Synthesis, thermal, and mechanical properties of fully biobased poly(hexamethylene 2,5-furandicarboxylate-co-diglycolate) copolyesters

In this research, a series of fully biobased poly(hexamethylene 2,5-furandicarboxylate-co-diglycolate) (PHFDG) copolyesters with hexamethylene diglycolate (HDG) unit contents from about 10 to 90 mol% were successfully synthesized through a two-stage melt polycondensation method. The basic thermal parameters, crystal structure, crystallization behavior, melting behavior, mechanical property, and hydrophobicity or hydrophilicity of the PHFDG copolymers were extensively studied and compared with those of the parent homopolymers poly(hexamethylene 2,5-furandicarboxylate) (PHF) and poly(hexamethylene diglycolate) (PHDG). Both the homopolymers and the copolyesters had relatively high intrinsic viscosity values. The physical properties of PHFDG copolymers displayed an obvious HDG unit content dependence. When the HDG unit content was not higher than 30 mol%, the copolymers showed a high melting temperature of about 116 °C and above. Depending on the HDG unit content, the copolymers displayed different crystal structures as that of PHF or that of PHDG. PHFDG copolymers displayed excellent mechanical properties. For instance, PHFDG20 (HDG unit content = 20 mol%) showed a Young's modulus of 500.9 ± 29.8 MPa, a tensile strength of 34.6 ± 2.3 MPa, and an elongation at break of 403.3 ± 10.5%. The hydrophilicity of PHFDG copolymers obviously increased with increasing the HDG unit due to the presence of ether oxygen. In sum, the PHFDG copolymers with low HDG unit content of 30 mol% and below may show comparable or even better thermal and properties than those of commercial biodegradable polymers, such as poly(butylene succinate) and poly(butylene adipate-co-terephthalate) and may thus find similar final end uses in the packaging materials field due to both the good thermal, mechanical, and barrier properties and the enhanced hydrophilicity.