Laboratory studies into how glass-reinforced plastic (GRP) vat surfaces can be repaired without causing migration of styrene into foodstuffs

Glass–fiber-reinforced plastic (GRP) vats are used widely for the storage of foodstuffs and potable water. As the inner surfaces deteriorate during decades of use, they need to be repaired. The unsaturated polyester resins that are used for recoating are crosslinked with styrene which can cause taint and odor problems. This article describes some coating parameters that affect the content of residual styrene and its subsequent migration. The influences of cure temperature and duration, along with the effect of washing with warm detergent solution, were investigated. Cured specimens were tested for their residual styrene content and for styrene migration into the food simulants, distilled water, 3% acetic acid, and 15% ethanol. The dominant factor in reducing the amount of residual styrene is the temperature. The resin self-heats as it cures, typically up to 50°C. Thus, any further lowering of the styrene content requires a higher cure temperature than this. A 3-h cure at 80°C reduced both the residual content and the migration levels by about 100-fold. At lower cure temperatures, the heating effect of washing at 60°C is more important than the washing effect of the detergent. When less catalyst was used the residual styrene levels rose dramatically, from 70 to 360 to 1300 mg/kg for the normal dose, half and quarter the normal dose, respectively. There was a linear relationship between residual content in the GRP and the migration levels. This correlation could be used for monitoring the quality of vats repaired in situ, using styrene-based coating resins.