Influence of cellulose nanocrystal surface chemistry and dispersion quality on latex nanocomposite stability, film formation and adhesive properties

The different surface functional groups on carboxylated and sulfated cellulose nanocrystals (CNCs) affect the latex CNC–polymer interactions. Cellulose nanocrystals (CNCs) are sustainably sourced, non-toxic, high-strength nanoparticles most often derived from wood pulp. The incorporation of CNCs into latexes via in situ semi-batch emulsion polymerization has been shown to improve the performance of latex nanocomposites, specifically latex-based pressure sensitive adhesives (PSAs). A bench-scale study was designed to compare the effect of incorporating CNCs with different surface chemistries and dispersion quality on the final latex properties, film formation, and adhesive performance. Poly(butyl acrylate/methyl methacrylate)-CNC latex nanocomposites (at 40 wt% solids) were successfully synthesized with 1 wt% sulfated CNCs and carboxylated CNCs (DextraCel™) with different storage methods (never-dried suspension vs. dried powder). All CNCs were well-dispersed in water using probe sonication prior to being incorporated into the latex polymerization reactions. Extensive characterization revealed differences in the latex and PSA film properties, with never-dried carboxylated CNCs and dried sulfated CNCs having the highest viscosities, lowest relative colloidal stabilities by visual inspection, and most enhanced adhesive performance. Additionally, PSA films containing dried carboxylated CNCs exhibited the greatest latex particle coalescence, as measured by atomic force microscopy, which correlated to improved cohesive strength. The ability to tune latex properties with CNCs may facilitate the widespread use of “greener” water-based polymerization methods, even for applications outside of adhesives, such as paints, coatings, inks, toners and rubbers.