Water damage in glass fibre/resin composites

Abstract

Thin films of polyester resin containing glass fibres of several different compositions have been exposed to water at three different temperatures (20, 60, 100°C) and examined by means of optical and scanning electron microscopy. The incidence and development of fibre debonding has been studied by using the optical anisotropy arising from resin shrinkage on to the fibres during cure. To aid interpretation of these experiments, measurements have been made of resin dimensional changes produced by water immersions. At each temperature, the first response to diffused water is resin swelling and, in hot water, this is superseded by shrinkage, the magnitude of which becomes considerable after prolonged immersion, e. g. 8% linear shrinkage after 2000 h in boiling water. Evidence is reported suggesting that this shrinkage is mainly due to leaching of low molecular weight material from the resin. The interfacial bond between resin and clean glass fibres is rapidly destroyed by diffused water at all three temperatures. However, the use of a coupling agent produces vast improvements in bond life. In fact, debonding in the presence of a coupling agent has been observed only for hot water immersions; even then, the bond withstands the interfacial tension present during early resin swelling and is destroyed very much later when the interfacial stress is compressive owing to resin shrinkage. The mechanism by which this debonding is eventually initiated depends on glass composition. With ‘E’ and ‘C’ glass fibres, bond fracture is due to osmotic pressure generated at the interface by water soluble constituents leached from the fibre, and is often accompanied by the growth of cracks into the resin from the fibre surface. With fused silica fibres, which contain negligible amounts of impurities, small regions of debonded interface appear at fibre ends after much longer immersion times and are attributed to high interfacial shear stresses caused by resin shrinkage. Debonding facilitates relative longitudinal movement between fibre and resin, enabling each fibre end to act as a rigid indentor pushing into the adjacent resin. In hot water, resin indentation cracks result and subsequent resin shrinkage and gross plastic deformation lead to their displacement along the fibres, followed by the successive nucleation and displacement of further indentation cracks.

Unsaturated Polyester Resin for Specialty Applications

“…Since many years, unsaturated polyester composites have been used in very varied technology fields as naval constructions, offshore applications, water piping, building construction and automotive applications. In spite of hydrolytic instability problems of these materials, mainly due to the fact of their pre-polymer ester functions [61][62], interest in unsaturated polyester resin comes from their low cost and easy processing. Due to their stable structure, they display good mechanical properties and furthermore, unsaturated polyester resin has good thermal stability.…”

The fracture toughness and fracture morphology of polyester resins

“…Water, particularly distilled water, is known to have a deleterious effect on polyester resins, alone [24] or with fibre reinforcement [25,26]. The absorption of water and several organic solvents into polyester samples was determined by weighing pieces, 7 mmx 12 mm x 28 mm in size, which were immersed in bottles containing the fluid until weighing, when the sample was withdrawn, the surfaces blotted dry and the sample weighed, after which it was replaced in the fluid.…”

Effect of sawdust impregnation on long coir fibers reinforced with epoxy matrix

“…Due to water absorbing nature of fiber and filler, porosity of filler led to weak matrix fiber interface which was noticed in flax fiber reinforced composite (Dhakal et al, 2007). Moisture penetrating into polymer matrix through voids and cracks can break down the structure of matrix (Ashbee and Wyatt, 1969). When in dissolved state, NaCl exists in the sea water as cations and anions would penetrate along with the water molecule into composite, causing damage to matrix, fiber and their interface.…”