Effects of irradiation and aging on the molecular and phase structure of poly(L-lactide): insights into degradation and recycling potential

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Fedorenko, Evgeny V. Grinyuk, Iryna A. Salnikova, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5716364/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The impact of high-dose e-beam and γ-irradiation, followed by long-term aging, on the structural properties of poly(L-lactide) (PLA) was investigated. Due to prolonged exposure, γ-irradiation caused more extensive oxidative degradation, accelerating the aging process compared to e-beam irradiation. Aging effects were most pronounced in samples irradiated at doses exceeding 600 kGy. Structural analysis using 1 H NMR revealed distinct mechanisms of chain scission during irradiation and aging, resulting in the formation of different end groups. Irradiation induced deterioration of PLA’s phase structure occurred during irradiation was observed, including the formation of conformationally disordered α’ crystalline form. Aging at doses exceeding 1000 kGy led to amorphization. The degradation behavior of aged PLA in water and its recycling potential were also evaluated. While partial dissolution of aged samples occurred in a short term, further degradation was hindered by water induced crystallization. Unirradiated and low-dose irradiated PLA demonstrated promising recyclability to lactide, highlighting its potential for industrial-scale chemical recycling as a sustainable alternative to landfilling or composting. polylactide irradiation aging 1H NMR degradation recycling Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction Polylactide (PLA) is an aliphatic polyester used for production of medical devices and packaging, as well as in agricultural and automotive industries. PLA is generally recognized as biodegradable polymer, as certain bacterial and fungal strains can degrade it in nature [ 1 ]. However, while the degree of PLA degradation is high in compost or sewage sludge, it is relatively low in soil or seawater [ 2 ]. The high salinity of marine environment makes it difficult for water to penetrate PLA [ 3 ]. Additionally, low temperatures further reduce rate of PLA degradation [ 4 ]. Furthermore, microbial consortia in seawater exhibit low efficacy in degrading PLA [ 5 ]. As a result, even in long-term experiments in marine environment, only minor PLA degradation has been observed [ 6 ]. The slow rate of PLA degradation can be explained by its degradation mechanism. When exposed to water, the first stage of PLA degradation is abiotic hydrolysis [ 7 ]. The low molecular weight products formed are then metabolized by microorganisms, converting PLA residues into water and carbon dioxide [ 8 ]. The rate-limiting step in PLA degradation is the reduction in its molecular weight during hydrolysis. Polymer irradiation is one of the approaches that can be used to accelerate the hydrolysis process. Radiation processing of polymers is a widely used technique for crosslinking, sterilization, structural modification, polymerization, and grafting [ 9 ]. Depending on the irradiation conditions and nature of the polymer, it either crosslinks or degrades. The latter predominates in polymers with quaternary carbon atoms, halogen atoms, or C–O–C bonds [ 10 ]. Due to the presence of ester group in its backbone, scission process dominates during PLA irradiation [ 11 ]. Interest in PLA irradiation is primarily driven by its use in medicine and, consequently, need for sterilization [ 12 ]. Radiation-induced backbone scission leads to a reduction in PLA molecular weight [ 13 ]. Effect of irradiation can be quantitatively expressed by the radiation chemical yield, defined as the number of products formed per 100 eV of absorbed energy [ 11 ]. Yield of chain scission for PLA ranges from 0.8 to 2.0 [ 13 ]. Indeed, a decrease in molecular weight, oxidative degradation, and rise of polymer hydrophilicity during irradiation accelerate PLA hydrolysis rate [ 13 – 15 ]. PLA degradation follows an autocatalytic model: –COOH end groups catalyze hydrolysis, and their concentration in the polymer matrix increases as hydrolysis progresses [ 16 , 17 ]. Consequently, the radiation-induced reduction in PLA molecular weight, which increases the concentration of –COOH end groups and enhances their mobility, accelerates polymer hydrolysis. Moreover, if irradiated PLA contains fraction of molecules with sufficiently low molecular weight, these molecules dissolve in water immediately upon hydrolysis, causing mass loss to occur without an induction period [ 15 ]. Both irradiation and hydrolysis are known to affect phase structure and crystallinity of PLA. PLA crystallization from melt, solution, or cold crystallization results in formation of α-form crystals [ 18 , 19 ]. The α-form is the most common and it is made up by left-handed 10 3 helixes packed into orthorhombic cell [ 19 , 20 ]. When crystallization temperature is below 120°C α’ crystals is formed along with α. Although these two forms share many similarities, the α’-form is conformationally disordered [ 21 , 22 ]. Coexistence of both forms in PLA sample leads to a multiple melting behavior in DSC curves [ 20 ]. Appearance of this behavior after irradiation has been reported in numerous studies and is attributed to decrease in PLA molecular weight and introduction of defects during irradiation [ 13 , 23 , 24 ]. However, role of α- and α’-forms in this phenomenon has not been discussed. Hydrolysis also influences crystallization behavior of PLA. Although PLA is not soluble in water [ 25 ], water can strongly affect its crystallinity, especially at elevated temperature. Incorporation of water molecules enhances PLA chain mobility, promoting crystal growth and formation of new crystals. Moreover, amorphous phase hydrolyzes faster and dissolves in water [ 26 ]. Therefore, crystallinity degree of PLA rises during hydrolysis. Effects of irradiation on the structure, properties, and hydrolysis of PLA has been extensively studied over the past two decades. However, no studies have yet investigated the aging of irradiated PLA. This research aims to determine how aging influences the properties of irradiated PLA. Specifically, it focuses on the structural changes caused by irradiation and further aging, as well as their impact on the polymer’s phase structure. Additionally, the behavior of aged PLA in water and its potential for chemical recycling were evaluated. 2. Experimental 2.1 Materials Semi-crystalline granules of poly(L-lactide) (PLA) 4043D were purchased from NatureWorks LLC (USA). The granules were γ-irradiated using a UGU-420 cobalt facility at temperature around 15°C. E-beam irradiation of PLA was performed on UELV10-10 multipurpose linear accelerator, operating in a mode that ensures uniform dose distribution and prevents excessive sample heating. Details of irradiation experiment are available elsewhere [ 27 ]. After irradiation part of the samples were analyzed, while the remaining samples were stored for 8 years in Zip-lock bags at room temperature in the dark for aging experiment. The names and absorbed dose values for unaged samples are listed in Table 1 . For aged samples suffix “-A” was added to the sample name. Table 1 Names of poly(L-lactide) samples before aging Sample name Irradiation source Dose, kGy PLA-0 - 0 PLA-irG-100 γ 100 PLA-irG-250 250 PLA-irG-500 500 PLA-irG-700 700 PLA-irG-1000 1000 PLA-irE-120 e-beam 120 PLA-irE-360 360 PLA-irE-600 600 PLA-irE-840 840 PLA-irE-1200 1200 2.2 Gel permeation chromatography (GPC) Molecular weight of PLA samples was evaluated using an Ultimate 3000 Thermo Scientific apparatus equipped with an Agilent PLgel 5 µm MIXED-C column (300 × 7.5 mm) thermostated at 30°C and a refractive index detector. Chloroform (CHCl 3 ) was used as the eluent, with a flow rate of 1.0 ml/min. For calibration purpose polystyrene standards were used. 2.3 Nuclear magnetic resonance (NMR) 1 H NMR spectra were recorded on a Bruker AVANCE-500 NMR spectrometer operating at 500 MHz, with CDCl 3 as a solvent. Chemical shifts were calibrated relative to the residual CHCl 3 peak. 2.4 Furrier transformed infrared spectroscopy (FTIR) FTIR spectra were obtained using an Optosky ATP8900 + spectrometer with a diamond ATR crystal. Each spectrum was the result of 24 scans at a resolution of 4 cm − 1 . Samples were prepared by dissolving PLA granules in CHCl 3 , placing a drop of the solution onto the ATR crystal, and recording the spectrum after solvent evaporation. 2.5 Differential scanning calorimetry (DSC) DSC measurements were performed using the following apparatus and conditions: i) PLA before aging – STA 449 C Jupiter calorimeter in air; ii) PLA after aging – STA 449 F3 Jupiter calorimeter under inert gas flow; iii) aged PLA after water treatment – Perkin Elmer calorimeter under inert gas flow. All samples were heated from room temperature at a rate of 5°C/min. 2.6 Wide-angle X-ray diffraction (WAXD) WAXD patterns were recorded using a PANalytical Empyrean diffractometer with monochromatized CuK α radiation, in the range of 4–50°. To evaluate the crystallinity degree ( χ c ), patterns were resolved into amorphous and crystalline components. Peak fitting was performed within the range of 8–26°. 2.7 Water treatment Granule of aged PLA was placed in serum vial containing 10 mL of distilled water and sealed. The vials were placed on laboratory shaker operating at 100 rpm and maintained at room temperature for 1, 5, 10 and 15 days. After the designated treatment period, mass of the wet samples (m w ) was measured. The granules were then dried in a vacuum oven at 40°C for 4 days, and their dry mass (m d ) were recorded. Each experiment was conducted in triplicate. Water uptake and mass loss were calculated as follows: Water uptake = [(m w – m d ) / m d ] × 100% Mass loss = [(m d – m 0 ) / m 0 ] × 100% where m 0 is the mass of the PLA granules before water treatment. 2.8 Depolymerization of PLA For the depolymerization experiment 5 g of PLA granules were placed into a 25 mL round-bottom flask. Subsequently, 0.005 mL of tin(II) 2-ethylhexanoate (Sn(Oct) 2 ) was added as a catalyst. The system was vacuumed, and the flask containing PLA was immersed in an oil bath, while the receiving flask was placed in an ice bath. Distillation was conducted in vacuum at 190–210°C until the reaction was complete. The resulting product was kept under argon to prevent hydrolysis. 