Sandwich-structured hemp fibre green laminates with biobased epoxy/benzoxazine resin: development to exposure in simulated weather conditions

In the current study, the waste hemp fibre (HF)-reinforced sandwich-structured green laminates with biobased epoxy/benzoxazine resin were developed and subjected to simulated weathering for several sets of humidity (50–90%) and temperature (20–40 °C). Effects of each set of simulated weathering conditions on moisture absorption and mechanical and thermal properties of sandwich-structured green laminates were systematically studied. The developed laminates showed moderate mechanical and thermal properties. The findings showed gradual enhancements in moisture absorption as the humidity and temperature were increased in the simulated weathering conditions. Moreover, experimental investigation established apparent adverse effects on tensile and flexural properties; samples exposed at 40 °C and 90% humidity yielded the lowest strength and modulus values, resulting in a 23.58 and 13.59% decline in tensile and flexural strengths, respectively. The impact strength results confirmed considerable differences compared to tensile and flexural properties; the recorded value (18.23 ± 0.26 kJ/m 2 ) after exposure to the simulated weathering at 40 °C and 90% humidity was 2.71 kJ/m 2 higher than the control specimen. Thermal stability analysis was conducted in terms of initial degradation temperature (T 5 and T 10 ), char yield, limiting oxygen index, and heat resistance index (HRI) values for the control sample, which were recorded as 344.8, 419.8 °C, 47.81%, 36.62%, and 206.58 °C, respectively. After exposure to the simulated weathering at 40 °C and 90% humidity, a significant decline was observed in all parameters. The heat tolerance of the composite specimen was recorded as 165 °C.