Sustainable composites based on bioplastics and hydrothermally carbonized wood waste

Implementing sustainability and circularity concepts involves the conscious use and treatment of various types of waste to promote the transition from a linear to a circular economy and reduce the carbon footprint. This study explores the use of wood waste that has undergone hydrothermal treatment as a sustainable filler in bioplastics, with the aim of formulating composite biomaterials as an alternative to fossil-based materials. Wood waste was subjected to a sustainable hydrothermal carbonization treatment at a temperature of 210 °C, the limiting temperature to avoid cellulose decomposition. The produced particles were then introduced into the poly(butylene succinate) (PBS) matrix via melt mixing, varying the processing time (2 min and 5 min) and screw rotation speed (20 rpm and 60 rpm), at different weight ratios. For comparison, biocomposites based on PBS and micro-crystalline cellulose have been produced following the same processing protocols.

The obtained composite materials were characterized using thermal (TGA/DTG), calorimetric (DSC), mechanical (tensile and DMTA tests) and rheological (oscillatory tests) analyses. Additionally, the materials were subjected to a degradation process to evaluate their resistance to hydrolytic and photo-oxidative degradation, as well as to burial in soil. All the results obtained highlight that the wood waste particles, subjected to hydrothermal carbonization (HTC), were dispersed uniformly and have a reinforcing action on the bioplastic matrix. The calorimetric analysis suggests a clear nucleating effect of both fillers, leading to a significant increase in the crystalline degree of the PBS matrix. The elastic modulus values of the biocomposites are significantly higher than the value of the neat matrix, and this increase is more pronounced for the materials containing hydrothermally treated particles.

In conclusion, hydrothermally treated wood particles can be considered as a valuable alternative to high-cost conventional micro-crystalline cellulose.