry due to their ability to disintegrate through biodegradation, as well as their biocompatibility, which allows for safe contact with the human body. Nevertheless, they also present issues, including poor mechanical strength, low thermal stability, and limited processability. In efforts to enhance their performance, blending with more robust bio-based polymers like PLA is being explored [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Zein, a protein extracted as a byproduct from the corn industry, has emerged as a promising candidate for such blends [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Despite its potential, zein is inherently rigid and brittle and poses difficulties during processing, especially under extrusion or injection molding conditions [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eTo address these challenges, the use of plasticizers is essential. Plasticizers help reduce intermolecular forces within the polymer structure, increasing flexibility and enhancing processability [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Selecting an appropriate plasticizer is critical to achieving effective plasticization. Commonly used plasticizers for zein include glycerol (GLY) [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], oleic acid (OA) [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], polyethylene glycol (PEG) [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], and dipropylene glycol (DPG) [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e], among others. DPG belongs to the glycol family and contains two hydroxyl groups\u003c/p\u003e\u003cp\u003e(\u0026ndash;OH), which can interact with the hydrophilic groups in zein, thereby improving its flexibility [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Furthermore, in PLA-zein blends, the plasticizer plays a crucial role not only in softening zein but also in promoting compatibility between the two phases.\u003c/p\u003e\u003cp\u003eThis study focuses on the development and comprehensive characterization of plasticized PLA-zein blends. Zein, derived from maize, was incorporated into PLA matrices at varying concentrations, with dipropylene glycol (DPG) used as a plasticizer to improve both the compatibility and processability of the system. The materials were compounded using twin-screw extrusion and shaped through injection molding to produce the test specimens.\u003c/p\u003e\u003cp\u003eA broad range of characterization techniques was applied to evaluate properties such as the mechanical, thermomechanical, morphological, and colorimetric properties of the prepared blends. Particular attention was given to the influence of DPG on the dispersion of zein within the PLA matrix and its role in modifying the structural and functional behavior of the resulting materials. The findings from this investigation provide meaningful insights into the performance of DPG plasticized PLA-zein systems and support their potential application in environmentally responsible packaging solutions and other biodegradable material markets.\u003c/p\u003e"},{"header":"2 Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1 Materials\u003c/h2\u003e\n \u003cp\u003eThe biopolymer was employed in this study was polylactic acid (PLA), acquired from Ercros (Barcelona, Spain), specifically ErcrosBio LL 712. This grade of PLA exhibits a mass flow rate of 4 g/10 min (ISO 1133-A 190 \u0026ordm;C and 2.16 kg). Zein was obtained in powder form from Sigma-Aldrich (CAS No.: 9010-66-6), with a moisture content below 8%. Prior to processing, both materials underwent drying for 8 hours at 80\u0026deg;C employing an MDEO dehumidifier manufactured by Industrial Mars\u0026eacute; (Barcelona, Spain). The plasticizer utilized was dipropylene glycol (DPG), with 134.18 g/mol molecular weight and a purification level exceeded 95%, and was procured from Tokyo Chemical Industry Co., LTD (TCI EUROPE) (Zwijndrecht, Belgium).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2 Compounding of multiple formulations\u003c/h2\u003e\n \u003cp\u003eThe materials were compounded employing a twin-screw extruder, in a Xplore Micro Compounder MC-40 (Sittard, The Netherlands). The initial step involved processing the zein\u0026thinsp;+\u0026thinsp;DPG (coded as Z) mixture at 130\u0026deg;C for 1 min. This blend was then pelletized using an air-cutting unit. Subsequently, neat PLA was processed independently at 180\u0026deg;C for 1 min. Finally, the formulations containing PLA and plasticized zein (Z) were extruded at 170\u0026deg;C for 1 min. In all cases, the screw speed was controlled at 100 rpm with a maximum torque of 40 N m. The nomenclature and the specific quantities used in the preparation of these formulations are presented in the following table.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eComposition and coding of the PLA blends with plasticized zein.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCode\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePLA (wt%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ezein\u0026thinsp;+\u0026thinsp;DPG (wt%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ezein (wt%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDPG (wt%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eZ (zein\u0026thinsp;+\u0026thinsp;DPG)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePLA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e100\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e90P-10Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e80P-20Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e70P-30Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e60P-40Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e50P-50Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3 Sample injection\u003c/h2\u003e\n \u003cp\u003eNormalized injection-molded specimens were produced using an Xplore Injection Moulder IM12 (Sittard, The Netherlands). Different injection conditions were applied depending on the formulation. For PLA, a nozzle temperature of 180\u0026deg;C, a mold temperature of 35\u0026deg;C, and an injection pressure of 8 bar were used for 7 s, followed by a packing time of 3 s. For the formulations containing plasticized zein, the nozzle temperature was set to 170\u0026deg;C, with the mold maintained at 35\u0026deg;C, an injection pressure of 6 bar was applied for 7 s, and 3 s of packing.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003e2.4 Mechanical behavior analysis\u003c/h2\u003e\n \u003cp\u003eThree separate tests were performed for the assessment of the mechanical properties. Tensile properties were evaluated using a universal testing machine, the IBERTEST ELIB-50 from S.A.E. Ibertest (Madrid, Spain), with a 10 kN load cell and operated at a crosshead speed of 10 mm/min. Specimens were prepared according to ISO 527-2:2012 using type 1BA geometry.\u003c/p\u003e\n \u003cp\u003eCharpy impact resistance was assessed following ISO 179-1:2010, using specimens measuring 80\u0026times;10\u0026times;4 mm\u0026sup3; and tested with a 6 J pendulum impact tester from Metrotec S.A. (San Sebastian, Spain).\u003c/p\u003e\n \u003cp\u003eShore D hardness was measured using a 637-D durometer from Instruments J. Bot S.A. (Barcelona, Spain), in compliance with ISO 868, allowing a stabilization period of 30 s before reading. All reported values represent the average of five replicates.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n \u003ch2\u003e2.5 Thermal behavior analysis\u003c/h2\u003e\n \u003cp\u003eDifferential scanning calorimetry (DSC) was employed to analyze the thermal behavior of the samples, on a DSC 25 unit from TA Instruments (Delaware, DE, USA). The analysis included multiple thermal cycles: an initial heating from \u0026minus;\u0026thinsp;50\u0026deg;C to 200\u0026deg;C at a rate of 10\u0026deg;C/min to eliminate any residual thermal history, followed by a cooling cycle from 200\u0026deg;C to -50\u0026deg;C at -10\u0026deg;C/min. A second heating cycle from \u0026minus;\u0026thinsp;50\u0026deg;C to 200\u0026deg;C at\u003c/p\u003e\n \u003cp\u003e10\u0026deg;C/min was then conducted to identify all relevant thermal transitions. A nitrogen atmosphere at 50 mL/min was used throughout the tests to inhibit oxidative degradation. The degree of crystallinity (X\u003csub\u003ec\u003c/sub\u003e) was determined using Eq.