Study on the Phase Behavior for PI-NMP-H_2O System

This paper adopts cloud-point titration to study the phase separation behavior and cloud-point composition of the ternary system(polyimide,1-methyl-2-pyrrolidinone and water,PI-NMP-H2O).The linear equation is gained through parametric regression of the cloud-point data measured when PI-NMP-H2O system reaches phase separation.The degree of linearity is relatively good with linear cloud-point equation.The PI-NMP-H2O ternary phase diagrams at different temperatures are gained in line with the components of cloud points with different concentrations deduced by linear equation.The results show that the position of bimodal line in the ternary phase diagram is close to PI-NMP axis;with the decreasing temperature,the bimodal line approaches PI-NMP axis.Therefore,the higher concentration of the spinning solution and the lower temperature of the coagulation bath can obtain polyimide as-spun fibers with dense structure,less holes,even distribution and better performance.