Thermodynamic study of solutions of polyvinyl acetate and cellulose tricarbanilate in the pre-critical region

Abstract

It has been found that endothermic mixing occurs in the pre-critical region in the polyvinylacetate (PVA)-methanol system, which has an upper critical temperature of mixing (UCTM) ( Δh m >0 and ∂ 2Δh m ∂x 2 2<0 ). In the cellulose tricarbanilate (CTC)-dibutyl ketone system, which has a lower critical temperature of mixing (LCTM), exothermic mixing occurs in the pre-critical region ( Δh m <0 and ∂ 2Δh m ∂x 2>0 ). Consequently for these two systems, with liquid phase separation, there are thermodynamic criteria of the UCTM and LCTM. In the system CTC-cyclohexanol, in which crystalline phase separation occurs, these criteria are not present. The mixing volumes were determined and the internal pressures and energies of mixing were calculated for all the systems. It was found that Δh p m≠ ΔU ν m, corresponding to exothermic mixing in the CTC-cyclohexanol system, is due to contraction of the system on mixing. The internal energy of mixing of this system is positive.