\u0026nbsp;1:\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv align=\"left\" class=\"colspec\"\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003e\u0026Delta;H\u003csub\u003em\u003c/sub\u003e and \u0026Delta;H\u003csub\u003ecc\u003c/sub\u003e (J/g) represent the melting enthalpy and cold crystallization enthalpy, respectively. The theoretical value of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varDelta\\:\\text{H}}_{\\text{m}}^{0}\\)\u003c/span\u003e\u003c/span\u003e (J/g), corresponding to 100% crystalline PLA, was taken as 93.0 J/g according to the literature [\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e]. The variable \u003cem\u003ew\u003c/em\u003e denotes the weight fraction of total additives present in the PLA blends.\u003c/p\u003e\n \u003cp\u003eThermogravimetric analysis (TGA) was employed to assess the thermal stability of the samples, using a TG-DSC2, by Mettler-Toledo (Columbus, OH, USA). The thermal behavior was examined by heating the specimens from 30\u0026deg;C to 700\u0026deg;C at a constant rate of 20\u0026deg;C/min under an oxygen flow of 50 mL/min. To ensure reproducibility and accuracy, all formulations were tested in triplicate.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e2.6 Thermomechanical behavior analysis\u003c/h2\u003e\n \u003cp\u003eDynamic mechanical thermal analysis (DMTA) was carried out to evaluate the mechanical behavior of the samples under thermal and dynamic conditions, the equipment used was Mettler-Toledo DTMT1 (Columbus, OH, USA). Specimens measuring 20\u0026times;4\u0026times;2 mm\u0026sup3; were subjected to a heating cycle from \u0026minus;\u0026thinsp;100\u0026deg;C to 100\u0026deg;C at increments of 2\u0026deg;C/min. The tests were conducted under dynamic loading at a frequency of 1 Hz, with a maximum displacement amplitude of 10 \u0026micro;m.\u003c/p\u003e\n \u003cp\u003eThermomechanical analysis (TMA) was employed to evaluate the dimensional stability of the materials using a Q400 instrument from TA Instruments (New Castle, DE, USA). Samples with dimensions of 10\u0026times;10\u0026times;4 mm\u0026sup3; were heated from \u0026minus;\u0026thinsp;70\u0026deg;C to 70\u0026deg;C at a rate of 2\u0026deg;C/min was applied in an air atmosphere, under a constant load of 0.02 N.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e2.7 Color characterization\u003c/h2\u003e\n \u003cp\u003eColorimetric properties were evaluated using a KONICA CM-3600d Colorflex-DIFF2 spectrophotometer from Hunter Associates Laboratory (Reston, VA, USA), based on the CIELab color scale [\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e]. Ten measurements were taken to determine the \u003cem\u003eL\u003c/em\u003e*, \u003cem\u003ea\u003c/em\u003e*, and \u003cem\u003eb\u003c/em\u003e* coordinates, where \u003cem\u003eL\u003c/em\u003e* represents lightness, \u003cem\u003ea\u003c/em\u003e* corresponds to the red-green axis, and \u003cem\u003eb\u003c/em\u003e* indicates the yellow-blue axis. The total color difference, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varDelta\\:E}_{ab}^{*}\\)\u003c/span\u003e\u003c/span\u003e, was calculated using Eq.\u0026nbsp;2.\u003c/p\u003e\n \u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/p\u003e\n \u003cp\u003eWhere \u0026Delta;\u003cem\u003eL\u003c/em\u003e*, \u0026Delta;\u003cem\u003ea\u003c/em\u003e*, and \u0026Delta;\u003cem\u003eb\u003c/em\u003e* represent the differences between the color coordinates of the samples and those of the reference. Color variation was evaluated according to the following criteria: unnoticeable difference (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varDelta\\:E}_{ab}^{*}\\)\u003c/span\u003e\u003c/span\u003e\u0026lt; 1), perceptible only to a trained observer (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varDelta\\:E}_{ab}^{*}\\)\u003c/span\u003e\u003c/span\u003e\u0026ge; 1 and \u0026lt;\u0026thinsp;2), noticeable by an untrained observer (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varDelta\\:E}_{ab}^{*}\\)\u003c/span\u003e\u003c/span\u003e\u0026ge; 2 and \u0026lt;\u0026thinsp;3.5), and clearly noticeable by all observers (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varDelta\\:E}_{ab}^{*}\\)\u003c/span\u003e\u003c/span\u003e \u0026ge; 3.5 and \u0026lt;\u0026thinsp;5) [\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e2.8 Fracture surface analysis\u003c/h2\u003e\n \u003cp\u003eFractured surface morphology of the charpy test specimens was examined using a ZEISS ULTRA 55 microscope from Oxford Instruments (Abingdon, UK) operating at an acceleration voltage of 3 kV. Prior to imaging, a gold\u0026ndash;palladium coating was applied using a SC7620 sputter coater from Quorum Technologies Ltd. (East Sussex, UK).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e2.9 Chemical characterization of the processed formulations\u003c/h2\u003e\n \u003cp\u003eFTIR analysis was carried out using a Vector 22 spectrometer from Bruker S.A. (Madrid, Spain), equipped with a PIKE MIRacle single-reflection diamond ATR accessory from PIKE Technologies (Madison, USA). Each sample was scanned 10 times with a spectral resolution of 4 cm⁻\u0026sup1; over a wavelength range of 4000 to 600 cm⁻\u0026sup1;.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Mechanical behavior of PLA\u0026ndash;zein blends.\u003c/h2\u003e\n \u003cp\u003eThe mechanical behavior of the processed samples containing different percentages of plasticized zein was evaluated using tensile testing, Charpy impact testing, and Shore D hardness measurements, as summarized in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea-c presents the results obtained from the tensile test. The results for PLA samples are consistent with those reported in numerous studies involving injection-molded samples [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e]. The material exhibited a high maximum tensile strength and a high elastic modulus, along with low elongation at break, this behavior is characteristic of rigid materials.\u003c/p\u003e\n \u003cp\u003eRegarding the mechanical properties of the PLA-zein blends, it is important to consider that their behavior is strongly influenced by their morphology, which will be discussed later. Figure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea-c illustrates a clear trend, as the amount of plasticized zein increases, both tensile strength and elastic modulus decrease while elongation at break increases. Similar behavior was observed in the study conducted by Bo Liu \u003cem\u003eet.al.\u003c/em\u003e [\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e], where blends of PLA with plasticized soy protein (SP) showed a reduction in mechanical strength and a partial improvement in elongation with increasing soy content. The highest elongation at break values were recorded for the 60P\u0026ndash;40Z and 50P\u0026ndash;50Z blends, reaching 25.5% and 56.2%, respectively. These samples also exhibited tensile strengths around 33 MPa and an elastic modulus of approximately 2100 MPa, indicating a reduction in both stiffness and strength. This effect is attributed to the increased amount of plasticizer in the final formulations. As more zein is incorporated into the PLA matrix, the overall plasticizer content also rises. The plasticizer molecules intercalate between PLA chains, enhancing chain mobility and facilitating their displacement. This plasticizing effect has been widely reported in the literature [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e] .