Synthesis, thermal, mechanical, and hydrolysis properties of poly(hexamethylene furandicarboxylate)-based copolyesters

To improve the hydrolysis ability of poly(hexamethylene furandicarboxylate) (PHF), novel biobased poly(hexamethylene-co-diethylene glycol furandicarboxylate) (PHDEGF) copolyesters were successfully synthesized by a two-step melt polycondensation method. The chemical structure and composition of the copolyesters were characterized using ¹H-NMR and ¹³C-NMR, revealing that the PHDEGF copolyesters were random. The intrinsic viscosity of all polyesters ranged from 0.76 to 0.87 dL/g, indicative of relatively high and close molecular weights. The thermal properties and crystallinity of the copolyesters were investigated with DSC, TGA, and WAXD. With the increase in diethylene glycol 2,5-furandicarboxylate (DEGF) unit content, both the thermal stability and the glass transition temperature of the copolyesters were improved. The crystallinity and melting point of the copolyesters gradually decreased when the DEGF unit was 21.2 mol% and below, while the copolyesters were amorphous when the DEGF unit was 41.6 mol% and above. In addition, the hydrolysis and mechanical properties of the polyester were further investigated. As the DEGF segment content increased, the water contact angle (WCA) value of the copolyesters gradually decreased; consequently, the hydrolysis rate accordingly increased. After 9 d of degradation at pH=14 and 37 ^oC, the remaining mass decreased from 92.9% for PHF to 7.1% for poly(diglycol furandicarboxylate). The mechanical properties of PHDEGF were increased by introducing a small amount of DEGF units. In particular, the elongation at break of PHDEGF30 (DEGF unit = 21.2 mol%) was comparable to that of poly(butylene adipate-co-terephthalate) (PBAT); moreover, its modulus exceeded that of poly(butylene succinate) (PBS). Therefore, PHDEGF30 has the potential to replace PBAT and PBS as a promising packaging material.