Who knows the Science of Polyester Resin and temperatures

[ShoreFun]

I have done some poking around the web looking for specific information. All I find is what people have done and thought it was ok.

I like to know how stuff works so I can make decisions based from facts. I have a physics background and sort of know chemistry, but not well.

My perspective, I am fixing up some Sunfish so we are not talking ocean going it has to be perfect. I am using polyester resin that I bought from the local glass supplier that all the local yards use. So it is the industrial quality, not consumer if there is any difference.

What happens to the resin when exposed to cold?

Does it stop curing or does it continue reactions once it gets above the proper temperature?

What processes are happening with the resin?
My basic intuition says it has solvents that vent and chemical reactions that form long string polymers (am I saying that right?).

I live in southern NJ and coming into temps that will be 50's to 60's during the day and dropping to high 30's to mid 40's at night.

I need to do some small patches under 6" round and a larger repair like 8" by 10" rebuilding a broken area.


Thanks!!

[coopec43]

I've done a lot of fiber glassing and my rules are to never f/g in direct sun, never when it it is humid and never when it is too cold. As far as I'm concerned it takes about a week (depending on conditons to fully cure)


What temperature does resin cure?
One of the most important factors to ensure your epoxy resin cures properly is temperature: the ideal temperature for both your ArtResin and your workspace is slightly warmer than room temperature: 75-85F or 24-30C.2 Apr 2020


https://www.google.com/search?q=What...w=1024&bih=626


















Can you cure resin in the oven?

[mike d.]

If you are able to use heat lamps, you can fiberglass/epoxy at, at least down to 15 to 20 degrees F! Been there done that ! I did my work next to the house, so that would be your only consideration, unless you had 24/7 power available where the work was being done ! The thing about cooler/colder temps is gives you more work time ! Also I would/have used non waxed resin only until final coat !

[Benz]

Cold temps slow the cure of polyester resin, but don't stop it. Worst that can happen is the resin will drip out of the glass before it gets a chance to gel over and you'll have dry spots. You can mix it hot (more catalyst) up to a certain point, but certainly not more than half again as much.
If you do your work while its 50, it'll be cured enough in an hour to not drip out even if things get cold.
Cooper, you can cure resin in an oven--most epoxy boats are post-cured in a giant oven (usually something makeshift made out of 4x8 insulation panels), and pre-preg epoxy requires baking to get the resin to flow and set.

[coopec43]

I tried to fix my previous post in regard to my reference to epoxy resin but the Administrator wouldn't allow me.

[Chotu]

So the catalyst (MEKp) encourages the polyester resin to polymerize. Heat helps all resins polymerize. That’s why they’re called thermoset resins. The more MEKp (up to a point), the hotter the batch is as it’s going off. Very desirable in the cold, not as desirable if it’s 90 degrees out and you need some working time.

Your intuition is correct. The resin just slows it’s cute when cold. Then will go again when warm.

It’s an art. A learned skill. You just have to try the various percentages of MEKp and see what you get for curing speed and temperatures.

In your case it’s really cold so I’d just start with the maximum MEKp percentage allowed by the resin manufacturer.

BenZ has it right (as usual) and it’ll probably go off at the warmest part of the day enough to stay put. But... it will be a very, very slow process on cold temperatures, so boosting it with a heater will certainly help.

Since it’s just a Sunfish, maybe you can do the work in a warm garage and vent out the styrene fumes?

In any case, protect everyone’s lungs and eyes from the styrene (the solvent).

[boatpoker]

Look up the terms Isopthalic resin, orthopthalic resin, waxed resin and unwaxed resin. Once you understand these four terms you'll be good to go with the proper polyester resin for any given marine job.

[rbk]

I’ll just add a few items to the above. Ensure you have unwaxed resin for the build up and waxed for the final ‘gel’ coat. Second is do not in any way allow it to get wet before it’s cured. Lastly, only add extra catalyst as a last resort, try every way to control the temp first, if you can’t, only then adjust the mixture.

[Spot]

Did the supplier provide technical and safety data sheets for the resin? I try to work at 'lab temp' 72 to 75 F (22-25 C) whenever possible.

[Wind River]

I glassed my decks with Vinyl Ester resin intentionally when the temp was below 55 degrees. I was wetting out huge roll's of glass by myself. 52 inches wide x 13 feet in several cases. The only way to get the entire layer wet out was to slow or stop the catalyzation. This low temperature allowed me to work with multiple 3 quart batches for over an hour before it would even slightly gel. If the temperature dropped to 50 degrees or below, the resin would still be just slightly gelled after sitting all night. As soon as it warmed to about 60 degrees it would kick off.
I did confirm with the resin manufacturer that this will not cause any issues with the cure.

