Another vinylester vs epoxy thread.

I have been using epoxy and polyester resins for more than 50 years, vinylester for probably 20 years.
Like most people i have generally assumed epoxy to be stronger than polyester with vinylester somewhere in between. I don't think i have used polyester since i discovered vinylester so i tend to pick a resin based on the project at hand, always epoxy when working with wood or secondary bonding composites but whenever building composite parts my go to is usually VE (unless smell is an issue) Recently i was on a forum with a discussion on epoxy vs vinylester. Unfortunately i have not been able to find my way back to that thread but the gist is that when i pointed out that vinylester was not a poor second choice to epoxy for the OP as the VE that i use has much higher physical properties than the common boatbuilding epoxies we use, people were saying that epoxies are stronger when post cured and that epoxies keep getting stronger. If i could remember where that thread was i would like to ask where i can find out about epoxies getting stronger over time, this is not something i had heard before but i heard someone else claim this in a you tube video again last week. I know that when using epoxies you can unclamp and work with it the next day but it does continue to cure for another week before it reaches it full cure. But i have not seen any claims from manufacturers that it continues to get stronger beyond that. Regarding post curing it seems that if you follow the manufacturers post curing schedule you should get an increase of 10 - 20% in physical properties. So if i were to post cure a laminate done with, for example, West 105/205 epoxy (which is the strongest combination) i would still fall well short of the tensile strength of the CORVE 8101 vinylester resin i use. This is an infusion resin but the VE we use for hand layup has similar properties. Of course most of us are not post curing except for specific highly loaded items. Anyone know if post curing VE yields similar results?

 

You’re correct. Epoxy continues to cure over time, but beyond the manufacturer’s recommended cure schedule, strength gains are modest. Post-curing at elevated temperatures can increase properties by 10–20%. Vinylester generally reaches near-full properties at room temperature, and post-curing provides smaller gains compared to epoxy. High-performance VE, like CORVE 8101, can exceed common boatbuilding epoxies in tensile strength even with epoxy post-cure. For most applications, VE is a strong choice, while epoxy’s post-curing benefits are mainly relevant for critical, highly loaded components.

 

Thanks for the reply. I assume that the information on the TDS is for fully cured resin, regardless of type. West epoxy 105/205 is about 7900 psi so after post curing and with a 20% improvement, at 9480psi it still falls 25% short of the 11800 psi of room temp cured VE, (CORVE8101) Thats huge. For me the most important specs are tensile strength, tensile elongation and viscosity and the ability to move the project along, so short cure times. Where i use epoxy is for secondary bonding and where smell matters, ie, working in the basement. Epoxy is certainly more versatile but for laminating composite parts VE is the go to.