Re: Polyester,+ Epoxy Age questions
I read all the time about using
Fresh poly resins,...
How old is Too Old,..??
What does poly do, or not do when it ages,..??
I also read Epoxy ages much slower,+ generally less overall,...
So,...
Same questions about Epoxy, as the questions above about Poly resin,..??
Btw,... Stored in the can, in a stabil environment, no freezin'...
Thanks guys,.....
When resin is made the ingredients are cooked at a specific temperature for a specific amount of time. As the resin cooks it starts to crosslink, at the right time inhibitors are added to stop the crosslink process. If allowed to cool the resin would appear to be a solid at room temperature, so styrene is added to thin it to a viscosity that will work for the intended use. Silica is added to stop it from sagging and draining out of the glass.
This was the short version of the story, its much more involved than this, but you get the idea.
Short term, polyester resin will typically get thinner (lower viscosity) and the gel time will become longer. This is because the silica used to thicken it starts to lose its effect on the resin, the gel time will lengthen as the inhibitors become a little more effective and the promoters become weaker.
As the resin ages for a longer period of time the inhibitors start to get used up and the crosslinking begins again. As this happens it will become thicker and lumpy, possibly with hard chunks. While it will eventually become hard, it isn't fully cured, so it will be very weak.
Typical resins have a shelf life of about three months, but not every type does, some will be shorter and some longer. Unpromoted resins will last much longer, but before use you need to add the promoters, common ones are cobalt and DMA.
When catalyst is added it first needs to overcome the inhibitors and then restart the crosslink process, too little or too much catalyst will result in an incomplete cure and a weak laminate.
Styrene will crosslink with the resin and help it cure to a certain point, too much or too little styrene will result in a weak resin though.
Epoxy will typically last longer, but both products will become less reactive over time, as this happens the physical properties of the resins are reduced.
Remember, this is the short version of what takes place.
