Improving the inter-laminar fracture behaviour of hemp/epoxy composites under mode-II loading using alkali treated fiber and CNT modified matrix: an emphasis at different in-situ elevated temperatures

Abstract

Hemp fiber reinforced epoxy composites are increasingly being explored for lightweight structural and semi-structural applications, particularly in automotive and construction sectors, although their delamination resistance and temperature-dependent performance remain insufficiently understood. This study investigates the interlaminar fracture toughness of epoxy composites reinforced with untreated hemp fabrics (i.e., UTHE), treated hemp fabrics (i.e., THE), and treated hemp fabrics reinforced with 0.2 wt% CNT-incorporated epoxy composites (i.e., 0.2% CNT-THE) at room temperature (RT), 50 °C, and 70 °C. The G_IIC of 0.2% CNT-THE was higher than UTHE by ~ 80%, ~ 96%, ~ 86% at RT, 50 °C, 70 °C, respectively. This indicates the synergistic influence of alkali treatment of hemp fabrics and CNT addition to epoxy on the G_IIC. As temperature increased from RT to 50 °C, the G_IIC of UTHE, THE and 0.2% CNT-THE dropped by ~ 23%, ~ 38%, and ~ 16%, respectively. Surprisingly, as temperature increased from RT to 70 °C, the G_IIC of all the UTHE, THE and 0.2% CNT-THE dropped by ~ 64%. THE composites were more sensitive to high temperatures due to the lower T_g as determined from differential scanning calorimetry. The improvement in fracture toughness resulting from effect of alkali treatment which removes impurities from fiber surface and addition of CNTs which bridges the cracks and arrests the river lines besides enhancing the stress transfer from epoxy to hemp fiber as confirmed by scanning electron microscopy, supported by contact angle measurement.