Influence of substrate and temperature on the biodegradation of polyester-based materials: Polylactide and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) as model cases

Abstract

[EN] The extended use of polymers from renewable resources such as aliphatic polyesters or polyhydroxyalkanoates boosted the necessity to understand their behaviour in an end-of-life scenario. Although they can be degraded in reasonable shorter times than traditional polymers, understanding the degradation mechanisms under dissimilar conditions will contribute to further developments in this field. This work aimed to study the effect of temperature and substrate in the degradation of polylactide (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) in a simulated laboratory scale to ascertain their contribution, separately or in combination. For this purpose, nine parallel degradation assays were performed by means of the combination of mesophilic (25 °C), thermophilic (58 °C) and hyperthermophilic (80 °C) temperatures with enriched synthetic medium, compost and standardised soil substrates. Although the analysis of the surface morphology, the thermal properties and the thermo-oxidative stability revealed changes as a function of time, the evaluation of the molar mass allowed for a more precise determination of the degradation. In general, chain scission was perceived in all cases as a function of time. The effect of temperature was critical, significantly more important than the effect of the substrate, which showed a less significant contribution, especially in terms of molar mass reduction. While for the PLA, biodegradation at 58 °C and thermal degradation at 80 °C resulted in similar consequences, for the PHBH the hyperthermophilic temperature of 80 °C was the most severe condition, regardless of the substrate. From a technological perspective, it may be highlighted that biodegradation at 58 °C may be the most cost-effective condition due to the lower energy supply required and the valuable contribution of the microorganisms.