Effect of organoclay and chain-transfer agent on molecular parameters and adhesion performance of emulsion pressure-sensitive adhesives

Organoclay-reinforced pressure-sensitive adhesives (PSAs) based on poly(butyl acrylate-co-vinyl acetate-co-acrylic acid) were prepared in the presence of an organically modified montmorillonite, that is, Cloisite15A (C15A), via in situ batch emulsion polymerization. The effect of C15A and chain transfer agent (CTA) level on the molecular parameters and adhesion properties of resulting reinforced PSA were investigated. Small-angle X-ray scattering (SAXS), gel permeation chromatography (GPC), transmission electron microscopy (TEM), dynamic mechanical thermal analysis (DMTA), and differential scanning calorimetry (DSC) were used to determine the characteristics of the neat and reinforced PSAs. The adhesion test results showed that the incorporation of C15A up to 1 wt% considerably increased the peel strength, shear and probe tack due to increasing the entanglement density of the PSA copolymer, while further increase lowered the peal and tack properties. Interestingly, the addition of 0.25 wt% CTA in the presence of 1 wt% C15A silicate layers resulted in PSA nanocomposite with the highest peal strength and probe tack. Although the CTA remarkably decreased the shear resistance of the neat PSA, the existence of C15A layers or tactoids in the reinforced PSAs decreased the rate of shear resistance decay due to the good interaction between the C15A and adhesive copolymer chains.