Composites industry news and market reports orbit around the technological advancements that drive product-related interest. However, in the broad scope of composites manufacturing, the traditional open molding process continues to represent the largest segment of composites related thermoset resin consumption.
The predominate use of styrenated polyester and vinyl ester resin systems in open molding also carries styrene emissions issues in its wake. In the pre-recession era, many molding operations were approaching their emissions permit caps. However, the impact of the economic recession on composites production took emissions out of the spotlight temporarily. Fast forward to today: Production volumes are back in the booming pre-recession range, and styrene emissions are once again a regulatory compliance issue for many companies.
Examining the Open Molding Emissions Profile
In open molding and vacuum infusion processes, gel coat is typically sprayed as an in-mold coating. With the hand lay-up laminating process, resin is often applied using atomized or non-atomized spray equipment. In the spray-up (chopping) laminating technique, resin and glass fiber are deposited on the mold through a specialized spray gun. Each of these application methods produces emissions during application and resin curing.
During the traditional gel coat application process about 50% of emissions are produced during the spraying stage of process and 50% during the curing phase. (See figure 1.) With the laminating process, 50% are produced during the resin application phase, 25% during roll-out and 25% during curing, according to industry test data. (See figure 2.)
These emissions profiles demonstrate the opportunities for emissions reduction during the different stages of the open molding process.
A Strategic Approach to Styrene Emissions Reduction
Considerations for the development of an emissions reduction strategy revolve around resin formulations, application methodology and the use of additives. The optimized combination of these factors can result in significant reductions in open molding operations.
Reducing Resin Monomer Content – There are significant effects on emissions by reducing monomer content. Unified Emission Factors (UEF) for Open Molding Composites, which were developed by ACMA, illustrate the effects of monomer content on resin and gel coat emissions. On the broad scale, these factors specifically address styrene and methyl methacrylate monomer levels in these products. As the UEF factors show, small reductions in resin monomer content can result in significant reductions of overall emissions generation.
There are alternatives to styrene and methyl methacrylate (MMA), however each of these replacement monomers are accompanied with a unique set of performance, regulatory and health issues that have inhibited wide-spread adoption across the industry. The result is that styrene and MMA remain the predominate constituents in open molding resins.