Toughened and High Temperature Stable Vinyl Esters based on Fatty Acid Modifictions for Liquid Molding Applications

摘要

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 for reducing styrene emissions from vinyl ester (VE) resins is to replace some or all of the styrene with fatty acid-based monomers. In this investigation, the styrene was reduced to 20 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 cure shrinkage. One disadvantage of these 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 acidbased 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. 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. Though marked enhancement in fracture toughness was achieved without sacrificing Tg, further improvement in fracture toughness was limited due to the immiscibility of ETBN and VTBN with VE resins evaluated. The miscibility problem can be mitigated by using high acrylonitrile content carboxyl terminated poly(butadiene-co-acrylonitrile) (CTBN) but in this case a slight loss in Tg was detected. Thus modifiers having appropriate miscibility with VE resins to improve the fracture toughness without sacrificing Tg need to be identified by further work.