Phase morphology, mechanical performance, and thermal properties of fully biodegradable polylactic acid/polybutylene adipate terephthalate crosslinked network induced by UV irradiation

Phase morphology, mechanical performance, and thermal properties of fully biodegradable polylactic acid/polybutylene adipate terephthalate crosslinked network induced by UV irradiation | 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 Phase morphology, mechanical performance, and thermal properties of fully biodegradable polylactic acid/polybutylene adipate terephthalate crosslinked network induced by UV irradiation Xueyan Bian, Suju Fan, Gang Xia, John Xin, Shouxiang Jiang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4001826/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract Over the past few decades, there has been growing interest in replacing some of the fossil-derived polymers with biobased or biodegradable ones due to environmental concerns. Biobased polylactic acid (PLA) has emerged as the most practical option because of its superior mechanical and thermal qualities compared to other types of biopolymers. However, due to the inherent deficiencies of PLA, modifications to PLA have been an ongoing endeavor. In this study, samples of neat PLA, neat polybutylene adipate terephthalate (PBAT), blends of PLA and PBAT, as well as their crosslinked blends were fabricated. The morphology, mechanical and thermal transition performances, and thermal stability of the fully biodegradable samples were then measured. The results show that the flexibility and toughness of PLA were significantly enhanced. Especially, the elongation at break of ABT-UV30 (PLA/PBAT/triallyisocyanurate (TAIC) exposed to ultraviolet (UV) light for 30 minutes) was increased 37.8 times as compared to neat PLA. The compatibility of PLA and PBAT was enhanced by the development of a crosslinked network structure. The thermalgravimetric analyzer thermograms show that a moderate amount of UV radiation can improve the thermal stability of the sample while an excessive amount of UV radiation can reduce the temperature at which the sample degrades. Bio-based polylactic acid polybutylene adipate terephthalate crosslinked structure Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1 Introduction Plastic production expanded quickly after World War II, dramatically improving people's lives and transforming contemporary society. However, the majority of plastic products are derived from fossil fuels and cannot be biodegraded. It is estimated that about 6.3 billion Mt of plastic waste had been produced by 2015, but only 9% of this plastic waste were recycled, leaving 91% to be burned, landfilled or left in the natural environment [ 1 ]. Over the past few decades, there has been an increasing interest in using biobased polymers with potential degradability to replace certain fossil-derived polymers, which would significantly reduce the consumption of natural resources and decrease environmental pollutants. Energy crops, food-based biomass waste, agricultural biomass residue, and forest biomass are the main sources of biobased polymers [ 2 ]. Polylactic acid (PLA) is an aliphatic polyester, primarily produced by the ring-opening polymerization of lactide and industrial polycondensation of lactic acid. The basic unit of PLA, lactic acid, is produced from renewable resources such as wheat, straw, corn, and sorghum, which is bio-based and can be decomposed into water and carbon dioxide by microbes. As a leading candidate of biobased polymer, PLA has gained widespread attention from both the academia and industry due to its high strength and modulus, good thermoplastic performance, and ability to be molded with a variety of methods. [ 3 ] However, PLA has several inherent shortcomings, such as high brittleness, poor ductility, low crystallization rate, and low heat resistance temperature, which greatly limit its wide use in industrial production [ 4 – 6 ]. To date, a number of approaches have been proposed to address these shortcomings, such as forming a stereocomplex (SC) structure, adding nucleating agents, promoting a crosslink reaction, plasticization, and blending with various tough polymers. [ 6 – 9 ] Ikada et al. first reported that poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) blended with a ratio of 1:1 can produce a SC crystallite structure. The SC crystallite has a melting point temperature (Tm) of about 230°C, which is 50°C higher than that of the PLLA or PDLA homocrystals. [ 10 ] However, the high cost of high-purity PDLA prevents its wide use in industrial production. According to the study from Tang’ group, the addition of a nucleating agent, ethylenebishydroxystearamide (EBH), can considerably increase the crystallinity and crystallization rate of PLA. After the annealing procedure, the heat deflection temperature (HDT) of nucleated PLA can be increased by 30°C. [ 11 ] Shaffer et al. has used two crosslinking agents, trimethylolpropane triacrylate (TMPTA) and triallyisocyanurate (TAIC) to modify PLA. It was reported that a crosslinking reaction that occurred close to the glass transition temperature (Tg) can significantly enhance the thermomechanical properties of the PLA polymer. [ 12 ] Tsou et al. prepared PLA with adipate ester as a plasticizer and concluded that the addition of adipate ester could improve the toughness of PLA, but reduced the cold crystallization and Tg. [ 13 ] Polymer blends are considered as materials with tunable qualities that can deliver a synergistic performance. Sadayuki et al. blended PLA with different polymers including polyethylene terephthalate (PET), polybutylene terephthalate (PBT), nylon (N6), nylon (N12), and polycarbonate (PC). The results indicated that both the tensile strength, elongation at break and HDT of these blends (with a PLA/polymer ratio of 80/20) were increased significantly. [ 14 ] However, these blends cannot be fully biodegraded due to the addition of fossil-based and nonbiodegradable polymers. Therefore, increasing attention has been attracted to modify PLA with biodegradable materials. PBAT is fossil-based but a fully biodegradable polymer. Compared to other biopolymers, such as poly(hydroxy valerate) (PHV), poly(hydroxy butyrate) (PHB), polycaprolactone (PCL), and polybutylene succinate (PBS), PBAT has relatively high elongation at break and impact strength, making it the most promising option to tough PLA. [ 15 ] However, the incompatibility between PLA and PBAT can cause interfacial separation, leading to an unsatisfactory enhancement in mechanical properties. [ 16 ] In this study, PBAT was added to improve the flexibility and toughness of PLA. The compatibility of PLA and PBAT was enhanced through the formation of the crosslink spatial network. TAIC was used as the crosslinking agent, and ultraviolet (UV) radiation was employed to induce the occurrence of crosslink reaction. The morphology, mechanical performance, phase transition temperature, and thermogravimetric analysis of samples were then evaluated, and the mechanisms were also investigated. 2 Experimental 2.1 Materials PLA was supplied by Anhui Fengyuan Bio-Fiber Co., Ltd. The PLA polymer has an average molecular weight of approximately 120,000 g/mol, a density of 1.24 g/cm 3 , and a melt mass-flow rate (MFR) of 4 g/10 min (190°C/2.16 kg). PBAT was purchased from Shanghai Macklin Biochemical Co., Ltd. The PBAT polymer has an average molecular weight of approximately 680,000 g/mol, a density of 1.21 g/cm 3 , and a MFR of 4.5 g/10 min (190°C/2.16 kg). TAIC was supplied by Thermo Fisher Scientific (USA). Dichloromethane (DCM), HPLC grade was purchase from Anaqua Global International Inc. Limited. 2.2 Sample preparation PLA and PBAT polymer masterbatches were immersed into an ultrasonic ethanol bath for 30 minutes to remove impurities, then rinsed five times with distilled water. Prior to usage, the cleaned masterbatches were dried in a vacuum oven at 60°C for 24 hours to eliminate surface moisture. An organic solvent, DCM, was used to dissolve a certain mass of PLA, PBAT, and PLA/PBAT blend polymers (weight ratio: 80/20) at a mass fraction of 10%. The PLA, PBAT, and PLA/PBAT solutions were stirred by using a magnetic stirrer at a temperature of 40°C, and all of the PLA and PBAT polymer masterbatches were completely dissolved after a 60-minute of stirring at a rotational speed of 500 rpm. The fully dissolved PLA/PBAT solution was poured into six transparent bottles. Five of them were added to TAIC at a mass percentage of 3% (to polymers) and stirred for 10 more minutes so that the TAIC could disperse uniformly in the solution. Then four bottles filled with the PLA/PBAT/TAIC solutions were placed in a UV light box (mode: fluorescent lamp, supported by Shanghai Xinxin Light Co., Ltd.) and exposed to UV light for various lengths of time—15, 30, 45, and 60 minutes. Following UV exposure, all of the solutions were used to cast films, and kept in a fume hood for 2 hours to allow the DCM solvent to evaporate. Then, all of the films were dried in a vacuum oven to further remove any residual DCM. The preparation recipe is shown in Table 1 . All of the samples were hot-pressed into sheets by using a compression molding machine (model: ZS-406B, Dongguan Zhuosheng Machinery Equipment Co., Ltd).The samples were heated at 180°C for 10 minutes, then pressed for 2 minutes at a pressure of five bars. Samples of neat PLA and PBAT, PLA/PBAT blend, PLA/PBAT/TAIC without UV treatment, and PLA/PBAT/TAIC exposed to UV radiation for 15, 30, 45, and 60 minutes were labeled as PLA, PBAT, AB, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60, respectively. Figure 1 is the schematic diagram of the sample preparation process. Table 1 Preparation recipe of samples. Sample Name Weight PLA (g) Weight PBAT (g) Weight TAIC (g) UV radiation (min) PLA 10 0 0 0 PBAT 0 10 0 0 AB 8 2 0 0 ABT-UV0 8 2 0.3 0 ABT-UV15 8 2 0.3 15 ABT-UV30 8 2 0.3 30 ABT-UV45 8 2 0.3 45 ABT-UV60 8 2 0.3 60 2.3 Characterization 2.3.1 Morphology The fractured morphology of the samples after being subjected to impact strength (IS) testing was observed through a field emission scanning electron microscope (FESEM Tescan MAIA3) at a SEM HV of 5 kV. A thin layer of gold film was sputtered onto the samples before being examined under the FESEM. 2.3.2 Fourier transform infrared spectroscopy A Fourier transform infrared (FTIR) spectrometer (Spectrum 100, PerkinElmer) was used to determine the interactions among PLA, PBAT, and TAIC. The FTIR curves were recorded in transmittance mode, with a constant spectral resolution of 4 cm − 1 , scanning number of 32, and scanning wavelength that ranged from 600 to 4000 nm. 2.3.3 Mechanical properties Tensile testing was conducted according to ISO 527 standard, by using INSTRON 5566, a universal testing machine. The samples were molded into a dumbbell shape, with an initial gauge length of 25 mm, width of 4 mm and thickness of 1 mm. They were then conditioned at a temperature of 25°C and humidity of 50% for 24 h before being tested. The tensile strength and elongation at break results were recorded based on the average results of five samples. Impact testing was conducted according to ISO 179 by using a Zwick Charpy impact machine with a 1 J hammer. The samples were prepared unnotched with dimensions of 80 ⅹ10 ⅹ 4 mm. The IS results were recorded as the average value of five samples. 