Tensile and Flexural Properties of Glass-Fibre-Reinforced Cyanate Ester Syntactic Foams

In this paper, an attempt has been made to improve the tensile and flexural properties of cyanate ester syntactic foams by glass-fibre reinforcement. Cyanate ester syntactic foams with varying glass-fibre reinforcements were processed and evaluated for tensile and flexural properties. The effect of concentration and length of fibre on these mechanical properties was investigated. In one approach, the concentration of fibre was varied (5–20 wt.%) and the length of fibre was fixed at 5 mm. Tensile and flexural strength increased with fibre concentration, reached a maximum at a fibre concentration of 16.6 wt.%, and decreased on further addition. The diminution in strength beyond a fibre concentration of 16.6 wt.% was ascribed to the poor wetting of fibre by resin, which leads to an easy pull-out of fibres. In another study, the fibre length was varied (5–25 mm) and the ‘cyanate ester:microballoon:glass fibre’ ratio (1:1:0.5 by weight) was kept constant. A fibre length of 20 mm gives the optimum tensile and flexural properties. Considerable improvement in tensile and flexural properties of cyanate ester syntactic foams was achieved by glass-fibre reinforcement. A scanning electron microscopic study was performed on failed samples to substantiate the observed trends in the mechanical properties.