Viscosity Behavior and Solvent Casting of Poly(ethylene Terephthalate) in the Mixed Solvent System

혼합용매계에서의 폴리에틸렌테레프탈레이트의 점성 거동 및 용액성막

The viscosity behavior of poly(ethylene terephthalate) (PET) solution in hexaBluoroisopropanol (HFIP)/dichloromethane and HFIP/chloroform mixed solvent systems was examined and this was considered in connection with the interaction between the polymer and solvent. The HFIP/dichloromethane mixed solvent system exhibited the viscosity behavior belonging to case R and the cosolvency phenomenon showing maximum solubility power at the 50 vol.% of HFIP composition was observed. On the other hand, the HFIP/chloroform mixed solvent system indicated the one belonging to case I and the solubility power decreased with an increase in the content of chloroform. The isothermal evaporation rate constant(k) of the PET solution was greatly different in the earlier(kl) and later(kE) parts of the evaporation. In the case of the HFIP/dichloromethane mixed solvent system k1 increased monotonously with an increase in the content of dichlommethane, but k2 had the minimum value at the 50 vol.% of HFIP composition. Contrary to this, in the case of the HFIP/chloroform mixed solvent system both k1 and k2 increased monotonously with an increase in the content of chloroform. In addition high molecular weight PET was dissolved in the HFIP/dichloromethane mixed solvent (5/5 in volume ratio). Optimum critical casting concentration was determined from the concentration-reduced viscosity curve of the PET solution and the film was prepared at this concentration. Maximum tensile modulus, 7.OGPa and maximum tensile strength, 0.62 GPa were obtained, and these values were considered to be similar to those of the phenol/tetrachloroethane(6/4 in weight ratio) cast film.