Crosslinkable latex-based acrylic adhesives containing functionalized cellulose nanocrystals (fCNCs)

In this study, crosslinkable acrylic adhesives with functionalized cellulose nanocrystal (fCNCs) were prepared via in situ emulsion polymerization at 80 °C for 3h. The neat acrylic pressure sensitive adhesives (PSAs) without any nanoparticles were prepared using butyl acrylate (BA), 65 wt%, and methyl methacrylate (MMA), 35 wt%, and various amounts of 2-hydroxyethyl methacrylate (HEMA), 1, 3, 5, 7 wt% based on total BA and MMA monomers. For preparing fCNCs reinforced adhesives, the cellulose nanocrystals (CNCs) were functionalized using various concentrations of 3-methacryloxypropyl trimethoxy silane (MPS), 5, 20, 40 mM. The cellulose nanocrystals (CNCs), functionalized cellulose nanocrystals (fCNCs), and the prepared adhesives were characterized by Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). The Adhesion performance of the adhesives was evaluated by lap shear and 180° peel tests. The results showed that increasing the HEMA content as crosslinking agent in the adhesive structure, enhanced its gel content, glass transition temperature (Tg), thermal stability, and adhesive performance, i.e. lap shear and peel strength. Finally, the adhesive containing 5 wt% HEMA was selected as the appropriate sample. Thereafter, the adhesives containing 5 wt% HEMA were synthesized in the presence of various amounts of fCNCs, i.e. 0.5, 1, 1.5 wt%. The Adhesion performance of the neat and reinforced adhesives indicated that increasing the fCNCs to the adhesive enhanced thermal stability, gel content, lap shear and peel strength. Additionally, the fCNCs prepared using higher concentration of MPS (40 mM) was more effective on the adhesion performance than the fCNCs prepared with the lower MPS contents, 5, 20 mM. The results showed that the adhesives prepared using 1 wt% and 1.5 wt% of fCNC40 (containing 40 mM MPS) exhibited better adhesion performance.