Adhesive properties of acrylate copolymers: Effect of the nature of the substrate and copolymer functionality

The adhesion behavior of statistical, uncrosslinked butyl acrylate-methyl acrylate copolymer on different surfaces (stainless steel, polyethylene, glass and Si-wafer) has been investigated using a combination of probe tack test and simultaneous video-optical imaging. Tack and stress peak values increase and the final number of cavities as well as cavity growth rate decreases with increasing surface energy of the substrate due to better wetting.The influence of the incorporation of an additional comonomer, namely, hydroxyethyl acrylate, methyl methacrylate and acrylic acid, on the adhesion of statistical, uncrosslinked butyl acrylate-methyl acrylate copolymer has been studied. Steel probes with different average surface roughness (Ra=2.9 and 291.7 nm) have been used for tack tests. The increasing polarity of the incorporated comonomer has no measurable effect on the surface tension but leads to an increase of shear modulus and consequently, to an increase in the stress peak, deformation at break, tack values, as well as the total number of cavities. The latter is a consequence of worse wetting. Cavity growth rate on the smooth surface is insensitive to copolymer composition, on the rough surface, the increase in the modulus associated with the additional monomers, leads to a decrease in the cavity growth rate. This indicates different cavity growth mechanisms: predominately lateral growth on the smooth surface and omnidirectional growth on the rough surface.The adhesion performance of uncrosslinked and crosslinked butyl acrylate-methyl acrylate copolymers is compared. The latter exhibit adhesive, and the former cohesive failure. The total number of cavities and cavity growth rate is found to be controlled by viscoelastic properties of PSA independent of the debonding mechanism and the latter decreases significantly with increasing shear modulus.