\u003c/p\u003e\n \u003cp\u003eIn terms of impact testing, it can be observed that the incorporation of plasticized zein leads to embrittlement of the samples. As the percentage increases, the impact strength decreases, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ed. A similar trend was reported in the study by Rui Zhu \u003cem\u003eet.al\u003c/em\u003e [\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e], where increasing amounts of SP in PLA resulted in reduced impact resistance. This embrittlement may be attributed to the higher concentration of particles formed by the agglomeration of plasticized zein within the PLA matrix, as noted in the research by Bo Liu \u003cem\u003eet.al.\u003c/em\u003e[\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eFinally, the hardness test results show similar values across the samples, indicating that the addition of plasticized zein does not significantly affect hardness. However, a slight decrease in hardness can be observed as the plasticized zein content increases. This reduction may be attributed to the presence of the plasticizer, as discussed earlier, which contributes to improved ductile behavior.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Thermal behavior of PLA\u0026ndash;zein blends.\u003c/h2\u003e\n \u003cp\u003eThe thermal behavior of the PLA\u0026ndash;zein blends was analyzed through a dynamic DSC test. Three different stages were scheduled and the analysis emphasized the intermediate cooling stage and the second heating cycle. Figure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e displays the corresponding DSC thermograms, and the main thermal parameters are represented in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. TGA was utilized to examine the thermal stability and decomposition profile of the materials by subjecting them to a single controlled heating cycle. The results of this analysis are presented in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eDSC analysis was used to obtain the characteristic thermal transitions of the processed formulations. One of the most relevant transitions is the glass transition temperature (T\u003csub\u003eg\u003c/sub\u003e), which marks the point at which the material shifts from a rigid solid to a rubbery state. In this case, neat PLA exhibited a T\u003csub\u003eg\u003c/sub\u003e of 59.5\u0026deg;C, a value consistent with those reported in the literature. However, the incorporation of zein\u0026thinsp;+\u0026thinsp;DPG led to a noticeable decrease in T\u003csub\u003eg\u003c/sub\u003e, reaching 39.9\u0026deg;C for the 50P\u0026ndash;50Z blend. This trend indicates that increasing the zein\u0026thinsp;+\u0026thinsp;DPG content results in a progressive reduction of T\u003csub\u003eg\u003c/sub\u003e, bringing it closer to room temperature, which justifies the improvement in ductility. A similar effect was reported by Shengzhe Yang \u003cem\u003eet.al.\u003c/em\u003e [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e], who observed a reduction in T\u003csub\u003eg\u003c/sub\u003e with higher amounts of SP in PLA based blends. They also noted that the presence of a single T\u003csub\u003eg\u003c/sub\u003e in each formulation suggests partial miscibility between components, since immiscible systems would typically exhibit two separate glass transitions. In the present study, each formulation displayed only one T\u003csub\u003eg\u003c/sub\u003e, supporting the conclusion of partial miscibility. This reduction can be explained by the inherently low T\u003csub\u003eg\u003c/sub\u003e values of plasticized zein. According to Rojas-Lema \u003cem\u003eet al.\u003c/em\u003e [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e], zein plasticized with 25 wt% glycerol exhibited a T\u003csub\u003eg\u003c/sub\u003e of 38.3\u0026deg;C. Therefore, the combination of PLA with increasing amounts of plasticized zein significantly lowers the overall T\u003csub\u003eg\u003c/sub\u003e of the blends. Additionally, the plasticizer contributes to this effect by inserting itself between polymer chains, reducing intermolecular forces and facilitating chain mobility. This mechanism, often described as a lubricating effect, has been widely reported in the literature [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eAnother relevant thermal transition is the cold crystallization temperature (T\u003csub\u003ecc\u003c/sub\u003e), which is shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb. A decrease in T\u003csub\u003ecc\u003c/sub\u003e is observed, promoted by the addition of plasticized zein [\u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e]. Additionally, the area under the curve, which corresponds to the enthalpy of crystallization (\u0026Delta;H\u003csub\u003ecc\u003c/sub\u003e), also decreases. This reduction is attributed to the increasing zein content, as zein is an amorphous material that does not undergo crystallization. Therefore, only the PLA phase contributes to the crystallization process.\u003c/p\u003e\n \u003cp\u003eRegarding the melting temperature (T\u003csub\u003em\u003c/sub\u003e), Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e shows that T\u003csub\u003em\u003c/sub\u003e decreases as the plasticized zein content increases. Additionally, the appearance of two melting peaks is observed. The appearance of multiple melting peaks is associated with the formation of various types of crystals of PLA; fewer perfect crystals melt at lower temperatures, while crystals with greater structural order tend to melt at elevated temperatures. The incorporation of plasticized zein promotes the formation of these crystal types in the matrix of PLA. A similar behavior was reported by Wen Zhang \u003cem\u003eet al.\u003c/em\u003e [\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e], who observed dual melting peaks in PLA\u0026ndash;SP blends at various ratios and noted that the addition of SP induces the formation of distinct crystalline structures. At this temperature, as in the previous case, only PLA contributes to the melting behavior, making it solely responsible for the observed melting peak. Consequently, Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e shows a reduction in the melting enthalpy (\u0026Delta;H\u003csub\u003em\u003c/sub\u003e), which corresponds to the decreasing PLA content in the formulations.\u003c/p\u003e\n \u003cp\u003eRegarding the degree of crystallinity (X\u003csub\u003ec\u003c/sub\u003e) of the blends, an increase is observed as the content of zein\u0026thinsp;+\u0026thinsp;DPG rises. This is attributed to the fact that although the amount of PLA, the phase capable of reorganizing to crystallize, decreases, the proportion of plasticizer used to plasticize the zein increases. As the plasticizer is incorporated between PLA chains, it enhances chain mobility and facilitates tighter packing, leading to a higher degree of crystallinity. Garcia-Garcia \u003cem\u003eet al.\u003c/em\u003e [\u003cspan class=\"CitationRef\"\u003e43\u003c/span\u003e] reported similar findings, demonstrating that increasing the plasticizer content in PLA improves chain rearrangement and consequently enhances crystallinity.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eThermal properties of the PLA\u0026ndash;zein blends obtained from the second heating cycle of the DSC test include: glass transition temperature (T\u003csub\u003eg\u003c/sub\u003e), cold crystallization temperature peak (T\u003csub\u003ecc\u003c/sub\u003e), first melting temperature peak (T\u003csub\u003em1\u003c/sub\u003e), second melting temperature peak (T\u003csub\u003em2\u003c/sub\u003e), cold crystallization enthalpy (\u0026Delta;H\u003csub\u003ecc\u003c/sub\u003e), melt enthalpy (\u0026Delta;H\u003csub\u003em\u003c/sub\u003e), and degree of crystallinity (X\u003csub\u003ec\u003c/sub\u003e).