The chemistry of the laminating resins used in surfboard construction is topic rich in polymer science, chemical catalysis, and photochemistry. My background in research chemistry enables me to view this topic through a highly scientific lens, and I wanted share some of it with you all. There have been a number of good threads/discussions. My background is in small molecule synthesis, which is quite different than polymer chemistry, but I’m doing my best to understand completely. If you guys have any questions you’d want to ask about the chemistry, I can look into them for you. I have access to the scientific literature. Also, FYI, patents are openly available online. It’s simply a matter of comprehending the material. It’s possible that numerous patents exist for resins.
First, there is the topic of catalysis. The laminating resin is either of the UV curing or MEKP cured. MEKP is methyl ethyl ketone peroxide. Peroxide oxygen-oxygne bonds are very weak, as most heteroatom bonds (other than carbon, i.e. sulfur-sulfur, chlorine-chlorine). Possible that the simple mechanical action of mixing the catalyst with resin causes the peroxide to react with a functional group present in the resin monomers. Slight heating observed (exotherm). This means the reaction is working. The MEKP is present in catalytic amounts – a very small equivalent sets off a chain reaction where the previously unreactive monomers become transformed into reactive intermediates. The monomers are set off and begin reacting with themselves. Most likely, the monomers (proprietary structures) have double bonds, and on homolytic cleavage of the oxygen oxygen bond, a single electron process is initiated. The double bonds break, new carbon-carbon single bonds form. Making carbon-carbon bonds is the holy grail of chemistry. You are now making a new material. And the catalyst isn’t even needed anymore! The radical species are propagating around and reacting very quickly. Typical liftetime of a radical species is on the order of 10^-14 sec. Look up the destruction of ozone, this is a famous radical reaction, which propagates through a single electron process. The key points here being that only a small amount of MEKP is required. The peroxide is highly reactive. Soon your liquid monomers will be something altogether very different. The rate that this occurs at (chemical kinetics), depends on the slowest (rate-limiting) step of the process. Also, rate increases with temperature and concentration–though technically we’re doing this “neat,” as highly concentrated as possible. It might be possible to run the polymerization in an inert solvent like benzene or toluene, or hexanes, but that would be just a curiousity and not useful for making surboards. The radicals do go away by the way, it is the last step of the process, when there are only two radicals left, they combine in a process called “termination.” Radical chemistry always goes through main three phases: initiation, propagation, and termination.
I suppose the curing occurs once this process has reached advanced progress – all the monomers have reacted and created a new, hard, gelled glass that is an entirely different chemical entity with much different (harder, water resistant, desired for surfing) material properties. It would be, if completely polymerized, technically one molecule. A very, very large molecule. Or it is also possible that it is an aggregation of several smaller oligomers/polymerizers each less rigorously, or at least differently, bound to each other than to their core units. Depends on the homogeniety of the process. Every board is going to be slightly different. It may or may not be noticeable. Reproducibility is a constant challenge in any scientific undertaking. Keep in mind no reaction ever goes to 100% completion. Some starting material is typically still there. Undesired byproducts usually form. Like I said, I’m not a polymer chemist– this is an approximation.
With UV cure, light is the catalyst. It is still a radical reaction, but you have initiators, like AIBN (classic chemistry example, azo-isobutryonitrile), that only form radicals in the presence of high energy (read, UV sunlight) radiation. Or heat will set them off, but typically that would be temperature from 30-60C. So no sunlight, no radicals, no polymerization. Add light, the photoinitiators rupture covalently into single electron species, and the process sets off on an otherwise identical pathway. I"m not sure why UV cure is so fast. It’s possible that the monomer structures are actually activated themselves by sunlight; in that case, I could imagine a faster process. I read in a thread here that to get the UV to kick that fast (5 min) you have to stir it up rigorously first. That would suggest there is a catalyst in the mixture that drives the process, since it would need to be evenly distributed. Chemicals like MEKP frequently go bad; they oxidize, they derivatize, they’re not really meant sit around. In the end, they just don’t seem to work as well as when you first cracked the bottle. Or maybe the batch is just bad. That happens. Remember the adage, “let it sit, goes to shit.” Store the MEKP in a dark cold place in the absence of water or oxygen (if possible). A freezer might work, one designated for storing chemicals, not in the same place as foods. Anyway, UV light is perennially “fresh,” and possibly a much more highly efficient catalyst in this context.
Some final thoughts on safety, you still would probably not want to get resin on your skin while it is curing. Definitely use heavy duty, latex gloves, and cotton/polypropylene protective coats/sleeves. Nomex is the ultimate in protective clothing material. The nitrile gloves will be useless. Consider that radicals can do some serious damage to DNA. That’s why we drink green tea. Because it contains anti-oxidants that scavenge free radicals. Damaged genetic material could lead to…well…serious health problems down the road. I would be most concerned about contact with skin/eyes/mouth directly. If you do get it on your skin, wash it off immediately with copious soap and water. The vapors are less concerning, more of a immediate problem. They will make you dizzy/high/nauseous. But daily exposure can lead to problems. Standard respirator fully advocated (for organic vapors). Also, don’t forget flammability! But just becuase something is dangerous doesn’t mean you shouldn’t do it. As long as you can run things safely, you won’t have any problems. Don’t be afraid of chemistry, just respect it.