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The methacrylate are the one that have an elongation at break of 100%. The one at 6% or less are epoxies.
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You can tailor epoxy to just about any elongation you want. Some of Shell's 'starting formulations' for flexible adhesives showed 150-200% elongation at break. The 3M 2216 system has 120% and is an off-the-shelf system from a highly reputable company and available worldwide.
Methacrylates work well, especially for NEW rather than repair applications. They are still not as 'wet' as epoxy (judged from droplet contact angles) and are therefore more sensitive to contamination, less forgiving of surface prep and cleanliness. Bonding over surface contamination is an area where epoxy is very forgiving. Also in Shell's 'starting formulations' were adhesives for bonding oily metals that cannot be adequately cleaned. You certainly could not do this with methacrylate.
The methacrylates have cure curves that make them very attractive to manufacturers; they cure fully without any post curing. Also they can bond some difficult materials like UHMW polyethylene better than epoxy. I used 3Ms methacrylate to bond UMMW milled sail track onto the back of a carbon mast. However, I never fully trusted the stuff and so also potted in SS blind nuts and used #8 flush head screws. The data sheet from 3m said I could expect about 900psi lap shear on UHMW initially but that the bond strength would fall to only about 500psi in a couple of years. I probably could have just put screws at the ends and been done with it, but I went and screwed the entire length.
Methacrylate has not yet replaced epoxy, especially for DIY and repair applications, where dirts and mistakes are common.
Jimbo
06-03-2009, 02:55 AM
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