Accelerator

A substance that initiates or speeds a resin's curing reaction without being consumed in stoichiometric amounts. In the GRP trade the organic peroxide added to polyester resin, usually MEKP, is called the catalyst, although strictly it acts as an initiator.

A chemical added in small amounts to a reactive resin to delay the onset of cure, extending shelf life and working time and protecting against premature gelation in storage or transport. Adjusting inhibitor level is one of the ways manufacturers tune the gel time of polyester and vinyl ester resins.

The time taken for a mixed resin to change from a workable liquid to a soft gel that can no longer be applied or moved. It marks the practical end of the working period and is quoted by resin suppliers at a stated temperature and catalyst addition.

A thermosetting resin dissolved in a reactive monomer, usually styrene, that cures by free-radical polymerisation when initiated with an organic peroxide such as MEKP. It is the workhorse matrix for glass-reinforced plastic in boat building, GRP roofing, tanks and vehicle panels, offering low cost and straightforward processing.