With open systems like spray-up laminating, the mixing of organic peroxide with a resin could happen with impingement of the peroxide into a stream of resin. If the stream of peroxide is not set correctly, it may not thoroughly mix into the stream of resin and cause hot spots on the part as well as expose workers to overspray containing raw peroxide. This is especially critical if the liquid OP is used in a heavily filled or highly viscous UPR.
In batch mixing of UPR with OP, as is done in pultrusion and cured-in-place pipe (CIPP), the most reactive organic peroxides used have decomposition temperatures near or below that of ambient/ room temperature. Quick and thorough incorporation of the organic peroxide into the UPR requires a mixing vortex to stop the possibility of having a decomposing liquid sit on the surface of a resin batch. The decomposition products of organic peroxides can be flammable and, in the presence of a source of ignition, can have major consequences.
The use of some OPs that are solids at room temperature requires a special step of dissolving the OP before addition to the UPR. There are two major products used in pultrusion and CIPP that fit this category. During the dissolving process, the reaction of the OP begins immediately. The peroxide, di-(4-tertbutylcyclohexyl) peroxydicarbonate (commonly known as Perkadox 16) reacts in styrene at 32 F (0 C). At 68 F (20 C) the reaction is faster and the styrene starts to rapidly turn into polystyrene as the mixture is held at this temperature. If allowed to sit for over an hour, there may be full polymerization resulting in a great amount of heat and smoke generation.
The final note in finding the best mixing techniques is simply this: Ask if you are unsure of what is a good practice. Consult the material safety data sheets, and look for support from suppliers to achieve the best results.
The guest columnist for this issue’s “Best Practices” column is Anthony Bennett,
technical development manager of thermoset products for AkzoNobel Polymer Chemicals, Organic Peroxides sBU. Email comments to firstname.lastname@example.org.