The influence of thermo-oxidative degradation on the measured interface strength of glass fibre-polypropylene

It has previously been found that thermal-oxidative degradation of the matrix can strongly affect the apparent interfacial shear strength (IFSS) in glass fibre-polypropylene (GF-PP) measured using the microbond method. In this work, different approaches were employed to further investigate this phenomenon. Hot-stage microscopy was used to establish a profile for dimensional loss of molten PP microdroplets during heat treatment. Under a given thermal load this reduction was found to be related to the initial droplet dimensions. A nanoindentation test was employed to directly probe the mechanical properties of the PP microdroplets, which also exhibited strong dimensional dependence in terms of property deterioration caused by the degradation. Characterisation of thermal mechanical properties and crystallinity was carried out on macroscopic PP samples to assist in elucidating how the polymer degradation affected the measured IFSS. Comparison of the degraded and non-degraded PP microbond samples for IFSS clearly showed the effect of thermal-oxidative degradation on adhesion.