3. Results and discussion Figure 1 a-f illustrates visual appearance of PLA granules before and after aging. Notable changes after irradiation were observed in PLA-irG-1000 sample, which was slightly yellowish, while other samples remained white. This discoloration can be attributed to the oxidative degradation of PLA. After aging PLA-irG-700-A and PLA-irE-840/1200-A samples also exhibited yellowish coloration. Moreover, while PLA-0-A granules retained their original appearance and plastic behavior, PLA-irG-1000-A and PLA-irE-1200-A samples transformed into a gel-like state, becoming easily deformable (Fig. 1 g, j). These findings indicate that aging significantly impacts PLA, particularly irradiated samples with lower molecular weights. To further investigate aging effect on irradiated PLA granules, their molecular weight was estimated by GPC, and the radiation chemical yield of scission (G s ) was determined using following equation: G s = N A (⟨M n,D ⟩ –1 – ⟨M n,0 ⟩ –1 ) / (6.24×10 6 ×D) where D represents the irradiation dose, ⟨M n,0 ⟩ is the number-average molecular weight of unirradiated PLA, and ⟨M n,D ⟩ is the number-average molecular weight of PLA irradiated to a specific dose. Following irradiation, the G s values for e-beam and γ-irradiated PLA was 2.20 and 2.86, respectively [ 27 ]. Higher G s observed for γ-irradiation can be attributed to the significantly longer treatment duration. Since irradiation occurs in the presence of air, prolonged exposure leads to increased oxidative degradation. This trend maintains after aging, with molecular weight reduction being more pronounced in γ-irradiated PLA compared to e-beam treated, particularly at doses exceeding 500 kGy. After aging, the G s value for γ-irradiated PLA reached 4.01, whereas it was 3.04 for e-beam irradiated PLA. The G s value is calculated based on difference in molecular weight after and before irradiation. Therefore, the increase of G s after aging indicates that the aging process accelerates in irradiated samples. Figure 2 presents 1 H NMR spectra of PLA before and after irradiation. The appearance of new peaks and the increased intensity of some peaks already presented on PLA-0 spectrum are attributed to the formation of additional chain ends caused by main chain scission during irradiation. Intensity of the end group CH signal at δ = 4.36 ppm increases relative to the main chain signal at δ = 5.16 ppm. Irradiated PLA have been previously studied by 1 H NMR spectroscopy in works [ 14 , 28 ]. However, some discrepancies exist between the results of this two works, likely due to significant differences in the dose range investigated. The 1 H NMR spectrum of PLA-irG-1000 and PLA-irE-1200 closely resemble those reported in [ 28 ], where high irradiation doses were also used. Thus, new peaks can be identified based on previously published findings. Signals corresponding to the new end group CH 3 –CH 2 –O–CO– appear at δ = 1.23 ppm (CH 3 ) and δ = 4.16 ppm (CH 2 ). Similarly, new signals of the end group CH 3 –CH 2 –CO–O– are detected at δ = 1.12 ppm (CH 3 ) and δ = 2.38 ppm (CH 2 ). New set of lower intensity peaks at δ = 7.97 ppm and δ = 8.05 ppm is assigned to H–CO–O– chain ends. Minor peaks at δ = 5.86 ppm, δ = 6.17 ppm and δ = 6.46 ppm correspond to CH 2 = CH–CO–O– end, and at δ = 5.59 and δ = 6.12 ppm to CH 2 = C(CH 3 )–CO–O– end. These observations indicate that minimum amount of chain scission events leads to formation of unsaturated or formic acid like chain ends. The cleavage of ester bonds, resulting in the formation of typical for PLA HO–CH(CH 3 )–CO–O– chain ends is more pronounced. However, the primary pathway for PLA backbone scission during irradiation involves the abstraction of hydrogen atom from the main chain, followed by rearrangement. This process causes backbone rapture, leading to the formation of CH 3 –CH 2 –O–CO– or CH 3 –CH 2 –CO–O– chain ends. These results correlate well with the main radicals formed during PLA irradiation reported in [ 29 ]. Notably, the new peaks observed in the 1 H NMR spectra and their corresponding chain ends are consistent across PLA-irG-1000, PLA-irE-1200, and even PLA irradiated in vacuum reported in [ 28 ]. However, the intensity of the peak at δ = 4.36 ppm, associated with ester bond cleavage, is higher compared to peaks of other chain ends for PLA-irG-1000 relative to PLA-irE-1200. Hence, the presence of oxygen and the longer exposure times during γ-irradiation intensify ester bond rupture, contributing to a more significant reduction in PLA molecular weight compared to e-beam irradiation. Figure 3 a shows 1 H NMR spectra of irradiated PLA after aging. Significant changes occurred in the samples during storage for 8 years, particularly in those irradiated at high doses. The most pronounced alteration in the spectra is the marked increase in intensity of signals at δ = 4.36 ppm and δ = 1.48 ppm, which are attributed to the HO–CH(CH 3 )–CO–O– chain end. The intensity of these signals rises with dose relative to the main chain signals at δ = 5.16 ppm and δ = 1.58 ppm, reflecting the reduction in PLA molecular weight during aging. Expanded 1 H NMR spectra of irradiated PLA after aging is presented in Fig. 3 b. A broad peak appears in the δ = 5.35–5.55 ppm range. Presumably it corresponds to hydrogen atom of –OH group at chain ends or in low molecular weight products of degradation and absorbed water. Signals characteristic of irradiated PLA remain in the spectra. The signals for CH 3 –CH 2 –O–CO– end group are observed at δ = 1.26 ppm (CH 3 ) and δ = 4.18 ppm (CH 2 ), while those for CH 3 –CH 2 –CO–O– end group appear at δ = 1.15 ppm (CH 3 ) and δ = 2.40 ppm (CH 2 ). However, in PLA-irG-1000-A and PLA-irE-1200-A intensity of these signals is much lower than that of the signal at δ = 4.36 ppm. Therefore, ester bond cleavage is the main mechanism responsible for the decrease in PLA molecular weight during aging. The upper spectrum in Fig. 3 b was recorded for PLA-irG-1000-A after 15 days in water and subsequent drying in vacuum oven. Following this treatment, peaks at δ = 5.35–5.55 ppm, δ = 2.54 ppm, δ = 2.20 ppm, δ = 2.11 ppm, δ = 1.80 ppm, and δ = 1.34 ppm either disappear or become less intense. These peaks are thus associated with low molecular weight degradation products that can dissolve in water. During storage in air PLA can absorb moisture from the environment. Apparently, even small amounts of water are sufficient to initiate hydrolytic degradation of PLA. Hydrolytic degradation during storage accelerates with increasing irradiation dose, as irradiation promotes the formation of –COOH end groups, which catalyze further hydrolysis. Figure 4 a presents FTIR spectra of aged PLA. For samples irradiated at doses up to 600 kGy, the FTIR spectra remain almost unchanged after aging. However, at higher doses, significant structural changes are evident in the polymer spectra. A broad band around 3000–3500 cm − 1 is observed and can be attributed to the stretching vibration of –OH group. Although –OH end groups are also present in PLA-0-A, their concentration is too low to be detected in the spectrum due to the high molecular weight of the polymer. In contrast, the –OH group signal is visible in PLA-irG-700/1000-A and PLA-irE-840/1200-A due to lower molecular weight and higher concentration of end groups. Moreover, these samples may contain degradation products, such as lactic acid and lactic acid lactate, which is relevant to changes observed in 1 H NMR spectra (Fig. 3 ). Further significant changes are observed in the 965 − 600 cm − 1 region. The spectrum of PLA-0-A is characteristic of this polymer, with peaks assigned to specific vibration modes as follows: 956 cm − 1 r(CH3) + ν (C − COO), 867 cm − 1 ν (C − COO), 736 cm − 1 δ(C = O), 702 cm − 1 γ(C = O) [ 30 , 31 ]. For irradiated samples, only peak at 867 cm − 1 remains almost unchanged. A new peak at 819 cm − 1 appears, attributed to lactic acid. Meanwhile, peaks at 736 cm − 1 and 702 cm − 1 become broader, less intense, and overlapped. Presumably, these changes may be associated with an increased number of hydrogen bonds involving C = O group. The ν (C = O) vibration mode peak in the FTIR spectra shifts to lower wavenumbers and broadens with increasing irradiation dose. For PLA-0-A the peak maximum is at 1748 cm − 1 with full width at half maximum (FWHM) of 26 cm − 1 . In comparison, for PLA-irG-700-A the peak maximum shifts to 1744 cm − 1 with a FWHM of 55 cm − 1 , and for PLA-irG-1000-A it further shifts to 1741 cm − 1 with a FWHM of 64 cm − 1 . Moreover, the ν (C = O) peak in aged irradiated at high doses PLA not only broadens but also appears to consist of two overlapping peaks. As the polymer was initially in a form of granules, achieving high quality spectra directly using ATR-mode was challenging. To overcome this, PLA samples were dissolved and cast into films for analysis. However, for a more detailed investigation of the ν (C = O) region, spectra were also recorded directly for granules of selected samples (Fig. 4 b). Difference in the 1250 − 600 cm − 1 region between the spectra of PLA granules and films reflect variations in phase structure and chain conformation. In the ν (C = O) region around 1745 cm − 1 , a single narrow peak is observed for PLA-0-A. For PLA-irG-700-A the peak develops a shoulder, and for PLA-irG-1000-A it separates into two overlapping peaks. Typically, vibrations of a single nature in different monomer units produce one signal, and separate signals for end groups are not observed. However, molecular weight of PLA-irG-1000-A is sufficiently low, leading to a comparable number of ester C = O groups in the backbone and carboxylic C = O groups at chain ends. Additionally, presence of degradation products, such as lactic acid, contributes to the division of the ν (C = O) peak into two components. The discussion of γ-irradiated aged PLA FTIR spectra made above is also relevant for e-beam irradiated samples. However, changes in the spectrum of PLA-irE-840-A are less pronounced than those in PLA-irG-700-A. This difference is likely due to a lower extent of oxidative degradation during e-beam irradiation compared to γ-irradiation. The change in the molecular structure of PLA induced by irradiation and subsequent aging results in alterations in its phase structure. Figure 5 a,b shows the DSC curves of e-beam and γ-irradiated PLA before aging, with corresponding data summarized in Table 2 . Absence of an exothermic cold crystallization peak in the area between 80 and 120°C and presence of an endothermic melting peak in the DSC curve of PLA-0, confirms that the polymer is semi-crystalline. For all irradiated samples melting temperature decreases as irradiation dose increases. This decrease can be attributed to chain scission caused by irradiation, which reduces the molecular weight of the polymer. In general, crystalline domains in polymers are less susceptible to irradiation induced damage compared to amorphous regions. However, the high irradiation doses used in this study were sufficient to disrupt PLA crystals. As a result, not only does the melting temperature decrease, but the width of melting peak increases, and bimodality of melting appears in irradiated samples. The lower temperature melting peak corresponds to α-form crystals, while the higher temperature peak is associated with the more defected α’-form crystals, which recrystallize during DSC heating. To quantify the fraction of each crystal form, peak separation was performed, and the results are presented in Table 2 . Not only α’-form appears in irradiated sample, but it is prominent in PLA-irE-360 and PLA-irG-250 samples. Irradiation-induced damage to PLA crystals is evident, but further increase in dose lead to a reduction in the α’-form fraction. This may be due to increased chain mobility in low molecular weight polymers, allowing defects to migrate from the crystalline to the amorphous phase. For example, the molecular weight decreases from 11,000 g/mol in PLA-irE-360 to 3,300 g/mol in PLA-irE-1200, enabling this process. Another possible explanation is that shorter polymer chains, resulting from reduced molecular weight at higher doses, interact weaker. This may cause partial melting of α’ crystals without subsequent recrystallization, contributing to the increased area of the lower-temperature melting peak. Table 2 Characteristics of melting peaks for unirradiated and irradiated PLA Sample T m1 , °C T m2 , °C φ 1 , % φ 2 , % PLA-0 150,7 - 100 - PLA-irE-360 141,2 144,8 31 69 PLA-irE-600 135,0 139,1 40 60 PLA-irE-840 126,5 133,9 56 43 PLA-irG-250 144,5 147,7 21 79 PLA-irG-500 138,6 143,5 34 66 PLA-irG-700 126,5 134,2 53 47 Figure 6 shows the WAXD pattern of PLA-0 resolved into crystalline and amorphous components. Since the α and α’ crystal forms are resembling their WAXD patterns overlap. However, the (004)/(103) and (211) reflexes, which are characteristic of α crystals [ 19 , 32 ], are evident in the WAXD pattern of PLA-0. This confirms the presence of the α crystal form in the polymer. The WAXD patterns of PLA-irE-120/1200 and PLA-irG-100/1000 remain largely unchanged, indicating that the α crystal form persists after irradiation. The polymer crystallinity degree, determined from WAXD data, is about 40% for both PLA-0 and irradiated samples. Therefore, irradiation doesn’t affect the overall crystallinity degree. Still, the DSC results suggest that irradiation alters structure of PLA crystals, introducing some disorder in polymer. Figure 5 c,d presents the DSC curves of PLA after aging. The melting behavior of PLA-0-A and samples irradiated at doses up to 600 kGy remains largely unchanged after aging, with their DSC curves closely resembling those of the unaged samples. However, at higher irradiation doses deterioration of the crystalline