\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCode\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eT\u003csub\u003eg\u003c/sub\u003e (\u0026deg;C)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eT\u003csub\u003ecc\u003c/sub\u003e (\u0026deg;C)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eT\u003csub\u003em1\u003c/sub\u003e (\u0026deg;C)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eT\u003csub\u003em2\u003c/sub\u003e (\u0026deg;C)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u0026Delta;H\u003csub\u003ecc\u003c/sub\u003e (J/g)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u0026Delta;H\u003csub\u003em\u003c/sub\u003e (J/g)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eX\u003csub\u003ec\u003c/sub\u003e (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePLA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e59.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e114.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e151.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e29.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e90P-10Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e55.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e106.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e148.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e156.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e26.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e32.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e80P-20Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e51.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e105.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e148.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e155.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e23.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e30.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e70P-30Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e45.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e110.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e143.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e150.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e18.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e60P-40Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e43.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e102.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e141.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e150.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e22.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e12.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e50Z-50P\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e39.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e92.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e135.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e147.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e14.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e23.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e18.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eIn TGA analysis, the onset of thermal degradation is commonly defined in the literature as the temperature at which a 5% mass reduction occurs [\u003cspan class=\"CitationRef\"\u003e44\u003c/span\u003e]. Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e presents the onset degradation temperature (T₅\u003csub\u003e%\u003c/sub\u003e) for the different formulations.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea displays the TGA curves of the processed materials. For neat PLA, a single degradation slope is observed. However, when plasticized zein is added, up to three distinct slopes appear, corresponding to the degradation of both zein and the plasticizer, due to their limited thermal stability. In the 90P\u0026ndash;10Z and 80P\u0026ndash;20Z blends, only two slopes are visible, as the degradation of DPG and zein overlaps due to their low concentrations. In contrast, the remaining formulations show three distinguishable slopes, which can be interpreted as follows. First slope, occurring in the range of 150\u0026deg;C and 220\u0026deg;C, is associated with the degradation of the plasticizer, which is known for its high volatility and low thermal stability [\u003cspan class=\"CitationRef\"\u003e45\u003c/span\u003e]. Second slope corresponds to the degradation of zein, which is more thermally stable than DPG but less than PLA, and occurs between 220\u0026deg;C and 350\u0026deg;C [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e]; the final slope corresponds to the thermal degradation of PLA. The highest T₅% value is observed for neat PLA, indicating its superior thermal stability compared to the blends. As the proportion of plasticized zein increases, the T₅% decreases, reaching 188.2\u0026deg;C for the 50P\u0026ndash;50Z blend. This demonstrates that the addition of zein\u0026thinsp;+\u0026thinsp;DPG reduces the overall thermal stability and significantly lowers the degradation temperature.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb shows the first derivative of the TGA curves, which identifies the temperature at which the degradation rate is at its maximum. These curves confirm the observations from the T₅\u003csub\u003e%\u003c/sub\u003e data, with multiple peaks corresponding to the degradation of the individual components. Neat PLA shows only one main degradation peak, while the formulations containing plasticized zein exhibit several. A similar trend was reported by Gonzalez \u003cem\u003eet al.\u003c/em\u003e [\u003cspan class=\"CitationRef\"\u003e46\u003c/span\u003e], who studied PLA blends with SP plasticized with glycerol and observed multiple degradation events due to the different thermal stabilities of the components. Finally, Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e shows that the residual mass at the end of the test increases with higher zein\u0026thinsp;+\u0026thinsp;DPG content. Similar behavior has been reported in the literature [\u003cspan class=\"CitationRef\"\u003e47\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e].\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eThermogravimetric properties derived from the TGA test include: onset of degradation temperature (T\u003csub\u003e5%\u003c/sub\u003e), maximum degradation rate temperature (T\u003csub\u003emax\u003c/sub\u003e), and residual mass (%).\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCode\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eT\u003csub\u003e5%\u003c/sub\u003e (ᵒC)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eT\u003csub\u003emax\u003c/sub\u003e (ᵒC)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e% Residual mass\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePLA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e360.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e389.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e90P-10Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e325.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e362.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e80P-20Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e286.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e345.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e70P-30Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e245.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e336.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e60P-40Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e189.9\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e335.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e50Z-50P\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e188.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e335.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15.1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 Dynamic-mechanical thermal analysis of PLA\u0026ndash;zein blends.\u003c/h2\u003e\n \u003cp\u003eThe samples were evaluated through DMTA t for a range of temperatures to determine their dynamic mechanical behavior. TMA was conducted to evaluate the influence of temperature on the dimensional stability of the samples. Table \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e presents the storage modulus (E\u0026apos;) at 0\u0026deg;C and 25\u0026deg;C, obtained from the DMTA test. Also, the coefficient of linear thermal expansion (CTLE) measured by means of TMA is studied.