Interlaminar fracture properties of fibre reinforced natural rubber/polypropylene composites

The effect of the addition of natural rubber (NR) on the interlaminar fracture properties of thermoplastic composites which is a measure of the resistance of the material to delamination crack propagation, has been studied. NR–polypropylene (PP) composites were prepared with increasing amounts of NR in PP at 5–20% compositions reinforced with 5% E-type chopped strand glass-fibre mat. Panels were produced by compression moulding technique and these have been tested for mode I interlaminar fracture using double cantilever beam specimen testing method. Tests have been undertaken at cross-head displacement rate of 5 mm/min for all the specimens. It was found that, as the amount of NR was increased, the interlaminar fracture toughness, GIC of the composite materials decreased. Scanning electron microscopy of the fracture surfaces is used to help explain these findings. The crack propagation areas showed all the fibres were bare with no matrix covering them. These were seen at 200× magnification. The smooth clean surface of the fibres is the result of poor interfacial debonding. No fibre bridging is observed between the fibres and the failure mainly occurred at the fibre–matrix interface as seen using scanning electron microscopy. This shows that the addition of rubber made the adhesion between the interface weaker.