Aliphatic-aromatic Copolyester Research Articles

Barrier Properties of Biodegradable Aliphatic–Aromatic Copolyesters (PBXT Series)

Barrier Properties of Biodegradable Aliphatic–Aromatic Copolyesters (PBXT Series)

Synthesis and Characterization of Aliphatic-Aromatic Copolyesters Based on Daidzein

Synthesis and Characterization of Aliphatic-Aromatic Copolyesters Based on Daidzein

Biodegradation of PHB/PBAT films and isolation of novel PBAT biodegraders from soil microbiomes

Polyhydroxyalkanoates (PHAs) are important candidates for replacing petroleum-based plastics. This transition is urgent for the development of a biobased economy and to protect human health and natural ecosystems. PHAs are biobased and biodegradable polyesters that when blended with other polymers, such as poly(butylene adipate-co-terephthalate) (PBAT), acquire remarkable improvements in their properties, which allow them to comply with the requirements of packaging applications. However, the biodegradation of such blends should be tested to evaluate the impact of those polymers in the environment. For instance, PBAT is a compostable aliphatic-aromatic copolyester, and its biodegradation in natural environments, such as soil, is poorly studied. In this work, we evaluated the biodegradation of a bilayer film composed of PHB and PBAT, by a soil microbiome.The bilayer film reached 47 ± 1 % mineralization in 180 days and PHB was no longer detected after this period. The increased crystallinity of the PBAT residue was a clear sign of biodegradation, indicating that the amorphous regions were preferentially biodegraded. Seven microorganisms were isolated, from which 4 were closely related to microorganisms already known as PHB degraders, but the other 3 species, closely related to Streptomyces coelicoflavus, Clonostachys rosea and Aspergillus insuetus, were found for the first time as PHB degraders. Most remarkably, two fungi closely related to Purpureocillium lilacinum and Aspergillus pseudodeflectus (99.83 % and 100 % identity by ITS sequencing) were isolated and identified as PBAT degraders. This is very interesting due to the rarity of isolating PBAT-degrading microorganisms.These results show that the bilayer film can be biodegraded in soil, at mesophilic temperatures, showing its potential to replace synthetic plastics in food packaging.

Barrier Properties of Biodegradable Aliphatic–Aromatic Copolyesters (PBXT Series)

AbstractIn this study, a series of biodegradable poly(butylene alkylene carboxylate‐co‐terephthalate) copolymers with varying methylene numbers in the alkylene units (0, 2, 4, and 8) are synthesized. These copolymers, namely, poly(butylene oxalate‐co‐terephthalate) (PBOT), poly(butylene succinate‐co‐terephthalate) (PBST), poly(butylene adipate‐co‐terephthalate) (PBAT), and poly(butylene sebacate‐co‐terephthalate) (PBSeT), are prepared with nearly identical structural and molar compositions. The objective of this study is to comprehensively examine the impact of alkylene unit length on the barrier properties of the materials, delving into aspects such as crystallinity, free volume, molecular chain mobility, as well as adsorption and diffusion of gases within the materials. The findings indicate a decrease in crystallinity from 17.2% for PBOT to 10.2% for PBSeT as the alkylene chain length increases, while maintaining the same chemical composition. Concurrently, the fractional free volume increases from 0.9% to 2.6%, and the melt flow activation energy decreases from 106.6 to 52.1 kJ mol−1. Importantly, theoretical calculations are performed, demonstrating that the predominant site for gas adsorption and diffusion is within the material's free volume. These combined observations indicate a gradual decrease in barrier properties as the number of methylene groups increases.

Fully Bio-Based 2,5-Furandicarboxylic Acid Polyester toward Plastics with Mechanically Robust, Excellent Gas Barrier and Fast Degradation.

