X-ray long period of poly(acrylonitrile) fibers prepared by solid-state coextrusion of nascent powder

This paper examines small-angle X-Ray scattering (SAXS) of poly(acrylonitri le] (PAN) fibers prepared by solid-state coextrusion of a him of nascent PA N formed under controlled conditions, as reported by Kumamaru et al. [J. Cr yst. Growth, 48, 202 (1980)]. Although solution-cast PAN films or fibers an d their drawn products generally show no X-Ray long-period scattering, the nascent PAN and the fibers prepared from it by solid-state coextrusion exhi bited a clear SAXS maximum, depending on the extrusion temperature (T-ext) and draw ratio (EDR). For extrusions below 110 degreesC or above 140 degree sC, the SAXS was too broad to determine the scattering maximum. Upon extrus ion at a T-ext of 110-140 degreesC and an EDR of 6-20, the long-period scat tering was clearly observed on the meridian. At a given T-ext, the long per iod stayed at a constant value, independently of the sample EDR in the EDR range of 6-20. However, at a higher EDR>20, no long period was distinguisha ble. It increased linearly with T-ext from the initial 7.7 to 11.5 nm for t he extrusion at T-ext = 140 degreesC, which was 177 degreesC lower than the estimated melting temperature of PAN (T-m = 317 degreesC). A possible mech anism of the long-period increase upon extrusion far below the T-m was disc ussed based on the enhanced chain mobility in the crystalline phase above t he crystal/crystal reversible transition combined with the heat evolved dur ing local necking upon extrusion drawing. These observations reveal that th e absence or presence of an X-Ray long-period scattering for PAN fibers dep ends on the initial morphology and the drawing variables.