Influence of ferulic acid and active rice straw extract on the composting behaviour of PHBV and PHBV/PCL blend films.

The biodegradation of polymer films is affected both by their composition and structure and by the environmental conditions. Composting behaviour of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) films was studied at lab-scale, according to ISO 20200:2023, as affected by its blend (1:1) with polycaprolactone (PCL), and the presence (6 % wt.) of active compounds (Ferulic acid: FA, and rice straw extract: RSE). The film disintegration (mass loss) was monitored over the composting time, by microstructural analysis, FTIR spectroscopy, and thermal analyses. All films disintegrated completely at the end of the test (84 days), but the disintegration rate was affected by the formulation. PHBV and blends films containing RSE exhibited the fastest disintegration whereas blend films without actives were the slowest. In every case, the surface erosion provoked by the biofilm action was the main mechanism responsible for the film thinning, but bulk hydrolysis also occurred to a different extent. RSE, with high content of carbohydrates, promoted the film porosity and bulk hydrolysis of both PHBV and its blend with PCL where the crystallinity of PCL was promoted. FA also accelerated the hydrolysis of the PHBV amorphous phase as well as the crystalline phases of PCL, as deduced from DSC analysis. Therefore, degradation rate was affected by overlapping of the different mechanism, depending on the film composition and structure. Promoting the water diffusion through the film favoured the hydrolytic processes and the enzymatic action of the biofilm microorganisms, whose population and activity could also be affected by film components.