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eThermomechanical properties obtained from the DMTA test E\u0026apos; at 0\u0026deg;C and 25\u0026deg;C and CTLE by means of TMA.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCode\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eE\u0026apos; at 0\u0026deg;C (MPa)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eE\u0026apos; at 25\u0026deg;C (MPa)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCTLE below Tg (mm/m\u0026middot;\u0026deg;C)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCTLE above Tg (mm/m\u0026middot;\u0026deg;C)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePLA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2059\u0026thinsp;\u0026plusmn;\u0026thinsp;31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1970\u0026thinsp;\u0026plusmn;\u0026thinsp;26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e85\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1440\u0026thinsp;\u0026plusmn;\u0026thinsp;15\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e90P-10Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2021\u0026thinsp;\u0026plusmn;\u0026thinsp;32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1904\u0026thinsp;\u0026plusmn;\u0026thinsp;24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e54\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e924\u0026thinsp;\u0026plusmn;\u0026thinsp;16\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e80P-20Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2064\u0026thinsp;\u0026plusmn;\u0026thinsp;23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1851\u0026thinsp;\u0026plusmn;\u0026thinsp;17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e93\u0026thinsp;\u0026plusmn;\u0026thinsp;10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e506\u0026thinsp;\u0026plusmn;\u0026thinsp;12\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e70P-30Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2058\u0026thinsp;\u0026plusmn;\u0026thinsp;34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1768\u0026thinsp;\u0026plusmn;\u0026thinsp;21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e109\u0026thinsp;\u0026plusmn;\u0026thinsp;14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e369\u0026thinsp;\u0026plusmn;\u0026thinsp;8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e60P-40Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1869\u0026thinsp;\u0026plusmn;\u0026thinsp;34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1502\u0026thinsp;\u0026plusmn;\u0026thinsp;18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e100\u0026thinsp;\u0026plusmn;\u0026thinsp;15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e603\u0026thinsp;\u0026plusmn;\u0026thinsp;9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e50Z-50P\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1779\u0026thinsp;\u0026plusmn;\u0026thinsp;30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1283\u0026thinsp;\u0026plusmn;\u0026thinsp;23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e119\u0026thinsp;\u0026plusmn;\u0026thinsp;12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2455\u0026thinsp;\u0026plusmn;\u0026thinsp;13\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eThe DMTA is especially effective in identifying variations in mechanical properties relative to temperature changes. Temperature plays a critical role in determining the behavior of polymeric materials. Above the T\u003csub\u003eg\u003c/sub\u003e, the material undergoes a shift from a rigid solid to a solid rubbery. As shown in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, a clear change in behavior is observed in the samples above this transition. Regarding the E\u0026rsquo;, its values approach 0 MPa as the material nears T\u003csub\u003eg\u003c/sub\u003e, reflecting the pronounced transition from a solid to a rubber-like phase at this temperature [\u003cspan class=\"CitationRef\"\u003e49\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eAs shown in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea, increasing the plasticized zein content has a significant effect on the E\u0026apos;. High concentrations, such as in the 60P\u0026ndash;40Z and 50P\u0026ndash;50Z blends, exhibit values nearing 0 MPa even before reaching their T\u003csub\u003eg\u003c/sub\u003e. This behavior is likely due to increased polymer chain mobility caused by the presence of the plasticizer, which increases the free volume and facilitates molecular movement. Additionally, the higher plasticized zein content contributes to this effect, as zein is an entirely amorphous material, and amorphous components require less energy to initiate molecular motion [\u003cspan class=\"CitationRef\"\u003e50\u003c/span\u003e]. A similar phenomenon was reported by Shengzhe Yang \u003cem\u003eet al.\u003c/em\u003e [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e], who observed a decrease in E\u0026apos; values with increasing SP content in PLA\u0026ndash;SP blends. Moreover, a noticeable change in thermal stability is observed across the formulations. As the proportion of plasticized zein increases, the plateau region before the transition becomes shorter, indicating a gradual and less abrupt change in material behavior. This trend suggests reduced thermal stability, which is also evident in Table \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, where samples with higher plasticized zein content exhibit a greater reduction in E\u0026apos; between 0\u0026deg;C and 25\u0026deg;C.\u003c/p\u003e\n \u003cp\u003eRegarding the damping factor (tan \u0026delta;), the peak values shift toward lower temperatures as the plasticized zein content increases. This shift confirms the reduction in T\u003csub\u003eg\u003c/sub\u003e with higher plasticizer and zein content, as previously observed in the DSC analysis. The decrease in T\u003csub\u003eg\u003c/sub\u003e is a result of the combined effect of the plasticizer, which enhances molecular mobility, and the amorphous nature of zein. The temperatures obtained in this test were consistent with those measured by DSC, supporting the validity of the results. Furthermore, only one peak was observed for each formulation, indicating a certain degree of miscibility between the components, Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb.\u003c/p\u003e\n \u003cp\u003eDimensional stability was evaluated using TMA, which enables the assessment of dimensional changes in the processed blends as a function of temperature. As shown in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e, two distinct regions can be identified: the first extends from the beginning of the test to approximately 45\u0026deg;C, where a linear relationship is observed between temperature increase and dimensional stability. The second region begins at around 45\u0026deg;C, corresponding to the T\u003csub\u003eg\u003c/sub\u003e of the materials, and is characterized by a pronounced change in slope due to the transition from a rigid solid to a rubbery state, where significant dimensional expansion occurs. To analyze the effect of zein\u0026thinsp;+\u0026thinsp;DPG incorporation, the CTLE was examined both below and above the T\u003csub\u003eg\u003c/sub\u003e to quantify the thermal response of each formulation. Neat PLA exhibited CTLE values of 85 \u0026micro;m/m\u0026middot;\u0026deg;C below T\u003csub\u003eg\u003c/sub\u003e and 1440 \u0026micro;m/m\u0026middot;\u0026deg;C above T\u003csub\u003eg\u003c/sub\u003e, which are consistent with previously reported data [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e]. The addition of zein\u0026thinsp;+\u0026thinsp;DPG increased the free volume and enhanced chain mobility, as supported by earlier mechanical tests showing more ductile behavior in these formulations. This dimensional change is attributed to the reduced PLA content and the plasticizing effect of DPG, which acts as a lubricant between PLA chains, lowering the matrix rigidity [\u003cspan class=\"CitationRef\"\u003e51\u003c/span\u003e]. As a result, formulations with higher zein\u0026thinsp;+\u0026thinsp;DPG content exhibit an earlier transition to a rubbery state and a more pronounced thermal expansion. For instance, the 50P\u0026ndash;50Z blend reached CTLE values of 119 \u0026micro;m/m\u0026middot;\u0026deg;C below T\u003csub\u003eg\u003c/sub\u003e and 2455 \u0026micro;m/m\u0026middot;\u0026deg;C above T\u003csub\u003eg\u003c/sub\u003e. Overall, these findings confirm that higher concentrations of zein\u0026thinsp;+\u0026thinsp;DPG promote earlier and more significant dimensional expansion in response to temperature.