structure is observed. For PLA-irE-840 crystal melting is still can be identified on DSC curves. For PLA-irG-700 only a broad low intensity peak is observed in the temperature range of 90–135°C. Melting was no longer evident in PLA-irE-1200-A and PLA-irG-1000-A samples. Hence, deterioration of crystalline structure can serve as a marker of the PLA aging process. The more pronounced amorphization observed during aging in PLA samples irradiated at higher doses can be attributed to their lower initial molecular weight. Lower molecular weight increases chain mobility and amount of –COOH end groups, which likely accelerates the degradation of PLA during storage. One of the key advantages of PLA is its hydrolytic degradability, as opposed to conventional plastics. Irradiated and aged PLA samples were immersed into water, and it was initially expected that PLA-irG-1000-A and PLA-irE-1200-A, due to low molecular weight, would completely dissolve in water within a few days. However, this did not occur. Figure 7 a,b shows change in the mass of PLA granules after 1–15 days in water. The mass of PLA-0-A and samples irradiated at low doses remained constant over this period. Meanwhile the mass of PLA-irE-840-A decreased by 10.7%, PLA-irE-1200-A by 55.2%, PLA-irG-700-A by 27.6%, and PLA-irG-1000-A by 61.1%. These results indicate that those samples contain a low molecular weight water soluble fraction. However, after the dissolution of this fraction, no obvious signs of polymer hydrolysis were observed. To further investigate the relationship between mass loss and molecular weight, latter was evaluated using GPC. The results showed no significant changes in PLA molecular weight, likely due to the insufficient resolution of the GPC method used for low molecular weight samples. To address this limitation, 1 H NMR spectroscopy was employed. The molecular weight of PLA samples determined by 1 H NMR is shown in Table 3 . For samples irradiated at lower doses, molecular weight remained unchanged, correlating with stable mass values. Their molecular weight was sufficiently high, and hydrolysis rate at room temperature was slow. Thus, over 15 days hydrolysis process cannot be detected for semi-crystalline PLA with M n greater than 5000 g/mol. For PLA samples irradiated at doses of 700 kGy and above, molecular weight measured by 1 H NMR increased significantly after 15 days in water. This phenomenon can be explained by the fact that M n reflects the average molecular weight of chains of varying lengths. In water, degradation products and low molecular weight PLA chains dissolve, leaving behind an insoluble fraction with higher molecular weight. Therefore, even aged PLA with critically low molecular weight cannot fully dissolve in water or be biodegraded by microorganisms in the short term. A slight increase in M n was also observed for PLA-irG-500-A, indicating the presence of a water-soluble fraction. This is likely due to the higher extent of initial oxidative degradation during exposure to γ-irradiation. Table 3 Molecular weight of aged PLA before and after 15 days of water treatment Sample name M n , g/mol 0 days 15 days PLA-irE-360-A 13380 13550 PLA-irE-600-A 5050 5170 PLA-irE-840-A 660 2440 PLA-irE-1200-A 130* 1440 PLA-irG-250-A 10530 10840 PLA-irG-500-A 4570 7610 PLA-irG-700-A 660 3170 PLA-irG-1000-A 120* 1230 * represents an average calculated based on contributions from both PLA and lactic acid The processes occurring in irradiated aged PLA during water treatment are of considerable interest. PLA is inherently hydrophobic, but untreated PLA typically contains some water absorbed from the environment. Upon immersion in water, water molecules diffuse into the polymer matrix, initiating hydrolysis. This process generates low molecular weight compounds, which subsequently diffuse into the solution. Figure 7 c,d shows the water absorption behavior of PLA. Water uptake by PLA-irE-1200-A and PLA-irG-1000-A is significantly higher than that by PLA-0-A. The decrease in molecular weight is accompanied by an increase in the number of hydrophilic –COOH and –OH groups on chain ends, resulting in higher water uptake. The swelling ratio of PLA-irG-1000-A and PLA-irG-700-A exceeds that of PLA-irE-1200-A and PLA-irE-840-A, likely due to more extensive oxidative degradation of PLA during γ-irradiation. Moreover, the dissolution of low molecular weight fraction and swelling in water lead to crystallization in PLA-irE-1200-A, PLA-irG-1000-A, and PLA-irG-700-A samples as was shown by DSC. Before treatment, these samples were amorphous. This recrystallization, induced by direct contact with liquid water, prolongs the degradation process. The dissolution of low molecular weight compounds is also supported by FTIR spectroscopy results. The broad band around 3000–3500 cm − 1 and the changes in 965 − 600 cm − 1 region observed in PLA-irE-840/1200-A and PLA-irG-700/1000-A (Fig. 4 b) almost disappear after immersion into water (Fig. 4 c). Additionally, the peak corresponding to the ν (C = O) vibration mode becomes narrower. After water treatment, the FWHM of the ν (C = O) peak is 26 cm − 1 for PLA-0-A, 33 cm − 1 for PLA-irG-700-A, and 39 cm − 1 for PLA-irG-1000-A. While the FWHM of the ν (C = O) peak remains unchanged for PLA-0-A, it decreases for PLA-irG-700/1000-A, indicating a more uniform composition after mass loss. Therefore, the FWHM of the ν(C = O) peak can serve as a useful measure of hydrolyzed aged PLA uniformity. If the hydrolytic degradation of high-performance semi-crystalline PLA remains rather low even after irradiation and aging, could it still be considered an eco-friendly plastic? One of PLA’s significant advantages is its ability to be efficiently depolymerized back to its monomer, lactide, which can be repolymerized to produce high quality PLA products [ 33 ]. Table 4 summarizes the chemical yields of PLA recycling into lactide. The structure of the recovered lactide was confirmed using 1 H NMR (Fig. 8 a). Scheme of PLA depolymerization is shown in Fig. 8 b. For PLA irradiated with high doses, the chemical yield decreases due to the polymer’s reduced molecular weight. Moreover, the recovered lactide was yellowish, and 1 H NMR analysis revealed a high content of linear oligo(lactic acid) in the product (δ = 4.36 ppm, δ = 1.47 ppm). However, PLA-0-A, PLA-irE-360-A, and PLA-irG-250-A samples were converted to lactide with high yields of approximately 90%, producing a much purer product. The experimental design for lactide preparation from PLA in this study closely mimics one of the steps in the industrial process for lactide production. Therefore, chemical recycling of PLA has the potential to be scaled up for industrial implementation. This approach would be a more eco-friendly alternative to landfilling or even composting, offering a sustainable solution to PLA waste management. Table 4 Chemical yield of PLA conversion into lactide Sample Chemical yield, % PLA-0-A 91 PLA-irE-360-A 88 PLA-irE-840-A 82 PLA-irG-250-A 94 PLA-irG-700-A 77 4. Conclusions The radiation chemical yield of chain scission is higher for γ-irradiated PLA compared to e-beam irradiated PLA, as the prolonged exposure during γ-irradiation results in increased oxidative degradation. After aging for eight years, this trend persists and intensifies in irradiated samples, particularly at doses above 600 kGy. The primary new end groups formed during radiation-induced backbone scission are CH 3 –CH 2 –O–CO– and CH 3 –CH 2 –CO–O–. Concurrently, the decrease in PLA molecular weight during aging is attributed to chain rupture at the ester bond, resulting in the formation of HO–CH(CH 3 )–CO–O– chain ends. As the radiation dose increases, PLA molecular weight decreases, while hydrophilicity and the number of –COOH end groups increase. These groups catalyze hydrolysis processes during storage. The more extensive aging observed in γ-irradiated PLA, compared to e-beam irradiated samples, is due to the initially higher extent of oxidative degradation. Irradiation also alters PLA phase structure, leading to the emergence of the conformationally disordered α’-form. While the phase structure of most samples remains largely unchanged after aging, amorphization occurs in samples irradiated to 1000 kGy and above. Samples irradiated up to 840 kGy contain a fraction soluble in water at room temperature. However, even in these cases, hydrolysis is hindered by water-induced crystallization. Chemical recycling of PLA was successfully performed for unirradiated PLA and samples irradiated up to 360 kGy. This process demonstrates the potential for industrial-scale implementation, offering a more eco-friendly alternative to landfilling or composting. Chemical recycling provides a sustainable solution to PLA waste management by enabling the recovery of high-quality lactide for polymer regeneration. Declarations Acknowledgments The authors are also pleased to express their grateful acknowledgements to Prof. Krul’ L.P., Dr. Butovskaya G.V. and Roginets L. P. for their help with the experiments. Funding Declaration This work was supported by the State Program for Scientific Research of Belarus under Grant number 1.3.04.05. Declaration of interests 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. Author contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Conceptualization: Fedorenko A.A., Kostjuk S.V.; methodology: Fedorenko A.A., Grinyk E.V., Skakovsky E.D.; investigation: Fedorenko A.A., Salnikova, I.A., Tychinskaya L. Yu., Skakovsky E.D.; writing—original draft preparation: Fedorenko A.A., Grinyk E.V.; writing—review and editing: Fedorenko A.A., Kostjuk S.V. References Satti SM, Shah AA (2020) Polyester‐based biodegradable plastics: an approach towards sustainable development. Lett Appl Microbiol 70:413–430. https://doi.org/10.1111/lam.13287 Afshar S V., Boldrin A, Astrup TF, et al (2024) Degradation of biodegradable plastics in waste management systems and the open environment: A critical review. J Clean Prod 434:140000. https://doi.org/10.1016/j.jclepro.2023.140000 Wang G, Huang D, Ji J, et al (2021) Seawater‐Degradable Polymers—Fighting the Marine Plastic Pollution. Adv Sci 8:. https://doi.org/10.1002/advs.202001121 Le Gall M, Niu Z, Curto M, et al (2022) Behaviour of a self-reinforced polylactic acid (SRPLA) in seawater. 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Polym Degrad Stab 133:293–302. https://doi.org/10.1016/j.polymdegradstab.2016.09.005 Milicevic D, Trifunovic S, Galovic S, Suljovrujic E (2007) Thermal and crystallization behaviour of gamma irradiated PLLA. Radiat Phys Chem 76:1376–1380. https://doi.org/10.1016/j.radphyschem.2007.02.035 Sato S, Gondo D, Wada T, et al (2013) Effects of various liquid organic solvents on solvent‐induced crystallization of amorphous poly(lactic acid) film. J Appl Polym Sci 129:1607–1617. https://doi.org/10.1002/app.38833 Limsukon W, Rubino M, Rabnawaz M, et al (2023) Hydrolytic degradation of poly(lactic acid): Unraveling correlations between temperature and the three phase structures. Polym Degrad Stab 217:110537. https://doi.org/10.1016/j.polymdegradstab.2023.110537 Krul’ LP, Butovskaya G V., Fedorenko AA, et al (2020) Gamma- and Electron Beam Radiation-Induced Degradation of Poly-L-Lactide. High Energy Chem 54:136–141. https://doi.org/10.1134/S0018143920020125 Babanalbandi A, Hill DJT, Whittaker AK (1997) Volatile products and new polymer structures formed on 60Co γ-radiolysis of poly(lactic acid) and poly(glycolic acid). Polym Degrad Stab 58:203–214. https://doi.org/10.1016/S0141-3910(97)00050-5 Babanalbandi A, Hill DJT, O’Donnell JH, et al (1995) An electron spin resonance study on γ-irradiated poly(l-lactic acid) and poly(d,l-lactic acid). Polym Degrad Stab 50:297–304. https://doi.org/10.1016/0141-3910(95)00150-6 Pan P, Yang J, Shan G, et al (2012) Temperature-Variable FTIR and Solid-State 13 C NMR Investigations on Crystalline Structure and Molecular Dynamics of Polymorphic Poly( l -lactide) and Poly( l -lactide)/Poly( d -lactide) Stereocomplex. Macromolecules 45:189–197. https://doi.org/10.1021/ma201906a Kister G, Cassanas G, Vert M (1998) Effects of morphology, conformation and