Design of Safe and Sustainable Hyperbranched Polyesters as Additives for PHAs

Introduction

Biopolyesters such as polyhydroxyalkanoates (PHAs) are promising biodegradable polymers for replacing conventional plastics, but their limited toughness and brittle fracture limit their industrial application. To improve these limitations, polymer additives are employed to enhance the mechanical properties. However, most of these are derived from non-renewable resources, and some of them have proven to be harmful to both the environment and human health. So, on these terms, the development of safe and sustainable alternatives is essential. Some of the most promising candidates are hyperbranched polymers (HBPs), characterized by a highly branched architecture and a high functional group density, making them candidates as biodegradable alternatives to common additives.

Results and discussion

This study focuses on the synthesis and functionalization of hyperbranched biopolyesters supported on microcrystalline cellulose (MCC) for use as an additive to improve the mechanical properties of poly(hydroxybutyrate-co-valerate) (PHBV). These polymers were synthesized via the polycondensation of 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) in the presence of MCC, followed by grafting of linear polycaprolactone chains to enhance the flexibility. The results of thermal and structural characterization (FTIR, TGA, NMR, and DSC) confirm successful synthesis and functionalization; however, they show a higher proportion of linear over branched polymers.

The mechanical properties demonstrate a significant improvement in PHBV's toughness, including the emergence of post-yield fracture behaviour and increased plastic deformation. Moreover, a slight decrease in crystallinity was also observed. This communication will present the results obtained with the newly synthesized additives, confirming their potential as sustainable additives in plastic formulations.

Acknowledgments: This research was supported by project PID2021-128749OB-C32, funded by MCIN/AEI/10.13039/501100011033 and FEDER, UE. This work was also funded by the UBE Chair for Sustainable Plastics, from the Universitat Jaume I.