Temperature dependence of the interfacial shear strength in glass–fibre polypropylene composites

The present work focuses on further investigation of the hypothesis that a significant fraction of the level of apparent IFSS in glass fibre-reinforced thermoplastic composites can be attributed to a combination of thermal residual stress and static friction at the fibre-polymer interface. In order to obtain information on the temperature dependence of glass fibre–polypropylene IFSS a thermo-mechanical analyser has been adapted to enable interfacial microbond testing to be carried out in a well controlled temperature environment. Test results obtained by TMA-microbond testing showed excellent comparability with those obtained by normal microbond testing. The temperature dependence of IFSS of glass fibre–polypropylene was measured in the range from −40 °C up to 100 °C. The IFSS showed a highly significant inverse dependence on testing temperature with a major increase in the glass transition region of the PP matrix. It is shown that approximately 70% of the apparent room temperature IFSS in this system can be attributed to residual radial compressive stress at the fibre–matrix interface.