Aliphatic-aromatic copolyesters offer a promising solution to mitigate plastic pollution, but high content of aliphatic units (>40 %) often suffer from diminished comprehensive performances. Poly(butylene oxalate-co-furandicarboxylate) (PBOF) copolyesters were synthesized by precisely controlling the oxalic acid content from 10 % to 60 %. Compared with commercial PBAT, the barrier properties of PBOF for H2O and O2 increased by more than 6 and 26 times, respectively. The introduction of the oxalic acid units allowed the water contact angle to be reduced from 82.5° to 62.9°. Superior hydrophilicity gave PBOF an excellent degradation performance within a 35-day hydrolysis. Interestingly, PBO20F and PBO30F also displayed obvious decrease of molecular weight during hydrolysis, with elastic modulus >1 GPa and tensile strength between 35-54 MPa. PBOF achieved the highest hydrolysis rates among the reported PBF-based copolyesters. The hydrolytic mechanism was further explored based on Fukui function analysis and density functional theory (DFT) calculation. Noncovalent analysis indicated that the water molecules formed hydrogen bonding interaction with adjacent ester groups and thus improved the reactivity of carbonyl carbon. PBOF not only meet the requirements of the high-performance packaging market but can quickly degrade after the end of their usage cycles, providing a new choice for green and environmental protection.

Investigating the influence of long chain branching and compositional changes of aliphatic-aromatic copolyesters on their rheological properties under shear and elongational flows

Investigating the influence of long chain branching and compositional changes of aliphatic-aromatic copolyesters on their rheological properties under shear and elongational flows

Effects of Biodegradable Plastic Mulch Film on Cabbage Agronomic and Nutritional Quality Traits, Soil Physicochemical Properties and Microbial Communities

The long-term use of polyethylene mulch (PEM) films can cause plastic film residual pollution that has an adverse effect on soil health and crop quality. To address this issue, poly(butylene adipate-co-terephthalate) (PBAT), an aliphatic–aromatic copolyester, is widely used in the production of commercially biodegradable plastic mulch (BDM) films. The use of BDMs can alleviate soil plastic pollution and reduce the labor cost of retrieving plastic film residues from the field. The effects of BDM and PEM on the agronomic and nutritional quality traits of cabbage cultivar ‘Sugan No. 35’, as well as the physicochemical properties and microbial communities of the soil were analyzed during two consecutive years of the experiment. No significant difference was observed in the cabbage agronomic and nutritional quality traits among three mulching treatments. Nonetheless, the mulching and degradation of BDM reduced the pH value and increased the organic matter content of the soil samples compared with PEM mulching. In the soil bacterial and fungal communities, Proteobacteria and Ascomycota were the most abundant bacterial phylum and fungal phylum across all the soil samples, respectively; the use of BDM increased the relative abundance of soil Proteobacteria and Ascomycota compared with PEM mulching. The overall cost of BDM mulching was much lower than that of PEM mulching during the cabbage production.

Characterization of Biodegradable Food Contact Materials under Gamma-Radiation Treatment.

Radiation is an example of one of the techniques used for pasteurization and sterilization in various packaging systems. There is a high demand for the evaluation of the possible degradation of new composites, especially based on natural raw materials. The results of experimental research that evaluated the impact of radiation technology on biodegradable and compostable packaging materials up to 40 kGy have been presented. Two commercially available flexible composite films based on aliphatic-aromatic copolyesters (AA) were selected for the study, including one film with chitosan and starch (AA-CH-S) and the other with thermoplastic starch (AA-S). The materials were subjected to the influence of ionizing radiation from 10 to 40 kGy and then tests were carried out to check their usability as packaging material for the food industry. The results showed that the mechanical properties of AA-S films improved due to the radiation-induced cross-linking processes, while in the case of AA-CH-S films, a considerable decrease in the elongation at break was observed. The results also showed a decrease in the WVTR in the case of AA-S and no changes in barrier properties in the case of AA-CH-S. Both materials revealed no changes in the odor analyzed by sensory analysis. In the case of the AA-S films, the higher the radiation dose, the faster the biodegradation rate. In the case of the AA-CH-S film, the radiation did not affect biodegradation. The performed research enables the evaluation of the materials intended for direct contact with food. AA-CH-S was associated with unsatisfactory parameters (exceeding the overall migration limit and revealing color change during storage) while AA-S showed compliance at the level of tests carried out. The study showed that the AA-CH-S composite did not show a synergistic effect due to the presence of chitosan.

