Sustainable biocomposites based on Mater-Bi and grape pomace for a circular economy: Performance evaluation and degradation in soil

Biodegradable polymers often exhibit inferior properties and higher cost compared to their fossil-derived counterparts. The addition of plant waste and by-products can improve their performances, providing in the meantime functional activity and reducing their cost. In this work, we summarize the preparation of different biocomposites (BioCs) incorporating two diverse amounts (10 % and 20 %) of grape pomace (GP) in a Mater-Bi (MB) sample. GP, MB as well as BioCs were fully characterized. The influence of addition of GP on the properties and degradation in soil of the biocomposites was evaluated in comparison with the neat MB. However, natural antioxidants and other active compounds from GP could be sensitive to temperature. Thus, GP and MB underwent heat treatment at 180 °C to simulate and induce possible degradation during BioCs processing. GP analysis (particle size 50 μm) showed only a slight decrease of antioxidant potency, despite the heat treatment simulating the BioCs processing. ¹H NMR of the MB soluble fraction in CDCl₃ displayed the presence of two polymeric components: polylactide (PLA) and poly(butylene adipate-co-butylene terephthalate) (PBAT). Introduction of GP in the polymer matrix induced a proportional increase of antioxidant property in the BioCs as well as in complex viscosity at low frequencies. Moreover, a slight increase in the elastic modulus was observed with increasing the crystallinity of the samples. Degradation rate in soil, monitored by weight loss, increased with filler content and time. Moreover, NMR showed that, in the recovered sample after 45 days, the composition of PBAT changed, with the terephthalic percentage increased.