Environmental Degradation of Carbon Nanofiber Reinforced Syntactic Foams

Hollow particle filled composites known as syntactic foams presently find applications in many high temperature, high moisture environments such as undersea drilling and oil exploration because of their low density and resistance to moisture uptake. Carbon nanofibers (CNFs) hold the promise of improving the strength of such composites. Syntactic foams with 1–5 wt.% carbon nanofiber-reinforced epoxy matrix and containing 15–50 vol.% glass hollow microballoons are characterized for environmental degradation using accelerated weathering in a 90°C water bath for two weeks and for residual flexural strength and modulus. The maximum weight gain observed after moisture exposure was 3.5% for the CNF/epoxy and 10% for the CNF/syntactic foam. Strength generally decreased after weathering by up to 69%, with the exception of the composites containing 5 wt.% CNF, which showed an increase in strength. This was attributed to swelling of the matrix leading to improved traction on the fibers.