2.3.4 Thermal transitions The thermal transitions of the samples were investigated by using a differential scanning calorimeter (PerkinElmer DSC 8000), supplied by Al instruments (Hong Kong) Limited. Samples that weighed approximately 3 mg were placed in aluminum pans for measurement. They were heated from 0°C to 300°C at 20°C/min, at a nitrogen flow rate of 50 ml/min. The Tg was determined by estimating the midpoint in proximity to the change in specific heat (ΔCp). The midpoint of the segment between the onset and offset of Tg was defined as the Tg [ 17 ]. The melting point (Tm) is the peak value according to the International Confederation for Thermal Analysis and Calorimetry (ICTAC) standards. A dynamic mechanical analyzer (DMA Q800, TA, USA) was used to determine the Tg of the samples. The measurement was performed by heating the samples (with dimensions of 60 ⅹ 10 ⅹ 1 mm) from room temperature to 120°C at a rate of 5°C/ min in a 3-point-bend mode. 2.2.5 Thermogravimetric analysis (TGA) The thermal stability of samples was evaluated by using a thermalgravimetric analyzer (PerkinElmer TGA 4000 System 100-240V/50-60HZ), supplied by Labware Analytical Company Limited. The samples were heated from 50°C to 800°C at 20°C/min, at a nitrogen flow rate of 20 ml/min. 3 Results and discussion 3.1 Morphology The scanning electron microscopy images of the fractured surfaces of PLA, PBAT, PLA/PBAT, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60 were observed with an FESEM at a magnification of 3 kx. As depicted in Fig. 2 (a), the neat PLA has a very smooth fractured surface without any visible plastic deformation, indicating its brittle property. Comparatively, the fractured surface of neat PBAT in Fig. 2 (b) shows obvious plastic deformation, which suggests the tough performance of PBAT. Figure 2 (c) shows that the AB sample is composed of two phases, the PBAT dispersed phase and the PLA matrix phase. Meanwhile, there is an obvious interfacial separation on the fractured surface, thus indicating low interfacial adhesion between PLA and PBAT. The incompatibility of PLA and PBAT has been reported in previous studies numerous times. [ 18 , 19 ]. The PBAT phase is usually distributed within the PLA matrix in the form of spheres or columns instead of uniformly blending into the PLA. PLA and PBAT are immiscible at the molecular level according to the Gibbs free energy formula: $${\varDelta G}_{mix}={\varDelta H}_{mix}-T{\varDelta S}_{mix}$$ where ΔG mix is the Gibbs free energy, and ΔH mix and ΔS mix represent the enthalpy and entropy changes, respectively. T denotes the temperature (Kelvin) [ 20 ]. According to this theory, a negative free energy of mixing homogeneous miscibility in polymer blends is required. The high molecular weight results in negligible mixing entropy. As the mixing enthalpy is positive and there is no specific interaction between these two polymers, the result is the immiscibility of the PLA and PBAT polymers [ 21 ]. As depicted in Fig. 2 (c), the PLA matrix undergone brittle fracture when an impact force was applied, while the PBAT phase was still continuous and under tension. The PBAT phase was detaching from the PLA matrix at the interface when tension was applied, so gaps and cavities was formed. In the end, the fracture of the PBAT phase occurred, and tough fractures of the PBAT phase formed. Figure 2 (d) shows that there is no obvious difference between ABT-UV0 and AB. However, the fractured surface of ABT-UV15 demonstrates increased compatibility of the PLA and PBAT phases after the sample was exposed to UV light for 15 minutes, see Fig. 2 (e). The width of the gaps that originated from the interfacial detachment is narrower and there are fewer cavities. This result might be due to the crosslinking reaction mechanism as detailed in Section 3.3 in which the PLA and PBAT molecular chains started to bond together because of the TAIC and UV radiation. Figures 2 (e) to 2(h) show that the two-phase interfaces cannot be differentiated from the fractured surface images as the UV radiation exposure time is over 30 minutes. This result indicates that as the crosslinking reaction progressed, the PBAT molecular chains distributed more uniformly in the PLA matrix. In contrast to the brittle and smooth fractured surface of the neat PLA, the fractured sections of ABT-UV30 and ABT-UV45 exhibit more fibrils pulling out, which suggests the enhanced toughness of the samples. However, there is less plastic deformation on the fractured surface of ABT-UV60. This is likely because excessive crosslinking reactions can increase rigidity, thus reducing the toughness of the sample. 3.2 Fourier transform infrared spectroscopy The chemical structures of PLA, PBAT, TAIC and ABT-UV30 were characterized by FTIR spectroscopy, as shown in Fig. 3 . In the case of PLA, the three peaks at 1044 cm − 1 , 1076 cm − 1 , and 1183 cm − 1 are related to the stretching vibrations of the ether groups (C–O–C). The characteristic peak at 1751 cm − 1 is assigned to the stretching vibrations of the carbonyl groups (C = O). The two peaks that appear at 2855 cm − 1 and 2925 cm − 1 belong to the stretching vibrations of the tertiary carbon and hydrogen bonds (C-H) on backbones [ 22 ]. The two characteristic peaks at 2942 cm − 1 and 2995 cm − 1 are the symmetric and asymmetric stretching vibrations of the methyl groups (CH 3 ) in saturated hydrocarbons, which are clearly visible in all of the FTIR spectra [ 23 ]. For the neat PBAT, the characteristic peak at 1018 cm − 1 is due to the vibrations of the hydrogen atom of the aromatic ring. Peaks that appear at 1104 cm − 1 and 1267 cm − 1 are the symmetric stretching vibrations of the carbon and oxygen groups (C–O). The characteristic peaks at 1409 cm − 1 and 2948 cm − 1 are assigned to the in-plane bending vibrations and the asymmetric stretching vibrations of the methylene groups (CH 2 ), respectively. The bands at 1504 cm − 1 and 1711 cm − 1 are the skeletal vibrations of the aromatic ring and the stretching vibrations of the C = O. In the FTIR curve of TAIC, the peaks at 1376 cm − 1 and 1756 cm − 1 are the tertiary amide absorption vibrations. The characteristic peaks at 1653 cm − 1 and 1695 cm − 1 are attributed to the stretching vibrations of the carbon-carbon double bonds (C = C) and the stretching vibrations of C = O [ 12 ]. In the curve of ABT-UV30, the peak of the C = C stretching vibrations of TAIC at 1653 cm − 1 is no longer there. This indicates the breakage of the C = C bond in TAIC under UV radiation and the formation of TAIC radicals. In addition, there are new bands at 3506 cm − 1 , which can be assigned to a hydroxyl group (–OH). The formation of hydroxyl groups is attributed to thermal degradation of PLA and PBAT macromolecules during the UV radiation or melting process [ 24 ]. 3.3 Mechanism The mechanisms of the crosslink reaction and molecular chain breakdown brought on by the UV light are shown in Fig. 4 . Figure 4 (a) describes the two steps of the crosslink reaction. In the first step, the carbon and hydrogen (C-H) bonds on the PLA backbones are broken under the influence of UV light. PLA free radicals formed as a result of the loss of protons of the tertiary carbon. Meanwhile, UV radiation also contributes to the formation of TAIC and PBAT radicals. In the second step, the PLA and PBAT free radicals combined with TAIC radicals mainly in three types of reactions as shown in Fig. 4 (a). The numbers 1, 2, and 3 which represent the three types of reactions also indicate the difficulty of the reaction. It is more difficult for Reaction Type 2 to happen than Reaction Type 1 mainly due to the steric hindrance. Malinowski et al. [ 22 ] reported that PLA has higher susceptibility to electromagnetic radiation than PBAT when radiation is used to promote chemical reactions. The presence of aromatic groupings in PBAT macromolecular chains can absorb some of the electromagnetic radiation and dissipate it in the form of heat. This so-called protective effect deactivates some of the active sites. As a result, it is more difficult for PBAT to form free radicals, and PBAT is less prone to have a crosslink reaction when compared to PLA. Therefore, it is more difficult for Reaction Type 3 to occur in comparison with Reaction Type 2. In addition to crosslink reactions, the chain scission of PLA may also occur when the samples are excessively exposed to UV radiation, as PLA is sensitive to UV radiation. This could be inferred from the new formation of hydroxyl group bands on the FTIR curves of ABT-UV30 as discussed in Section 3.2 . Besides, samples exposed to UV light for a prolonged period of time also lose some of their mechanical and thermal properties, as will be discussed in more details in Sections 3.4 and 3.6 . 