Pushing the Limits with Cellulose Nanocrystal Loadings in Latex-Based Pressure-Sensitive Adhesive Nanocomposites

Cellulose nanocrystals (CNCs) are a naturally sourced, nontoxic, nanoparticle known to improve tack, peel strength, and shear resistance simultaneously when incorporated into nanocomposite latexes produced for pressure-sensitive adhesive (PSA) applications. In this study, methods for incorporating CNCs into a butyl acrylate/styrene/acrylic acid (91.5/4.5/4.0 wt%) seeded semibatch emulsion polymerization for the production of PSAs are presented. Past work has revealed a limit of 1.0-2.0 wt% (based on monomer) CNC loadings due to latex instability. In this work, CNC loadings of up to 4.0 wt% in a stable latex with 40 wt% solids are achieved by utilizing all of the available water in the formulation to maximize CNC redispersion. The CNC addition method is studied (i.e., in the seed, in the feed, or partitioned in both) and adhesive performance results indicate that there are no significant benefits to where the CNCs are dispersed in situ during polymerization. However, the quality of the CNC-water dispersion is pivotal to ensuring latex homogeneity and therefore, adhesive film quality. Though CNCs improved adhesive strength at low concentrations, their enhancing effects are modest when used with a commercially competitive base-case PSA formulation.