Adhesive properties of liquid crystalline hydroxypropyl cellulose–propylene glycol blends

Abstract

Adhesion (tack) of the liquid crystalline hydroxypropyl cellulose–propylene glycol (HPC/PG) systems has been studied under various loading modes as well as their rheology and phase state. The system with the optimum tack according to the Dahlquist criterion (HPC/PG = 85/15 wt.%) was chosen based on its rheological properties (viscosity, storage and loss moduli at 20 and 50 °C). Tack measurements were carried out for this system. Rheological measurements revealed the presence of the critical stress detected by the abrupt drop of viscosity. The adhesive behavior of the system deviates significantly from one of the conventional pressure sensitive adhesives (PSAs): almost no tack is observed when using contact force and contact time typical for a PSA. To achieve good adhesion with this system one needs substantially higher pressure and contact time. At 20 °C, adhesive failure is observed in most cases and high contact forces (over 500–600 g) are required to overcome critical stress and obtain noticeable tack characteristics. At 50 °C, fibrillation and cohesive failure are usually observed with some residue of the system on the probe after debonding. Usage of high contact forces (600–1000 g) and contact times (up to 1000 s) allows us to reach significant values of the maximum debonding stress (up to 1.25 MPa) and energy (up to 420 J/m2). These values are on the same level or even higher than the corresponding values for standard PSAs.