3.4 Mechanical properties The tensile strength, elongation at break and impact strength of PLA, PBAT, AB, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60 were tested and the results are listed in Table 2 . The results are also plotted in bar graphs in Fig. 5 to visually show the changes in these mechanical properties. As shown in Table 2 , the tensile strength of neat PLA is 68.0 MPa and the elongation at break is only 9.2%, thus indicating that PLA is a hard and brittle polymer at room temperature. Comparatively, PBAT has a low tensile strength of 9.5 MPa and a high elongation at break of 525.0%, which indicate its weak and flexible properties. As shown in Figs. 5 (a) and 5(b), the elongation at break of AB was increased to 315.1%, which is approximately 33 times higher than neat PLA. This shows that the addition of PBAT can greatly increase the flexibility of PLA. Meanwhile, the tensile strength of AB was slightly decreased compared to neat PLA, which could be brought on by the defects resulting from the two-phase interface separation. The effect of PBAT on the mechanical properties of PLA is consistent with the results reported in previous studies [ 25 , 26 ]. After the addition of TAIC, both the tensile strength and the elongation at break slightly declined. The PLA and PBAT molecular chains were lubricated by the miniscule TAIC molecules, which decreased the entanglement and connectivity between the chains and consequently reduced the tensile strength of ABT-UV0. As shown in Table 2 , both the tensile strength and elongation at break of the samples increased initially as the UV radiation period was increased from 15 to 60 minutes, but started to decline when the UV radiation time exceeded 30 minutes. The crosslinked spatial network developed during the crosslinking reaction may have contributed to the increase in tensile strength of ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60. UV radiation can, however, also cause chain scissions in the PLA macromolecular chains, which reduces the tensile strength of the samples. As depicted in Table 2 and Fig. 5 (c), the toughness of PBAT is significantly higher than that of PLA, with unnotched impact strength values of 17.4 KJ/m 2 and 2.9 KJ/m 2 , respectively. The impact strength of AB was increased by 179.3% by the addition of PBAT at a mass proportion of 20%. The further enhancement of the impact strength of the samples was, however, constrained by the poor interfacial adhesion between the PLA and PBAT elements. The impact strength was initially increased as the UV radiation time was increased from 0 to 60 minutes, then decreased once the UV radiation time exceeded 30 minutes. The toughening effect of PBAT and the increased compatibility of PLA and PBAT as a result of the branched copolymer generated during the crosslinking reaction were the key contributors to the improvement in the impact strength. However, the formation of the crosslinking network can also lead to rigidity, which reduces the impact strength of the samples. Table 2 Mechanical properties of PLA, PBAT, AB, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60. Sample name Tensile strength (MPa) Elongation at break (%) Unnotched impact strength (KJ/m 2 ) PLA 68.0 ± 3.1 9.2 ± 1.4 2.9 ± 0.1 PBAT 9.5 ± 1 525.0 ± 18.2 45.2 ± 0.6 AB 51.1 ± 4.2 315.1 ± 12.7 7.1 ± 0.4 ABT-UV0 53.8 ± 3.8 327.7 ± 19.9 8.5 ± 0.5 ABT-UV15 58.2 ± 4.6 363.5 ± 16.3 12.3 ± 1.0 ABT-UV30 63.1 ± 4.9 389.4 ± 28.8 18.2 ± 1.3 ABT-UV45 58.3 ± 2.1 357.2 ± 23.9 15.7 ± 0.8 ABT-UV60 56.2 ± 4.9 316.8 ± 15.8 10.3 ± 0.5 3.5 Thermal transitions Thermal transition properties can greatly influence the mechanical performance of composites. Specifically, the Tg represents the transition point between the glassy and brittle state and the elastic and ductile state. To understand the thermal transitions of the samples, the DSC and DMA tan delta-temperature thermograms of PLA, PBAT, AB, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60 were investigated. The Tg obtained from the tan delta-temperature curves and Tm obtained from the DSC thermograms are detailed in Table 3 and illustrated in Fig. 6 . According to Table 3 , PLA has a Tg of 63.4°C, which shows that PLA has brittle behavior at ambient temperatures below 63.4°C. The non-elastic nature of the material is also demonstrated by the large tan delta value shown in Fig. 6 (c) [ 27 ]. According to [ 28 ], the Tg of PBAT is at around − 35°C, which means PBAT maintains its elastic and ductile performances at room temperature. As shown in Table 3 , the addition of PBAT reduced the Tg of PLA in AB from 63.4°C to 55.3°C. The lower Tg shows that the addition of flexible PBAT molecular chains improved the mobility of PLA molecular chains in the amorphous area. As a result, PLA molecular chains require a lower temperature to complete the phase transition, i.e., changing from a rigid glassy state to a highly elastic state. The Tg of the samples was gradually increased as the UV radiation exposure period was increased from 0 to 60 minutes. This is because the crosslinking reaction produced a crosslinked spatial network, which made it difficult for polymer chains to move locally and thus the Tg was increased [ 29 ]. The Tg curve of the ABT samples was not clearly apparent on the DSC thermograms, possibly as a result of the varying degrees of restrictions of the different crosslinking networks on the mobility of the PLA molecular chains in the amorphous region. As a result, the PLA molecular chains began to move over a wider temperature range, which was reflected in the inconspicuous exothermic trend on the DSC thermograms. Table 3 shows that the melting point temperature (Tm) of neat PLA is 164.7°C, while that of PBAT is only 127.7°C. Bunn [39] reported that PBAT with many methylene groups has a very low Tm as the methylene groups are very light and flexible so very less thermal energy is required to make the chain move. The Tm of PLA is slightly reduced in the AB sample. This is due to the fact that the addition of flexible PBAT molecular chains enhanced the mobility of the PLA molecular chains, which interfared with their crystallization process, thus resulting in a decrease in Tm [ 30 ]. As the length of the UV radiation was increased from 0 to 60 minutes, the crosslinking reaction increasingly progressed. The Tm of PLA was decreased while that of PBAT was increased at the same time. On the one hand, the crosslinked spatial network in PLA reduced the chain orientation, and a low molecular packing efficiency of the crystals can reduce the melting point. On the other hand, when the crystals start to melt, the rigid molecular chain needs to move as a whole, while in a flexible chain, distortion at one point can produce waves along the chain arising from the movement of the entire chain [ 31 ]. The introduction of flexible PBAT chains enhances the movement of the entire chain, thus reducing the Tm of PLA. The Tm of PBAT was increased at the same time, because a higher thermal energy is required to break the bonds of the crosslinked network and cause movement of the individual PBAT chains. The crosslinking density influences the melting point of each type of polymer. As a result, the melting point peaks of PLA and PBAT became increasingly closer and eventually coincide with a longer UV radiation time. The crosslinking reaction resulted in sufficiently strong interactions between the PLA and PBAT polymers. Table 3 Thermal transition temperatures. Sample name Tg-PLA (°C) Tm-PLA (°C) Tg-PBAT (°C) PLA 63.4 164.7 N/A PBAT N/A N/A 127.6 AB 55.3 161.2 127.4 ABT-UV0 52.2 154.8 139.5 ABT-UV15 66.6 154.3 137.4 ABT-UV30 67.9 153.4 140.4 ABT-UV45 68.7 152.1 152.1 ABT-UV60 72.9 152.4 152.4 3.6 Thermal stability The thermal degradation performance of PLA, PBAT, AB, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60 was determined by using a TGA. Figure 7 (a) shows that both the PLA and PBAT polymers underwent a one-step thermal degradation process. The former started to degrade at 342.7°C and the degradation curve tended to flatten at 422.6°C, while PBAT began to degrade at 380.4°C and had almost no residue at 483.1°C. PBAT maintains a higher thermal degradation temperature than PLA due to the presence of an aromatic structure in its macromolecular chains, and PBAT has a longer segment compared to PLA. Figure 7 clearly shows that samples of AB, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60 underwent a two-step thermal degradation process, which corresponds to the thermal degradation process of PLA and PBAT [ 16 ]. Figure 7 (b) is the enlarged view of the onset of the degradation process, which shows that AB and ABT-UV0 have a very similar onset degradation temperature as PLA due to the dominant role of PLA in the sample. As the duration of the UV radiation was increased from 0 to 60 minutes, the onset degradation temperature was initially increased, then decreased when the UV exposure time was over 15 minutes. The onset degradation temperature of ABT-UV 15 was increased to around 350°C, which indicates that the crosslinking structure can increase the degradation temperature. However, as the UV radiation time was prolonged to 60 minutes, the onset degradation temperature was reduced to 326.9°C, which is even lower than that of neat PLA. This might because the prolonged UV exposure can also cause the degradation of PLA, which promote its thermal decomposition. The offset degradation is shown in Fig. 7 (c), where the samples with a lower onset degradation temperature also have a lower offset degradation temperature. 4 Conclusion The fabrication of fully biodegradable PLA/PBAT blends with a crosslinked network structure was carried out in this study. The results show that the introduction of PBAT can improve the toughness and flexibility of PLA. The compatibility of PLA and PBAT was enhanced due to the formation of a crosslinked network structure. ABT-UV30 overall has the optimal mechanical properties. The elongation at break and impact strength of this sample were increased 37.8 times and 3.9 times, respectively, when compared to PLA. The Tg of the samples was increased gradually when the UV radiation exposure time was extended from 0 to 60 minutes. At the same time, the melting point temperature of PBAT was also increased gradually until it is eventually the same as that of PLA. The TGA thermograms show that an appropriate amount of UV radiation exposure can increase the thermal degradation temperature, while excessive UV radiation exposure can reduce the thermal degradation temperature of the samples. The PLA-based biodegradable materials with high-toughness can be used as an alternative for nonbiodegradable plastics, which can be applied in packaging, disposable box & bottles, tableware, textiles and flexible intelligent electronics. Declarations CRediT authorship contribution statement Bian Xueyan: Conceptualization, Methodology, Investigation, Writing - original draft. Fan Suju: Investigation, Writing - review & editing. Xia Gang: Investigation, Writing - review & editing. Xin John Haozhong: Conceptualization, Methodology, Writing - review & editing, Resources. Jiang Shouxiang: Writing - review & editing, Project administration, Resources. Conflicts of interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments This study was supported by Innovation and Technology Fund (Ref No. PRP/104/20TI) of Hong Kong Special Administrative Region, Wuyi University-Hong Kong Joint Research Fund under the Hong Kong Polytechnic University and Wuyi University collaborative flamework agreement, Wuyi University–Hong Kong/Macau Joint Research Funds (2019WGALH05). The authors also appreciated the PhD scholarship provided by the Hong Kong Polytechnic University. References Geyer, R., J.R. Jambeck, and K.L. Law, Production, use, and fate of all plastics ever made. Science advances, 2017. 3 (7): p. e1700782. Irmak, S., Biomass as Raw Material for Production of High‐Value Products . 2017, InTech. Zhou, Y., et al., A facile and sustainable approach for simultaneously flame retarded, UV protective and reinforced poly(lactic acid) composites using fully bio-based complexing couples. Composites Part B: Engineering, 2021. 215 : p. 108833. Wang, W.Z., et al., 3D printing of PLA/n-HA composite scaffolds with customized mechanical properties and biological functions for bone tissue engineering. Composites Part B-Engineering, 2021. 