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Open-molding study gives tips on cutting styrene emissions.

Do you know the most effective ways to cut styrene emissions from open molds? Elements of material formulation, work practices, gun set-up, and spraying technique that can have the most immediate impact are prescribed in a new report from the Composites Fabricators Association (CFA), McLean, Va. The report gives conclusions of Phase I of its baseline study of factors affecting styrene emissions from hand lay-up, gel coating, and spray-up.

The CFA-sponsored study was conducted at the Freeport, Texas, laboratories of Dow Plastics. Preliminary results for hand lay-up were released last year (see PT, Jan. '96, p. 25).


The study used a male mold of 37 sq ft surface area, an orthophthalic resin, a standard gel coat, and air-assist/airless spray equipment. In all three open-mold processes, styrene content was a major factor affecting emissions. Laminate or gel coat thickness, gel time, and resin flow rate also affected emissions to varying degrees. Air-flow rate over the mold turned out to be an insignificant factor in all cases (see accompanying pie charts).

For all three processes, the lowest styrene emissions were obtained with a combination of a thick laminate or gel coat plus low styrene content and fast gel time.

Phase I results indicate that real-world emissions levels are higher than EPA estimates contained in the agency's 1988 document AP-42 (Compilation of Air Pollutant Factors). However, CFA says that substantial reductions in emissions are achievable through relatively minor changes in resin or gel coat formulation and refinements in application techniques.


CFA's study indicates that reduction of overspray through optimized spray-gun set-up and controlled spraying technique can reduce gel coat emissions by 25-36% and spray-up emissions by 13-30%. These bring the emissions within the range of EPA AP-42 estimates.

CFA recommends containing over-spray, minimizing spray-gun distance from the mold, and spraying perpendicular to the mold surface. Helpful hints for achieving clean spray technique include these:

* Spray tips should be sized for the application - i.e., in order to allow spraying as close to the mold as possible.

* The spray gun should be adjusted to the lowest possible tip pressure that gives an acceptable fan pattern.

* Operator training in proper spray techniques is critical to emissions reduction.

* A wide flange on molds is recommended to help capture overspray.


Phase II of the baseline study, which is to be concluded in this first quarter, focuses on quantifying the effectiveness of various emissions-reduction techniques such as styrene suppressants, filled systems, and alternative application equipment. The study also explores the effects of molding a large female part.

CFA is also developing a model that will allow processors to calculate styrene emissions at their facilities, based on the particular techniques they are actually using.

For a copy of a report on Phase I of the baseline study, you can call CFA at (703) 610-9025.

Three Important Techniques for Reducing Styrene Emissions:

1 Contain overspray as close to the perimeter of the mold as possible.

2 Minimize spray-gun distance from the mold (12-18 in. in most cases).

3 Keep the fan pattern as close to perpendicular to the mold surface as possible.
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Copyright 1997, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:Composites Fabricators Association research
Author:De Gaspari, John
Publication:Plastics Technology
Date:Jan 1, 1997
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