Tech Briefs

Fatty acid monomers are substituted for major proportions of styrene.

Liquid resins that are suitable for use in molding composite- material structural panels and that contain and emit smaller amounts of air-polluting volatile organic compounds than do corresponding commercial resins have been invented. In particular, these resins are under study as less-polluting potential substitutes for commercial vinyl ester and unsaturated polyester resins heretofore used in making lightweight composite panels for some military vehicles.

The commercial resins in question contain volatile, polluting reactive diluents (e.g., styrene and methyl methacrylate) that serve to reduce resin viscosities sufficiently to enable liquid molding. Typical styrene contents of the commercial resins range from 40 to 60 weight percent. Some other commercial resins contain as little as 33 weight percent of styrene, but they exhibit unacceptably high viscosities and unacceptably low fracture toughnesses. In contrast, the resins of the present invention contain no more than 25 weight percent of styrene, their viscosities are low enough for liquid molding processes of the vacuum infusion type, and the mechanical properties of polymers and polymer-matrix composites made from them are similar to those of polymers and composites made from commercial vinyl ester resins.

A Methacrylated Fatty Acid molecule is synthesized in a simple addition reaction.
The main difference between a resin according to the invention and a corresponding commercial vinyl ester resin is that most of the styrene in the commercial vinyl ester resin is replaced with monomers based on fatty acids. Of various alternative fatty-acid monomers, methacrylated fatty acid (MFA) monomers have been found to be best for making composite materials. MFA monomers are synthesized in simple addition reactions between the carboxylic acid groups of fatty acid molecules and the epoxide groups of glycidyl methacrylate molecules to form single product molecules (see figure). Typical reaction temperatures range from room temperature to 80 °C and typical synthesis process times are a few hours.