Film formation of poly (p-phenylene terephthalamide) from sulphuric acid solution.

A novel process for the formation of poly (p-phenylene terephthalamide) (PPTA) film from liquid crystalline sulphuric acid solution was developed. A homogeneous and transparent PPTA film is very difficult to obtain from sulphuric acid solution owing to the highly anisotropic flow properties of the solution. A biaxially balanced PPTA film could be formed by using the optically anisotropic to isotropic transition appeared in the phase diagram of the PPTA sulphuric acid solution. The phase transition was generated by controlling temperature and/or polymer concentration of the solution. The anisotropic solution was cast on a flat glass plate. The cast dope was carried into a conditioning chamber (air oven) in which the phase transition occurred before it was immersed into the coagulation bath. The isotropic cast dope was coagulated and dried holding dimensions constant. The adjustment of temperature and water content of the cast dope plays an important role in the process and directly affects the properties of the film obtained. The conditioning at 100°C was suitable for the film properties in a series of experiments. The Young's modulus of 14 GPa and tensile strength of 450 MPa were obtained for the film heat-treated at 350°C during 20min. This process can be applied to a continuous large scale process.