New biodegradable polyesters synthesized from 2,5-thiophenedicarboxylic acid with excellent gas barrier properties

Lacking available eco-friendly aliphatic-aromatic copolyesters with balanced mechanical properties, gas barrier properties and biodegradability is a foremost challenge in the field of degradable materials. 2,5-thiophenedicarboxylic acid (2,5-TDCA) as a new aromatic monomer with five-membered aromatic-ring can be synthesized from the renewable glucaric or muconic acid. In this work, a series of poly(butylene succinate-co-butylene 2,5-thiophenedicarboxylate) (PBSTh) copolyesters with TDCA units ranging from 10 to 80 mol% were synthesized by melt polycondensation. The results of 1H-NMR, 13C-NMR and GPC revealed that the obtained random copolyesters possessed high number-average molecular weight from 54,800 to 88,600 g/mol. The copolymerized TDCA units was beneficial to improve the thermal stability, and Td,5% in N2 rose from 324°C of poly(butylene succinate) (PBS) to 344∼371°C of PBSThs. The mechanical properties of PBSThs were good with tensile modulus >29 MPa, tensile strength >11.4 MPa and elongation at break >523%, respectively. PBSThs showed better gas barrier properties than the well-known poly(butylene adipate-co-butylene terephthalate) (PBAT) and the BIFps of CO2 and O2 were 5.1∼60.2 times and 5.1∼32.0 times to PBAT, respectively. Also, the excellent biodegradability was proved both in enzymatic and compost environments and PBSThs have higher degradation rates than PBAT when the content of TDCA unit is lower than 60 mol%. In conclusion, the investigation of PBSThs has shown that the incorporation of 2,5-TDCA is effective in enhancing the overall properties of PBS and PBSTh can be a promising candidate in the field of biodegradable polymers.

Effect of aliphatic segment length and content on crystallization and biodegradation properties of aliphatic-aromatic co-polyesters

In this work, dimethyl terephthalate (DMT), 1,4-butanediol (BDO) and different diacids were introduced to investigate the effects of variations in aliphatic chain length and component content in aliphatic aromatic terpolymers on the basic thermal properties, crystalline morphology, mechanical properties and biodegradability of the polyesters. The experimental results from nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FT-IR) and Gel permeation chromatography (GPC) indicate the successful synthesis of the anticipated aliphatic aromatic co-polyesters. The variation of melting and crystallization temperatures with aliphatic chain segment length and content were analyzed by differential scanning calorimetry (DSC). The Wide-angle X-ray diffraction (WAXD) results suggest that the coexistence of both crystals formed by rigid and flexible chain segments can be achieved by varying the length and component content of the aliphatic chain segments in the co-polyesters. The scanning electron microscopy (SEM) and composting experiment results indicate that the type of crystals formed with the more flexible chain segments and the lower degree of crystallinity have a positive effect on the biodegradability.

Biodegradable Aromatic–Aliphatic Copolyesters Derived from Bis(2-Hydroxyethyl) Terephthalate for Sustainable Flexible Packaging Applications

Bis(2-hydroxyethyl) terephthalate (BHET) is one of the major products in the process of chemical recycling of waste poly(ethylene terephthalate) (PET). In this study, we synthesized a series of biodegradable aromatic–aliphatic random copolymers, poly(ethylene aliphatate-co-terephthalate), directly from BHET together with aliphatic dicarboxylic acids including succinic acid (SA), adipic acid (AA), sebacic acid (Seb), and dodecanedioic acid (DDDA) via a two-step melt polycondensation reaction. The composition of the copolymers was adjusted precisely to optimize their crystallinity, thermo-mechanical properties, and biodegradation performance. In particular, the aromatic–aliphatic copolymer films exhibited excellent elastic properties, displaying tensile strength <27 MPa and elongation at break near 700%, as well as excellent optical transparency (haze <10%), thereby outperforming the conventional petroleum-derived and biodegradable polymers. The biodegradable aromatic–aliphatic copolymers synthesized based on BHET with excellent transparency, mechanical properties, and biodegradability show remarkable potential for open-loop recycling from PET waste and sustainable packaging applications.

