Behaviour of photopolymerized silicate glass fibre-reinforced dimethacrylate composites subjected to hydrothermal ageing Part II Hydrolytic stability of mechanical properties

The flexural properties and failure morphologies of dimethacrylate-copolymer composites reinforced with either S2-glass® or quartz fibres (33–66 vol%) were examined after hydrothermal ageing (0–3 mon at 37 °C). Initially the S2-glass® composites were generally stiffer and stronger than comparably reinforced quartz composites, but within 1 wk the properties of S2-glass® composites decreased by 12%–26%. The properties ofquartz composites were relatively stable, except for those of composites with the least reinforcement (35 vol%), which decreased by roughly 15%. Scanning electron microscopy revealed that in all composites buckling had occurred at the site of load application. Evidence of good fibre–matrix adhesion was observed for both types of composites under all conditions. Modelling of degradation between 1 wk and 3 mon revealed that: (1) the only temporal change was a slight increase in the stiffness of S2-glass® composites; and (2) higher reinforcement levels reduced the retention of strength in S2-glass® composites but had the opposite effect (on both properties) for quartz composites (p<0.05). For the most highly reinforced S2-glass® composites, susceptibility to degradation was offset by high initial properties; and after ageing (elastic modulus 50 GPa, strength 1.2 GPa), these composites were still, on average, approximately 25% stiffer and 50% stronger than the more hydrostable quartz counterparts. © 1998 Kluwer Academic Publishers