Polymer emulsions used in pressure-sensitive adhesives (PSAs) often have relatively simple particle structures, with surfactants and ionized or polar side chains on the particle surface surrounding a hydrophobic core. These particles coalesce to form the PSA film during drying, but boundary layers of hydrophilic components remain. These boundary layers are thought to compromise the performance of waterborne PSAs relative to solvent-borne PSAs, which have more uninterrupted film structures.
In this work, an alternative particle architecture was investigated for enhanced PSA properties. A pre-strained interpenetrating network was designed into each particle through a multistage polymerization process. Based on prior work, such a network was expected to favor polymer chain scission upon mechanical deformation of the film, leading to higher stress at break and higher observed peel force. The PSA properties and polymer rheology of films made from these designed polymer particles were investigated to identify opportunities to improve the adhesion/cohesion balance of waterborne PSAs.