Pressure sensitive adhesive (PSA) films were prepared from in situ semi‐batch emulsion polymerizations using isobutyl acrylate, n‐butyl acrylate, and methyl methacrylate in the presence of cellulose nanocrystals (CNCs). The CNCs at loadings of up to 1 wt% with respect to monomer resulted in significant and simultaneous improvement in tack, peel strength and shear strength for the PSA films. While most latex properties were unchanged, the CNCs also led to increased latex viscosity. A range of compositions were used to test the limits of the application. Microscopy was used to demonstrate that the CNCs were dispersed throughout the latex but outside of the polymer particles. Comparison to latex/CNC blends showed that the in situ technique provided higher shear strength PSA films. POLYM. COMPOS., 40:1365–1377, 2019. © 2018 Society of Plastics Engineers

Cellulose nanocrystals (CNCs) are safe, “green,” hydrophilic nanoparticles. CNCs are added in situ during a semibatch 2‐ethyl hexyl acrylate (EHA)/n‐butyl acrylate (BA)/methyl methacrylate (MMA) emulsion polymerization. As EHA is a more hydrophobic monomer, manipulation of the monomer feed composition allows for the evaluation of the effect of hydrophobicity on CNC distribution in the nanocomposite and ultimately on adhesive properties. The adhesive properties (loop tack, peel strength, and shear strength) of three different EHA/BA/MMA latex formulations are shown to simultaneously improve with increasing CNC loading. However, the hydrophobicity of the EHA leads to a nonuniform distribution of CNCs in the latex films. Comparison of the in situ polymerized nanocomposites to their blended counterparts is also made.

Front Cover: Cellulose nanocrystals (CNCs) have a profound effect on adhesive properties in emulsion based latex formulations. The CNC‐acrylic nanocomposite films show simultaneous improvement of tack, peel strength and shear strength – a result which resolves a well‐known challenge in adhesive production. Further details can be found in the article by Alexandra Ouzas, Elina Niinivaara, Emily D. Cranston, and Marc A. Dubé in article number https://doi.org/10.1002/mren.201700068.

Emulsion polymerized latex-based pressure-sensitive adhesives (PSAs) are more environmentally benign because they are synthesized in water but often underperform compared to their solution polymerized counterparts. Studies have shown a simultaneous improvement in the tack, and peel and shear strength of various acrylic PSAs upon the addition of cellulose nanocrystals (CNCs). This work uses atomic force microscopy (AFM) to examine the role of CNCs in (i) the coalescence of hydrophobic 2-ethyl hexyl acrylate/ n -butyl acrylate/methyl methacrylate (EHA/BA/MMA) latex films and (ii) as adhesion modifiers over multiple length scales. 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 favourably with the latex polymer and are uniformly dispersed throughout the adhesive film. This article is part of the theme issue ‘Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)’.

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