configuration on the IR and Raman spectra of various poly(lactic acid)s. Polymer (Guildf) 39:267–273. https://doi.org/10.1016/S0032-3861(97)00229-2 Kawai T, Rahman N, Matsuba G, et al (2007) Crystallization and Melting Behavior of Poly ( L -lactic Acid). Macromolecules 40:9463–9469. https://doi.org/10.1021/ma070082c McGuire TM, Buchard A, Williams C (2023) Chemical Recycling of Commercial Poly(l-lactic acid) to l-Lactide Using a High-Performance Sn(II)/Alcohol Catalyst System. J Am Chem Soc 145:19840–19848. https://doi.org/10.1021/jacs.3c05863 Supplementary Files GraphicalAbstract.png Cite Share Download PDF Status: Posted Version 1 posted 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-5716364","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":401827121,"identity":"57559cee-43d4-4695-92ca-7143b54bee63","order_by":0,"name":"Alexandra A. Fedorenko","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Alexandra","middleName":"A.","lastName":"Fedorenko","suffix":""},{"id":401827122,"identity":"cb6884b6-4ff0-45fb-8b95-4c9a52f8f98e","order_by":1,"name":"Evgeny V. Grinyuk","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Evgeny","middleName":"V.","lastName":"Grinyuk","suffix":""},{"id":401827123,"identity":"53397e01-4593-4f85-9be2-f31d2302e2a9","order_by":2,"name":"Iryna A. Salnikova","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Iryna","middleName":"A.","lastName":"Salnikova","suffix":""},{"id":401827124,"identity":"a3de56dd-eaaa-426f-b926-74d17a0f6fbf","order_by":3,"name":"Lyudmila Yu. Tychinskaya","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Lyudmila","middleName":"Yu.","lastName":"Tychinskaya","suffix":""},{"id":401827125,"identity":"b8a3c0a2-d346-4667-aca3-2073c94941b1","order_by":4,"name":"Evgeny D. Skakovsky","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Evgeny","middleName":"D.","lastName":"Skakovsky","suffix":""},{"id":401827126,"identity":"83b5fa16-dcf0-4bd7-84d3-37615118e653","order_by":5,"name":"Sergei V. Kostjuk","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAv0lEQVRIiWNgGAWjYBACCQiRwMAPYjE2EKeFsQGkRXIGSVoYgFoMbhCrRbK9/fkDy7Y0e+Pb7c8kGHccJqxFmueMYYNkW07itjtnzCQYzxChRU4ihxGopSLB7EYOmwRjG1Fa0h+CtNgbz0h/RpwWaYkEsMMYN0gkmBGnRbLnjOEMiXNpiTPunDG2SDyTTliLxPH2B58lypLt+We3P7zxcYc1YS0gwCwBYyUwNBOnhfEDgl1HnJZRMApGwSgYUQAAjy06z8mGXF0AAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0002-7466-3662","institution":"Belarusian State University","correspondingAuthor":true,"prefix":"","firstName":"Sergei","middleName":"V.","lastName":"Kostjuk","suffix":""}],"badges":[],"createdAt":"2024-12-26 13:18:51","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5716364/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5716364/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":73856962,"identity":"10e296e9-c790-4f87-93db-6a12b22c25f5","added_by":"auto","created_at":"2025-01-15 10:29:24","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":53266,"visible":true,"origin":"","legend":"\u003cp\u003eVisual appearance of the samples: a) PLA-0; b) PLA-irE-1200; c) PLA-irG-1000; d) PLA-0-A; e) PLA-irE-1200-A; f) PLA-irG-1000-A; g) undeformed granule of PLA-irG-1000-A; j) manually deformed PLA-irG-1000-A granule\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5716364/v1/8b860455976f7c65a8eb9d83.png"},{"id":73856964,"identity":"11a9c9b9-6bdb-4aa3-b644-216381558701","added_by":"auto","created_at":"2025-01-15 10:29:24","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":8790,"visible":true,"origin":"","legend":"\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH NMR spectra of PLA before and after irradiation\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5716364/v1/dd1a22701623d0be86f6db63.png"},{"id":73856959,"identity":"ecad9cd1-b3be-41af-8730-ece56bc15ada","added_by":"auto","created_at":"2025-01-15 10:29:24","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":9904,"visible":true,"origin":"","legend":"\u003cp\u003ea) \u003csup\u003e1\u003c/sup\u003eH NMR spectra of unirradiated and γ-irradiated PLA after aging; b) expanded \u003csup\u003e1\u003c/sup\u003eH NMR spectra of PLA-0-A, PLA-irG-1000-A, and PLA-irG-1000-A after 15 days in water and drying in vacuum oven (W)\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5716364/v1/6449c39d20f8e87294898572.png"},{"id":73856971,"identity":"b6a32738-0c0e-45fd-b965-9d4c3fe7c80b","added_by":"auto","created_at":"2025-01-15 10:29:24","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":21638,"visible":true,"origin":"","legend":"\u003cp\u003ea) FTIR spectra of unirradiated and γ-irradiated aged PLA (after dissolution in CHCl\u003csub\u003e3\u003c/sub\u003e); b) FTIR spectra of unirradiated and γ-irradiated aged PLA granules; c) FTIR spectra of unirradiated and γ-irradiated aged PLA after water treatment (after dissolution in CHCl\u003csub\u003e3\u003c/sub\u003e)\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5716364/v1/345e1f96b6c9b18062ad62d9.png"},{"id":73856953,"identity":"36b45a45-a51b-4274-96e5-b676456e71d3","added_by":"auto","created_at":"2025-01-15 10:29:23","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":23425,"visible":true,"origin":"","legend":"\u003cp\u003ea) DSC curves of PLA before and after e-beam irradiation; b) DSC curves of PLA before and after γ-irradiation; c) DSC curves of unirradiated and e-beam irradiated PLA after aging; d) DSC curves of unirradiated and γ-irradiated PLA after aging\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5716364/v1/28ac11fe36bd5dd2fce4d365.png"},{"id":73857562,"identity":"2f97d399-11d5-4593-8252-8e926ea7e6bb","added_by":"auto","created_at":"2025-01-15 10:37:24","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":5505,"visible":true,"origin":"","legend":"\u003cp\u003eWAXD pattern of PLA-0 resolved into amorphous and crystalline components\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5716364/v1/a61c441e322ca9301d7ab60a.png"},{"id":73856970,"identity":"b057dc09-5511-4eb6-8a2d-8fd4add18e1e","added_by":"auto","created_at":"2025-01-15 10:29:24","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":26973,"visible":true,"origin":"","legend":"\u003cp\u003eMass loss during water treatment for: a) unirradiated and e-beam irradiated PLA after aging, b) unirradiated and γ-irradiated PLA after aging; Water uptake of: c) unirradiated and e-beam irradiated PLA after aging, d) unirradiated and γ-irradiated PLA after aging\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5716364/v1/d163d3c382de6f68973259e0.png"},{"id":73856995,"identity":"02ca8029-af8e-4ba8-a171-ab92f782c872","added_by":"auto","created_at":"2025-01-15 10:29:25","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":14731,"visible":true,"origin":"","legend":"\u003cp\u003ea) \u003csup\u003e1\u003c/sup\u003eH NMR of aged PLA depolymerization products; b) scheme of PLA depolymerization\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5716364/v1/01131a08f4e5a93b72fab8df.png"},{"id":79713177,"identity":"ee13040e-0811-4ad3-96b1-027b95d56e7d","added_by":"auto","created_at":"2025-04-01 21:15:08","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":894951,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5716364/v1/0f0f65a8-c495-4667-89b8-710b677eeba6.pdf"},{"id":73856952,"identity":"0d7e0ed2-0c99-4126-a59e-879fdc79107a","added_by":"auto","created_at":"2025-01-15 10:29:23","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":61545,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstract.png","url":"https://assets-eu.researchsquare.com/files/rs-5716364/v1/e84b649ae68e3157f9f61919.png"}],"financialInterests":"","formattedTitle":"Effects of irradiation and aging on the molecular and phase structure of poly(L-lactide): insights into degradation and recycling potential","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003ePolylactide (PLA) is an aliphatic polyester used for production of medical devices and packaging, as well as in agricultural and automotive industries. PLA is generally recognized as biodegradable polymer, as certain bacterial and fungal strains can degrade it in nature [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. However, while the degree of PLA degradation is high in compost or sewage sludge, it is relatively low in soil or seawater [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. The high salinity of marine environment makes it difficult for water to penetrate PLA [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Additionally, low temperatures further reduce rate of PLA degradation [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Furthermore, microbial consortia in seawater exhibit low efficacy in degrading PLA [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. As a result, even in long-term experiments in marine environment, only minor PLA degradation has been observed [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. The slow rate of PLA degradation can be explained by its degradation mechanism. When exposed to water, the first stage of PLA degradation is abiotic hydrolysis [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. The low molecular weight products formed are then metabolized by microorganisms, converting PLA residues into water and carbon dioxide [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. The rate-limiting step in PLA degradation is the reduction in its molecular weight during hydrolysis. Polymer irradiation is one of the approaches that can be used to accelerate the hydrolysis process.\u003c/p\u003e \u003cp\u003eRadiation processing of polymers is a widely used technique for crosslinking, sterilization, structural modification, polymerization, and grafting [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Depending on the irradiation conditions and nature of the polymer, it either crosslinks or degrades. The latter predominates in polymers with quaternary carbon atoms, halogen atoms, or C\u0026ndash;O\u0026ndash;C bonds [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Due to the presence of ester group in its backbone, scission process dominates during PLA irradiation [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Interest in PLA irradiation is primarily driven by its use in medicine and, consequently, need for sterilization [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Radiation-induced backbone scission leads to a reduction in PLA molecular weight [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Effect of irradiation can be quantitatively expressed by the radiation chemical yield, defined as the number of products formed per 100 eV of absorbed energy [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Yield of chain scission for PLA ranges from 0.8 to 2.0 [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIndeed, a decrease in molecular weight, oxidative degradation, and rise of polymer hydrophilicity during irradiation accelerate PLA hydrolysis rate [\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. PLA degradation follows an autocatalytic model: \u0026ndash;COOH end groups catalyze hydrolysis, and their concentration in the polymer matrix increases as hydrolysis progresses [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Consequently, the radiation-induced reduction in PLA molecular weight, which increases the concentration of \u0026ndash;COOH end groups and enhances their mobility, accelerates polymer hydrolysis. Moreover, if irradiated PLA contains fraction of molecules with sufficiently low molecular weight, these molecules dissolve in water immediately upon hydrolysis, causing mass loss to occur without an induction period [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eBoth irradiation and hydrolysis are known to affect phase structure and crystallinity of PLA. PLA crystallization from melt, solution, or cold crystallization results in formation of α-form crystals [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The α-form is the most common and it is made up by left-handed 10\u003csub\u003e3\u003c/sub\u003e helixes packed into orthorhombic cell [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. When crystallization temperature is below 120\u0026deg;C α\u0026rsquo; crystals is formed along with α. Although these two forms share many similarities, the α\u0026rsquo;-form is conformationally disordered [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Coexistence of both forms in PLA sample leads to a multiple melting behavior in DSC curves [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Appearance of this behavior after irradiation has been reported in numerous studies and is attributed to decrease in PLA molecular weight and introduction of defects during irradiation [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. However, role of α- and α\u0026rsquo;-forms in this phenomenon has not been discussed. Hydrolysis also influences crystallization behavior of PLA. Although PLA is not soluble in water [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], water can strongly affect its crystallinity, especially at elevated temperature. Incorporation of water molecules enhances PLA chain mobility, promoting crystal growth and formation of new crystals. Moreover, amorphous phase hydrolyzes faster and dissolves in water [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Therefore, crystallinity degree of PLA rises during hydrolysis.