Mechanical reinforcement of waterborne latex pressure-sensitive adhesives with polymer-grafted nanoparticles

Waterborne pressure sensitive adhesives (PSAs) consisting of polymer microparticle emulsions (i.e. latex) are more commonly used in commercial applications than solvent-borne alternatives, as the use of water as a suspension medium provides better consumer safety and reduces environmental impact. However, the lower mechanical performance of waterborne PSAs prevents their use in applications requiring permanent adhesion or strong bonding between substrates. This reduction in mechanical strength is often attributed to void spaces that form during water evaporation and coalescence of the latex particles, and thus a potential strategy to improve PSA strength would be to add filler materials to occupy these voids. Fundamental studies investigating how interfacial interactions between the latex and fillers affect the collective strength of the films would enable better design of adhesive compositions to tailor PSA mechanical properties. Here we report the use of polymer brush-grafted nanoparticles (PGNPs) as a means of mechanically reinforcing the PSAs, and determine how different aspects of the particle and polymer brush designs enable this improvement in adhesive performance. The PGNPs investigated here are intentionally designed to phase segregate into the aqueous phase of the initial latex suspension, which allows them to both fill free pore volume and also form multivalent supramolecular interactions with the latex particles to form polymer bridges that improve the interconnectivity of the final film. These studies provide insight into potential design strategies for tuning PSA properties with PGNPs, and enable up to 32% improvements to the cohesive strength of the PSAs without the typical deterioration of adhesive strength observed in PSAs using non-brush-coated particle fillers.