Development of silanized nano-biochar from palm kernel shell for enhanced thermal insulation in polyethylene composites

Abstract This study presents the synthesis, characterization, and application of silanized nano-biochar (SNB) derived from palm kernel shell for the development of high-performance low-density polyethylene (LDPE) composites with enhanced thermal insulation and flame retardancy. Nano-biochar was produced via ball milling of pyrolyzed biomass and surface functionalized using 3-aminopropyltriethoxysilane (APTES) at varying concentrations (1–5% v/v). FTIR analysis confirmed that 2% APTES yielded the most effective silanization, as evidenced by the distinct appearance of Si-O-Si, Si-O-C, and N-H functional peaks, along with a reduction in hydroxyl groups. SNB was then incorporated into LDPE at loadings of 1, 3, 5, and 10 wt% to evaluate its effect on thermal, structural, and mechanical properties. The 5 wt% SNB/LDPE composite exhibited optimal multifunctional performance, achieving a 25% reduction in thermal conductivity, improved thermal diffusivity and heat capacity, and enhanced tensile strength and modulus. XRD and DSC analyses revealed a minor reduction in crystallinity and thermal transitions, indicating good matrix compatibility. Flame retardancy was further improved by integrating 10 wt% of commercial flame retardants; ammonium polyphosphate (APP), aluminum hydroxide, and magnesium hydroxide into the optimized composite. The SNB/APP system showed superior performance with a limiting oxygen index (LOI) of 32.5%, UL-94 V-0 rating, and 51% Peak heat release rate (PHRR) reduction. These results demonstrate a synergistic effect between SNB and APP, attributed to intumescent char formation and thermal barrier reinforcement. This study highlights the potential of silanized nano-biochar as a sustainable, multifunctional additive for thermoplastic composites in advanced thermal and fire-protection applications.