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Reducing Volatile Emissions in the Fiber Reinforced Plastics Industry (FRP)

Most FRP processors are major sources of volatile emissions. The emissions from FRP processing facilities include styrene, the volatile component of polyester resin and gelcoat; and acetone, a solvent used to clean tools and other surfaces contaminated with resin.

This fact sheet describes the ways in which FRP operations may obtain these benefits.

Low-Styrene Emission Resins
Low-styrene emission resins are grouped into two general categories including reduced styrene resins and vapor-suppressed resins.

Reduced styrene resins contain 35 percent or less styrene on a weight basis than conventional resins. The chemistry of low-styrene resin has low viscosity and the desired appearance of a final laminate. However, their viscosity is higher than conventional resins and roll out over reinforcing material may be tougher. The viscosity is much more sensitive to temperature fluctuations, which may require improved temperature control. The cost of low-styrene resins is comparable to conventional resins. The Unified Emission Factors developed by the Composites Fabricators Association (CFA)1 show that a decrease in the styrene content from 40 to 35 percent will reduce styrene emissions by 20 to 50 percent, depending on the application method employed.

Vapor-suppressed resins contain an additive that forms a barrier inhibiting the release of styrene during the laminate cure process. In the past, the additives were wax-like, but problems with secondary bonding limited their acceptance. The reactivity of the newer vapor suppressing additives safeguard secondary bonding, which allows crosslinking to occur within the vapor suppressing film. Appropriate concentration levels of the additive, ranging from 0.2 to 1.0 percent, are crucial as high levels reduce effective secondary bonding. Tests done by BYK-Chemie,2 a resin manufacturer, suggest the use of vapor-suppressed resins reduces styrene emissions in excess of 50 percent.

Upgrading Application Equipment
Many FRP processors apply resin or gelcoat using conventional spray equipment, which requires high fluid pressure or compressed air to create a finely divided spray. All conventional spray technologies produce misting, which results in overspray. Transfer efficiency decreases when material misses the mold surface. Misting—and particularly the resulting overspray—increases the surface area of the resin or gelcoat particles exposed to air during application, causing a higher evaporation rate which increases emissions.

In order to mitigate these negative effects, new application equipment technologies have been developed. These include non-spray and non-atomized technologies, such as flow coaters and fluid impingement equipment. Non-atomized technologies are viable in almost all open-molding operations.

Flow coaters are internal mix guns that produce low-pressure streams of resin. These guns can be equipped with a glass chopper to simultaneously apply catalyzed resin and reinforcing media. Because flow coaters rely on internal mixing of the resin and catalyst, the operator must periodically flush the mixing chamber with an appropriate solvent to minimize contamination build-up. Depending on the solvent used, this may affect hazardous waste generation.

Fluid impingement application equipment can be either internal or external mix. In both cases, the resin or gelcoat exits the gun in two low-pressure streams which cross each other. Their collision creates a fan pattern. As with the flow coaters, chopped glass can be simultaneously combined. The Coating Applications Research Laboratory (CARL) at Purdue University found that the fluid impingement technology gelcoat system generated 32 percent fewer styrene emissions than conventional equipment.3

To successfully implement non-atomized application technologies, several issues must be addressed. First, non-atomized spray appears to wet-out slower than conventional spray. Although it takes slightly longer to saturate the glass, it will wet-out quickly once the roll out process begins if the equipment is adjusted for the appropriate glass-resin ratio. The operator must be trained on this aspect because the tendency is to apply excess resin and glass. Secondly, capturing the chopped glass in the resin stream is another concern. The chop chute needs to be adjusted more precisely than traditional equipment. Failure to do so results in a wider distribution than desired. A final concern is the electrical charge that may occur during spraying. On the extreme, glass is repelled away from the resin stream. Either proper grounding of the equipment or glass roving with a charge opposite of the system's may be required. It is best to consult the equipment supplier when addressing this issue.

Converting Closed-Mold Process
Another alternative is to convert open-mold processes to closed-mold processes. The closed-mold process not only reduces emissions but optimizes the glass-resin ratio, producing a higher quality laminate. The two techniques presented here include vacuum bagging and resin infusion.

Vacuum bagging technique applies resin and reinforcement in the traditional manner. Before the laminate starts to cure, a thin plastic film is placed over the uncured laminate and a vacuum is drawn over the system. This creates a pressure of one atmosphere over the laminate surface and forces excess resin from the system. Vacuum bagging techniques increase the glass to resin ratio, enhance physical properties of the laminate and reduce the amount of resin used. If the bag is not reusable, solid waste from applying this technique will increase.

Resin infusion technique converts existing open-molds by fitting a flexible membrane around the mold perimeter. Reinforcements are tacked into place, the membrane is sealed around the mold edge and a vacuum is drawn on the system. The membrane stretches to make contact with the reinforcing media. A valve is opened and resin is sucked into and through the reinforcing media. Resin infusion reduces styrene emissions by eliminating the exposure of liquid resin to the environment during the manufacturing process. No overspray and less flashing waste are produced, while a minimum quantity of resin is used. Resin infusion increases part quality and part-to-part consistency. Reduced labor helps justify its large capital expense. Solid waste may increase, but the membrane can be used multiple times. Waste increase is typically less than vacuum bagging.

