Evaluating the potential of high SSA biochar particles produced via microwave pyrolysis as reinforcing filler in pultruded fiber-reinforced polymer composites

Abstract

This research project focuses on the design, manufacturing, characterization, and mechanical testing of a novel biocomposite by combining two materials research areas, namely fiber-reinforced polymer composites and renewable biomaterials. High specific-surface-area (SSA) biochar particles were synthesized via microwave-assisted (MW) pyrolysis of biomass. Two feedstocks were wood-based, namely maple and spruce, and the third was an agricultural biomass, switchgrass. Produced biochar was characterized, with an emphasis on porosity and surface area properties. Wood-based feedstocks performed favorably compared to switchgrass, with spruce having a surface area in excess of 200 m2/g. Biochar particles were introduced into a biocomposite design-of-experiments via an in-house pultrusion machine, employing E-glass fibers and a vinylester polymer resin. Three-point-bending tests were conducted to evaluate the flexural strength and modulus properties of the biocomposites and were compared to their conventional GFRP counterpart. Spruce-based biochar biocomposite, at 10% volume fraction, demonstrated a flexural strength of 970 MPa, showing a significant increase compared to the 450 MPa flexural strength of the control GFRP. Control GFRP composites showed a compressive-dominant failure, where the polymer matrix folded over at the point of load application. Biochar particles, due to their inherent hardness, significantly enhanced the compressive performance of the biocomposites, allowing for higher flexural stresses to be withstood, yielding a tensile-dominant failure. Moreover, a mechanical interlocking was observed between the resin and biochar structure, describing the variation in flexural strengths of produced biocomposites.