\u003c/p\u003e \u003cp\u003eEffects of irradiation on the structure, properties, and hydrolysis of PLA has been extensively studied over the past two decades. However, no studies have yet investigated the aging of irradiated PLA. This research aims to determine how aging influences the properties of irradiated PLA. Specifically, it focuses on the structural changes caused by irradiation and further aging, as well as their impact on the polymer\u0026rsquo;s phase structure. Additionally, the behavior of aged PLA in water and its potential for chemical recycling were evaluated.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eSemi-crystalline granules of poly(L-lactide) (PLA) 4043D were purchased from NatureWorks LLC (USA). The granules were γ-irradiated using a UGU-420 cobalt facility at temperature around 15\u0026deg;C. E-beam irradiation of PLA was performed on UELV10-10 multipurpose linear accelerator, operating in a mode that ensures uniform dose distribution and prevents excessive sample heating. Details of irradiation experiment are available elsewhere [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. After irradiation part of the samples were analyzed, while the remaining samples were stored for 8 years in Zip-lock bags at room temperature in the dark for aging experiment. The names and absorbed dose values for unaged samples are listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. For aged samples suffix \u0026ldquo;-A\u0026rdquo; was added to the sample name.\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\u003eNames of poly(L-lactide) samples before aging\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\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\u003eIrradiation source\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDose, kGy\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irG-100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003eγ\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irG-250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irG-500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irG-700\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e700\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irG-1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irE-120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003ee-beam\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irE-360\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e360\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irE-600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e600\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irE-840\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e840\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irE-1200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1200\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Gel permeation chromatography (GPC)\u003c/h2\u003e \u003cp\u003eMolecular weight of PLA samples was evaluated using an Ultimate 3000 Thermo Scientific apparatus equipped with an Agilent PLgel 5 \u0026micro;m MIXED-C column (300 \u0026times; 7.5 mm) thermostated at 30\u0026deg;C and a refractive index detector. Chloroform (CHCl\u003csub\u003e3\u003c/sub\u003e) was used as the eluent, with a flow rate of 1.0 ml/min. For calibration purpose polystyrene standards were used.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Nuclear magnetic resonance (NMR)\u003c/h2\u003e \u003cp\u003e \u003csup\u003e1\u003c/sup\u003eH NMR spectra were recorded on a Bruker AVANCE-500 NMR spectrometer operating at 500 MHz, with CDCl\u003csub\u003e3\u003c/sub\u003e as a solvent. Chemical shifts were calibrated relative to the residual CHCl\u003csub\u003e3\u003c/sub\u003e peak.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Furrier transformed infrared spectroscopy (FTIR)\u003c/h2\u003e \u003cp\u003eFTIR spectra were obtained using an Optosky ATP8900\u0026thinsp;+\u0026thinsp;spectrometer with a diamond ATR crystal. Each spectrum was the result of 24 scans at a resolution of 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Samples were prepared by dissolving PLA granules in CHCl\u003csub\u003e3\u003c/sub\u003e, placing a drop of the solution onto the ATR crystal, and recording the spectrum after solvent evaporation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Differential scanning calorimetry (DSC)\u003c/h2\u003e \u003cp\u003eDSC measurements were performed using the following apparatus and conditions: i) PLA before aging \u0026ndash; STA 449 C Jupiter calorimeter in air; ii) PLA after aging \u0026ndash; STA 449 F3 Jupiter calorimeter under inert gas flow; iii) aged PLA after water treatment \u0026ndash; Perkin Elmer calorimeter under inert gas flow. All samples were heated from room temperature at a rate of 5\u0026deg;C/min.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6 Wide-angle X-ray diffraction (WAXD)\u003c/h2\u003e \u003cp\u003eWAXD patterns were recorded using a PANalytical Empyrean diffractometer with monochromatized CuK\u003csub\u003eα\u003c/sub\u003e radiation, in the range of 4\u0026ndash;50\u0026deg;. To evaluate the crystallinity degree (\u003cem\u003eχ\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e), patterns were resolved into amorphous and crystalline components. Peak fitting was performed within the range of 8\u0026ndash;26\u0026deg;.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.7 Water treatment\u003c/h2\u003e \u003cp\u003eGranule of aged PLA was placed in serum vial containing 10 mL of distilled water and sealed. The vials were placed on laboratory shaker operating at 100 rpm and maintained at room temperature for 1, 5, 10 and 15 days. After the designated treatment period, mass of the wet samples (m\u003csub\u003ew\u003c/sub\u003e) was measured. The granules were then dried in a vacuum oven at 40\u0026deg;C for 4 days, and their dry mass (m\u003csub\u003ed\u003c/sub\u003e) were recorded. Each experiment was conducted in triplicate. Water uptake and mass loss were calculated as follows:\u003c/p\u003e \u003cp\u003eWater uptake = [(m\u003csub\u003ew\u003c/sub\u003e \u0026ndash; m\u003csub\u003ed\u003c/sub\u003e) / m\u003csub\u003ed\u003c/sub\u003e] \u0026times; 100%\u003c/p\u003e \u003cp\u003eMass loss = [(m\u003csub\u003ed\u003c/sub\u003e \u0026ndash; m\u003csub\u003e0\u003c/sub\u003e) / m\u003csub\u003e0\u003c/sub\u003e] \u0026times; 100%\u003c/p\u003e \u003cp\u003ewhere m\u003csub\u003e0\u003c/sub\u003e is the mass of the PLA granules before water treatment.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e2.8 Depolymerization of PLA\u003c/h2\u003e \u003cp\u003eFor the depolymerization experiment 5 g of PLA granules were placed into a 25 mL round-bottom flask. Subsequently, 0.005 mL of tin(II) 2-ethylhexanoate (Sn(Oct)\u003csub\u003e2\u003c/sub\u003e) was added as a catalyst. The system was vacuumed, and the flask containing PLA was immersed in an oil bath, while the receiving flask was placed in an ice bath. Distillation was conducted in vacuum at 190\u0026ndash;210\u0026deg;C until the reaction was complete. The resulting product was kept under argon to prevent hydrolysis.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea-f illustrates visual appearance of PLA granules before and after aging. Notable changes after irradiation were observed in PLA-irG-1000 sample, which was slightly yellowish, while other samples remained white. This discoloration can be attributed to the oxidative degradation of PLA. After aging PLA-irG-700-A and PLA-irE-840/1200-A samples also exhibited yellowish coloration. Moreover, while PLA-0-A granules retained their original appearance and plastic behavior, PLA-irG-1000-A and PLA-irE-1200-A samples transformed into a gel-like state, becoming easily deformable (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg, j). These findings indicate that aging significantly impacts PLA, particularly irradiated samples with lower molecular weights.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo further investigate aging effect on irradiated PLA granules, their molecular weight was estimated by GPC, and the radiation chemical yield of scission (G\u003csub\u003es\u003c/sub\u003e) was determined using following equation:\u003c/p\u003e \u003cp\u003eG\u003csub\u003es\u003c/sub\u003e = N\u003csub\u003eA\u003c/sub\u003e(⟨M\u003csub\u003en,D\u003c/sub\u003e⟩\u003csup\u003e\u0026ndash;1\u003c/sup\u003e \u0026ndash; ⟨M\u003csub\u003en,0\u003c/sub\u003e⟩\u003csup\u003e\u0026ndash;1\u003c/sup\u003e) / (6.24\u0026times;10\u003csup\u003e6\u003c/sup\u003e\u0026times;D)\u003c/p\u003e \u003cp\u003ewhere D represents the irradiation dose, ⟨M\u003csub\u003en,0\u003c/sub\u003e⟩ is the number-average molecular weight of unirradiated PLA, and ⟨M\u003csub\u003en,D\u003c/sub\u003e⟩ is the number-average molecular weight of PLA irradiated to a specific dose.\u003c/p\u003e \u003cp\u003eFollowing irradiation, the G\u003csub\u003es\u003c/sub\u003e values for e-beam and γ-irradiated PLA was 2.20 and 2.86, respectively [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Higher G\u003csub\u003es\u003c/sub\u003e observed for γ-irradiation can be attributed to the significantly longer treatment duration. Since irradiation occurs in the presence of air, prolonged exposure leads to increased oxidative degradation. This trend maintains after aging, with molecular weight reduction being more pronounced in γ-irradiated PLA compared to e-beam treated, particularly at doses exceeding 500 kGy. After aging, the G\u003csub\u003es\u003c/sub\u003e value for γ-irradiated PLA reached 4.01, whereas it was 3.04 for e-beam irradiated PLA. The G\u003csub\u003es\u003c/sub\u003e value is calculated based on difference in molecular weight after and before irradiation. Therefore, the increase of G\u003csub\u003es\u003c/sub\u003e after aging indicates that the aging process accelerates in irradiated samples.