CONTINUOUS PLASTICIZED MELT-EXTRUSION OF POLYACRYLONITRILE HOMOPOLYMER

In this work, it is shown that polyacrylonitrile (PAN) powder which ha d been plasticized by propylene carbonate (PC) could be 'melted' and e xtruded continuously into filaments. The 'molten' extrudate solidified on-line as a result of cooling, without the need for coagulation. In this respect, PAN-PC solutions behaved differently when compared with other solutions commonly used in the wet-spinning of PAN fibres. Spont aneous solidification on cooling meant that the filament could be woun d-up on a take-up system without the need to pass it through a coagula tion bath. The solidification occurred as a result of the rapid crysta llization of the PAN from the propylene carbonate solution. The X-ray diffraction pattern of the solidified filament (which contained 40-50 wt% of solvent) was different from that of the dry PAN powder, indicat ing that a different polymorph had been formed. Drawing of the filamen ts, however, led to the normal hexagonal polymorph. A PAN:PC (50:50 by wt) 'melt' had a shear viscosity comparable with that of a convention al thermoplastic such as extrusion-grade polyethylene. The plasticized melt showed shear-thinning behaviour.