Materials

Microcapsule additive allows underwater glues to set in one minute

Microcapsule additive allows u...
Each polyurea microcapsule contains a liquid catalyst and crosslinker
Each polyurea microcapsule contains a liquid catalyst and crosslinker
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Each polyurea microcapsule contains a liquid catalyst and crosslinker
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Each polyurea microcapsule contains a liquid catalyst and crosslinker

Although there are glues that can be applied to underwater objects, they typically require at least 24 hours to set – which can be tricky in chaotic marine environments. A new additive, however, reportedly allows underwater resin adhesives to set in just 60 seconds.

Developed by scientists at Maryland's Johns Hopkins Applied Physics Laboratory, the material takes the form of a white powder that is mixed into a base isocyanate resin. That powder is made up of tiny polyurea capsules, each one containing a tertiary amine catalyst liquid that causes the resin to set quickly, along with a polyol crosslinker that ensures a strong hold.

When the resin/microcapsule glue is initially applied to an underwater surface, the capsules remain intact, so nothing happens. Once the user has everything lined up and in place, they apply pressure to the glue – this can be done just by rubbing it between their fingers, or by pressing the objects together with the glue in between. Doing so causes the outer shells of the microcapsules to rupture, in turn causing the catalyst and crosslinker to be released into the resin.

As a result, the resin sets in just one minute. In lab tests, it achieved a 400-lb (181-kg) bonding strength on untreated aluminum surfaces within 60 seconds of being pressed. That said, the glue reportedly achieves a bonding strength 10 times stronger within 24 hours, if the bonded underwater items are able to sit in place for that long.

"Having a pressure-activated, high-strength adhesive that works in minutes has myriad potential applications," says the project manager, Chris Hoffman. "Our adhesive works great both in and out of water, so you can imagine using it to repair your boat or reattach shingles. The ease with which our microcapsules can be applied to an existing glue is a significant added bonus."

A paper on the research was recently published in the journal Applied Polymer Materials.

Source: Johns Hopkins Applied Physics Laboratory

1 comment
Baker Steve
Strange then that an idea as old as micro-encapsulation hasn't been applies to conventional two-part adhesives, such as epoxies.