Latex-Based Pressure Sensitive Adhesives with Unmodified vs. Polymer-Grafted Cellulose Nanocrystals

Meeting the requirements for “green” materials, cellulose nanocrystals (CNCs) have been demonstrated as good additives and stabilizers in emulsions, however their exact role is not always clear. Our work on miniemulsion, microsuspension, and seeded semi-batch emulsion polymerization has demonstrated that polymer latex properties (e.g. size, surface charge, surface roughness, polymer degree of polymerization) can be highly tuned through the incorporation of CNCs. Most notably, the addition of CNCs always improves all performance metrics in latex-based pressure sensitive adhesives (PSAs). This is uncommon given that additives that increase adhesive properties normally decrease cohesive properties and vice versa. We have investigated nano-scale adhesive properties and their link to macroscopic tack, peel and shear strength to elucidate how CNCs act as “anchor points” for polymer entanglement, improve wettability and latex film coalescence, and form percolated networks throughout PSA films. Most recently, we have studied the effect of CNC surface chemistry (sulfated vs. carboxylated) as well as polymer-modified CNCs on PSA properties – the trends are not straightforward as changing the CNC surface affects aggregation/dispersibility, colloidal stability, the location of CNCs in the latex, and the tendency for coagulation to occur during polymerization. This talk will explain the main conclusions across a series of papers on CNCs in latex-based PSAs and recommendations for when/if to modify CNC surface chemistry. While the focus is on latex-based PSAs we believe the work is translatable to a range of latex products including paints, coatings, inks, toners and rubbers.