Baltimore, Maryland – Scientists at Johns Hopkins University’s applied physics laboratory have developed a way to use microcapsules to speed up the cure time of PU adhesives under water. Cure time is a particular problem in maritime applications, they said.
Interstitial water is a problem for glues, and most work best on pretreated surfaces. However, in an underwater environment, both make the gluing process difficult.
‘You can imagine, in a marine environment, how needing 24 hours to cure and hold at full strength could be an issue,’ said Reid Messersmith, the chemist who led the research. ‘So, we made it strong and fast. From 24 hours to one minute was our speed increase, and if you can actually let it sit for 24 hours, it’ll hold at 10 times the strength.’
While adding a tertiary amine catalyst and a polyol crosslinker to the isocyanate resin allowed it to hold immediately, they found this did not work in practice because a time lag is required between application and the start of the cure to allow for repositioning.
The answer lay in containing the catalyst and crosslinker within a microcapsule, which are added to an isocyanate resin. Although the microcapsules remain intact on storage and with gentle mixing, applying a small shear force breaks the shell. As soon as the contents leak out, the glue cures instantly, even under water.
It worked effectively on surfaces including aluminium, stainless steel, glass and plastic. It gave a bonding strength of about nearly 3MPa in 60 seconds on untreated aluminium surfaces.
The team speculates that it has many potential applications, both in and out of the water. These could include boat repairs and reattaching shingles to houses.
The work has been published in the journal ACS Applied Polymer Materials.