Protein-based biochars as potential renewable fillers in styrene-butadiene rubber composites

In this study, chicken feather meal (CFM) and canola protein (CP) were converted into biochar and their suitability as reinforcing fillers in styrene-butadiene rubber (SBR) composites was evaluated. The protein-based feedstocks were pyrolyzed at 700 °C for 1 h, at a heating rate of 50 °C/min under different pyrolysis atmospheric conditions (N2, CO2, and steam). The flow rate of N2 and CO2 was 700 ml/min, while that of steam was 31 ml/min. Also, biochar was produced under N2 and CO2 gas flow and subsequently activated using steam. The physicochemical properties of the resulting CFM and CP biochars were characterized based on elemental and proximate analyses, surface area, Fourier-transform infrared spectroscopy (FTIR), and thermal field emission scanning electron microscopy. Results showed that activated CP, pyrolyzed under nitrogen and subsequently steam cooled (CP N2 + SC), had enhanced physicochemical properties such as lower ash content, higher fixed carbon content, and reduced polar surface functional groups compared to the other studied biochars in this study. Results also showed that CFM and CP pyrolyzed under nitrogen and subsequently steam cooled displayed higher final moduli and better filler dispersion in rubber than the other biochar samples produced in this study. Given that results showed favorable physicochemical properties and higher final moduli for CP N2 + SC, this sample was further tested using dynamic mechanical analysis (DMA) and results showed slight differences with carbon black regarding the temperature dependence of the shear storage modulus (G′) and the loss tangent (tan δ). These differences were attributed to increased filler-filler interactions, reduced filler-rubber interactions, and a lower dispersion in rubber than carbon black. The observed differences were not large enough to explain the inability of the biochar to adequately reinforce the rubber. However, the biochar filled rubber sample had a comparable viscoelastic behavior to carbon black over the studied temperature range.