Self-Cross-Linking Latex Pressure-Sensitive Adhesives: Preparation and Investigation on Adhesion, Linear Viscoelastic, and Nonlinear Large-Strain Properties

The ability to design environmentally friendly latex pressure-sensitive adhesives (PSAs) with suitable adhesion performance with guaranteed removability without the need for an external cross-linking agent during the film formation process is highly desirable from a practical point of view. A series of self-cross-linking latex nanoparticles were synthesized using emulsion copolymerization of butyl acrylate and different low contents of methacryloxypropyltrimethoxysilane as a self-cross-linking monomer (SCM). The presence of SCM in the polymer chain enabled chemical cross-linking during polymerization within the polymer droplets and also during the film formation process between adjacent polymer nanoparticles. The results of the adhesion tests revealed that the addition of even an extremely low amount of SCM, 0.01 or 0.025 wt %, besides guaranteeing the removability and maintaining a high tack (23.4 N), leads to a significant improvement in the creep resistance of the resulting PSAs. Accordingly, the shear holding time increased from 77 min for poly(butyl acrylate) to 324 and 1248 h for the PSAs containing 0.01 and 0.025 wt % SCM. The rheological studies revealed that the addition of SCM affects the linear viscoelastic properties mainly at low frequencies, and its effect diminishes at high frequencies. However, the addition of SCM essentially affects the adhesion properties by controlling the nonlinear large-strain properties and, as a result, the maximum fibril deformation before debonding. The trend of changes in the calculated peel energy, by considering the strain corresponding to the onset of strain hardening as a debonding criterion and using the nonlinear large-strain data, was in relatively good qualitative and quantitative agreement with the experimental results. In addition to exhibiting proper adhesion, the synthesized PSAs had high transparency, which makes them suitable candidates for use in optics applications.