Comparison of the roles of two shrinkage‐controlled low‐profile additives in water aging of polyster resin–glass fiber composites

Abstract A model previously formulated or water sorption in polyester resin‐glass fiber composites has been applied to the kinetic analysis of experimental data for two composites containing a hydrolysable (polyvinyl acetate‐PVAc) and a non‐hydrolyzable (polystyrene‐PS) shrinkage‐controlling low‐profile additive (LPA) respectively. It was found that the equilibrium water uptake in the composites and their unreinforced matrix is not drastically affected by the type of LPA. The kinetics of water sorption in the composites, however, were substantially different. The PVAc composite displayed a two‐stage sorption process, the first stage being attributed to diffusion combined with hydrolysis, and the second to matrix swelling and plasticizing. A maximum in the kinetic curve was observed, and was due to changes in water solubility inside the matrix during sorption. In contrast, the PS composite displayed the typical kinetics of materials with slowly increasing hydrophilicity.