224 . Meng, L.H., et al., Preparation, microstructure and performance of poly (lactic acid)-Poly (butylene succinate-co-butyleneadipate)-starch hybrid composites. Composites Part B-Engineering, 2019. 177 . Nofar, M., et al., Ductility improvements of PLA-based binary and ternary blends with controlled morphology using PBAT, PBSA, and nanoclay. Composites Part B-Engineering, 2020. 182 . Jalali, A., et al., Peculiar crystallization and viscoelastic properties of polylactide/polytetrafluoroethylene composites induced by in-situ formed 3D nanofiber network. Composites Part B-Engineering, 2020. 200 . Jia, Y.W., et al., Synergy effect between quaternary phosphonium ionic liquid and ammonium polyphosphate toward flame retardant PLA with improved toughness. Composites Part B-Engineering, 2020. 197 . Lay, M., et al., Comparison of physical and mechanical properties of PLA, ABS and nylon 6 fabricated using fused deposition modeling and injection molding. Composites Part B-Engineering, 2019. 176 . Ikada, Y., et al., Stereocomplex formation between enantiomeric poly(lactides). Macromolecules, 1987. 20 (4): p. 904-906. Tang, Z., et al., The crystallization behavior and mechanical properties of polylactic acid in the presence of a crystal nucleating agent. Journal of Applied Polymer Science, 2012. 125 (2): p. 1108-1115. Shaffer, S., et al., On reducing anisotropy in 3D printed polymers via ionizing radiation. Polymer, 2014. 55 (23): p. 5969-5979. Tsou, C.-H., et al., Preparation and characterization of poly(lactic acid) with adipate ester added as a plasticizer. Polymers and Polymer Composites, 2018. 26 (8-9): p. 446-453. Kobayashi, S., S. Ochiai, and J. Kumaki, Polylactic acid resin composition and method for producing the same. JP2004250549A, 2003. Balla, E., et al., Poly(lactic Acid): A Versatile Biobased Polymer for the Future with Multifunctional Properties—From Monomer Synthesis, Polymerization Techniques and Molecular Weight Increase to PLA Applications. Polymers, 2021. 13 (11): p. 1822. Fu, Y., et al., Biodegradation Behavior of Poly(Butylene Adipate-Co-Terephthalate) (PBAT), Poly(Lactic Acid) (PLA), and Their Blend in Freshwater with Sediment. Molecules, 2020. 25 (17): p. 3946. Parodi, E., L.E. Govaert, and G. Peters, Glass transition temperature versus structure of polyamide 6: A flash-DSC study. Thermochimica Acta, 2017. 657 . Rafał Malinowski , K.M.a.A.R.-K., Studies on the Uncrosslinked Fraction of PLA/PBAT Blends Modified by Electron Radiation. Materials, 2020. Wu, D., et al., Effect of the multi-functional epoxides on the thermal, mechanical and rheological properties of poly(butylene adipate-co-terephthalate)/polylactide blends. Polymer Bulletin, 2021. 78 : p. 1-25. Koning, C., et al., Strategies for compatibilization of polymer blends. Progress in Polymer Science, 1998. 23 (4): p. 707-757. Yue Ding, B.L., Junhui Ji, Compatibilization Strategies of PLA-Based Biodegradable Materials. Progress in Chemistry, 2020. 32 (6): p. 738-751. Malinowski, R., K. Moraczewski, and A. Raszkowska-Kaczor, Studies on the Uncrosslinked Fraction of PLA/PBAT Blends Modified by Electron Radiation. Materials, 2020. 13 (5): p. 1068. Mehmet Kodal, A.A.W., Guralp Ozkoc, The mechanical, thermal and morphological properties of γ-irradiated PLA/TAIC and PLA/OvPOSS. Radiation Physics and Chemistry, 2018. 153 : p. 214-225. Rytlewski, P., et al., Influence of some crosslinking agents on thermal and mechanical properties of electron beam irradiated polylactide. Radiation Physics and Chemistry, 2010. 79 (10): p. 1052-1057. Ming, M., et al., Effect of polycarbodiimide on the structure and mechanical properties of PLA/PBAT blends. Journal of Polymer Research, 2022. 29 (9). Mohammadi, M., et al., Morphological and Rheological Properties of PLA, PBAT, and PLA/PBAT Blend Nanocomposites Containing CNCs. Nanomaterials, 2021. 11 (4): p. 857. Wasti, S., et al., Influence of plasticizers on thermal and mechanical properties of biocomposite filaments made from lignin and polylactic acid for 3D printing. Composites Part B: Engineering, 2021. 205 : p. 108483. Pietrosanto, A., et al., Evaluation of the Suitability of Poly(Lactide)/Poly(Butylene-Adipate-co-Terephthalate) Blown Films for Chilled and Frozen Food Packaging Applications. Polymers, 2020. 12 (4): p. 804. Ding, Y., et al., Effect of talc and diatomite on compatible, morphological, and mechanical behavior of PLA/PBAT blends. e-Polymers, 2021. 21 : p. 234-243. Kumar, M., et al., Effect of glycidyl methacrylate (GMA) on the thermal, mechanical and morphological property of biodegradable PLA/PBAT blend and its nanocomposites. Bioresource Technology, 2010. 101 (21): p. 8406-8415. Bunn, C.W., The melting points of chain polymers. Journal of Polymer Science Part B: Polymer Physics, 1996. 34 (5): p. 799-819. Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 13 Mar, 2024 Reviewers invited by journal 13 Mar, 2024 Editor invited by journal 03 Mar, 2024 Editor assigned by journal 28 Feb, 2024 First submitted to journal 27 Feb, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4001826","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":279392365,"identity":"3ba10112-6385-414f-818d-dbb9236c5f51","order_by":0,"name":"Xueyan Bian","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0003-4591-2591","institution":"The Hong Kong Polytechnic University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Xueyan","middleName":"","lastName":"Bian","suffix":""},{"id":279392366,"identity":"5d82c495-ef23-48fd-a7aa-73152881c548","order_by":1,"name":"Suju Fan","email":"","orcid":"","institution":"","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Suju","middleName":"","lastName":"Fan","suffix":""},{"id":279392367,"identity":"3acad391-a8a2-4797-9655-de9cca7450db","order_by":2,"name":"Gang Xia","email":"","orcid":"","institution":"","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Gang","middleName":"","lastName":"Xia","suffix":""},{"id":279392368,"identity":"3944353b-fe1f-45a3-817f-7454bb57c631","order_by":3,"name":"John Xin","email":"","orcid":"","institution":"","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"John","middleName":"","lastName":"Xin","suffix":""},{"id":279392369,"identity":"a692c546-f443-4db2-a112-6d347985474b","order_by":4,"name":"Shouxiang Jiang","email":"","orcid":"","institution":"","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Shouxiang","middleName":"","lastName":"Jiang","suffix":""}],"badges":[],"createdAt":"2024-03-01 02:53:07","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4001826/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4001826/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":52895681,"identity":"45e072e2-3529-4a29-ac13-a1ce1a060709","added_by":"auto","created_at":"2024-03-18 12:52:36","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":773473,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of sample preparation.\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4001826/v1/50c97d40d6ab7b9a64bb7390.jpeg"},{"id":52895678,"identity":"75c23378-bcd9-4aac-812d-eb04cd1e04b5","added_by":"auto","created_at":"2024-03-18 12:52:36","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1861177,"visible":true,"origin":"","legend":"\u003cp\u003eScanning electron microscopy images of (a) neat PLA, (b) neat PBAT, (c) blended PLA/PBAT, (d) untreated PLA/PBAT/TAIC, (e) PLA/PBAT/TAIC exposed to UV light for 15 minutes, (f) PLA/PBAT/TAIC exposed to UV light for 30 minutes, (g) PLA/PBAT/TAIC exposed to UV light for 45 minutes, and (f) PLA/PBAT/TAIC exposed to UV light for 60 minutes.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4001826/v1/3ad33ddf5a91ce4c0eeec3b9.png"},{"id":52895680,"identity":"be10789f-e4c4-4040-9d67-004518ad7aa2","added_by":"auto","created_at":"2024-03-18 12:52:36","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":508123,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR of (a) PLA, PBAT, and TAIC, (b) enlarged view of PLA, (c) AB and ABT-UV30, and (d) enlarged view of AB and ABT-UV30 .\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4001826/v1/83546c3491eaf6444f168d78.png"},{"id":52895682,"identity":"70dd8520-f4cc-415e-9ff9-c74ff671143a","added_by":"auto","created_at":"2024-03-18 12:52:36","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":990618,"visible":true,"origin":"","legend":"\u003cp\u003e(a)\u003cstrong\u003e \u003c/strong\u003eCrosslinking reaction processes and (b) degradation of PLA macromolecular chain.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4001826/v1/5ddb236fda03ea7d2890abfb.png"},{"id":52895679,"identity":"554eb7f2-9677-43a1-8fdc-af841ab9527d","added_by":"auto","created_at":"2024-03-18 12:52:36","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":120981,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Tensile strength, (b) elongation at break, and (c) impact strength of PLA, PBAT, AB, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4001826/v1/2e10ff57ce079195f7aff74f.png"},{"id":52896360,"identity":"96f59f00-3de0-48c5-b3c4-a727ade0e300","added_by":"auto","created_at":"2024-03-18 13:00:45","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":558237,"visible":true,"origin":"","legend":"\u003cp\u003eDSC thermograms of (a) PLA and PBAT, and (b) AB, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60. (c) DMA thermograms of all samples.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-4001826/v1/3c5d7850971ab90cb9701d85.png"},{"id":52895684,"identity":"7703df14-dbdc-474b-bddd-57fa28971f4c","added_by":"auto","created_at":"2024-03-18 12:52:36","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":679960,"visible":true,"origin":"","legend":"\u003cp\u003eTGA thermograms of PLA, PBAT, AB, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60: (a) full image, (b) \u0026nbsp;enlarged view of onset degradation process, and (c) enlarged view of offset degradation process.