Understanding the effect of chain extender on poly(butylene adipate-co-terephthalate) structure

We investigated poly(butylene adipate-co-terephthalate) (PBAT), a biodegradable polymer, under the influence of a chain extender (a multifunctional epoxide oligomer, Joncryl ADR-4370S^®, ADR) at different concentrations, and correlated their properties concerning the molecular interaction between the active sites of the structures. Several studies have used ADR in poly(lactic acid)-PBAT blends; however, the effect of ADR in terms of chemical and physical interaction with PBAT is not investigated in-depth, which can limit its applications. The chain extender is usually applied to improve the mechanical and thermal properties and PBAT resistance to thermal degradation. The developed materials were evaluated by high-resolution solid-state nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), mechanical and thermal properties, and rheological measurements. NMR and FTIR indicate an interaction between the carboxylic sites of PBAT and the epoxy sites of ADR. PBAT-2%ADR shows higher tensile properties, probably due to the hydrogen bonds and interactions of π–π nature between the materials; in this case, the ADR can act as a reinforcing agent. High contents of chain extender can change the nature of the interaction and influence the final properties of the polymer. The effect of this additive was found to be strongly dependent on the content used and the polymer processing. It was observed that ADR could act as an internal lubricant during processing (due to the low molecular weight of this additive), demonstrating the importance of processing parameters control.