Fatty Acid-Based Vinyl Ester Composites with Low Hazardous Air Pollutant Contents

Fatty acid monomers have recently been shown to be a potential alternative for styrene monomer in vinyl ester and unsaturated polyester resins. These monomers are non-volatile, and therefore reduce the hazardous air pollutant (HAP) and volatile organic compound (VOC) content of these resins. Vinyl ester formulations containing various amounts of vinyl ester monomer, styrene, and fatty acid monomer were prepared. Two fatty acid monomers were used to determine the effect of fatty acid type on resin, polymer, and composite performance: methacrylated lauric acid (MLau) and methacrylated hexanoic acid (MHex). Both monomers contain one vinyl group capable of polymerizing with styrene and vinyl ester, but MLau monomer is six carbon atoms longer than MHex. The viscosity of the fatty acid formulations were within the range of commercial vinyl ester resins, but MHex resins had slightly lower viscosities than the MLau resins due to the shorter chain length of MHex. Similarly, the glass transition temperatures (T-g) of MHex polymers were slightly higher than that of MLau polymers. Regardless, some formulations were established that had similar T-g relative to commercial vinyl ester resins. Neat flexural properties of the resins decreased significantly for the fatty acid-based resins as the styrene content was reduced below 20 wt%. This reduction was more significant for MLau-based resins because of their lower T(g)s. On the other hand, flexural and inter-laminar properties of fatty acid-based resins were similar to that of commercial resins for all resin formulations tested. This indicates that improved fiber-matrix adhesion could be occurring in fatty acid-based composites relative to composites made using commercial resins.