Development of flame retardant and thermally stable acoustic green composites from waste hemp fibers reinforcement in fully biobased epoxy and benzoxazine hybrid thermosets

This study presents an in-depth investigation of eco-friendly and renewable resources-based composites for lightweight structural applications by reinforcing waste hemp fibers (AWHF) in isosorbide (ISE) and neopentylglycol (NGDE) epoxy resins and epoxy/hydroquinone-furfurylamine (H-fa) benzoxazine hybrid matrix. The NGDE epoxy composite specimen produced the lowest results, and the sandwich-structured hybrid laminate specimen produced the best mechanical and thermal properties. The flexural strength and modulus values of sandwich structure hybrid laminate were recorded as 154.43 ± 7.14 MPa and 10.10 ± 0.35 GPa, respectively, while T₅, T_10, and Y_c values were recorded as 329 °C, 353 °C, and 23.78 %, respectively, and temperature tolerance (HRI) was estimated up to 178 °C. Moreover, the ISB/H-fa hybrid laminate showed self-extinguishing behaviour by crossing the LOI threshold value and got a V-0 rating for flame retardancy. The acoustic studies confirmed that the ISB-hybrid laminate had the highest sound absorption coefficient. The produced biobased sandwich structure composites with ISB/H-fa hybrid matrix showed better flame retardancy, sound absorption capacity, and mechanical strength are suitable for under-hood structural components in automobiles and other lightweight structural applications.