THERMOPLASTIC FIBER-REINFORCED COMPOSITES FOR DENTISTRY .2. EFFECT OFMOISTURE ON FLEXURAL PROPERTIES OF UNIDIRECTIONAL COMPOSITES

The effect of a deterioration of matrix and matrix fibre interface, ca used by moisture, on the flexural properties (modulus, strength and ul timate strain) of unidirectional E-glass fibre-reinforced thermoplasti cs [polycarbonate, poly(ethyleneterephthalate glycol) and nylon 12] wa s investigated. Specimens of span/thickness ratio varying from 15 to 3 0, prepared from pultruded thermoplastic prepregs, were tested in dire ctions parallel to and perpendicular to the fibre orientation as mould ed and after immersion in water at 85-degrees-C for 100 h. No signific ant reduction in longitudinal properties, controlled by fibre behaviou r, resulted from exposure to water. A significant reduction in transve rse properties, controlled by the matrix and interface behaviour, was observed. Polycarbonate/bare E-glass fibre composite annealed at 275-d egrees-C for 1 h before immersion in water exhibited a superior resist ance to moisture attack. This phenomenon is attributed to the ''transc rystalline'' interphase near the fibre surface and good wetting of fib res by the matrix. Resistance against moisture favours this material f or further clinical application as an orthodontic wire.