Biobased and biodegradable polyester amides based on nylon 6,6 and polybutylene adipate via straightforward bulk polymerization

Abstract

Aliphatic polyesters are generally known for their limited thermal and mechanical properties, but are prone to biodegradation. On the other hand, aliphatic polyamides, mainly represented by nylons, feature high thermal transition points and enhanced mechanical strength, but are usually classified as nonbiodegradable. In this work, the properties of the aliphatic polyester polybutylene adipate and nylon 6,6 were combined by synthesizing polyester amides. Relatively low- and high-molecular weight series, $\overline{M_n}$ 7000 and 14400 g/mol, respectively, were synthesized via a straightforward bulk polymerization process by utilizing biobased starting materials: butanediol, adipic acid and nylon 6,6 salt. The amide-to-ester ratio was varied to analyze the influence of the amide content on the molecular structure, thermal properties, mechanical properties, hydrophilicity and biodegradability. Strong relationships between the amide content and the T_g, T_m, degree of crystallinity, and mechanical properties were observed. Water contact angle measurements revealed that all the polyester amides were hydrophilic. Finally, the biodegradation experiments demonstrated that all polyester amides are prone to biodegradation in activated sludge and that the amide content had a major influence on the biodegradation rate. This work supports the high potential of biobased polyester amides for applications in numerous fields due to their versatility in terms of polymeric properties and sustainable character.