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4 Color characterization of PLA\u0026ndash;zein blends.\u003c/h2\u003e\n \u003cp\u003eA clear visual distinction was observed between the virgin PLA samples and those containing PLA-zein. Table \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e presents the color coordinate values, while Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e offers a visual comparison that highlights the differences among the various formulations.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab5\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eColorimetric properties of the PLA-zein samples.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCode\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eL\u003c/em\u003e*\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003ea\u003c/em\u003e*\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eb\u003c/em\u003e*\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varDelta\\:E}_{ab}^{*}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePLA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e90P-10Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e49.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e30.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e31.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e80P-20Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e59.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e42.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e70P-30Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e58.9\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e38.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e43.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e60P-40Z\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e56.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e38.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e42.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e50Z-50P\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e56.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e30.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e35.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eThe \u003cem\u003eL*\u003c/em\u003e parameter, which indicates sample luminance, increased significantly with the addition of zein, suggesting a lightening effect as the zein content increased. Neat PLA exhibited the lowest luminance value (37.3), while blends 80P-20Z and 70P-30Z showed the highest values (59.8 and 58.9, respectively), reflecting a shift toward brighter and whiter tones. The low \u003cem\u003eL*\u003c/em\u003e value in neat PLA is attributed to its high transparency, which allows significant light transmission and thus results in low diffuse reflectance. Consequently, a reduced \u003cem\u003eL*\u003c/em\u003e value in this context does not indicate opacity, but rather the material\u0026rsquo;s limited light reflection due to its transparent nature.\u003c/p\u003e\n \u003cp\u003eThe \u003cem\u003ea*\u003c/em\u003e parameter, representing the red-green axis, showed a near-neutral tone for PLA\u003c/p\u003e\n \u003cp\u003e(-0.3). However, all zein samples displayed a marked shift toward the red region, with values ranging from 5.8 (90P-10Z) to 11.0 (60P-40Z), indicating the presence of red tones introduced by zein. Regarding the \u003cem\u003eb*\u003c/em\u003e parameter represents the yellow-blue axis, changed notably with zein incorporation. While neat PLA showed a slightly yellow hue (2.2), zein formulations reached \u003cem\u003eb*\u003c/em\u003e values as high as 38.6 (70P-30Z), indicating a pronounced yellowish appearance, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eThe total color difference (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varDelta\\:E}_{ab}^{*}\\)\u003c/span\u003e\u003c/span\u003e) supports these observations, with values exceeding 30 for all zein-based formulations, confirming significant visual differences compared to neat PLA. The most substantial change was recorded in 70P-30Z (43.3), indicating a clearly perceptible color deviation, also illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. These shifts are consistent with modifications in surface morphology and polymer interactions induced by zein, resulting in altered optical behavior. Even when comparing only zein-containing materials among themselves, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varDelta\\:E}_{ab}^{*}\\)\u003c/span\u003e\u003c/span\u003e values exceeded 5, implying that noticeable visual distinctions persist across different plasticized zein concentrations.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\n \u003ch2\u003e3.5 Morphological characterization of PLA\u0026ndash;zein blends.\u003c/h2\u003e\n \u003cp\u003eThe images obtained from the optical analysis reveal the fracture surface morphology of each formulation. Distinct morphological differences are evident among the various samples, as illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eThe PLA sample (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ea) exhibited characteristic features of brittle fracture, with a smooth, laminar surface and no visible signs of plastic deformation [\u003cspan class=\"CitationRef\"\u003e52\u003c/span\u003e]. This brittle nature aligns with the mechanical behavior previously discussed.\u003c/p\u003e\n \u003cp\u003eIn contrast, the PLA-zein blends (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eb\u0026ndash;f) showed progressively more heterogeneous morphologies as the zein content increased. The 90P\u0026ndash;10Z and 80P\u0026ndash;20Z samples (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eb\u0026ndash;c) displayed dispersed spherical domains, indicative of phase separation between the PLA matrix and plasticized zein rich regions, suggesting partial miscibility and the presence of protein aggregates. As the zein proportion increased further (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ed\u0026ndash;f), the fracture surfaces became increasingly rough, porous, and irregular, with noticeable cavities and voids. The 50P\u0026ndash;50Z blend (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ef) exhibited the highest porosity and most pronounced phase separation, reflecting poor interfacial adhesion between the components. Similar findings were reported by Kun Fang \u003cem\u003eet al.\u003c/em\u003e [\u003cspan class=\"CitationRef\"\u003e53\u003c/span\u003e], who observed aggregate formation in PLA- SP blends.\u003c/p\u003e\n \u003cp\u003eAs the plasticized zein content increased in the formulations, the polymer chain mobility was enhanced due to the higher plasticizer concentration within the PLA matrix [\u003cspan class=\"CitationRef\"\u003e54\u003c/span\u003e]. However, this also promoted zein aggregation and phase separation at higher concentrations, as clearly observed in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\n \u003ch2\u003e3.6 Analysis of the chemical structure of PLA\u0026ndash;zein blends.