Use of Biochar as inexpensive lubricant filler in poly(butylene succinate-co-adipate) biocomposites

This study focused on the development of a novel bio-composite material formed by a thermoplastic biodegradable polyester, poly(butylene succinate-co-adipate) (PBSA), and a carbonaceous filler as biochar (BC) derived by the pyrolysis of woody biomass waste. Composites with various BC contents (5, 10, 15, and 20 wt.%, PBSA5, PBSA10, PBSA15, and PBSA20, respectively) were obtained by melt extrusion and investigated in terms of their processability, thermal, rheological, and mechanical properties. BC lowered melt viscosity in all the composites, behaving as a lubricant, and enhancing composite extrudability and injection molding at high temperatures up to 20 wt.% of biochar. While the use of biochar did not significantly change composite thermal stability, it increased its stiffness (Young modulus). Differential scanning calorimeter (DSC) revealed the presence of a second crystal phase induced by the filler addition. Furthermore, results suggest that biochar may form a particle network that hinders polymer chain disentanglement, reducing polymer flexibility. A biochar content of 10 weight % was selected as the best trade-off concentration to improve the composite processability and cost competitiveness without compromising excessively the tensile properties. The findings support the use of biochar as a sustainable renewable filler and pigment for PBSA. Biochar is a suitable candidate to replace more traditional carbon black pigments for agricultural applications.