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-4001826/v1/11703ae3cc03d957aaf1243c.png"},{"id":52896380,"identity":"240555b5-26bd-41d1-b90e-f68aa447dfb6","added_by":"auto","created_at":"2024-03-18 13:00:56","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2328721,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4001826/v1/81e65694-f8d7-4707-be7b-8fe0051a7448.pdf"}],"financialInterests":"","formattedTitle":"Phase morphology, mechanical performance, and thermal properties of fully biodegradable polylactic acid/polybutylene adipate terephthalate crosslinked network induced by UV irradiation","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003ePlastic production expanded quickly after World War II, dramatically improving people's lives and transforming contemporary society. However, the majority of plastic products are derived from fossil fuels and cannot be biodegraded. It is estimated that about 6.3\u0026nbsp;billion Mt of plastic waste had been produced by 2015, but only 9% of this plastic waste were recycled, leaving 91% to be burned, landfilled or left in the natural environment [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Over the past few decades, there has been an increasing interest in using biobased polymers with potential degradability to replace certain fossil-derived polymers, which would significantly reduce the consumption of natural resources and decrease environmental pollutants. Energy crops, food-based biomass waste, agricultural biomass residue, and forest biomass are the main sources of biobased polymers [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePolylactic acid (PLA) is an aliphatic polyester, primarily produced by the ring-opening polymerization of lactide and industrial polycondensation of lactic acid. The basic unit of PLA, lactic acid, is produced from renewable resources such as wheat, straw, corn, and sorghum, which is bio-based and can be decomposed into water and carbon dioxide by microbes. As a leading candidate of biobased polymer, PLA has gained widespread attention from both the academia and industry due to its high strength and modulus, good thermoplastic performance, and ability to be molded with a variety of methods. [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] However, PLA has several inherent shortcomings, such as high brittleness, poor ductility, low crystallization rate, and low heat resistance temperature, which greatly limit its wide use in industrial production [\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo date, a number of approaches have been proposed to address these shortcomings, such as forming a stereocomplex (SC) structure, adding nucleating agents, promoting a crosslink reaction, plasticization, and blending with various tough polymers. [\u003cspan additionalcitationids=\"CR7 CR8\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] Ikada et al. first reported that poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) blended with a ratio of 1:1 can produce a SC crystallite structure. The SC crystallite has a melting point temperature (Tm) of about 230\u0026deg;C, which is 50\u0026deg;C higher than that of the PLLA or PDLA homocrystals. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] However, the high cost of high-purity PDLA prevents its wide use in industrial production. According to the study from Tang\u0026rsquo; group, the addition of a nucleating agent, ethylenebishydroxystearamide (EBH), can considerably increase the crystallinity and crystallization rate of PLA. After the annealing procedure, the heat deflection temperature (HDT) of nucleated PLA can be increased by 30\u0026deg;C. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] Shaffer et al. has used two crosslinking agents, trimethylolpropane triacrylate (TMPTA) and triallyisocyanurate (TAIC) to modify PLA. It was reported that a crosslinking reaction that occurred close to the glass transition temperature (Tg) can significantly enhance the thermomechanical properties of the PLA polymer. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] Tsou et al. prepared PLA with adipate ester as a plasticizer and concluded that the addition of adipate ester could improve the toughness of PLA, but reduced the cold crystallization and Tg. [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/p\u003e \u003cp\u003ePolymer blends are considered as materials with tunable qualities that can deliver a synergistic performance. Sadayuki et al. blended PLA with different polymers including polyethylene terephthalate (PET), polybutylene terephthalate (PBT), nylon (N6), nylon (N12), and polycarbonate (PC). The results indicated that both the tensile strength, elongation at break and HDT of these blends (with a PLA/polymer ratio of 80/20) were increased significantly. [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] However, these blends cannot be fully biodegraded due to the addition of fossil-based and nonbiodegradable polymers. Therefore, increasing attention has been attracted to modify PLA with biodegradable materials. PBAT is fossil-based but a fully biodegradable polymer. Compared to other biopolymers, such as poly(hydroxy valerate) (PHV), poly(hydroxy butyrate) (PHB), polycaprolactone (PCL), and polybutylene succinate (PBS), PBAT has relatively high elongation at break and impact strength, making it the most promising option to tough PLA. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] However, the incompatibility between PLA and PBAT can cause interfacial separation, leading to an unsatisfactory enhancement in mechanical properties. [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eIn this study, PBAT was added to improve the flexibility and toughness of PLA. The compatibility of PLA and PBAT was enhanced through the formation of the crosslink spatial network. TAIC was used as the crosslinking agent, and ultraviolet (UV) radiation was employed to induce the occurrence of crosslink reaction. The morphology, mechanical performance, phase transition temperature, and thermogravimetric analysis of samples were then evaluated, and the mechanisms were also investigated.\u003c/p\u003e"},{"header":"2 Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003ePLA was supplied by Anhui Fengyuan Bio-Fiber Co., Ltd. The PLA polymer has an average molecular weight of approximately 120,000 g/mol, a density of 1.24 g/cm\u003csup\u003e3\u003c/sup\u003e, and a melt mass-flow rate (MFR) of 4 g/10 min (190\u0026deg;C/2.16 kg).\u003c/p\u003e \u003cp\u003ePBAT was purchased from Shanghai Macklin Biochemical Co., Ltd. The PBAT polymer has an average molecular weight of approximately 680,000 g/mol, a density of 1.21 g/cm\u003csup\u003e3\u003c/sup\u003e, and a MFR of 4.5 g/10 min (190\u0026deg;C/2.16 kg).\u003c/p\u003e \u003cp\u003eTAIC was supplied by Thermo Fisher Scientific (USA).\u003c/p\u003e \u003cp\u003eDichloromethane (DCM), HPLC grade was purchase from Anaqua Global International Inc. Limited.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Sample preparation\u003c/h2\u003e \u003cp\u003ePLA and PBAT polymer masterbatches were immersed into an ultrasonic ethanol bath for 30 minutes to remove impurities, then rinsed five times with distilled water. Prior to usage, the cleaned masterbatches were dried in a vacuum oven at 60\u0026deg;C for 24 hours to eliminate surface moisture. An organic solvent, DCM, was used to dissolve a certain mass of PLA, PBAT, and PLA/PBAT blend polymers (weight ratio: 80/20) at a mass fraction of 10%. The PLA, PBAT, and PLA/PBAT solutions were stirred by using a magnetic stirrer at a temperature of 40\u0026deg;C, and all of the PLA and PBAT polymer masterbatches were completely dissolved after a 60-minute of stirring at a rotational speed of 500 rpm.\u003c/p\u003e \u003cp\u003eThe fully dissolved PLA/PBAT solution was poured into six transparent bottles. Five of them were added to TAIC at a mass percentage of 3% (to polymers) and stirred for 10 more minutes so that the TAIC could disperse uniformly in the solution. Then four bottles filled with the PLA/PBAT/TAIC solutions were placed in a UV light box (mode: fluorescent lamp, supported by Shanghai Xinxin Light Co., Ltd.) and exposed to UV light for various lengths of time\u0026mdash;15, 30, 45, and 60 minutes. Following UV exposure, all of the solutions were used to cast films, and kept in a fume hood for 2 hours to allow the DCM solvent to evaporate. Then, all of the films were dried in a vacuum oven to further remove any residual DCM. The preparation recipe is shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eAll of the samples were hot-pressed into sheets by using a compression molding machine (model: ZS-406B, Dongguan Zhuosheng Machinery Equipment Co., Ltd).The samples were heated at 180\u0026deg;C for 10 minutes, then pressed for 2 minutes at a pressure of five bars. Samples of neat PLA and PBAT, PLA/PBAT blend, PLA/PBAT/TAIC without UV treatment, and PLA/PBAT/TAIC exposed to UV radiation for 15, 30, 45, and 60 minutes were labeled as PLA, PBAT, AB, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60, respectively. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e is the schematic diagram of the sample preparation process.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePreparation recipe of samples.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample Name\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWeight \u003csub\u003ePLA\u003c/sub\u003e (g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWeight \u003csub\u003ePBAT\u003c/sub\u003e (g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eWeight \u003csub\u003eTAIC\u003c/sub\u003e (g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eUV radiation (min)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePBAT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eABT-UV0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eABT-UV15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eABT-UV30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eABT-UV45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e45\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eABT-UV60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Characterization\u003c/h2\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.3.1 Morphology\u003c/h2\u003e \u003cp\u003eThe fractured morphology of the samples after being subjected to impact strength (IS) testing was observed through a field emission scanning electron microscope (FESEM Tescan MAIA3) at a SEM HV of 5 kV. A thin layer of gold film was sputtered onto the samples before being examined under the FESEM.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.3.2 Fourier transform infrared spectroscopy\u003c/h2\u003e \u003cp\u003eA Fourier transform infrared (FTIR) spectrometer (Spectrum 100, PerkinElmer) was used to determine the interactions among PLA, PBAT, and TAIC. The FTIR curves were recorded in transmittance mode, with a constant spectral resolution of 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, scanning number of 32, and scanning wavelength that ranged from 600 to 4000 nm.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.3.3 Mechanical properties\u003c/h2\u003e \u003cp\u003eTensile testing was conducted according to ISO 527 standard, by using INSTRON 5566, a universal testing machine. The samples were molded into a dumbbell shape, with an initial gauge length of 25 mm, width of 4 mm and thickness of 1 mm. They were then conditioned at a temperature of 25\u0026deg;C and humidity of 50% for 24 h before being tested. The tensile strength and elongation at break results were recorded based on the average results of five samples.\u003c/p\u003e \u003cp\u003eImpact testing was conducted according to ISO 179 by using a Zwick Charpy impact machine with a 1 J hammer. The samples were prepared unnotched with dimensions of 80 ⅹ10 ⅹ 4 mm. The IS results were recorded as the average value of five samples.