[ShoreFun]

Just a bit more.

I have garages, but they are kind of filled up and unheated. I have a couple of antique cars. Though I might make some room in the unpowered back garage.

I am aware of the toxic nature of the vapors and have been working outside with the resin. I could suit up and I even have a pressure fed hood from doing auto paint work. But that is too much work for these small jobs I need to do.

One of my learning tasks is how to get the repair over larger area below grade so I can lay in the gelcoat. I am learning as I go. I am used to making accurate patches in metal and then TIG welding them in place. Then I do finish work in the metal and only ever need a few coats of building primer to level. I mostly use a thin filler to cover some rust pitted areas.

These are just simple and really fun Sunfish. So I am forgoing making them perfect and working for nice looking and functional.

My belief is I need to get the resin cured enough to be hard before letting them get cool. I have to worry about condensation here where I live from temp changes and moisture is bad until cured enough is what I take out of various sources. So I believe I can get away with Halogen painting lamps to keep the temp up for a few hours. Then maybe expose the area to some sun for a few days.

This is the resin I have. https://www.aoc-resins.com/pdf/web_H596.pdf

[jack630]

Hi ShoreFun,

To be clear, we're talking polyester, not epoxy. Two different chemical reactions.

Most conventional polyester resin systems are composed of short chain polyester polymers dissolved in a reactive solvent. The "solvent" in the conventional polyester system is actually styrene monomer which produces the strong odor of the resin. The polyester resin is cured through a radical reaction that is initiated with a peroxide such as MEKP. When the peroxide is added to the polyester resin it decomposes to radical initiators that initiates the polymerization. The styrene co-polymerizes with the polyester molecules tying everything together producing the rigid polymer.

The rate of polymerization is governed by temperature so the lower the temperature the slower the reaction. However, there is a competing reaction. That is the reaction of oxygen with the radical initiator and propagating chain ends. The reaction of the radical with oxygen terminates the reaction. If too much of this occurs, then you end up with an incomplete cure, technically called, a gooey mess. So you want the polymerization to run at a reasonable rate before the oxygen can screw it up. Several things can be done to mitigate the oxygen termination reaction, mainly by preventing oxygen from getting to the polymerizing reaction. Some resins put a wax into the resin that blooms to the surface and slows oxygen from diffusing in and the other is to put a film on the surface such as Saran Wrap on the surface to prevent oxygen from getting in. Also, running the reaction at a higher rate helps but you may still get a soft surface. I would recommend running a couple of trials under your conditions to ensure that you have the conditions right.

Polyester resin technology is an old technology that has evolved over time. Wikipedia has a decent description of the developments. The best polyester resin, in terms of mechanical and chemical properties is the vinyl ester resins.

[Squanderbucks]

Here in South Florida not working with fiberglass with polyester, vinylester or epoxy without being in direct sunlight is pretty hard when you are repairing boats in the boatyard.

If it is cool the resin will cure slower. If it is cold it won't cure either at all or poorly depending on how long the cold is maintained before heating up. If only for a short window it may cure ok. but if delayed too long it may never fully cure or get it's best physical properties. To answer you question directly - if applied in a cold environment merely later putting it in a warm environment will not necessarily work. there is a finite lifespan to the catalyst and if can't fully react during that time the applying heat later will not work to compensate. In the winter in Northern latitudes it requires indoor work where spaces can be heated safely.

If 50F or above you may be able to get by with additional catalyst and or heat lamps for polyester and vinylester (not epoxy). But most don't try until the temp is above 60F - even then use a little extra catalyst and/or heatlamps.

As far as the opposite temp range - over 90F it is necessary to use smaller batches and/or reduced catalyst. If the boat is in full sunlight it may be needed to provide shade by tarps or other ventilated structures.

Also to be considered is the layup thickness of the fiberglass/resin to be worked with - the thicker it is then the internal heat of the material will accelerate the process. NOt unusual to see pots of resin start to "kick off" early and smoke and crack right in the pot. Resins mixed "too hot" will also have lesser physical properties and increased shrinkage and cracking.

The recommended ratios of resin to hardener is just a starting point and can be applied for "normal" temp ranges and project sizes but often needs modification only based on accounting for all the variables and experience.

[nortonscove]

I've not given much thought to the chemistry but my preference is the glass in cool conditions for better control. Seems any extreme will cause changes in the amount of hardener required.

[nortonscove]

I've not seen this being an issue. Worked for years in an unheated shed and found no difference other than adjusting the amount of catalyst. Always found heat to be more of an issue especially on days with warm wind. Kicked so fast that it was tricky getting things right. My thinking is that you need to speak to people with experience in your region.