Non-isothermal crystallization and thermo-mechanical properties of poly(butylene adipate-co-ethylene terephthalate) random copolyesters

Random aliphatic-aromatic copolyesters are synthesized through melt polycondensation of bis(2-hydroxybutyl) adipate (BHBA) with 0–15 mol% of bis(2-hydroxyethyl) terephthalate (BHET) oligomers. Regarding the random ester-interchange reactions, the sequence length distribution of butylene adipate (BA) units reduces with increasing BHET. Crystallization of copolyesters is investigated by differential scanning calorimetry. Crystallization peak temperatures (Tc) and melting peaks (Tm1, Tm2, and Tm3) of all samples decrease with increasing cooling rate. Moreover, increasing BHET results in the reduction of crystallinity. Regarding the results of Avrami, Tobin, Ozawa, and Mo's models for non-isothermal crystallization, the crystallization rate decreases as the BHET content increases. Using the isoconversional method of Friedman, it is revealed that copolymerization leads to a reduction of the absolute enthalpy of crystallization. According to the wide-angle X-ray diffraction (WAXD) results, the crystalline dimensions reduce with copolymerization, and flawed crystals are developed in copolyesters.

Enhanced degradation and gas barrier of PBAT through composition design of aliphatic units

Aliphatic–aromatic copolyesters are indispensable in degradable plastics, but their properties are limited by low strength and modulus, and slow degradation rates in natural environment. Herein, we report a novel molecular design method to prepare poly(butylene adipate–co–diglycolate–co–terephthalate)(PBADT) copolyesters. In detail, the aromatic unit is fixed at 50% molar content of butylene terephthalate (BT) units, while the aliphatic units are consisted of butylene adipate (BA) and butylene diglycolate (BD) units. The PBADT copolyesters have melting temperatures higher than 130 °C and manifest rapid crystallization, high elastic modulus (>129 MPa) and satisfied ductile tensile behavior (>770%). Their gas barrier performance and hydrophilicity all increase with increasing BD units. Compared with PBAT, faster hydrolysis and seawater degradation are observed, which is explained by the more hydrophilic structure of diglycolate. This work provides insights and direction for the development of high-performance yet environmentally degradable alternatives to conventional biodegradable aliphatic–aromatic polyesters.

Design of 2,5-furandicarboxylic based polyesters degraded in different environmental conditions: Comprehensive experimental and theoretical study

Nowadays, the promotion and application of aliphatic-aromatic copolyesters, such as poly (butylene adipate–co–terephthalate) (PBAT), are growing into a general trend. Although the structures of diacids exerted substantial impacts on degradation behavior, the underlying mechanisms have rarely been studied. In this work, 2,5-Furandicarboxylic acid was combined with succinic acid (PBSF), adipic acid (PBAF) and diglycolic acid (PBDF) to prepare three kinds of copolyesters. They showed unique degradation behaviors in buffer, enzyme environment and artificial seawater. These characteristics are closely related to the structural compositions of diacids. PBAFs displayed impressive biodegradability when catalyzed by Candida antarctica lipase B (CALB), while the more hydrophilic PBDFs exhibited faster hydrolysis in both buffer and artificial seawater. PBSFs, with hydrophobic and short segments, obtained a relatively slower rate of hydrolysis and enzymatic degradation. The reactivity sites and hydrolytic pathway were revealed by the combination of DFT calculation and Fukui function analysis. MD simulations, QM/MM optimizations and theozyme calculations showed that PBAF-CALB was prone to form a pre-reaction state, leading to the reduced energy barrier in the acylation process. This work revealed the effects of different structural features of diacids on polymer degradation and paved a way to design target biodegradable polymers in different degradation conditions.