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e presents \u003csup\u003e1\u003c/sup\u003eH NMR spectra of PLA before and after irradiation. The appearance of new peaks and the increased intensity of some peaks already presented on PLA-0 spectrum are attributed to the formation of additional chain ends caused by main chain scission during irradiation. Intensity of the end group CH signal at δ\u0026thinsp;=\u0026thinsp;4.36 ppm increases relative to the main chain signal at δ\u0026thinsp;=\u0026thinsp;5.16 ppm. Irradiated PLA have been previously studied by \u003csup\u003e1\u003c/sup\u003eH NMR spectroscopy in works [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. However, some discrepancies exist between the results of this two works, likely due to significant differences in the dose range investigated. The \u003csup\u003e1\u003c/sup\u003eH NMR spectrum of PLA-irG-1000 and PLA-irE-1200 closely resemble those reported in [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], where high irradiation doses were also used. Thus, new peaks can be identified based on previously published findings. Signals corresponding to the new end group CH\u003csub\u003e3\u003c/sub\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;O\u0026ndash;CO\u0026ndash; appear at δ\u0026thinsp;=\u0026thinsp;1.23 ppm (CH\u003csub\u003e3\u003c/sub\u003e) and δ\u0026thinsp;=\u0026thinsp;4.16 ppm (CH\u003csub\u003e2\u003c/sub\u003e). Similarly, new signals of the end group CH\u003csub\u003e3\u003c/sub\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;CO\u0026ndash;O\u0026ndash; are detected at δ\u0026thinsp;=\u0026thinsp;1.12 ppm (CH\u003csub\u003e3\u003c/sub\u003e) and δ\u0026thinsp;=\u0026thinsp;2.38 ppm (CH\u003csub\u003e2\u003c/sub\u003e). New set of lower intensity peaks at δ\u0026thinsp;=\u0026thinsp;7.97 ppm and δ\u0026thinsp;=\u0026thinsp;8.05 ppm is assigned to H\u0026ndash;CO\u0026ndash;O\u0026ndash; chain ends. Minor peaks at δ\u0026thinsp;=\u0026thinsp;5.86 ppm, δ\u0026thinsp;=\u0026thinsp;6.17 ppm and δ\u0026thinsp;=\u0026thinsp;6.46 ppm correspond to CH\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;CH\u0026ndash;CO\u0026ndash;O\u0026ndash; end, and at δ\u0026thinsp;=\u0026thinsp;5.59 and δ\u0026thinsp;=\u0026thinsp;6.12 ppm to CH\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;C(CH\u003csub\u003e3\u003c/sub\u003e)\u0026ndash;CO\u0026ndash;O\u0026ndash; end.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThese observations indicate that minimum amount of chain scission events leads to formation of unsaturated or formic acid like chain ends. The cleavage of ester bonds, resulting in the formation of typical for PLA HO\u0026ndash;CH(CH\u003csub\u003e3\u003c/sub\u003e)\u0026ndash;CO\u0026ndash;O\u0026ndash; chain ends is more pronounced. However, the primary pathway for PLA backbone scission during irradiation involves the abstraction of hydrogen atom from the main chain, followed by rearrangement. This process causes backbone rapture, leading to the formation of CH\u003csub\u003e3\u003c/sub\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;O\u0026ndash;CO\u0026ndash; or CH\u003csub\u003e3\u003c/sub\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;CO\u0026ndash;O\u0026ndash; chain ends. These results correlate well with the main radicals formed during PLA irradiation reported in [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eNotably, the new peaks observed in the \u003csup\u003e1\u003c/sup\u003eH NMR spectra and their corresponding chain ends are consistent across PLA-irG-1000, PLA-irE-1200, and even PLA irradiated in vacuum reported in [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. However, the intensity of the peak at δ\u0026thinsp;=\u0026thinsp;4.36 ppm, associated with ester bond cleavage, is higher compared to peaks of other chain ends for PLA-irG-1000 relative to PLA-irE-1200. Hence, the presence of oxygen and the longer exposure times during γ-irradiation intensify ester bond rupture, contributing to a more significant reduction in PLA molecular weight compared to e-beam irradiation.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea shows \u003csup\u003e1\u003c/sup\u003eH NMR spectra of irradiated PLA after aging. Significant changes occurred in the samples during storage for 8 years, particularly in those irradiated at high doses. The most pronounced alteration in the spectra is the marked increase in intensity of signals at δ\u0026thinsp;=\u0026thinsp;4.36 ppm and δ\u0026thinsp;=\u0026thinsp;1.48 ppm, which are attributed to the HO\u0026ndash;CH(CH\u003csub\u003e3\u003c/sub\u003e)\u0026ndash;CO\u0026ndash;O\u0026ndash; chain end. The intensity of these signals rises with dose relative to the main chain signals at δ\u0026thinsp;=\u0026thinsp;5.16 ppm and δ\u0026thinsp;=\u0026thinsp;1.58 ppm, reflecting the reduction in PLA molecular weight during aging.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eExpanded \u003csup\u003e1\u003c/sup\u003eH NMR spectra of irradiated PLA after aging is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb. A broad peak appears in the δ\u0026thinsp;=\u0026thinsp;5.35\u0026ndash;5.55 ppm range. Presumably it corresponds to hydrogen atom of \u0026ndash;OH group at chain ends or in low molecular weight products of degradation and absorbed water. Signals characteristic of irradiated PLA remain in the spectra. The signals for CH\u003csub\u003e3\u003c/sub\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;O\u0026ndash;CO\u0026ndash; end group are observed at δ\u0026thinsp;=\u0026thinsp;1.26 ppm (CH\u003csub\u003e3\u003c/sub\u003e) and δ\u0026thinsp;=\u0026thinsp;4.18 ppm (CH\u003csub\u003e2\u003c/sub\u003e), while those for CH\u003csub\u003e3\u003c/sub\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;CO\u0026ndash;O\u0026ndash; end group appear at δ\u0026thinsp;=\u0026thinsp;1.15 ppm (CH\u003csub\u003e3\u003c/sub\u003e) and δ\u0026thinsp;=\u0026thinsp;2.40 ppm (CH\u003csub\u003e2\u003c/sub\u003e). However, in PLA-irG-1000-A and PLA-irE-1200-A intensity of these signals is much lower than that of the signal at δ\u0026thinsp;=\u0026thinsp;4.36 ppm. Therefore, ester bond cleavage is the main mechanism responsible for the decrease in PLA molecular weight during aging. The upper spectrum in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb was recorded for PLA-irG-1000-A after 15 days in water and subsequent drying in vacuum oven. Following this treatment, peaks at δ\u0026thinsp;=\u0026thinsp;5.35\u0026ndash;5.55 ppm, δ\u0026thinsp;=\u0026thinsp;2.54 ppm, δ\u0026thinsp;=\u0026thinsp;2.20 ppm, δ\u0026thinsp;=\u0026thinsp;2.11 ppm, δ\u0026thinsp;=\u0026thinsp;1.80 ppm, and δ\u0026thinsp;=\u0026thinsp;1.34 ppm either disappear or become less intense. These peaks are thus associated with low molecular weight degradation products that can dissolve in water.\u003c/p\u003e \u003cp\u003eDuring storage in air PLA can absorb moisture from the environment. Apparently, even small amounts of water are sufficient to initiate hydrolytic degradation of PLA. Hydrolytic degradation during storage accelerates with increasing irradiation dose, as irradiation promotes the formation of \u0026ndash;COOH end groups, which catalyze further hydrolysis.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea presents FTIR spectra of aged PLA. For samples irradiated at doses up to 600 kGy, the FTIR spectra remain almost unchanged after aging. However, at higher doses, significant structural changes are evident in the polymer spectra. A broad band around 3000\u0026ndash;3500 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is observed and can be attributed to the stretching vibration of \u0026ndash;OH group. Although \u0026ndash;OH end groups are also present in PLA-0-A, their concentration is too low to be detected in the spectrum due to the high molecular weight of the polymer. In contrast, the \u0026ndash;OH group signal is visible in PLA-irG-700/1000-A and PLA-irE-840/1200-A due to lower molecular weight and higher concentration of end groups. Moreover, these samples may contain degradation products, such as lactic acid and lactic acid lactate, which is relevant to changes observed in \u003csup\u003e1\u003c/sup\u003eH NMR spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Further significant changes are observed in the 965\u0026thinsp;\u0026minus;\u0026thinsp;600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e region. The spectrum of PLA-0-A is characteristic of this polymer, with peaks assigned to specific vibration modes as follows: 956 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e r(CH3) + \u003cem\u003eν\u003c/em\u003e(C\u0026thinsp;\u0026minus;\u0026thinsp;COO), 867 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e \u003cem\u003eν\u003c/em\u003e(C\u0026thinsp;\u0026minus;\u0026thinsp;COO), 736 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e δ(C\u0026thinsp;=\u0026thinsp;O), 702 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e γ(C\u0026thinsp;=\u0026thinsp;O) [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. For irradiated samples, only peak at 867 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e remains almost unchanged. A new peak at 819 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e appears, attributed to lactic acid. Meanwhile, peaks at 736 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 702 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e become broader, less intense, and overlapped. Presumably, these changes may be associated with an increased number of hydrogen bonds involving C\u0026thinsp;=\u0026thinsp;O group.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe \u003cem\u003eν\u003c/em\u003e(C\u0026thinsp;=\u0026thinsp;O) vibration mode peak in the FTIR spectra shifts to lower wavenumbers and broadens with increasing irradiation dose. For PLA-0-A the peak maximum is at 1748 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with full width at half maximum (FWHM) of 26 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. In comparison, for PLA-irG-700-A the peak maximum shifts to 1744 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with a FWHM of 55 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and for PLA-irG-1000-A it further shifts to 1741 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with a FWHM of 64 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Moreover, the \u003cem\u003eν\u003c/em\u003e(C\u0026thinsp;=\u0026thinsp;O) peak in aged irradiated at high doses PLA not only broadens but also appears to consist of two overlapping peaks. As the polymer was initially in a form of granules, achieving high quality spectra directly using ATR-mode was challenging. To overcome this, PLA samples were dissolved and cast into films for analysis. However, for a more detailed investigation of the \u003cem\u003eν\u003c/em\u003e(C\u0026thinsp;=\u0026thinsp;O) region, spectra were also recorded directly for granules of selected samples (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). Difference in the 1250\u0026thinsp;\u0026minus;\u0026thinsp;600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e region between the spectra of PLA granules and films reflect variations in phase structure and chain conformation. In the \u003cem\u003eν\u003c/em\u003e(C\u0026thinsp;=\u0026thinsp;O) region around 1745 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, a single narrow peak is observed for PLA-0-A. For PLA-irG-700-A the peak develops a shoulder, and for PLA-irG-1000-A it separates into two overlapping peaks. Typically, vibrations of a single nature in different monomer units produce one signal, and separate signals for end groups are not observed. However, molecular weight of PLA-irG-1000-A is sufficiently low, leading to a comparable number of ester C\u0026thinsp;=\u0026thinsp;O groups in the backbone and carboxylic C\u0026thinsp;=\u0026thinsp;O groups at chain ends. Additionally, presence of degradation products, such as lactic acid, contributes to the division of the \u003cem\u003eν\u003c/em\u003e(C\u0026thinsp;=\u0026thinsp;O) peak into two components. The discussion of γ-irradiated aged PLA FTIR spectra made above is also relevant for e-beam irradiated samples. However, changes in the spectrum of PLA-irE-840-A are less pronounced than those in PLA-irG-700-A. This difference is likely due to a lower extent of oxidative degradation during e-beam irradiation compared to γ-irradiation.\u003c/p\u003e \u003cp\u003eThe change in the molecular structure of PLA induced by irradiation and subsequent aging results in alterations in its phase structure. