High performance fatty acid-based vinyl ester resin for liquid molding

Liquid resins used for molding composite structures are a significant source of volatile organic compounds (VOC) and hazardous air pollutant (HAP) emissions. One effective method of reducing styrene emissions from vinyl ester (VE) resins is to replace some or all of the styrene with fatty acid-based monomers. In our investigation, the styrene was reduced to 20-25 wt% compared to 40-60 wt% associated with commercial products. In addition, fatty acid-based monomers can bring about other benefits like higher toughness, lower exothermal heat and low volume shrinkage. One disadvantage of fatty acid-based VE resins, however, is the reduction in glass transition temperature (Tg) which limits their use in high temperature environments. Therefore, the specific focus of this work was to design high Tg fatty acid-based VE resins with low viscosities and high fracture properties. These high Tg resins were designed by blending fatty acid monomers with novolac vinyl esters. Various low viscosity formulations were established with Tgs as high as 147°C. Moreover, approaches to further improve the fracture toughness of the resin were investigated. Vinyl terminated poly(butadiene-co-acrylonitrile) (VTBN) and epoxy terminated poly(butadiene-co-acrylonitrile) (ETBN) were used as modifiers to these fatty acid vinyl ester resins. Compared with commercial novolac VE resin, marked improvement in fracture toughness (167 J/m² versus 56 J/m ²) was achieved.