LIQUID RESINS WITH LOW VOC EMISSIONS

One method of reducing styrene emissions from vinyl ester (VE) resins is to replace some or all of the styrene with fatty acid-based monomers. Fatty acid monomers are ideal candidates because they are inexpensive, have low volatilities, and promote global sustainability because they are derived from renewable resources. VE resins with no more than 20 wt % styrene were prepared using methacrylate terminated lauric acid. The viscosities of these resins were below 500 cP, allowing the use of vacuum assisted resin transfer molding for composite production. The polymer properties were similar to that of commercial resins, including Tg greater than 120ºC, flex strength greater than 100 MPa, modulus of approximately 3 GPa, and fracture toughness greater than 200 J/m2. To prove that these resins can be used to produce large scale structures, a composite hood for an M35-A3 truck was fabricated using a low VOC resin containing 15 % fatty acid monomers and only 20% styrene. Bimodal molecular weight distributions of VE monomers reduce styrene emissions while still maintaining low resin viscosities and high fracture properties. Low molecular weight monomers reduce the resin viscosity while high molecular weight monomers increase the fracture toughness. It was found that resin viscosity decreased exponentially as both the styrene content and the number average molecular weight of the VE monomers increased in the resin. In fact, the viscosity was a predictable function of these variables allowing us to determine the minimum possible styrene content in a given resin. Using bimodal blends, styrene contents as low as 30 wt. % still resulted in similar resin viscosities and fracture properties compared to commercial VE resins with far greater styrene contents