Waste management of straw to manufacture biochar: An alternative reinforcing filler for natural rubber biocomposites

To achieve climate neutrality, alternative processes and materials should be proposed to replace those currently in use, which excessively burden the environment. Fossil fuels are non-renewable, and their resources are slowly being depleted, leading to increased prices. The aim of this work was to determine the potential of using agro-industrial residues in the form of oat straw for the production of biochar and its utilization as a filler in natural rubber biocomposites. The process of pyrolysis of plant material was used to obtain biochar with a high carbon content and a characteristic structure, which can affect selected rubber properties. The influence of the applied temperature of the pyrolysis process on the properties of the filler was determined. In this work, analysis techniques were used to enable the evaluation of both filler activity and specific properties of the final vulcanizates. The course of straw pyrolysis process, the carbon content in the fillers, and the size distribution of the bio-additive were examined. The structural, morphological, dispersion, processing, and functional properties of the compositions were examined. The reference in assessing the impact of the produced bio-additive on the properties of the product were composites filled with a commercial carbon black. The conducted research proved that the pyrolysis of straw at a temperature of 600 °C was as effective as that carried out at a higher temperature, with comparable weight loss for both samples. The increase in torque was the highest in the case of biochar samples (torque gain 4,4–6,5 dNm), indicating greater intensity of the cross-linking process after the use of this type of additive. This was also confirmed by differential scanning calorimetry. Moreover, the obtained biocomposites were characterized by much higher strength parameters (tensile strength 18,3–21,3 MPa) than conventional composites. Unfortunately, vulcanizates containing biochar as a filler exhibited poor resistance to thermo-oxidative aging (aging factor 0,24–0,54). • The process temperature didn’t affect the properties of biochar as a polymer filler. • Biochar contributed to the development of the spatial structure of biocomposites. • Biochar improved the strength of rubber composites compared to commercial filler. • Biochar performed great potential as an alternative carbon filler for rubber.