Development of vinyl ester resins with improved flame retardant properties for structural marine applications

This work builds on our previous experience of blending and co-curing an unsaturated polyester resin with other relatively inexpensive, but more flame retardant resins such as chemically modified phenolic resins, and extends this technology to the almost equally flammable vinyl ester resins, commonly used in marine composites. It has been demonstrated that two commercial vinyl ester resins (Scott-Bader, UK), one epoxy based (Crystic VE 676) and the other novolac based (Crystic VE 673), may be blended with two different commercial low molecular weight phenolic resoles (Sumitomo Bakelite Europe NV), one unmodified (Durez 33156) and the other containing allyl groups (Methylon 75108) and the blends cured (crosslinked) to give blended resins with good flame retardance, in several respects better than that of the unblended vinyl ester resins. Compatibility of the vinyl esters with the Methylon resole is however better than with the Durez, which tends to give phase-separated blends, and thus blends having poor physical and mechanical properties. Moreover, the compatibility of the novolac-based VE with both Durez and Methylon is worse than blends of the unsaturated polyester with Methylon and Durez. This compatibility issue and derived flammability properties of different blends are discussed in terms of their chemical structures.