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.3.4 Thermal transitions\u003c/h2\u003e \u003cp\u003eThe thermal transitions of the samples were investigated by using a differential scanning calorimeter (PerkinElmer DSC 8000), supplied by Al instruments (Hong Kong) Limited. Samples that weighed approximately 3 mg were placed in aluminum pans for measurement. They were heated from 0\u0026deg;C to 300\u0026deg;C at 20\u0026deg;C/min, at a nitrogen flow rate of 50 ml/min. The Tg was determined by estimating the midpoint in proximity to the change in specific heat (ΔCp). The midpoint of the segment between the onset and offset of Tg was defined as the Tg [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. The melting point (Tm) is the peak value according to the International Confederation for Thermal Analysis and Calorimetry (ICTAC) standards.\u003c/p\u003e \u003cp\u003eA dynamic mechanical analyzer (DMA Q800, TA, USA) was used to determine the Tg of the samples. The measurement was performed by heating the samples (with dimensions of 60 ⅹ 10 ⅹ 1 mm) from room temperature to 120\u0026deg;C at a rate of 5\u0026deg;C/ min in a 3-point-bend mode.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.2.5 Thermogravimetric analysis (TGA)\u003c/h2\u003e \u003cp\u003eThe thermal stability of samples was evaluated by using a thermalgravimetric analyzer (PerkinElmer TGA 4000 System 100-240V/50-60HZ), supplied by Labware Analytical Company Limited. The samples were heated from 50\u0026deg;C to 800\u0026deg;C at 20\u0026deg;C/min, at a nitrogen flow rate of 20 ml/min.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n\u003ch2\u003e3.1 Morphology\u003c/h2\u003e\n\u003cp\u003eThe scanning electron microscopy images of the fractured surfaces of PLA, PBAT, PLA/PBAT, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60 were observed with an FESEM at a magnification of 3 kx. As depicted in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(a), the neat PLA has a very smooth fractured surface without any visible plastic deformation, indicating its brittle property. Comparatively, the fractured surface of neat PBAT in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(b) shows obvious plastic deformation, which suggests the tough performance of PBAT. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(c) shows that the AB sample is composed of two phases, the PBAT dispersed phase and the PLA matrix phase. Meanwhile, there is an obvious interfacial separation on the fractured surface, thus indicating low interfacial adhesion between PLA and PBAT. The incompatibility of PLA and PBAT has been reported in previous studies numerous times. [\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e]. The PBAT phase is usually distributed within the PLA matrix in the form of spheres or columns instead of uniformly blending into the PLA. PLA and PBAT are immiscible at the molecular level according to the Gibbs free energy formula:\u003c/p\u003e\n\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equa\" class=\"mathdisplay\"\u003e$${\\varDelta G}_{mix}={\\varDelta H}_{mix}-T{\\varDelta S}_{mix}$$\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003ewhere \u0026Delta;G\u003csub\u003emix\u003c/sub\u003e is the Gibbs free energy, and \u0026Delta;H\u003csub\u003emix\u003c/sub\u003e and \u0026Delta;S\u003csub\u003emix\u003c/sub\u003e represent the enthalpy and entropy changes, respectively. T denotes the temperature (Kelvin) [\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e]. According to this theory, a negative free energy of mixing homogeneous miscibility in polymer blends is required. The high molecular weight results in negligible mixing entropy. As the mixing enthalpy is positive and there is no specific interaction between these two polymers, the result is the immiscibility of the PLA and PBAT polymers [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e]. As depicted in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(c), the PLA matrix undergone brittle fracture when an impact force was applied, while the PBAT phase was still continuous and under tension. The PBAT phase was detaching from the PLA matrix at the interface when tension was applied, so gaps and cavities was formed. In the end, the fracture of the PBAT phase occurred, and tough fractures of the PBAT phase formed.\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(d) shows that there is no obvious difference between ABT-UV0 and AB. However, the fractured surface of ABT-UV15 demonstrates increased compatibility of the PLA and PBAT phases after the sample was exposed to UV light for 15 minutes, see Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(e). The width of the gaps that originated from the interfacial detachment is narrower and there are fewer cavities. This result might be due to the crosslinking reaction mechanism as detailed in Section \u003cspan class=\"InternalRef\"\u003e3.3\u003c/span\u003e in which the PLA and PBAT molecular chains started to bond together because of the TAIC and UV radiation. Figures\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(e) to 2(h) show that the two-phase interfaces cannot be differentiated from the fractured surface images as the UV radiation exposure time is over 30 minutes. This result indicates that as the crosslinking reaction progressed, the PBAT molecular chains distributed more uniformly in the PLA matrix. In contrast to the brittle and smooth fractured surface of the neat PLA, the fractured sections of ABT-UV30 and ABT-UV45 exhibit more fibrils pulling out, which suggests the enhanced toughness of the samples. However, there is less plastic deformation on the fractured surface of ABT-UV60. This is likely because excessive crosslinking reactions can increase rigidity, thus reducing the toughness of the sample.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n\u003ch2\u003e3.2 Fourier transform infrared spectroscopy\u003c/h2\u003e\n\u003cp\u003eThe chemical structures of PLA, PBAT, TAIC and ABT-UV30 were characterized by FTIR spectroscopy, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. In the case of PLA, the three peaks at 1044 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1076 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and 1183 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are related to the stretching vibrations of the ether groups (C\u0026ndash;O\u0026ndash;C). The characteristic peak at 1751 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is assigned to the stretching vibrations of the carbonyl groups (C\u0026thinsp;=\u0026thinsp;O). The two peaks that appear at 2855 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 2925 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e belong to the stretching vibrations of the tertiary carbon and hydrogen bonds (C-H) on backbones [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e]. The two characteristic peaks at 2942 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 2995 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are the symmetric and asymmetric stretching vibrations of the methyl groups (CH\u003csub\u003e3\u003c/sub\u003e) in saturated hydrocarbons, which are clearly visible in all of the FTIR spectra [\u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e]. For the neat PBAT, the characteristic peak at 1018 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is due to the vibrations of the hydrogen atom of the aromatic ring. Peaks that appear at 1104 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1267 cm \u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are the symmetric stretching vibrations of the carbon and oxygen groups (C\u0026ndash;O). The characteristic peaks at 1409 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 2948 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are assigned to the in-plane bending vibrations and the asymmetric stretching vibrations of the methylene groups (CH\u003csub\u003e2\u003c/sub\u003e), respectively. The bands at 1504 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1711 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are the skeletal vibrations of the aromatic ring and the stretching vibrations of the C\u0026thinsp;=\u0026thinsp;O. In the FTIR curve of TAIC, the peaks at 1376 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1756 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are the tertiary amide absorption vibrations. The characteristic peaks at 1653 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1695 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are attributed to the stretching vibrations of the carbon-carbon double bonds (C\u0026thinsp;=\u0026thinsp;C) and the stretching vibrations of C\u0026thinsp;=\u0026thinsp;O [\u003cspan class=\"CitationRef\"\u003e12\u003c/span\u003e]. In the curve of ABT-UV30, the peak of the C\u0026thinsp;=\u0026thinsp;C stretching vibrations of TAIC at 1653 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is no longer there. This indicates the breakage of the C\u0026thinsp;=\u0026thinsp;C bond in TAIC under UV radiation and the formation of TAIC radicals. In addition, there are new bands at 3506 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which can be assigned to a hydroxyl group (\u0026ndash;OH). The formation of hydroxyl groups is attributed to thermal degradation of PLA and PBAT macromolecules during the UV radiation or melting process [\u003cspan class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n\u003ch2\u003e3.3 Mechanism\u003c/h2\u003e\n\u003cp\u003eThe mechanisms of the crosslink reaction and molecular chain breakdown brought on by the UV light are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e(a) describes the two steps of the crosslink reaction. In the first step, the carbon and hydrogen (C-H) bonds on the PLA backbones are broken under the influence of UV light. PLA free radicals formed as a result of the loss of protons of the tertiary carbon. Meanwhile, UV radiation also contributes to the formation of TAIC and PBAT radicals. In the second step, the PLA and PBAT free radicals combined with TAIC radicals mainly in three types of reactions as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e (a). The numbers 1, 2, and 3 which represent the three types of reactions also indicate the difficulty of the reaction. It is more difficult for Reaction Type 2 to happen than Reaction Type 1 mainly due to the steric hindrance. Malinowski et al. [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e] reported that PLA has higher susceptibility to electromagnetic radiation than PBAT when radiation is used to promote chemical reactions. The presence of aromatic groupings in PBAT macromolecular chains can absorb some of the electromagnetic radiation and dissipate it in the form of heat. This so-called protective effect deactivates some of