The effect of spraying and rolling process factors on styrene emission during the application of unsaturated polyester resins

In the recent years the awareness of the problems caused by the styrene emission during the processing of unsaturated polyester resins has enlarged. The spray-up application of gel coats is especially problematic and it produces high styrene emission rates. The emission of styrene has been reduced through material changes, work practice controls and add-on controls. However, the influence of the spray-up process factors on the styrene emission has not been studied before. The aim of this study was to examine possibilities to reduce the styrene emission by optimization of the spray-up process factors. The following factors were studied under controlled laboratory conditions: orifice size and angle of the spray gun tip, spraying pressure, distance between spray gun and mold as well as the shape of the mold. The influence of the rolling pattern during the lamination was also studied. Several significant factors were found: High pressure and long spraying distance increased both the unit styrene emission and the emission rate. The orifice size had two effects; a large orifice decreased the amount of styrene emitted per sprayed amount of resin but increased the emission rate of styrene. The shape of the mold did not affect the styrene emission. The styrene emission is greater if the entire mold area is rolled. To achieve lower emission is it necessary to roll an area as small as possible, this is especially important if a large mold is laminated. The results showed that emission of styrene can be reduced significantly by a optimal selection of the spray gun settings and the way of working. Optimal settings also increased the transfer efficiency resulting in decreased material loss.