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea,b shows the DSC curves of e-beam and γ-irradiated PLA before aging, with corresponding data summarized in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Absence of an exothermic cold crystallization peak in the area between 80 and 120\u0026deg;C and presence of an endothermic melting peak in the DSC curve of PLA-0, confirms that the polymer is semi-crystalline. For all irradiated samples melting temperature decreases as irradiation dose increases. This decrease can be attributed to chain scission caused by irradiation, which reduces the molecular weight of the polymer. In general, crystalline domains in polymers are less susceptible to irradiation induced damage compared to amorphous regions. However, the high irradiation doses used in this study were sufficient to disrupt PLA crystals. As a result, not only does the melting temperature decrease, but the width of melting peak increases, and bimodality of melting appears in irradiated samples. The lower temperature melting peak corresponds to α-form crystals, while the higher temperature peak is associated with the more defected α\u0026rsquo;-form crystals, which recrystallize during DSC heating. To quantify the fraction of each crystal form, peak separation was performed, and the results are presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Not only α\u0026rsquo;-form appears in irradiated sample, but it is prominent in PLA-irE-360 and PLA-irG-250 samples. Irradiation-induced damage to PLA crystals is evident, but further increase in dose lead to a reduction in the α\u0026rsquo;-form fraction. This may be due to increased chain mobility in low molecular weight polymers, allowing defects to migrate from the crystalline to the amorphous phase. For example, the molecular weight decreases from 11,000 g/mol in PLA-irE-360 to 3,300 g/mol in PLA-irE-1200, enabling this process. Another possible explanation is that shorter polymer chains, resulting from reduced molecular weight at higher doses, interact weaker. This may cause partial melting of α\u0026rsquo; crystals without subsequent recrystallization, contributing to the increased area of the lower-temperature melting peak.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCharacteristics of melting peaks for unirradiated and irradiated PLA\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=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eT\u003csub\u003em1\u003c/sub\u003e, \u0026deg;C\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eT\u003csub\u003em2\u003c/sub\u003e, \u0026deg;C\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eφ\u003csub\u003e1\u003c/sub\u003e, %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eφ\u003csub\u003e2\u003c/sub\u003e, %\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e150,7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irE-360\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e141,2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e144,8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e69\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irE-600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e135,0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e139,1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irE-840\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e126,5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e133,9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e43\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irG-250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e144,5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e147,7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e79\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irG-500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e138,6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e143,5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e66\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irG-700\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e126,5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e134,2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e47\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\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the WAXD pattern of PLA-0 resolved into crystalline and amorphous components. Since the α and α\u0026rsquo; crystal forms are resembling their WAXD patterns overlap. However, the (004)/(103) and (211) reflexes, which are characteristic of α crystals [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e], are evident in the WAXD pattern of PLA-0. This confirms the presence of the α crystal form in the polymer. The WAXD patterns of PLA-irE-120/1200 and PLA-irG-100/1000 remain largely unchanged, indicating that the α crystal form persists after irradiation. The polymer crystallinity degree, determined from WAXD data, is about 40% for both PLA-0 and irradiated samples. Therefore, irradiation doesn\u0026rsquo;t affect the overall crystallinity degree. Still, the DSC results suggest that irradiation alters structure of PLA crystals, introducing some disorder in polymer.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec,d presents the DSC curves of PLA after aging. The melting behavior of PLA-0-A and samples irradiated at doses up to 600 kGy remains largely unchanged after aging, with their DSC curves closely resembling those of the unaged samples. However, at higher irradiation doses deterioration of the crystalline structure is observed. For PLA-irE-840 crystal melting is still can be identified on DSC curves. For PLA-irG-700 only a broad low intensity peak is observed in the temperature range of 90\u0026ndash;135\u0026deg;C. Melting was no longer evident in PLA-irE-1200-A and PLA-irG-1000-A samples. Hence, deterioration of crystalline structure can serve as a marker of the PLA aging process. The more pronounced amorphization observed during aging in PLA samples irradiated at higher doses can be attributed to their lower initial molecular weight. Lower molecular weight increases chain mobility and amount of \u0026ndash;COOH end groups, which likely accelerates the degradation of PLA during storage.\u003c/p\u003e \u003cp\u003eOne of the key advantages of PLA is its hydrolytic degradability, as opposed to conventional plastics. Irradiated and aged PLA samples were immersed into water, and it was initially expected that PLA-irG-1000-A and PLA-irE-1200-A, due to low molecular weight, would completely dissolve in water within a few days. However, this did not occur. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea,b shows change in the mass of PLA granules after 1\u0026ndash;15 days in water. The mass of PLA-0-A and samples irradiated at low doses remained constant over this period. Meanwhile the mass of PLA-irE-840-A decreased by 10.7%, PLA-irE-1200-A by 55.2%, PLA-irG-700-A by 27.6%, and PLA-irG-1000-A by 61.1%. These results indicate that those samples contain a low molecular weight water soluble fraction. However, after the dissolution of this fraction, no obvious signs of polymer hydrolysis were observed. To further investigate the relationship between mass loss and molecular weight, latter was evaluated using GPC. The results showed no significant changes in PLA molecular weight, likely due to the insufficient resolution of the GPC method used for low molecular weight samples. To address this limitation, \u003csup\u003e1\u003c/sup\u003eH NMR spectroscopy was employed. The molecular weight of PLA samples determined by \u003csup\u003e1\u003c/sup\u003eH NMR is shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. For samples irradiated at lower doses, molecular weight remained unchanged, correlating with stable mass values. Their molecular weight was sufficiently high, and hydrolysis rate at room temperature was slow. Thus, over 15 days hydrolysis process cannot be detected for semi-crystalline PLA with M\u003csub\u003en\u003c/sub\u003e greater than 5000 g/mol. For PLA samples irradiated at doses of 700 kGy and above, molecular weight measured by \u003csup\u003e1\u003c/sup\u003eH NMR increased significantly after 15 days in water. This phenomenon can be explained by the fact that M\u003csub\u003en\u003c/sub\u003e reflects the average molecular weight of chains of varying lengths. In water, degradation products and low molecular weight PLA chains dissolve, leaving behind an insoluble fraction with higher molecular weight. Therefore, even aged PLA with critically low molecular weight cannot fully dissolve in water or be biodegraded by microorganisms in the short term. A slight increase in M\u003csub\u003en\u003c/sub\u003e was also observed for PLA-irG-500-A, indicating the presence of a water-soluble fraction. This is likely due to the higher extent of initial oxidative degradation during exposure to γ-irradiation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMolecular weight of aged PLA before and after 15 days of water treatment\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSample name\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eM\u003csub\u003en\u003c/sub\u003e, g/mol\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0 days\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15 days\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irE-360-A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13380\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e13550\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irE-600-A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5050\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5170\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irE-840-A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e660\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2440\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irE-1200-A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e130*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1440\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irG-250-A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10530\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10840\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irG-500-A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4570\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e7610\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irG-700-A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e660\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3170\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irG-1000-A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e120*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1230\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"3\"\u003e* represents an average calculated based on contributions from both PLA and lactic acid\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe processes occurring in irradiated aged PLA during water treatment are of considerable interest. PLA is inherently hydrophobic, but untreated PLA typically contains some water absorbed from the environment. Upon immersion in water, water molecules diffuse into the polymer matrix, initiating hydrolysis. This process generates low molecular weight compounds, which subsequently diffuse into the solution. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec,d shows the water absorption behavior of PLA. Water uptake by PLA-irE-1200-A and PLA-irG-1000-A is significantly higher than that by PLA-0-A. The decrease in molecular weight is accompanied by an increase in the number of hydrophilic \u0026ndash;COOH and \u0026ndash;OH groups on chain ends, resulting in higher water uptake. The swelling ratio of PLA-irG-1000-A and PLA-irG-700-A exceeds that of PLA-irE-1200-A and PLA-irE-840-A, likely due to more extensive oxidative degradation of PLA during γ-irradiation. Moreover, the dissolution of low molecular weight fraction and swelling in water lead to crystallization in PLA-irE-1200-A, PLA-irG-1000-A, and PLA-irG-700-A samples as was shown by DSC. Before treatment, these samples were amorphous. This recrystallization, induced by direct contact with liquid water, prolongs the degradation process. The dissolution of low molecular weight compounds is also supported by FTIR spectroscopy results. The broad band around 3000\u0026ndash;3500 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the changes in 965\u0026thinsp;\u0026minus;\u0026thinsp;600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e region observed in PLA-irE-840/1200-A and PLA-irG-700/1000-A (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb) almost disappear after immersion into water (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). Additionally, the peak corresponding to the \u003cem\u003eν\u003c/em\u003e(C\u0026thinsp;=\u0026thinsp;O) vibration mode becomes narrower. After water treatment, the FWHM of the \u003cem\u003eν\u003c/em\u003e(C\u0026thinsp;=\u0026thinsp;O) peak is 26 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for PLA-0-A, 33 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for PLA-irG-700-A, and 39 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for PLA-irG-1000-A. While the FWHM of the \u003cem\u003eν\u003c/em\u003e(C\u0026thinsp;=\u0026thinsp;O) peak remains unchanged for PLA-0-A, it decreases for PLA-irG-700/1000-A, indicating a more uniform composition after mass loss. Therefore, the FWHM of the ν(C\u0026thinsp;=\u0026thinsp;O) peak can serve as a useful measure of hydrolyzed aged PLA uniformity.