Injection moulding of long glass fibre reinforced poly(ethylene terephtalate): Influence of carbon black and nucleating agents on impact properties

This paper aims at highlighting the influence of different additives (carbon black and nucleating agents) on both the notched and unnotched Charpy impact properties of long glass fibre reinforced poly(ethylene terephtalate) injection mouldings. The relationship with the polymer matrix and composite microstructure modifications (variations of crystalline morphology and local fibre content) was investigated. Adding carbon black alone decreases the impact performances. This highly conductive additive actually increases the cooling rate, and therefore the fibre 'frettage' effect (higher internal stresses). It also acts as filler, which increases the material brittleness. The nucleating agents allow reducing the mould temperature, but their effect on the impact strength may be favourable or not depending on the processing temperatures. The addition of such additives induces perturbations of the polymer melt rheology in the mould cavity and of the cooling kinetics of the part, which both act on the fibre distribution during mould filling and on the degree of crystallinity of the composite parts.