Mechanical Properties of Adhesive Films Obtained from PU-Acrylic Hybrid Particles

The mechanical and adhesive properties of films made from novel hybrid urethane/acrylic dispersions have been investigated. The adhesive films were obtained from the drying of bicomponent acrylic urethane latexes prepared by miniemulsion polymerization. In the companion paper, phase separation at the macroscopic scale was avoided by using a NCO end-functionalized polyurethane (PU) prepolymer and a hydroxyethyl methacrylate (HEMA) reactive comonomer in the acrylic backbone. The effect of two compositional parameters on the mechanical and adhesive properties was specifically studied : the PU weight fraction and the degree of grafting of the PU prepolymer on the acrylic backbone, controlled by the ratio between grafting agent HEMA and chain extender Bisphenol A (BPA). Swelling, rheological, tensile, and probe tack tests were used in parallel with an analysis of the macroscopic adhesive properties of the films. Results show that the PU weight fraction modifies significantly the small strain elastic modulus and the gel fraction in the latex particle while the ratio HEMA/BPA can be used to adjust the chain length of the PU incorporated in the network. This ratio affects significantly the finite extensibility of the PSA while Causing only relatively small changes in the low strain elastic modulus and gel fraction. An increase in the degree of grafting at fixed PU content is found to improve the resistance to shear of the adhesive without reducing its adhesion energy in a peel or probe tack test.