Use of composite materials for construction of DoD weapons platforms is approaching 200 million pounds per year. Vinyl ester resin (VER) is a low-cost resin that can be processed at ambient temperature using vacuum-assisted resin transfer molding (VARTM) into massive carbon-fiber-reinforced composite structures such as ship hulls and transportation vehicles. But since VER production is highly dependent on oil, it is subject to fluctuating prices and supply limitations. The continued viability of this strategic DoD weapons material is further jeopardized by the manufacturing need for hazardous materials, epichlorohydrin and styrene. Because of its increasing use for military weapon systems, VER is considered a strategic DoD resource. However, the resin as currently manufactured has three important disadvantages.
First and foremost, VER is currently synthesized from petroleum feedstock, so as mentioned it is subject to price volatility with the supply unreliable and limited in times of oil shortages.
Second, VER is synthesized from epichlorohydrin, a known environmental hazard that produces acute toxicity from inhalation, oral, and dermal exposure. (It is also classified by the EPA as a Group B2 probable human carcinogen.)
Third, the styrene monomer, a major reactive diluent (RD) component of VER, is environmentally hazardous, being volatile, flammable, and toxic, and in addition to being an irritant, styrene can affect the gastrointestinal and central nervous systems and has been categorized by the EPA as a hazardous air pollutant and possible carcinogen for humans.
To ensure the continued viability of this strategic VER material, it is essential to develop VER synthesis routes that are not dependent on petroleum. In this task, UMass Lowell also intends to investigate VER synthesis routes that eliminate use of epichlorohydrin and to conceive resin formulations that do not contain hazardous components such as styrene. To assure sustainability of the new processing route, starting materials should be derived from readily available renewable resources. Finally, the resultant VER must retain the desirable economic and performance characteristics of the current products. Figures 1 illustrate the UMass Lowell approach to ‘Green’ Vinyl Ester Resin from Renewable Resources.
The UMass Lowell-synthesized GVER will be processed using vacuum-assisted resin transfer molding (VARTM) into lightweight composites. Performance equivalent to currently used DoD composite weapons systems components will be demonstrated via mechanical-property testing. UMass Lowell's sponsorship includes the US Air Force, Navy, and Army. Ashland Inc., a VER manufacturer, has been approached to guide UMass Lowell toward development of appropriate military composite materials and component structures.
The GVER structures will be made predominantly from biowaste, namely lignin, recovered from wood wastes, and glycerin, recovered from biodiesel wastes. These source materials are renewable, low-cost, and are becoming increasingly abundant, and thus will eliminate dependence on imported oil. Furthermore, another key environmental objective is to eliminate use of epichlorohydrin from the GVER synthesis route.
Finally, the performance of all refined materials produced in the program will be demonstrated by standard characterization tests. The reactive diluent (RD) used in the final GVER formulation will be selected from those currently used by DoD and Ashland in military VER-based composites. Ideally, this RD will be an environmentally safe drop-in replacement for the hazardous styrene monomer RD used previously in commercial VER formulations, with equivalent composite performance as demonstrated by testing at UMass Lowell, DoD and Ashland.