Effects of solid-state polymerization on the structure and properties of degraded poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Abstract

In the transition from a linear to a circular economy, polymer source and end-of-life scenarios must be considered when selecting a plastic for a given application. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a highly promising alternative to fossil fuel-based polymers in certain applications, because it is a biodegradable and biobased polymer with some good properties. When possible, mechanical recycling is the best option, over chemical and organic recycling, for PHBV waste. However, it must be considered that PHBV is a biopolyester that can undergo significant degradation during its use, and that degraded PHBV residues generate low-performance recycled materials, thus greatly reducing the feasibility of mechanical recycling. In this context, solid-state polymerization (SSP) is proposed as a simple, green, and cost-effective alternative to reverse the effect of the degradation and valorize the residues. In this work, PHBV residues with different levels of degradation have been obtained and subjected to SSP in vacuum for different times and temperatures, without solvents or catalysts, in order to study the effects of SSP on the structure and properties of the residues and optimize the process. The effect of SSP on the viscosity of the recycled material, obtained by melt processing the waste, has also been studied. The results indicate that the effects of the SSP depend largely on the level of degradation of the waste and that significant improvement in molecular weights and viscosities (up to 40 %), and thermal stability, can be achieved when wastes with significant degradation are treated.