Effects of synthesis conditions on chemical structures and physical properties of copolyesters from lactic acid, ethylene glycol and dimethyl terephthalate

Abstract

Lactic acid/ethylene terephthalate copolyesters were synthesized by the standard melt polycondensation of lactic acid (L), ethylene glycol (EG) and dimethyl-terephthalate (DMT). Effects of reaction temperatures and types of catalysts on the structures and properties of the copolymers were examined. In addition, feasibility of promoting the copolymerization process by a novel synthesis step of using thermo-stabilizers was investigated. The results show that a reaction temperature of higher than 180°C is necessary to produce copolymers with appreciable molecular weight. However, degradation was observed when the reaction temperature is higher than 220°C. Triphenyl phosphate (TPP) shows promising results as a potential thermo-stabilizer to minimize this problem. It was found that Sb2O3 and Tin(II) octoate are most effective among 4 types of catalysts employed in this study. 1H-NMR results indicate that copolymers have a random microstructure composed mainly of single L units alternately linked with ET blocks at various sequential lengths. The longer ET sequence in the chain structure leads to the increase in melting temperature of the copolymer. TGA results show that the resulting copolymers possessed greater thermal stability than commercially-available aliphatic PLA, as a result of the inclusion of T (terephthalate) units in the chain structure

Synthesis and characterizations of degradable aliphatic-aromatic copolyesters from lactic acid, dimethyl terephthalate and diol: Effects of diol type and monomer feed ratio

“…1 H NMR spectra of copolymers derived from the three diol systems at a 2:1:2 monomer feed ratio, and their signal assignments are shown in Figures 3-5. Band assignments of the copolymer derived from EG are similar to those described earlier [14,16]. 1 blocks (B) are also calculated from 1 H NMR spectra by employing the methodology described elsewhere [14][15][16][18][19][20].…”

“…Band assignments of the copolymer derived from EG are similar to those described earlier [14,16]. 1 blocks (B) are also calculated from 1 H NMR spectra by employing the methodology described elsewhere [14][15][16][18][19][20]. Results on chemical structure of the as-synthesized copolyesters are summarized in Table 1, where solubility and thermal properties results are also shown.…”

“…The corresponding copolymers are then coded by the name of diol and the appropriated feed ratio, for example, EG212 refers to a copolymer synthesized from EG diol with a feed ratio of 2:1:2. The synthesis procedure is adopted from our previous work [16]. Essentially, the copolymers were polymerized in a 2-neck round bottom flask under N 2 atmosphere at 0.2 mbar.…”

“…In our previous work, lactic acid-based aliphatic/aromatic copolyester was synthesized from dimethyl terephthalate (DMT), lactic acid and ethylene glycol. The copolymer's chemical structure and properties were characterized [16]. In this study, aliphatic/aromatic copolyesters are systematically synthesized from lactic acid (LA), dimethyl terephthalate (DMT), and diols with various methylene lengths.…”

Fiber association and network formation in PLA/lignocellulosic fiber composites

“…Plasticization [1][2][3][4][5], copolymerization [6][7][8][9][10][11], chemical modification [12], blending [13,14] are all used to adjust the properties of the polymer to the intended application. When PLA is used as structural material, its stiffness and strength can be improved by the incorporation of fillers or reinforcing fibers.…”