\u003c/h2\u003e\n \u003cp\u003eFTIR analysis was conducted to identify the main functional groups present in the PLA-zein blends and to detect possible molecular interactions among their components.\u003c/p\u003e\n \u003cp\u003eAll spectra exhibited a strong absorption band around 1745 cm⁻\u0026sup1;, corresponding to the stretching vibration of the carbonyl (C\u0026thinsp;=\u0026thinsp;O) group typical of PLA [\u003cspan class=\"CitationRef\"\u003e55\u003c/span\u003e]. This band remained present in the zein blends, although slight changes in intensity and shape were observed, suggesting interactions between the ester groups of PLA and the functional groups of zein or the plasticizer.\u003c/p\u003e\n \u003cp\u003eAs the plasticized zein content increased, new bands appeared or existing signals intensified in the 1650\u0026ndash;1530 cm⁻\u0026sup1; region, which are associated with amide I and II vibrations characteristic of zein. These signals confirm the incorporation of the protein into the polymer matrix [\u003cspan class=\"CitationRef\"\u003e56\u003c/span\u003e]. In the 3200\u0026ndash;3400 cm⁻\u0026sup1; range, a progressive broadening of the O\u0026ndash;H and N\u0026ndash;H stretching band was observed, indicating a higher presence of hydroxyl groups and the potential formation of hydrogen bonds between PLA and zein\u0026thinsp;+\u0026thinsp;DPG [\u003cspan class=\"CitationRef\"\u003e46\u003c/span\u003e]. Additionally, variations were detected in the 2800\u0026ndash;3000 cm⁻\u0026sup1; region, corresponding to aliphatic C\u0026ndash;H stretching, suggesting structural changes related to the dispersion of the components and the effect of the plasticizer [\u003cspan class=\"CitationRef\"\u003e57\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eOverall, the spectra indicate partial miscibility between the components, with the presence of physical interactions particularly hydrogen bonding, but no clear evidence of chemical reactions between the phases. These findings are consistent with the morphological results.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003eThis study evaluates the development of PLA-zein blends. To this effect a corn-derived protein was plasticized with DPG as a natural plasticizer. Plasticized protein help modify the properties of PLA, in this case making it more ductile. The materials were processed through twin-screw extrusion and injection molding. Various concentrations of plasticized zein with DPG were integrated into the PLA matrix to assess their combined influence on processability and overall performance. Mechanical testing reveals that increasing the plasticized zein content enhances the ductility of the material. In contrast, as the concentration of plasticized zein rises, tensile strength and elastic modulus decrease. This effect is related to the plasticizer\u0026rsquo;s ability to disrupt the polymer chains, allowing greater mobility and improved flexibility. Notably, the 60P-40Z and 50P-50Z blends achieved elongation values of 25.5% and 56.25%, respectively. In contrast, Charpy impact resistance declines with higher plasticized zein content, likely due to the increased aggregation and heterogeneity between the PLA and zein phases, which leads to greater brittleness. For instance, the impact strength drops from 42.2 kJ/m\u0026sup2; for neat PLA to 11.5 kJ/m\u0026sup2; for the 50P-50Z blend. Shore D hardness remains relatively stable, though a slight reduction is observed at higher plasticizer concentrations, decreasing from 82.9 for neat PLA to 77.4 for 50P-50Z, indicating a softening effect due to the plasticizer. Thermal analysis using DSC shows that all blends exhibit a single T\u003csub\u003eg\u003c/sub\u003e, suggesting partial miscibility between the components. T\u003csub\u003eg\u003c/sub\u003e decreases as the plasticized zein content increases, from 59.5\u0026deg;C for neat PLA to 39.9\u0026deg;C for the 50P-50Z sample, consistent with the expected plasticizing effect. TGA demonstrates that the thermal stability of the materials declines with higher zein\u0026thinsp;+\u0026thinsp;DPG content. The T\u003csub\u003e5%\u003c/sub\u003e drops significantly, from 360.0\u0026deg;C for PLA to 188.2\u0026deg;C for 50P-50Z. Additionally, residual mass at the end of the TGA test increases with greater plasticized zein loading, reflecting the contribution of non-volatile protein and plasticizer residues. Thermomechanical analysis via DMTA supports the previous findings. The results confirm that samples with higher plasticized zein content exhibit more ductile behavior and lower T\u003csub\u003eg\u003c/sub\u003e values, consistent with a more flexible molecular structure. TMA analysis revealed that the incorporation of zein\u0026thinsp;+\u0026thinsp;DPG into PLA-based blends significantly affected their dimensional stability. Colorimetric evaluation indicates a notable change in the visual appearance of the material. The lightness parameter (\u003cem\u003eL*\u003c/em\u003e) increases, while the color shifts toward red (\u003cem\u003ea*\u003c/em\u003e) and yellow (\u003cem\u003eb*\u003c/em\u003e) hues. The total color difference (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varDelta\\:E}_{ab}^{*}\\)\u003c/span\u003e\u003c/span\u003e) exceeds a value of 5, indicating visibly distinguishable samples. Morphological analysis corroborates the mechanical findings. As the zein\u0026thinsp;+\u0026thinsp;DPG content increases, more surface inclusions appear, highlighting the partial miscibility and limited compatibility between phases. The fracture surfaces become rougher, consistent with enhanced ductility, compared to the smooth fracture of neat PLA. Finally, FTIR analysis confirms the presence of physical interactions and some degree of miscibility between PLA and zein, further supporting the interpretation of the mechanical and thermal results. Overall, the incorporation of zein and DPG into the PLA matrix results in a more ductile material, while simultaneously enhancing the mechanical performance and processability of the zein\u0026ndash;DPG phase. This combination of materials presents an interesting alternative due to its natural origin that helps to reduce petroleum dependency. In addition, biocompatibility, and biodegradability, making it interesting for various industries, including food packaging and biomedical applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research is a part of the grant PID2023-152869OB-C22, and the grant TED2021-131762A-I00, funded by MCIN/AEI/10.13039/501100011033 and by the European Union “NextGenerationEU”/PRTR. The authors also thank Generalitat Valenciana - GVA, grant number CIGE/2023/46 and CIAICO/2023/253, for supporting this work. C. Lazaro-Hdez thanks Generalitat Valenciana - GVA for funding a predoc position through the CIACIF program co-funded by ESF Investing in your future, grant number CIACIF/2023/244.\u0026nbsp;M. Miranda-Pinzon thanks Vice-rectorate for Research of the\u0026nbsp;Universitat Politècnica de València (UPV)\u0026nbsp;for funding a predoctoral contract in the PAID-01-24 program. J. Ivorra-Martinez thanks Generalitat Valenciana - GVA for funding a postdoc position through the CIAPOS program co-funded by ESF Investing in your future, grant number CIAPOS/2023/362. Microscopy services at UPV are also acknowledged for their help in collecting and analyzing FESEM images.\u0026nbsp;Funding for open access charge: CRUE-Universitat Politècnica de València.