(Bio)degradable biochar composites – Studies on degradation and electrostatic properties

In this work, biochar was introduced as a filler into the aliphatic-aromatic copolyester and polylactide blend. Properties and the changes during degradation of obtained materials were evaluated. A new application path was also determined by lowering the surface resistivity by increasing the biochar content. Measurements of electrostatic properties showed that surface resistivity of the poly(1,4-butylene adipate-co-1,4-butylene terephthalate)/polylactide/biochar composites is strongly dependent on the biochar content. Six-fold reduction of the surface resistivity after introduction of the 30 wt% of carbon to the reference specimen was observed. Degradation tests were conducted under abiotic and composting conditions. Visual evaluation indicated that the increase of biochar content had caused cracks to increase on the sample surfaces. The values of thermal properties after degradation do not indicated on the biochar influence on polymer matrix degradation mechanism. Nuclear magnetic resonance analysis revealed that after 42 days of hydrolytic degradation amount of polylactide was 0–2%.

Superior Gas Barrier Properties of Biodegradable PBST vs. PBAT Copolyesters: A Comparative Study.

As a bio-based counterpart of poly(butylene adipate-co-terephthalate) (PBAT), the well-known commercially available biodegradable aliphatic-aromatic copolyester, poly(butylene succinate-co-terephthalate) (PBST) has comparable physical and mechanical properties, but its gas barrier properties, which are very important for packaging material and mulch film applications, have not yet been reported in literature. In this paper, the O2, CO2 and water vapor barrier properties of PBST vs. PBAT were comparatively studied and reported for the first time. Theoretical calculation of O2 and CO2 permeation coefficients via group contribution method was also conducted. The barrier properties of PBST show clear copolymer composition dependence due to different contribution of BS and BT repeat units and composition-dependent crystallinity. Comparing with PBAT, PBST with close copolymer and three-phase (crystalline, amorphous, rigid amorphous) compositions shows 3.5 times O2 and CO2 and 1.5 times water vapor barrier properties. The slower segment movement and less free volume of PBST, and therefore slower gas diffusion in PBST, accounts for its superior O2 and CO2 barrier, while the better hydrophilicity of PBST counteracts partial contribution of slower segment movement so that the improvement in water vapor barrier is not as high as in O2 and CO2 barrier.

Lipase-catalyzed synthesis of furan-based aliphatic-aromatic biobased copolyesters: Impact of the solvent

• CALB allows the synthesis of furan based polyesters with high aromatic content. • Growing chains precipitation for high aromatic contents results in low molar masses. • Improved solubility in acetophenone leads to higher Mn and thermal properties. Enzymatic polymerization is a promising route for a greener synthesis of biobased polyesters. However, this approach is still often limited to aliphatic polyesters, which present limited properties such as low thermal resistance. In this context and till now, introduction of aromatic monomers into polyesters very often resulted in low molar mass chains. Herein, aliphatic–aromatic copolyesters based on dimethyl-2,5-furandicarboxylate were enzymatically synthesized using immobilized Candida antarctica lipase B with a particular focus on the influence of the solvent used. Two series of poly(hexylene adipate)–co-(hexylene furanoate) and poly(butylene adipate)–co-(butylene furanoate) copolyesters were successfully synthesized in diphenyl ether, displaying high molar masses (M n up to 19 000 g.mol −1 ) for aromatic monomer contents up to 70 and 50%, respectively. High aromatic content resulted in reduced molar masses due to a loss of solubility of the growing aromatic chains. Replacing diphenyl ether by acetophenone, which had never been used before as solvent for enzymatic synthesis of polyesters, led to significantly enhanced solubility and thus an increase in the average molar masses of poly(hexylene furanoate) and poly(butylene furanoate). The resulting polyesters showed greater thermal stability and higher T g , offering new perspectives for expanding the potential applications of such enzymatically-produced biobased aromatic copolyesters.

Shear-Induced and Nanofiber-Nucleated Crystallization of Novel Aliphatic-Aromatic Copolyesters Delineated for In Situ Generation of Biodegradable Nanocomposites.

