Durability and performance of sustainable composite films from aliphatic-aromatic polyester with biomass-derived carbon-based filler particles

• Biocomposites with extended durability and good performance. • Poly(butylene adipate-co-terephthalate) containing biochar from biomass food waste. • Slow pyrolysis and hydrothermal to produce biochar particles. • Biochar particles provide reinforcement and thermomechanical stability. • Biochar particles protect against photooxidative ageing of PBAT films. Additives are known to improve the properties of biopolymers, but most additives have environmental or performance concerns that limit their use. In this context, the recovery and use of bio-waste and biomass for the formulation of sustainable bio-composites is a challenging issue for the transition from a linear to a more sustainable circular economy. Recently, the replacement of carbon-based fillers in polymers and biopolymers with biochar particles derived from thermochemical treatments of biomass waste has attracted increasing attention for its potentially critical role.In this work, sustainable bio-composites based on biodegradable poly(butylene adipate-co-terephthalate), PBAT, and biochar, produced by controlled thermochemical treatments of biomass waste, were prepared by melt blending and their durability and performance were investigated in detail. Firstly, carob waste, after syrup extraction, was subjected to dry and wet thermochemical processes, i.e. slow pyrolysis at 280, 340 and 400 °C and hydrothermal carbonisation at 220, 250 and 280 °C, to obtain slow pyrolyzed biochar (SP-BC) and hydrothermal carbonised biochar (HTC-BC) particles. The SP-BC and HTC-BC, i.e. the solid phases resulting from the thermochemical processes, were characterised by elemental analysis and spectroscopy to study their physicochemical properties and by microscopy to analyse their morphology. Pure PBAT, PBAT/SP-BC and PBAT/HTC-BC bio-composites containing 10 % by weight of SP-BC and HTC-BC respectively were characterised by thermal, morphological, rheological and mechanical analyses. The results indicate that both types of particles exerted a reinforcing effect on PBAT and the resulting bio-composites were more thermo-mechanically stable compared to pure PBAT. Considering the potential application of these bio-composites as sustainable packaging materials, particular attention was paid to the photo-oxidation behaviour of these materials under accelerated artificial weathering conditions. Interestingly, both SP-BC and HTC-BC exerted a protective effect against the photooxidative ageing of PBAT, and this effect was more pronounced when HTC-BC was used.