Rubber toughening of plastics

The tensile behaviour of a rubber-toughened polyamide 6,6 (RTPA66) is compared with that of the corresponding untoughened polyamide (PA66). At constant strain rate, moistureconditioned specimens of RTPA66 show a substantial increase in volume ΔV with increasing extension ε, whereas PA66 becomes denser. At ε=40%, ΔV is 60% in RTPA66, but −1.4% in PA66. In creep experiments on both polymers, extension follows the Andrade equation ε(t)=ε(0)+bt ^1/3. Eyring plots of logb against applied stress σ are linear for the PA66, but the RTPA66 shows a sharp increase ind logb/dσ above 30 MPa, where significant dilatation begins. Scanning electron micrographs of tensile and impact specimens reveal that dilatation in RTPA66 is due to formation of voids within the rubber particles, leading to fibrillation of the nylon matrix at high strains. It is concluded that this cavitation accelerates shear yielding in the nylon matrix.