DEVELOPMENT OF ORIENTED STRUCTURE DURING ULTRA-DRAWING OF NASCENT POLYACRYLONITRILE POWDER

Nascent atactic polyacrylonitrile (PAN) powder was precipitated during polymerization of acrylonitrile in solution under the controlled cond itions. It was characterized by C-13 NMR and consisted of aggregates o f single crystals, as reported. The powder film obtained by filtering the crystal suspension was brittle, but could be successfully drawn by solid state coextrusion at 25-200 degrees C. At an optimum draw tempe rature of similar to 140 degrees C, the film could be extrusion drawn to draw ratios 68. The high ductility of nascent PAN is ascribed to th e characteristic starting morphology and the presence of a crystalline relaxation at 110 degrees C. The deformation of the powder film has b een studied by wide-angle (WAXS) and small-angle X-ray scattering (SAX S), scanning electron microscopy, optical microscopy, and density. A S AXS long period was observed for a series of drawn samples, as well as their change with draw ratio. Crystalline chain orientation and the t otal chain orientation, measured as a function of draw ratio, indicate that PAN has a two-phase structure consisting of the crystalline and noncrystalline regions, as opposed to the single-phase structure propo sed by others. Further, the crystal structure of PAN is better describ ed by an orthorhombic unit cell with a = 1.06, b = 0.586, and c = 2.45 nm. Tensile properties were affected by draw ratio and by flaw format ion which depended on extrusion temperatures. A maximum ambient tensil e modulus and strength of 13 and 0.43 GPa, respectively, were obtained for extrusion at 140 degrees C to a draw ratio of 20. The former corr esponds to 45% of the uncertain crystal modulus of atactic PAN.