the active sites. As a result, it is more difficult for PBAT to form free radicals, and PBAT is less prone to have a crosslink reaction when compared to PLA. Therefore, it is more difficult for Reaction Type 3 to occur in comparison with Reaction Type 2. In addition to crosslink reactions, the chain scission of PLA may also occur when the samples are excessively exposed to UV radiation, as PLA is sensitive to UV radiation. This could be inferred from the new formation of hydroxyl group bands on the FTIR curves of ABT-UV30 as discussed in Section \u003cspan class=\"InternalRef\"\u003e3.2\u003c/span\u003e. Besides, samples exposed to UV light for a prolonged period of time also lose some of their mechanical and thermal properties, as will be discussed in more details in Sections \u003cspan class=\"InternalRef\"\u003e3.4\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e3.6\u003c/span\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n\u003ch2\u003e3.4 Mechanical properties\u003c/h2\u003e\n\u003cp\u003eThe tensile strength, elongation at break and impact strength of PLA, PBAT, AB, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60 were tested and the results are listed in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. The results are also plotted in bar graphs in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e to visually show the changes in these mechanical properties. As shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, the tensile strength of neat PLA is 68.0 MPa and the elongation at break is only 9.2%, thus indicating that PLA is a hard and brittle polymer at room temperature. Comparatively, PBAT has a low tensile strength of 9.5 MPa and a high elongation at break of 525.0%, which indicate its weak and flexible properties. As shown in Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e(a) and 5(b), the elongation at break of AB was increased to 315.1%, which is approximately 33 times higher than neat PLA. This shows that the addition of PBAT can greatly increase the flexibility of PLA. Meanwhile, the tensile strength of AB was slightly decreased compared to neat PLA, which could be brought on by the defects resulting from the two-phase interface separation. The effect of PBAT on the mechanical properties of PLA is consistent with the results reported in previous studies [\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]. After the addition of TAIC, both the tensile strength and the elongation at break slightly declined. The PLA and PBAT molecular chains were lubricated by the miniscule TAIC molecules, which decreased the entanglement and connectivity between the chains and consequently reduced the tensile strength of ABT-UV0. As shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, both the tensile strength and elongation at break of the samples increased initially as the UV radiation period was increased from 15 to 60 minutes, but started to decline when the UV radiation time exceeded 30 minutes. The crosslinked spatial network developed during the crosslinking reaction may have contributed to the increase in tensile strength of ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60. UV radiation can, however, also cause chain scissions in the PLA macromolecular chains, which reduces the tensile strength of the samples.\u003c/p\u003e\n\u003cp\u003eAs depicted in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e(c), the toughness of PBAT is significantly higher than that of PLA, with unnotched impact strength values of 17.4 KJ/m\u003csup\u003e2\u003c/sup\u003e and 2.9 KJ/m\u003csup\u003e2\u003c/sup\u003e, respectively. The impact strength of AB was increased by 179.3% by the addition of PBAT at a mass proportion of 20%. The further enhancement of the impact strength of the samples was, however, constrained by the poor interfacial adhesion between the PLA and PBAT elements. The impact strength was initially increased as the UV radiation time was increased from 0 to 60 minutes, then decreased once the UV radiation time exceeded 30 minutes. The toughening effect of PBAT and the increased compatibility of PLA and PBAT as a result of the branched copolymer generated during the crosslinking reaction were the key contributors to the improvement in the impact strength. However, the formation of the crosslinking network can also lead to rigidity, which reduces the impact strength of the samples.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab2\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eMechanical properties of PLA, PBAT, AB, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eSample\u003c/p\u003e\n\u003cp\u003ename\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eTensile strength\u003c/p\u003e\n\u003cp\u003e(MPa)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eElongation at break\u003c/p\u003e\n\u003cp\u003e(%)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eUnnotched impact strength\u003c/p\u003e\n\u003cp\u003e(KJ/m\u003csup\u003e2\u003c/sup\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\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e68.0\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e9.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e2.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003ePBAT\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e9.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e525.0\u0026thinsp;\u0026plusmn;\u0026thinsp;18.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e45.2\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\u003eAB\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e51.1\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e315.1\u0026thinsp;\u0026plusmn;\u0026thinsp;12.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e7.1\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\u003eABT-UV0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e53.8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e327.7\u0026thinsp;\u0026plusmn;\u0026thinsp;19.9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e8.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eABT-UV15\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e58.2\u0026thinsp;\u0026plusmn;\u0026thinsp;4.6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e363.5\u0026thinsp;\u0026plusmn;\u0026thinsp;16.3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e12.3\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\u003eABT-UV30\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e63.1\u0026thinsp;\u0026plusmn;\u0026thinsp;4.9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e389.4\u0026thinsp;\u0026plusmn;\u0026thinsp;28.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e18.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eABT-UV45\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e58.3\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e357.2\u0026thinsp;\u0026plusmn;\u0026thinsp;23.9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e15.7\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\u003eABT-UV60\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e56.2\u0026thinsp;\u0026plusmn;\u0026thinsp;4.9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e316.8\u0026thinsp;\u0026plusmn;\u0026thinsp;15.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e10.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\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=\"Sec16\" class=\"Section2\"\u003e\n\u003ch2\u003e3.5 Thermal transitions\u003c/h2\u003e\n\u003cp\u003eThermal transition properties can greatly influence the mechanical performance of composites. Specifically, the Tg represents the transition point between the glassy and brittle state and the elastic and ductile state. To understand the thermal transitions of the samples, the DSC and DMA tan delta-temperature thermograms of PLA, PBAT, AB, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60 were investigated. The Tg obtained from the tan delta-temperature curves and Tm obtained from the DSC thermograms are detailed in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e and illustrated in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. According to Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, PLA has a Tg of 63.4\u0026deg;C, which shows that PLA has brittle behavior at ambient temperatures below 63.4\u0026deg;C. The non-elastic nature of the material is also demonstrated by the large tan delta value shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e(c) [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e]. According to [\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e], the Tg of PBAT is at around \u0026minus;\u0026thinsp;35\u0026deg;C, which means PBAT maintains its elastic and ductile performances at room temperature. As shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, the addition of PBAT reduced the Tg of PLA in AB from 63.4\u0026deg;C to 55.3\u0026deg;C. The lower Tg shows that the addition of flexible PBAT molecular chains improved the mobility of PLA molecular chains in the amorphous area. As a result, PLA molecular chains require a lower temperature to complete the phase transition, i.e., changing from a rigid glassy state to a highly elastic state. The Tg of the samples was gradually increased as the UV radiation exposure period was increased from 0 to 60 minutes. This is because the crosslinking reaction produced a crosslinked spatial network, which made it difficult for polymer chains to move locally and thus the Tg was increased [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e]. The Tg curve of the ABT samples was not clearly apparent on the DSC thermograms, possibly as a result of the varying degrees of restrictions of the different crosslinking networks on the mobility of the PLA molecular chains in the amorphous region. As a result, the PLA molecular chains began to move over a wider temperature range, which was reflected in the inconspicuous exothermic trend on the DSC thermograms.