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCarlos Lazaro-Hdez\u003c/strong\u003e: Investigation, Data curation, Validation, Writing original draft, Writing – review \u0026amp; editing, Visualization, Methodology. \u003cstrong\u003eMario Miranda-Pinzon\u003c/strong\u003e: Investigation, Resources, Methodology, Formal analysis, Data curation, Visualization. \u003cstrong\u003eMaria del Puig Vicente-Vinas\u003c/strong\u003e: Investigation, Formal analysis, Validation, Data curation. \u003cstrong\u003eTeodomiro Boronat\u003c/strong\u003e: Conceptualization, Supervision, Validation, Project administration, Writing – review \u0026amp; editing, Funding acquisition. \u003cstrong\u003eJuan Ivorra-Martinez\u003c/strong\u003e: Conceptualization, Supervision, Writing – review \u0026amp; editing, Funding acquisition\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement:\u003c/strong\u003eData will be made available on request\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest:\u0026nbsp;\u003c/strong\u003eThe authors declare no conflicts of interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eLeal Filho, W., et al., \u003cem\u003eAn assessment of attitudes towards plastics and bioplastics in Europe.\u003c/em\u003e Science of the Total Environment, 2021. \u003cstrong\u003e755\u003c/strong\u003e: p. 142732.\u003c/li\u003e\n \u003cli\u003eHenderson, L. and C. 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Zhang, \u003cem\u003eCompatibilizing effects of maleated poly (lactic acid)(PLA) on properties of PLA/soy protein composites.\u003c/em\u003e Industrial \u0026amp; Engineering Chemistry Research, 2012. \u003cstrong\u003e51\u003c/strong\u003e(22): p. 7786-7792.\u003c/li\u003e\n \u003cli\u003eYang, S., et al., \u003cem\u003eCharacterization and biodegradation behavior of bio-based poly (lactic acid) and soy protein blends for sustainable horticultural applications.\u003c/em\u003e Green Chemistry, 2015. \u003cstrong\u003e17\u003c/strong\u003e(1): p. 380-393.\u003c/li\u003e\n \u003cli\u003eJeong, H., et al., \u003cem\u003eLactide-derived ester oligomers for highly compatible poly (lactide) plasticizer produced through an eco-friendly process: renewable resources, biodegradation, enhanced flexibility, and elastomeric performance.\u003c/em\u003e Green Chemistry, 2021. \u003cstrong\u003e23\u003c/strong\u003e(19): p. 7549-7565.\u003c/li\u003e\n \u003cli\u003eTurco, R., et al., \u003cem\u003eCynara cardunculus biomass recovery: an eco-sustainable, nonedible resource of vegetable oil for the production of poly (lactic acid) bioplasticizers.\u003c/em\u003e ACS Sustainable Chemistry \u0026amp; Engineering, 2019. \u003cstrong\u003e7\u003c/strong\u003e(4): p. 4069-4077.\u003c/li\u003e\n \u003cli\u003eCalabria, L., et al., \u003cem\u003eSoy protein isolate/poly(lactic acid) injection-molded biodegradable blends for slow release of fertilizers.\u003c/em\u003e Industrial Crops and Products, 2012. \u003cstrong\u003e36\u003c/strong\u003e(1): p. 41-46. 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Strumia, and C.I. Alvarez Igarzabal, \u003cem\u003eCross-linked soy protein as material for biodegradable films: Synthesis, characterization and biodegradation.\u003c/em\u003e Journal of Food Engineering, 2011. \u003cstrong\u003e106\u003c/strong\u003e(4): p. 331-338. DOI: https://doi.org/10.1016/j.jfoodeng.2011.05.030.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymers-and-the-environment","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jooe","sideBox":"Learn more about [Journal of Polymers and the Environment](https://www.springer.com/journal/10924)","snPcode":"10924","submissionUrl":"https://submission.nature.com/new-submission/10924/3","title":"Journal of Polymers and the Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Polylactic acid, Zein, Dipropylene glycol, Blend","lastPublishedDoi":"10.21203/rs.3.rs-7869492/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7869492/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study explores the development of polylactic acid (PLA) blends incorporating plasticized zein, a corn-derived protein, and dipropylene glycol (DPG) as a biobased plasticizer to enhance compatibility and processability. Blends were produced via twin-screw extrusion and injection molding, with plasticized zein content ranging from 10 to 50 wt%. Mechanical testing showed a significant increase in ductility, with elongation at break rising from 6.3% (neat PLA) to 56.3% (50 wt% zein), accompanied by reduced tensile strength (58.4 MPa to 22.7 MPa) and impact resistance (42.2 kJ/m\u003csup\u003e2\u003c/sup\u003e to 11.5 kJ/m\u003csup\u003e2\u003c/sup\u003e), due to phase separation and limited compatibility. Shore D hardness slightly declined (from 82.9 to 77.4). Thermal analysis revealed a single glass transition temperature (T\u003csub\u003eg\u003c/sub\u003e) in all blends, indicating partial miscibility, with T\u003csub\u003eg\u003c/sub\u003e decreasing from 59.5\u0026deg;C to 39.9\u0026deg;C as zein content increased. Thermogravimetric analysis showed reduced thermal stability with zein addition, dropping the initial degradation temperature from 360.0\u0026deg;C to 188.2\u0026deg;C. Morphological analysis indicated greater heterogeneity at higher zein levels due to partial miscibility. Colorimetric data showed visible changes, and FTIR spectra confirmed physical interactions and partial miscibility between PLA and zein.\u003c/p\u003e","manuscriptTitle":"Development and characterization of ductile polylactic acid blends with plasticized zein for injection molding applications","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-07 14:02:12","doi":"10.21203/rs.3.rs-7869492/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-11-20T10:22:03+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-08T14:34:50+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-08T14:34:16+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-08T10:17:32+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-07T18:15:06+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-03T02:53:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"299246588235150063153302159427604651145","date":"2025-11-03T02:29:06+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-02T02:50:27+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"85966244822663791395223675406271984196","date":"2025-10-31T02:55:25+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"175549394420359563028337755920873516482","date":"2025-10-31T01:20:06+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"207118933968523916885151715948938312133","date":"2025-10-30T22:31:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"130166151461542382404007329809998625455","date":"2025-10-29T19:05:51+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"259103905470489546389454061890037249379","date":"2025-10-28T22:00:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"267589455770781469818298406379701461638","date":"2025-10-28T18:04:05+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-10-28T14:46:18+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-10-16T18:32:50+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-10-16T18:32:24+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Polymers and the Environment","date":"2025-10-15T14:46:35+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymers-and-the-environment","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jooe","sideBox":"Learn more about [Journal of Polymers and the Environment](https://www.springer.com/journal/10924)","snPcode":"10924","submissionUrl":"https://submission.nature.com/new-submission/10924/3","title":"Journal of Polymers and the Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"7b4f4600-758d-4ef9-9c24-43210d74d221","owner":[],"postedDate":"November 7th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-03-30T16:24:08+00:00","versionOfRecord":{"articleIdentity":"rs-7869492","link":"https://doi.org/10.1007/s10924-026-03813-7","journal":{"identity":"journal-of-polymers-and-the-environment","isVorOnly":false,"title":"Journal of Polymers and the Environment"},"publishedOn":"2026-03-27 16:10:33","publishedOnDateReadable":"March 27th, 2026"},"versionCreatedAt":"2025-11-07 14:02:12","video":"","vorDoi":"10.1007/s10924-026-03813-7","vorDoiUrl":"https://doi.org/10.1007/s10924-026-03813-7","workflowStages":[]},"version":"v1","identity":"rs-7869492","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7869492","identity":"rs-7869492","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}