Covercoat retardation of permeation through sheet molding compound

摘要

AbstractPermeation of gases through polymers may be retarded by applying to the polymers a coating of a less permeable material. We have devised techniques to quantitatively measure rates of water vapor permeation at typical atmospheric pressures and compositions through polymer and coating films, and we apply these techniques here to a crosslinked polyester resin with glass fiber reinforcement, coated with a crosslinked thio‐ene formulation. The coating is shown to inhibit water vapor permeation by about a factor of thirty over the uncoated value. H2S permeation constants are also derived; they are some three orders of magnitude smaller than those of H2O but show similar coated/uncoated permeation effects. The controlling factor in the retardation is suggested by experimental evidence to be a graft copolymer formed at the covercoat–sheet molding compound interface by the ultraviolet curing proc