Phase separation in styrenated polyester resin containing a PVAc low profile additive and metallic stearates

Abstract

Unsaturated Polyester Resins(UP) that contain compatible low-profile additives (PVAc) are used in BMC composite materials (Bulk Molding Compound). The general morphology of the UP/PVAc matrix is made up of small polyester nodules embedded in a matrix-rich thermoplastic additives. An internal mold-release agent (often a Calcium Stearate) is incorporated into the UP/PVAc mixture to facilitate the extraction of the curing materials. Although used in small quantity, this agent does have an effect on the final morphology of the curing mixture. Some of the internal mould-release agents provoke the formation of a polyester rich phase in the form of large spherical globules (roughly 60 micrometers). The formation of the “globular” polyester phase seems to depend largely on the nature of the metallic ion and the solubility (in the styrene) of the mould-release agent. If this phase occurs, most of the internal mould-release agents are trapped inside the polyester globules. Given its particular affinity for mineral materials, this phase tends to coat filler and glass fibbers. Consequently, this phase strongly conditions the mechanical characteristics of the final composite.