Viscoelasticity and tack of poly(vinyl pyrrolidone)-poly (ethylene glycol) blends

The adhesive properties of blends of high molecular weight poly vinyl pyrrolidone) (PVP) and low molecular weight poly(ethylene glycol) (PEG) were systematically investigated with a probe test and correlated with their viscoelastic properties. The material parameters that were varied were the PEG content (31-41 wt %) and the hydration rate. The 36% PEG showed the best balance of properties for a pressure- sensitive adhesive. At low debonding rates, the debonding took place through the formation of a fibrillar structure, whereas at high debonding rates, the debonding was brittle. This transition was attributed to the breakage and reformation of hydrogen bonds between PVP units and OH groups on PEG during the large strain of the polymer chains in elongation. This transition was observed, albeit shifted in frequency, for all three compositions, and the characteristic relaxation times of the hydrogen-bonded network were estimated. A comparison between the tack properties of the adhesives and their linear viscoelastic properties showed a very strong decoupling between the small-strain and large-strain properties of the adhesive, which was indicative of a pronounced deviation from rubber elasticity in the behavior of the blends. This deviation, also seen during tensile tests, was attributed to the peculiar phase behavior of the blends. (C) 2002 Wiley Periodicals, Inc.