Study On The Rheological Properties Of A Kind Of Polyamic Acid Solution

Polyimides are one kind of high-performance polymers which contain imide groups in their configuration. They are widely used in the fields such as aircraft, electric, communication and automobile industry because of their excellent properties of heat-resistance, radiation-resistance, and their good mechanical and electrical performance. Films are the main products of polyimides. These years the demand for polyimide films has rised with the development of microelectronic industry. The method of tape-casting is a major technique for the preparation of polyimide films. In the process of tape-casting, the rheological property is an important factor which effects quality of the polyamic acid (PAA) solution. As a measurement of rheological, viscosity reflects the friction between molecules when they are flowing. So the PAA solution is needed to have proper viscosity. If the viscosity is too high, the conveying, defoaming and filteration of PAA solution will be difficult. Contrarily, the polyamic acid solution will be easy to be shrinked. For the purpose to help the polyimide films production, the viscosity of PAA solution was measured and its factors were also discussed.The rheological properties of PAA solution was measured by the HADV-â…¡+cone-plate rheometer. The results showed that the PAA solution was the shear-thinning fluid, exhibiting the character of non-Newtonian pseudoplastic fluid. Based on the regression analysis, the apparent viscosity and shear rate were accord with the power law. The consistency coefficient was affected by the temperature and concentration, lifting up with the falling of temperature or the rising of the concentration. Simultaneously, the PAA solution had the characters of rheopectic fluid, which showed the shear rate thixotropic curve became a significant hysteresis and the apparent viscosity decreased clearly after the solution was sheared. The rheopectical property became more and more obvious with the narrow distribution of molecular weight and the low temperature.The effects of concentration, temperature, shear rate, shear stress and molecular weight distribution on the rheological properties of PAA solution were investigated. And the simple mathematical equation based on concentratin, temperature and shear rate and...