Pressure–volume–temperature results and pressure dependency on the viscosity of three liquid crystalline cellulose derivatives

Abstract

The combined analyses of pressure–volume–temperature tests and oscillatory flow measurements for three thermotropic liquid crystalline cellulose derivatives, one acetoxypropylcellulose and two hydroxypropylcelluloses, are presented. This combined analysis allows for the determination of the pressure–viscosity coefficient b = ∂lnη0/∂P. It was observed that the activation energy of flow, dT g /dP, the compressibility coefficient and the pressure–viscosity coefficient obtained for the investigated thermotropic systems lie within the range of the values of these parameters reported for conventional polymers. However, the values of the thermal expansion coefficient below T g are considerably lower, reflecting the effect of the liquid crystalline order. The differences found between the three systems are explained considering microstructural factors, such as (average molar substitution), length of branching and hydrogen bonds.