The shear-induced and cellulose-nanofiber nucleated crystallization of two novel aliphatic–aromatic copolyesters is outlined due to its significance for the in situ generation of biodegradable nanocomposites, which require the crystallization of nanofibrous sheared inclusions at higher temperatures. The shear-induced non-isothermal crystallization of two copolyesters, namely, poly(butylene adipate-co-succinate-co-glutarate-co-terephthalate) (PBASGT) and poly(butylene adipate-co-terephthalate) (PBAT), was studied following a light depolarization technique. To have a deep insight into the process, the effects of the shear rate, shear time, shearing temperature and cooling rate on the initiation, kinetics, growth and termination of crystals were investigated. Films of 60 μm were subjected to various shear rates (100–800 s−1) for different time intervals during cooling. The effects of the shearing time and increasing the shear rate were found to be an elevated crystallization temperature, increased nucleation density, reduced growth size of lamella stacks and decreased crystallization time. Due to the boosted nucleation sites, the nuclei impinged with each other quickly and growth was hindered. The effect of the cooling rate was more significant at lower shear rates. Shearing the samples at lower temperatures, but still above the nominal melting point, further shifted the non-isothermal crystallization to higher temperatures. As a result of cellulose nanofibers’ presence, the crystallization of PBAT, analyzed by DSC, was shifted to higher temperatures.

Synthesis, characterization and properties of poly(butanediol sebacate–butanediol terephthalate) (PBSeT) copolyesters using glycerol as cross-linking agent

High molecular weight aliphatic-aromatic copolyesters were synthesized from Sebacic acid, terephthalic acid, 1, 4-butanediol and glycerol via two-step esterification and polycondensation. Copolyesters were characterized with intrinsic viscosity, gel permeation chromatography, X-ray diffraction, Fourier infrared spectroscopy, nuclear magnetic resonance, differential scanning calorimetry, thermogravimetric analysis, rheological analysis, tensile and puncture testing. All the copolyesters had a weight-average molecular weight over 20,000 g/mol or intrinsic viscosity over 1.1 dL/g when the glycerol content was in the range from 0.04 to 0.1 mol. Particularly, in addition to a small reduction in the tensile strength and elongation at break, the molecular weight, crystallinity, and intrinsic viscosity of the polyester were increased when the glycerol content was 0.04 mol, and the puncture resistance reached its maximum, which would improve the performance of the copolyester film. Obviously, the addition of glycerol did not significantly affect the melting temperature, glass transition temperature and thermal stability of polyesters, which would make it possible to use copolyester as a base material for cold-resistant hydrogels. As a whole, the level of glycerol within 0.1 mol is sufficient to improve the properties of copolyesters, which is beneficial to promote the generalization of them for films and hydrogels.

PERFORMANCE OF BIODEGRADABLE FLOATING DIRECT COVERS IN THE FIELD PRODUCTION OF BUTTERHEAD LETTUCE DURING SPRING AND AUTUMN TRIALS

Non-degradable polypropylene nonwovens are difficult to dispose and their utilization represents high economic costs. This study was conducted on lettuce cultivated during the spring and autumn seasons in the southern part of Poland to test biodegradable nonwovens as plant covers. Several nonwovens were developed from aliphatic-aromatic copolyesters (ACC), one without modifiers (SB48/11) and three with the addition of fatty acid dimers: two commercial variants (SB20/13, SB21/13) and one made from plant biomass (SB28/13). Nonwoven polypropylene (PP) fleece was included as a control cover. One week after covering with SB48/11, stomatal conductance (gs) increased in lettuce plants in parallel with higher transpiration rate (E) and sub-stomatal CO2 concentration (Ci) relative to the control, but differences in these parameters evened out in mature plants. In the spring, degradable covers with their higher mass per unit area, caused a decrease in marketable yield of lettuce compared to the control PP, resulting mainly from the deterioration of plant quality and lower mean weight per head. In the autumn season, yield was statistically not different between treatments. Yield of spring lettuces was 78% higher compared to the autumn cultivation period. Plants grown under SB20/13 had the lowest dry weight and L-ascorbic acid, while plants under SB21/13 had the highest dry weight and L-ascorbic acid content. Plants under SB28/13 had higher chlorophyll a content. Generally, no effect of covers was noted for carotenoid concentrations. The content of dry weight, L-ascorbic acid, and carotenoids were higher in plants harvested in spring, while no effects of crop season on chlorophyll level were observed. All tested biodegradable nonwovens are a potential substitute for standard polypropylene in autumn trials, but for spring covering unit weight of these materials should be reduced.