How latex film formation and adhesion at the nanoscale correlate to performance of pressure sensitive adhesives with cellulose nanocrystals

EHA/BA/MMA. Thin films with varying solids content and CNC loading were prepared by spin coating. AFM revealed that CNCs lowered the solids content threshold for latex particle coalescence during film formation.

This improved the cohesive strength of the films, which was directly reflected in the increased shear strength of the EHA/BA/MMA PSAs with increasing CNC loading. Colloidal probe AFM indicated that the nano-adhesion of thicker continuous latex films increased with CNC loading when measured over small contact areas where the effect of surface roughness was negligible. Conversely, the beneficial effects of the CNCs on macroscopic PSA tack and peel strength were outweighed by the effects of increased surface roughness with increasing CNC loading over larger surface areas.

This highlights that CNCs can improve both cohesive and adhesive PSA properties, however, the effects are most pronounced when the CNCs interact favorably with the latex polymer and are uniformly dispersed throughout the adhesive film.

Methods

MFP-3D Atomic Force Microscope (Asylum Research – Oxford Instruments, Santa Barbara, CA, USA) Igor Pro 6.0 running Asylum Research AFM software (version 13.17)