Possibilities for controlling strength and impact resistance of natural fibre reinforced plastics

The mechanical properties of reinforced plastics are controlled by the inte rface/interphase between the fibre and the matrix. This paper deals with ef fects of a strong interface which is formed by a silane coupling agent and a weak, energy-consuming interphase which is formed by a silicone interlaye r, on the mechanical properties of natural-fibre reinforced polyurethanes. A maximum increase in composite strength of about 35% due to the coupling a gent was found. The weak interlayer led to a general improvement of Charpy impact energy with a maximum of 100%, dependent on interphase thickness. Fu rther it was found that the composite strength decreases linearly with incr easing composite toughness. SEM fracture surface analysis illustrated the i nfluence of the type of fibre-matrix interaction on the fracture mechanism of these composites. For the composites with a strong interphase, more cohe sive failures on the fibre surfaces were found, while the composites with a n energy consuming interphase showed significant plastic deformations in th is layer.