I have almost used my first batch of 3 gallons worth of resin. It has been a learning experience working with this much resin and trying to find a way to reduce waste. One problem is that the resin is sticky and a pain to clean. Spilling it not only is annoying but also costs me money. It is cheaper to buy it in bulk, but harder to work with too. My resin dispensing system that used garden sprayers was an okay solution and I think with some tweaks could be a viable option for others too. But one problem that I ran into was the resin will set up without being mixed.

After a couple of weeks I noticed that the top layer of resin in my garden sprayer had hardened. This was a big problem. If the resin could not be stored for very long it would make it difficult to work with. So I started looking at the data sheet for my resin. Smooth-On PMC-770 Datasheet

One interesting section states the following:

"IMPORTANT: Shelf life of product is reduced after opening. Remaining product should be used as soon as possible. Immediately replacing the lids on both containers after dispensing product will help prolong the shelf life of the unused product. XTEND-IT® Dry Gas Blanket (available from Smooth-On) will significantly prolong the shelf life of unused liquid urethane products"

This was quite encouraging because it meant that this was a common problem and documented solutions existed. The mention their product Xtend-It Dry Gas Blanket. So I decided to take a look at the datasheet for that.

Xtend-It Technical Bulletin

Xtend-It SDS

From the technical bulletin my best understanding is that the resin is reacting with moisture in the air. This product is a gas which is heavier than air and displaces the moist air and creates a barrier above the resin. For the average user dumping the resin from a 1 gallon bucket this product is just okay. But in my situation is is even better. Since I load my resin inside a keg and never let the air out, I could potentially use this product one time every time i fill the keg. My kegs can easily hold 4 gallons of resin with pleanty of headroom.

I decided to take a look at the SDS and it says that this product is >99% 1,1,1,2-tetrafluoroethane. I recognized this name from somewhere but could not place it. So I did a quick google search to find out this is common A/C refrigerant R134a. This is also used in some gas dusters (AKA canned air). What is nice about this is that it is quite easy to get this from an auto parts store. It also can be pumped into my keg through the gas in line. I put of this in with my resin when I filled the kegs. Now all I can do is wait and see.

One thing that came up was that fact that I am using this under pressure. The Xtend-It product is designed to be sprayed into a bucket for storing the resin. The fact that mine is under pressure posed a few good questions. First of these was will the R134a remain heavier than air while under pressure? Since R134a is used quite often there are some very helpful tools like this one:

Calculation of thermodynamic state variables of tetrafluorethane - R134a

You can put in the temperature and pressure and you get a page worth of details about it. One of these details is the density. I checked the range of pressures up to 130 PSI and found that R134a remains about 3 times as dense as compressed air. The second question was at what pressure does R134a become a liquid? It would probably be bad if the pressure in my keg caused the r134a to become a liquid and sit on top of the resin. One nice part of that online calculator is that it shows the state of aggregation of r134a. I choose a temperature of 65f and a baseline because I thought that was about as cold as I would ever let the tanks get. For this the r134a becomes a liquid between 75 - 80 psi. So as long as I keep my pressure under that I should be good. For now I am getting good results at 35 - 40 psi.

This raised an interesting question for me though. If the main issue is moisture in the air, can I solve this problem without the use of R134a at all. Could I use a moisture trap to remove the moisture from the air coming out of my compressor. Would it be possible to use something like this:

EWO Filter Water Separator

They claim 98%+ moisture removal. I have seen this type of filter / moisture trap sell for anywhere from $15 up to a few hundred. Anyone have experience with them? I was thinking that it wouldn't be a bad idea to use one of these to clean my compressed air anyway. Even if I continue to use the r134a.

Another option would be to use CO2. CO2 is what most people use to dispense beer in these kegs. So it would be quite easy to set up. But this would cost more than just filtering my compressed air. Another option would be to go all the way to nitrogen. But again I think this is over kill and more costly.

But it does pose an interesting experiment. Put a known amount of resin in a contain with each of these options and record how long until the resin hardens. Standard air, compressed air, filtered compressed air, CO2, nitrogen and r134a. Maybe that is a project for another day.