Comparison of the roles of two shrinkage-control led low-profile additivesin water aging of polyester resin-glass fiber composites

A model previously formulated or water sorption in polyester resin-glass fi ber composites has been applied to the kinetic analysis of experimental dat a for two composites containing a hydrolysable (polyvinyl acetate-PVAc) and a non-hydrolyzable (polystyrene-PS) shrinkage-controlling low-profile addi tive (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 so rption 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 solubili ty inside the matrix during sorption. In contrast, the PS composite display ed the typical kinetics of materials with slowly increasing hydrophilicity.