Synthesis, structural study and hydrolytic degradation of copolymer based on glycolic acid and bis-2-hydroxyethyl terephthalate

Synthesis and Characterization of High Glycolic Acid Content Poly(glycolic acid-co-butylene adipate-co-butylene terephthalate) and Poly(glycolic acid-co-butylene succinate) Copolymers with Improved Elasticity

Poly(glycolic acid) (PGA) is a biodegradable polymer with high gas barrier properties, mechanical strength, and heat deflection temperature. However, PGA's brittleness severely limits its application in packaging, creating a need to develop PGA-based copolymers with improved elasticity that maintain its barrier properties and hydrolytic degradability. In this work, a series of PGBAT (poly(glycolic acid-co-butylene) adipate-co-butylene terephthalate) copolymers containing 21-92% glycolic acid (nGA) with Mw values of 46,700-50,600 g mol-1 were synthesized via melt polycondensation, and the effects of altering the nGA on PGBAT's thermomechanical properties and hydrolysis rate were investigated. Poly(glycolic acid-co-butylene succinate) (PGBS) and poly(glycolic acid-co-butylene terephthalate) (PGBT) copolymers with high nGA were synthesized for comparison. DSC analysis revealed that PGBAT21 (nGA = 21%) and PGBAT92 were semicrystalline, melting between 102.8 and 163.3 °C, while PGBAT44, PGBAT86-89, PGBT80, and PGBS90 were amorphous, with Tg values from -19.0 to 23.7 °C. These high nGA copolymers showed similar rates of hydrolysis to PGA, whereas those containing <50% GA showed almost no mass loss over the testing period. Their mechanical properties were highly dependent upon their crystallinity and improved significantly after annealing. Of the high nGA copolymers, annealed PGBS90 (Mw 97,000 g mol-1) possessed excellent mechanical properties with a modulus of 588 MPa, tensile strength of 30.0 MPa, and elongation at break of 171%, a significant improvement on PGA's elongation at break of 3%. This work demonstrates the potential of enhancing PGA's flexibility by introducing minor amounts of low-cost diols and diacids into its synthesis.

Enhanced degradation of poly(ethylene terephthalate) by the addition of lactic acid / glycolic acid: composting degradation, seawater degradation behavior and comparison of degradation mechanism

The degradability improvement of poly(ethylene terephthalate) (PET), one of the most widely used but non-degradable disposable packaging material, is of great significance. However, the balance between degradability and mechanical properties remains a huge challenge. Herein, simple hydroxy acids, lactic acid (LA) and glycolic acid (GA) as easy hydrolysis sites were introduced into non-degradable PET via melt polycondensation. A series of high molecular weight poly(ethylene terephthalate-co-L‑lactide) (PETL) and poly(ethylene terephthalate-co-glycolate) (PETG) copolyesters were synthesized with an excellent tensile strength greater than 50 MPa, much higher than that of most commercially available degradable polymers. The introduction of hydroxy acid endows PET with significantly improved composting and seawater degradation performance. Furtherly, the degradation rate of PETG with hydrophilic GA unit was faster than that of PETL, and the mineralization rate of PETG80 reaches 22.0%. The density of functional theory (DFT) calculation revealed that adding hydroxy acid to the PET molecular chain reduced the energy barrier of the hydrolysis reaction. The molecular polarity index (MPI) analysis furtherly confirmed that the higher affinity between the GA unit and water may be the primary reason for the faster degradation of PETG.

Synthesis, Properties, and Biodegradability of Novel Sequence-Controlled Copolyesters Composed of Glycolic Acid, Dicarboxylic Acids, and C3 or C4 Diols

We have previously reported that sequence-controlled copolyesters such as poly((ethylene diglycolate) terephthalate) (poly(GEGT)) showed higher melting temperatures than those of the corresponding random copolymers and high biodegradability in seawater. In this study, to elucidate the effect of the diol component on their properties, a series of new sequence-controlled copolyesters composed of glycolic acid, 1,4-butanediol or 1,3-propanediol, and dicarboxylic acid units was studied. 1,4-Butylene diglycolate (GBG) and 1,3-trimethylene diglycolate (GPG) were prepared by the reactions of 1,4-dibromobutane or 1,3-dibromopropane with potassium glycolate, respectively. Polycondensation of GBG or GPG with various dicarboxylic acid chlorides produced a series of copolyesters. Terephthalic acid, 2,5-furandicarboxylic acid, and adipic acid were used as the dicarboxylic acid units. Among the copolyesters bearing terephthalate or 2,5-furandicarboxylate units, the melting temperatures (T_m) of the copolyesters containing 1,4-butanediol or 1,2-ethanediol units were substantially higher than those of the copolyester containing the 1,3-propanediol unit. Poly((1,4-butylene diglycolate) 2,5-furandicarboxylate) (poly(GBGF)) showed a T_m at 90 °C, while the corresponding random copolymer was reported to be amorphous. The glass-transition temperatures of the copolyesters decreased as the carbon number of the diol component increased. Poly(GBGF) was found to show higher biodegradability in seawater than that of poly(butylene 2,5-furandicarboxylate) (PBF). On the other hand, the hydrolysis of poly(GBGF) was suppressed in comparison with that of poly(glycolic acid). Thus, these sequence-controlled copolyesters have both improved biodegradability compared to PBF and lower hydrolyzability than PGA.

Melt-spun bio-based PLA-co-PET copolyester fibers with tunable properties: Synergistic effects of chemical structure and drawing process

The fabrication of bio-based copolyester fiber with adjustable crystallization, orientation structure and mechanical property still remains a great challenge. In this study, a series of copolyester fibers based on terephthalic acid (PTA), ethylene glycol (EG) and l-Lactide (L-LA) were prepared via melt copolymerization and spinning. The resultant PLA-co-PET (PETLA) fibers exhibited tunable structure and property due to the synergistic effects of chemical structure and drawing process. The chemical structure of PETLA was confirmed by NMR, FTIR and XRD, which suggested that the random degree of copolymer increased with LA content and the viscosity decreased with the increase of LA content. The crystallization behavior, melting characteristic, thermal stability and rheological property were investigated by DSC, TGA and rheometer, the results indicated that all the PETLA exhibited the crystallization capacity, melting temperature and thermal stability were slightly affected by LA segment. The synergistic effects of LA segment and spinning process on PETLA structure and property were analyzed by WAXD and SAXS. The breaking strength of PETLA fibers dropped from 5.3 cN/dtex of PET to 2.8 cN/dtex of PET₈₅LA₁₅, which still met the requirements of most textile applications. Therefore, our work presented a feasible approach to prepare bio-based polyester fibers with tunable property.

Biodegradable Polymers

Biodegradable materials are used in packaging, agriculture, medicine and other areas. In recent years there has been an increase in interest in biodegradable polymers. Two classes of biodegradable polymers can be distinguished: synthetic or natural polymers. There are polymers produced from feedstocks derived either from petroleum resources (non renewable resources) or from biological resources (renewable resources). In general natural polymers offer fewer advantages than synthetic polymers. The following review presents an overview of the different biodegradable polymers that are currently being used and their properties, as well as new developments in their synthesis and applications.