Resin infusion has been successful when parts require multiple reinforcing layers. For example, Larson Boats, part of Genmar Holdings in Minneapolis, Minnesota, makes boat hulls using the Virtual Engineered Composition (VEC™) process. The VEC™ process is a closed-mold approach to boat building that incorporates sophisticated automation to produce high quality high strength parts with part-to-part weight consistencies within one percent. The entire molding process is enclosed, reducing styrene emissions by 77 percent and solid waste by 50 percent.4

Implementing Controlled Spraying Programs
Controlled spraying is an effective work practice that reduces styrene emissions in conventional open molding processes up to 25 percent. By minimizing spray gun atomization and reducing overspray loss, a manufacturer improves the transfer efficiency of resin or gelcoat. This approach is most effective for operations using atomization spray equipment, but certain aspects may benefit operations using non-atomized spray equipment as well. A controlled spray program is comprised of three elements: containment flanges around the mold perimeter, spray gun pressure calibration and spray operator training.

Containment flanges may be designed for new molds or added to existing mold designs. Masking may also be applied around the mold perimeter as a temporary flange. In each case, the flange acts as a barrier to potential overspray, which is captured and accumulated at the flange. Because resin and gelcoat particles have less surface area exposed to the air, styrene emissions are reduced.

Operator training is crucial to producing high quality work and reducing styrene emissions. Precise spray gun aim is necessary in order to put as much material into the final part as possible. Operators need to develop a high level of concentration because application rate and gun movement determine an even thickness across the part. The use of a thickness gauge helps ensure proper material thickness, as well as part-to-part consistency and optimal material use. When spraying the perimeter, keep within the area of the containment flange. Overspray that hits the floor increases styrene emissions.

Improved Process Control
Robots
A tight labor market allows FRP open-molding processes to consider the use of robots. A robot with the appropriate automation is the ultimate in controlled spraying. Robots guarantee proper positioning of the spray gun and ensures optimized coverage. Although somewhat capital intensive, these systems produce parts faster, improve part-to-part consistency, optimize materials use, reduce plant ventilation requirements and reduce ergonomic injuries. Some robots are also capable of collecting production data.

Weight tolerance of parts is greatly improved resulting in significant material savings. Overall material use for manual application is higher because excess overspray and weight difference from part to part will have a larger statistical spread. For example, if part-to-part weights for manual application have a spread of +/- 10 percent and robotic application has a spread of +/- 5 percent, then a robotic application consuming 1,000 pounds of material per day will save more than 50 pounds of material.6 Material savings, increased rates of production and improved part quality ensure a quick payback on the system.

Maintenance issues may require additional training for personnel. On site computer programming and fitting new products into the process may require extra expertise.

Raw Material Monitoring Systems
Raw material monitoring systems are electronic devices capable of delivering real time information concerning resin, glass and catalyst application. These systems allow processors to keep track of material used and to achieve part weight goals. As a result, part-to-part consistency is maintained and overall material use decreases resulting in fewer emissions. Data from these systems can be transferred to a computer for improved costing or record monitoring. A payback of one year or less is achievable.

Reducing Acetone Emissions
Acetone is a commonly used solvent for cleaning uncured polyester resin and gelcoat from tools and contaminated surfaces. In a typical FRP operation, more than 50 percent of the solvent used can be lost to air through evaporation. The remaining spent solvent can be processed on-site to reclaim the acetone or disposed of off-site as hazardous waste. Still-bottoms remaining from the reclamation step must also be disposed of as hazardous waste.

Even though acetone is classified as a non-volatile organic compound (VOC), its hazardous qualities are still strong incentives for FRP shops to implement alternatives. These qualities include fire hazards associated with elevated concentrations of vapors and waste management of the spent hazardous solvent. Acetone substitutes can be used to reduce volatile emissions. These substitutes are grouped into two general categories including higher-boiling solvents and aqueous cleaners.

Higher-boiling Solvents
These solvents work the same way as acetone, by dissolving the resin. When using higher-boiling substitutes the liquid film remaining on the part may be removed with a towel or by some other means, as these solvents do not evaporate as readily.

Higher-boiling solvents can be substituted for acetone in many applications. However, their effectiveness needs to be verified for each cleaning situation. Carefully review the Material Safety Data Sheet (MSDS) to note any potential safety or worker exposure hazards. Protective equipment such as splash goggles and gloves may be necessary.

Aqueous Cleaners
Aqueous cleaners rely on mechanical action, such as brushing, to clean resin from contaminated surfaces. The mechanical action separates resin from the part surface and the resin droplets are wetted by the aqueous cleaner. The coated resin settles to the bottom of the cleaning tank. A towel or a stream of air can then be used to dry the tool prior to reuse.

Although aqueous cleaners eliminate volatile emissions, they create two other waste streams including the spent aqueous solution and the under-cured resin material collected in the cleaning tank.

Both higher-boiling solvents and aqueous cleaners are effective substitutes, but special attention is demanded when educating employees about new cleaning procedures. Lack of training usually results in poor cleaning, and employees lack of acceptance causes implementation to fail.

Managing Small Amounts of Waste Resin or Gelcoat
Small batches of uncured resin or gelcoat can be disposed of as nonhazardous solid waste if they are hardened by adding an appropriate amount of catalyst. Refer to the Minnesota Pollution Control Agency’s Best Management Practices for Treating Waste Polyester-Resin and Gelcoat7 fact sheet for the requirements and proper procedures.

(05/01-75)