Effect of thermal processing on the integrity of polyurea microcapsules for underwater adhesives

Adhesives that rely on a curing mechanism struggle to function in underwater environments due to detrimental interactions with water. One strategy to overcome this involves protecting sensitive components in mechanically responsive microcapsules. In this way, a two-part adhesive can be achieved via a single mixture, applied as one would apply a pressure sensitive adhesive. This work focused on improving polyurea microcapsule shell integrity, specifically focusing on the effect of additional thermal processing. The improved microcapsule shells displayed limited payload leakage with only an 8 % loss in pot life compared to the base isocyanate resin alone. A mixture of optimized microcapsules and isocyanate resin was evaluated against a wide range of substrates and conditions, including dry and wet environments. When microcapsules were intentionally ruptured to release the catalyst and crosslinker payload, the microcapsule-isocyanate mixture had improved adhesive strength (506 %) compared to the base isocyanate resin without microcapsules.