Evaluation of Tack and Shear Strength of Pressure-Sensitive Adhesives Comprised of Polyurethane and Acrylic Copolymer Blend

In recent years, several studies have been performed for improving the adhesion properties of polyurethane and acrylic pressure-sensitive adhesives (PSAs). Generally, polyurethane PSAs are of higher shear strength, while acrylic PSAs have higher tack. This research is a feasibility study of exploiting the properties of both of these adhesives through a simple blending method, and the adhesion properties were evaluated.

 First, acrylic copolymer (Ac) consisting of 82 vol. % butyl acrylate and 18 vol. % methyl methacrylate was solution polymerized. On the other hand, a thermoplastic polyurethane (TPU) containing 17.5 wt. % hard segment was prepared by bulk polymerization. Blending of these two polymers was performed by solution mixing. Solutions of the pure polymers and their blends at different contents were cast on polyethylene terephthalate backing and dried at room temperature. Fourier transform infrared spectroscopy, gel permeation chromatography, and differential scanning calorimetry were used to identify TPU and Ac. Loop tack, static shear strength, dynamic mechanical behavior, contact angle of sessile drop, morphology, and haze of the PSAs were evaluated.

Tack of the acrylic PSA was higher than TPU PSA. Tack of the blend PSAs containing 20, 40, and 60 wt. % TPU was higher than the pure components and that of the blend containing 40 wt. % TPU was maximum. This blend demonstrated the lowest water contact angle compared to the other blends and the shortest relaxation time compared to the pure polymers, which resulted in better wetting and higher tack. The shear strength of the PSAs increased with increase in the content of TPU to higher than 40 wt. % in the blends compared to the acrylic PSA; so that the pure TPU showed the highest modulus at various frequencies and hence exhibited high-shear PSA characteristics in the Chang’s viscoelastic window and the highest adhesion strength. The immiscibility of the blends was confirmed by measuring the haze and calculating the Hansen solubility parameter.