Water transmission through polyester/glass laminates, a study of the behaviour of polyester resins and laminates when exposed to water at 50[sup][degrees]C

This thesis is an investigation of the relationships between unsaturated polyester resin composition and permeability to water. The permeabilities of cured unreinforced resins (castings) and glass reinforced polyesters (G.R.P.) made with different resins were studied at 50[sup]oC. In addition, the effect of applied strain on the permeability of castings and laminates made form a single resin were investigated. Six commercial resins were examined in all. Three variables were studied: 1. The effect of chemical constitution of the resin on transmission rate of water. 2. The effect of glass reinforcement on permeability. 3. The effect of applied strain on the permeability of castings and laminates made from a single resin. It was shown that, in the absence of any external strain, the castings made from various resins behaved differently. Castings made from a moderately crosslinked resin shows the highest resistance to water transmission. Castings made from resins with either higher or lower unsaturation showed a higher permeability to water. The dietyhylene propylene fumarate isophthalate resin has an advantage over the propylene fumarate isophthalate resin in having a lower water transmission rate. The permeability of the polyester resin increases with increase in the acid value of the resin. Another feature observed in the study is the decrease in the rate of transmission of water as the volume fraction of glass fibres in the laminates increases. This effect becomes more pronounced for laminates made from resins with high un-saturation. Results show that the observed transmission rates of water through laminates are always less than the product of resin volume fraction and resin permeability. The difference between the calculated and observed values of permeability become larger as the fibre orientation changes from random to bidirectional. This suggests that fibre orientation, as well as fibre volume fraction, is an important factor affecting water transmission through laminates. The effect of external strain on resins and laminates depends on the nature of the resin used. In general, applied strain increases water transmission rates, both in castings and laminates. An exception to this rule was found with laminates made from a moderately crosslinked resin. Glass laminates made from this resin allow the passage of water when under low strain than when unstrained. However permeability increases when the applied strain is higher