Accelerated environmental degradation and residual flexural analysis of carbon nanofiber reinforced composites

Hollow particle filled composites known as syntactic foams presently find numerous applications in structures exposed to high moisture and high temperature environments. Carbon nanofiber (CNF) reinforcement is attractive in these composites because of the possibility of increased strength with negligible density variation. In the present study, syntactic foams containing 15-50 vol% glass microballoons (GMB) and 1-5 wt% CNF reinforcement as well as CNF/epoxy composites containing 1-5 wt% CNF were exposed to accelerated weathering by immersion in 90 °C water for two weeks and characterized for their residual flexural properties. In the worst performing composites, a maximum weight gain of 3.5% and 10% was observed for CNF/epoxy and CNF/syntactic foam composites, respectively. The syntactic foams tested were observed to generally decrease in strength after weathering with the exception of the composites containing 5 wt% CNF and 15 vol% GMB, which were observed to increase in strength by 41-51% after weathering. The composite containing 5 wt% CNF was also shown to increase in strength by 27% after weathering. Strength retention is attributed to the presence of CNF, along with competing weathering effects on composite structure and morphology.