\u003c/p\u003e \u003cp\u003eIf the hydrolytic degradation of high-performance semi-crystalline PLA remains rather low even after irradiation and aging, could it still be considered an eco-friendly plastic? One of PLA\u0026rsquo;s significant advantages is its ability to be efficiently depolymerized back to its monomer, lactide, which can be repolymerized to produce high quality PLA products [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e summarizes the chemical yields of PLA recycling into lactide. The structure of the recovered lactide was confirmed using \u003csup\u003e1\u003c/sup\u003eH NMR (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea). Scheme of PLA depolymerization is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb. For PLA irradiated with high doses, the chemical yield decreases due to the polymer\u0026rsquo;s reduced molecular weight. Moreover, the recovered lactide was yellowish, and \u003csup\u003e1\u003c/sup\u003eH NMR analysis revealed a high content of linear oligo(lactic acid) in the product (δ\u0026thinsp;=\u0026thinsp;4.36 ppm, δ\u0026thinsp;=\u0026thinsp;1.47 ppm). However, PLA-0-A, PLA-irE-360-A, and PLA-irG-250-A samples were converted to lactide with high yields of approximately 90%, producing a much purer product. The experimental design for lactide preparation from PLA in this study closely mimics one of the steps in the industrial process for lactide production. Therefore, chemical recycling of PLA has the potential to be scaled up for industrial implementation. This approach would be a more eco-friendly alternative to landfilling or even composting, offering a sustainable solution to PLA waste management.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChemical yield of PLA conversion into lactide\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eChemical yield, %\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-0-A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e91\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irE-360-A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e88\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irE-840-A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e82\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irG-250-A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e94\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePLA-irG-700-A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e77\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThe radiation chemical yield of chain scission is higher for γ-irradiated PLA compared to e-beam irradiated PLA, as the prolonged exposure during γ-irradiation results in increased oxidative degradation. After aging for eight years, this trend persists and intensifies in irradiated samples, particularly at doses above 600 kGy. The primary new end groups formed during radiation-induced backbone scission are CH\u003csub\u003e3\u003c/sub\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;O\u0026ndash;CO\u0026ndash; and CH\u003csub\u003e3\u003c/sub\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;CO\u0026ndash;O\u0026ndash;. Concurrently, the decrease in PLA molecular weight during aging is attributed to chain rupture at the ester bond, resulting in the formation of HO\u0026ndash;CH(CH\u003csub\u003e3\u003c/sub\u003e)\u0026ndash;CO\u0026ndash;O\u0026ndash; chain ends. As the radiation dose increases, PLA molecular weight decreases, while hydrophilicity and the number of \u0026ndash;COOH end groups increase. These groups catalyze hydrolysis processes during storage. The more extensive aging observed in γ-irradiated PLA, compared to e-beam irradiated samples, is due to the initially higher extent of oxidative degradation. Irradiation also alters PLA phase structure, leading to the emergence of the conformationally disordered α\u0026rsquo;-form. While the phase structure of most samples remains largely unchanged after aging, amorphization occurs in samples irradiated to 1000 kGy and above. Samples irradiated up to 840 kGy contain a fraction soluble in water at room temperature. However, even in these cases, hydrolysis is hindered by water-induced crystallization. Chemical recycling of PLA was successfully performed for unirradiated PLA and samples irradiated up to 360 kGy. This process demonstrates the potential for industrial-scale implementation, offering a more eco-friendly alternative to landfilling or composting. Chemical recycling provides a sustainable solution to PLA waste management by enabling the recovery of high-quality lactide for polymer regeneration.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors are also pleased to express their grateful acknowledgements to Prof. Krul’ L.P., Dr. Butovskaya G.V. and Roginets L. P. for their help with the experiments.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding Declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the State Program for Scientific Research of Belarus under Grant number 1.3.04.05.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of interests\u003c/strong\u003e\u003c/p\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\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Conceptualization: Fedorenko A.A., Kostjuk S.V.; methodology: Fedorenko A.A., Grinyk E.V., Skakovsky E.D.; investigation: Fedorenko A.A., Salnikova, I.A., Tychinskaya L. Yu., Skakovsky E.D.; writing—original draft preparation: Fedorenko A.A., Grinyk E.V.; writing—review and editing: Fedorenko A.A., Kostjuk S.V.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eSatti SM, Shah AA (2020) Polyester‐based biodegradable plastics: an approach towards sustainable development. Lett Appl Microbiol 70:413\u0026ndash;430. https://doi.org/10.1111/lam.13287\u003c/li\u003e\n\u003cli\u003eAfshar S V., Boldrin A, Astrup TF, et al (2024) Degradation of biodegradable plastics in waste management systems and the open environment: A critical review. J Clean Prod 434:140000. https://doi.org/10.1016/j.jclepro.2023.140000\u003c/li\u003e\n\u003cli\u003eWang G, Huang D, Ji J, et al (2021) Seawater‐Degradable Polymers\u0026mdash;Fighting the Marine Plastic Pollution. Adv Sci 8:. https://doi.org/10.1002/advs.202001121\u003c/li\u003e\n\u003cli\u003eLe Gall M, Niu Z, Curto M, et al (2022) Behaviour of a self-reinforced polylactic acid (SRPLA) in seawater. Polym Test 111:107619. https://doi.org/10.1016/j.polymertesting.2022.107619\u003c/li\u003e\n\u003cli\u003eRichert A, Dąbrowska GB (2021) Enzymatic degradation and biofilm formation during biodegradation of polylactide and polycaprolactone polymers in various environments. Int. J. Biol. Macromol. 176:226\u0026ndash;232\u003c/li\u003e\n\u003cli\u003ePelegrini K, Donazzolo I, Brambilla V, et al (2016) Degradation of PLA and PLA in composites with triacetin and buriti fiber after 600 days in a simulated marine environment. J Appl Polym Sci 133:. https://doi.org/10.1002/app.43290\u003c/li\u003e\n\u003cli\u003eHus\u0026aacute;rov\u0026aacute; L, Pekařov\u0026aacute; S, Stloukal P, et al (2014) Identification of important abiotic and biotic factors in the biodegradation of poly(l-lactic acid). Int J Biol Macromol 71:155\u0026ndash;162. https://doi.org/10.1016/j.ijbiomac.2014.04.050\u003c/li\u003e\n\u003cli\u003eSangwan P, Wu DY (2008) New insights into polylactide biodegradation from molecular ecological techniques. Macromol. Biosci. 8:304\u0026ndash;315\u003c/li\u003e\n\u003cli\u003eNaikwadi AT, Sharma BK, Bhatt KD, Mahanwar PA (2022) Gamma Radiation Processed Polymeric Materials for High Performance Applications: A Review. Front Chem 10:. https://doi.org/10.3389/fchem.2022.837111\u003c/li\u003e\n\u003cli\u003eAshfaq A, Clochard M-C, Coqueret X, et al (2020) Polymerization Reactions and Modifications of Polymers by Ionizing Radiation. Polymers (Basel) 12:2877. https://doi.org/10.3390/polym12122877\u003c/li\u003e\n\u003cli\u003eHill DJT, Whittaker AK (2016) Radiation Chemistry of Polymers. In: Encyclopedia of Polymer Science and Technology. Wiley, pp 1\u0026ndash;58\u003c/li\u003e\n\u003cli\u003eP\u0026eacute;rez Davila S, Gonz\u0026aacute;lez Rodr\u0026iacute;guez L, Chiussi S, et al (2021) How to Sterilize Polylactic Acid Based Medical Devices? Polymers (Basel) 13:2115. https://doi.org/10.3390/polym13132115\u003c/li\u003e\n\u003cli\u003eNugroho P, Mitomo H, Yoshii F, Kume T (2001) Degradation of poly(L-lactic acid) by \u0026gamma;-irradiation. Polym Degrad Stab 72:337\u0026ndash;343. https://doi.org/10.1016/S0141-3910(01)00030-1\u003c/li\u003e\n\u003cli\u003eLoo SCJ, Tan HT, Ooi CP, Boey YCF (2006) Hydrolytic degradation of electron beam irradiated high molecular weight and non-irradiated moderate molecular weight PLLA. Acta Biomater 2:287\u0026ndash;296. https://doi.org/10.1016/j.actbio.2005.10.003\u003c/li\u003e\n\u003cli\u003eFedorenko AA, Grinyuk E V., Salnikova IA, Kostjuk S V. (2022) Effect of gamma-irradiation on hydrolysis of commercial poly(L-lactide) at elevated temperature. 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J Am Chem Soc 145:19840\u0026ndash;19848. https://doi.org/10.1021/jacs.3c05863\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"polylactide, irradiation, aging, 1H NMR, degradation, recycling","lastPublishedDoi":"10.21203/rs.3.rs-5716364/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5716364/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe impact of high-dose e-beam and γ-irradiation, followed by long-term aging, on the structural properties of poly(L-lactide) (PLA) was investigated. Due to prolonged exposure, γ-irradiation caused more extensive oxidative degradation, accelerating the aging process compared to e-beam irradiation. Aging effects were most pronounced in samples irradiated at doses exceeding 600 kGy. Structural analysis using \u003csup\u003e1\u003c/sup\u003eH NMR revealed distinct mechanisms of chain scission during irradiation and aging, resulting in the formation of different end groups. Irradiation induced deterioration of PLA\u0026rsquo;s phase structure occurred during irradiation was observed, including the formation of conformationally disordered α\u0026rsquo; crystalline form. Aging at doses exceeding 1000 kGy led to amorphization. The degradation behavior of aged PLA in water and its recycling potential were also evaluated. While partial dissolution of aged samples occurred in a short term, further degradation was hindered by water induced crystallization. Unirradiated and low-dose irradiated PLA demonstrated promising recyclability to lactide, highlighting its potential for industrial-scale chemical recycling as a sustainable alternative to landfilling or composting.\u003c/p\u003e","manuscriptTitle":"Effects of irradiation and aging on the molecular and phase structure of poly(L-lactide): insights into degradation and recycling potential","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-01-15 10:29:18","doi":"10.21203/rs.3.rs-5716364/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"34ec0893-bf70-4419-aa49-3f8cab12806e","owner":[],"postedDate":"January 15th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-04-01T21:07:01+00:00","versionOfRecord":[],"versionCreatedAt":"2025-01-15 10:29:18","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5716364","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5716364","identity":"rs-5716364","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}