Post
by Ibrew2be » Sat Dec 05, 2015 6:38 pm
I worked in the polyester resin industry as a university student more years ago than I care to count, and well remember the use of wax in resin formulations.
Wax is used as an "air dry" additive in laminating resins, the resins used with glass fiber to go on over top of the gel coat to build up the structure of the hull. Polyester resins cure via a chemical reaction known as a free radical reaction. (The "catalyst" which is added to polyester resin is usually an organic peroxide such as MEKP, methyl ethyl ketone peroxide, which generates free radicals when added to the resin and thus commences the reaction which leads to the resin gelling and curing.)
The oxygen in air stabilizes free radicals which makes them less reacitve and thereby inhibits the gelling and curing of the resin at the air/resin interface, and can leave the surface sticky for an unmanageably long period of time. The wax provides a barrier between the air and the curing resin, allowing the reaction to go to completion, and hence no stickiness. Wax is added to laminating resins only. Resins such as gelcoat, for example, do not use wax, because you want the laminating resin to be able to bond to the gelcoat.
Similarly, the resins manufactured for use in "car patch" (generic term) compounds also do not have wax added. If wax were used, it would interfere with bonding of one layer of car patch compound with the next, in situations where multiple layers are needed.
Polyester resin will harden on its own over time because the cross linking agent, styrene, is in the resin formulation from the beginning. Styrene functions not just as a cross linker, but also as a viscosity reducer, to get the resin into a viscosity range where it can be sprayed or brushed. Polyester resins of all types are formulated with "inhibitors", which function as free radical scavengers, to slow down the inevitable and give the polyester resin an acceptable shelf life.
Barry Shantz
Imp built and launched. Thinking hard about Boat 2.0