\u003c/p\u003e\n\u003cp\u003eTable\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e shows that the melting point temperature (Tm) of neat PLA is 164.7\u0026deg;C, while that of PBAT is only 127.7\u0026deg;C. Bunn [39] reported that PBAT with many methylene groups has a very low Tm as the methylene groups are very light and flexible so very less thermal energy is required to make the chain move. The Tm of PLA is slightly reduced in the AB sample. This is due to the fact that the addition of flexible PBAT molecular chains enhanced the mobility of the PLA molecular chains, which interfared with their crystallization process, thus resulting in a decrease in Tm [\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e]. As the length of the UV radiation was increased from 0 to 60 minutes, the crosslinking reaction increasingly progressed. The Tm of PLA was decreased while that of PBAT was increased at the same time. On the one hand, the crosslinked spatial network in PLA reduced the chain orientation, and a low molecular packing efficiency of the crystals can reduce the melting point. On the other hand, when the crystals start to melt, the rigid molecular chain needs to move as a whole, while in a flexible chain, distortion at one point can produce waves along the chain arising from the movement of the entire chain [\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e]. The introduction of flexible PBAT chains enhances the movement of the entire chain, thus reducing the Tm of PLA. The Tm of PBAT was increased at the same time, because a higher thermal energy is required to break the bonds of the crosslinked network and cause movement of the individual PBAT chains. The crosslinking density influences the melting point of each type of polymer. As a result, the melting point peaks of PLA and PBAT became increasingly closer and eventually coincide with a longer UV radiation time. The crosslinking reaction resulted in sufficiently strong interactions between the PLA and PBAT polymers.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab3\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eThermal transition temperatures.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eSample\u003c/p\u003e\n\u003cp\u003ename\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eTg-PLA\u003c/p\u003e\n\u003cp\u003e(\u0026deg;C)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eTm-PLA\u003c/p\u003e\n\u003cp\u003e(\u0026deg;C)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eTg-PBAT\u003c/p\u003e\n\u003cp\u003e(\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=\"left\"\u003e\n\u003cp\u003e63.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e164.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eN/A\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003ePBAT\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eN/A\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eN/A\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e127.6\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAB\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e55.3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e161.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e127.4\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eABT-UV0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e52.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e154.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e139.5\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eABT-UV15\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e66.6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e154.3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e137.4\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eABT-UV30\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e67.9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e153.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e140.4\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eABT-UV45\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e68.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e152.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e152.1\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eABT-UV60\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e72.9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e152.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e152.4\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=\"Sec17\" class=\"Section2\"\u003e\n\u003ch2\u003e3.6 Thermal stability\u003c/h2\u003e\n\u003cp\u003eThe thermal degradation performance of PLA, PBAT, AB, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60 was determined by using a TGA. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e(a) shows that both the PLA and PBAT polymers underwent a one-step thermal degradation process. The former started to degrade at 342.7\u0026deg;C and the degradation curve tended to flatten at 422.6\u0026deg;C, while PBAT began to degrade at 380.4\u0026deg;C and had almost no residue at 483.1\u0026deg;C. PBAT maintains a higher thermal degradation temperature than PLA due to the presence of an aromatic structure in its macromolecular chains, and PBAT has a longer segment compared to PLA. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e clearly shows that samples of AB, ABT-UV0, ABT-UV15, ABT-UV30, ABT-UV45, and ABT-UV60 underwent a two-step thermal degradation process, which corresponds to the thermal degradation process of PLA and PBAT [\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e(b) is the enlarged view of the onset of the degradation process, which shows that AB and ABT-UV0 have a very similar onset degradation temperature as PLA due to the dominant role of PLA in the sample. As the duration of the UV radiation was increased from 0 to 60 minutes, the onset degradation temperature was initially increased, then decreased when the UV exposure time was over 15 minutes. The onset degradation temperature of ABT-UV 15 was increased to around 350\u0026deg;C, which indicates that the crosslinking structure can increase the degradation temperature. However, as the UV radiation time was prolonged to 60 minutes, the onset degradation temperature was reduced to 326.9\u0026deg;C, which is even lower than that of neat PLA. This might because the prolonged UV exposure can also cause the degradation of PLA, which promote its thermal decomposition. The offset degradation is shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e(c), where the samples with a lower onset degradation temperature also have a lower offset degradation temperature.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eThe fabrication of fully biodegradable PLA/PBAT blends with a crosslinked network structure was carried out in this study. The results show that the introduction of PBAT can improve the toughness and flexibility of PLA. The compatibility of PLA and PBAT was enhanced due to the formation of a crosslinked network structure. ABT-UV30 overall has the optimal mechanical properties. The elongation at break and impact strength of this sample were increased 37.8 times and 3.9 times, respectively, when compared to PLA. The Tg of the samples was increased gradually when the UV radiation exposure time was extended from 0 to 60 minutes. At the same time, the melting point temperature of PBAT was also increased gradually until it is eventually the same as that of PLA. The TGA thermograms show that an appropriate amount of UV radiation exposure can increase the thermal degradation temperature, while excessive UV radiation exposure can reduce the thermal degradation temperature of the samples. The PLA-based biodegradable materials with high-toughness can be used as an alternative for nonbiodegradable plastics, which can be applied in packaging, disposable box \u0026amp; bottles, tableware, textiles and flexible intelligent electronics.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eCRediT authorship contribution statement\u003c/h2\u003e\n\u003cp\u003e\u003cstrong\u003eBian Xueyan:\u003c/strong\u003e Conceptualization, Methodology, Investigation, Writing - original draft. \u003cstrong\u003eFan Suju:\u003c/strong\u003e Investigation, Writing - review \u0026amp; editing. \u003cstrong\u003eXia Gang:\u003c/strong\u003e Investigation, Writing - review \u0026amp; editing. \u003cstrong\u003eXin\u003c/strong\u003e \u003cstrong\u003eJohn Haozhong:\u003c/strong\u003e Conceptualization, Methodology, Writing - review \u0026amp; editing, Resources. \u003cstrong\u003eJiang Shouxiang:\u0026nbsp;\u003c/strong\u003eWriting - review \u0026amp; editing, Project administration, Resources.\u003c/p\u003e\n\u003ch2\u003eConflicts of interest\u003c/h2\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003ch2\u003eAcknowledgments\u003c/h2\u003e\n\u003cp\u003eThis study was supported by Innovation and Technology Fund (Ref No. PRP/104/20TI) of Hong Kong Special Administrative Region, Wuyi University-Hong Kong Joint Research Fund under the Hong Kong Polytechnic University and Wuyi University collaborative flamework agreement, Wuyi University\u0026ndash;Hong Kong/Macau Joint Research Funds (2019WGALH05). The authors also appreciated the PhD scholarship provided by the Hong Kong Polytechnic University.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eGeyer, R., J.R. Jambeck, and K.L. 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Biobased polylactic acid (PLA) has emerged as the most practical option because of its superior mechanical and thermal qualities compared to other types of biopolymers. However, due to the inherent deficiencies of PLA, modifications to PLA have been an ongoing endeavor. In this study, samples of neat PLA, neat polybutylene adipate terephthalate (PBAT), blends of PLA and PBAT, as well as their crosslinked blends were fabricated. The morphology, mechanical and thermal transition performances, and thermal stability of the fully biodegradable samples were then measured. The results show that the flexibility and toughness of PLA were significantly enhanced. Especially, the elongation at break of ABT-UV30 (PLA/PBAT/triallyisocyanurate (TAIC) exposed to ultraviolet (UV) light for 30 minutes) was increased 37.8 times as compared to neat PLA. The compatibility of PLA and PBAT was enhanced by the development of a crosslinked network structure. The thermalgravimetric analyzer thermograms show that a moderate amount of UV radiation can improve the thermal stability of the sample while an excessive amount of UV radiation can reduce the temperature at which the sample degrades.\u003c/p\u003e","manuscriptTitle":"Phase morphology, mechanical performance, and thermal properties of fully biodegradable polylactic acid/polybutylene adipate terephthalate crosslinked network induced by UV irradiation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-18 12:52:32","doi":"10.21203/rs.3.rs-4001826/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-03-14T02:21:27+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-03-14T02:13:36+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Journal of Polymer Research","date":"2024-03-03T13:41:58+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-02-29T02:41:48+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Polymer Research","date":"2024-02-28T02:31:23+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"7b713a21-2f9e-48f3-a316-753e8bc3be26","owner":[],"postedDate":"March 18th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-05-24T10:45:05+00:00","versionOfRecord":[],"versionCreatedAt":"2024-03-18 12:52:32","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4001826","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4001826","identity":"rs-4001826","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}