Production of oriented polyacrylonitrile films by flow-induced chain extension and crystallization from solution

Abstract

Polyacrylonitrile [-CH₂-CH(CN)-]_n is not considered to be a thermoplastic polymer. Fibres may be wet spun from solution, but oriented films are, in particular, difficult to produce by a coagulation process. In previous work, it was shown that when liquid propylene carbonate (PC) is blended with polyacrylonitrile (PAN) powder, the polymer can be processed like a thermoplastic. Thus, it was possible to make plasticized gel films by compression moulding. In the present work, it is shown that the gel films may be “remelted” and drawn, to give uniaxially or biaxially oriented PAN films. The process involves flow-induced chain extension and crystallization from solvent, and differs from other methods of producing PAN film or fibre which involve coagulation. The solvent can be removed from the film after drawing, to give oriented films with good mechanical properties. Infrared dichroism studies on uniaxially oriented films containing residual solvent suggested that the carbonyl group of the PC molecule was paired with the nitrile group of the PAN by dipolar interaction. X-ray diffraction experiments showed differences between PAN reactor powder, unoriented plasticized gel film and drawn films; these appear to be related to the presence of solvent.