Influence of nano-sized palm kernel shell biochar (n-PKSB) as a potential bio-filler on characterization and mechanical properties of natural rubber vulcanizates

This study aims to evaluate the suitability of nano-sized palm kernel shell biochar (n-PKSB) as a reinforcing bio-filler in natural rubber (NR) vulcanizates. In Part A, the characterization of n-PKSB was carried out using particle size analyser (PSA), ultimate and proximate analyser, Fourier Transform Infrared Spectroscopy (FTIR), Brunauer–Emmett–Teller (BET), Field Emission Scanning Electron Microscope (FESEM), and Energy Dispersive X-ray (EDX) spectrometry. Whereas Part B, the performance of n-PKSB filled NR vulcanizates at loadings from 0 to 10 parts per hundred rubber (phr) was assessed through cure characteristics measurement, bound rubber content (BRC), swelling measurements, tensile test, abrasion test, hardness test and compression set test. The n-PKSB exhibited nano-sized particle (10–11 nm) with high carbon content (60–66%). The size reduction enhanced surface functionality with the presence of C=C, C–O, and C–H groups, increased surface area (47–50 m²/g), and formation of micropores with irregular and rough surface. The addition of n-PKSB had minimal effect on curing characteristics of NR vulcanizates. Based on results, 5 phr is the optimum n-PKSB loading. Incorporating n-PKSB into NR increased the crosslink density, BRC, tensile strength and abrasion resistance due to mechanical interlocking between n-PKSB and NR matrix. Therefore, this study demonstrates the potential of n-PKSB as a sustainable and alternative bio-filler in rubber compounding which reduces biomass waste and minimizes environmental impacts.