Title: Application of Serial X-Ray Scattering for Microstructure Optimization of Polyacrylonitrile Fibres Produced by Wet Spin Processing

Authors: David Fox, Anthony Pierlot, Jasjeet Kaur, Linda Hillbrick, Claudia Creighton, and Peter Lynch

DOI: 10.33599/nasampe/c.19.0861

Abstract: A new serial fibre X-ray scattering method is presented that is used to better understand the relationship between microstructure and mechanical properties of wet spun polyacrylonitrile (PAN) fibre. During continuous processing, fibres were extracted from five points along the wet spinning line. Sample points included the coagulation bath, wash bath, hot water stretch, steam stretch and final PAN creel. By application of synchrotron small and wide angle X-ray scattering (SAXS-WAXS), data from 20-25 individual fibres was recorded at each sample point down the white fibre line. By simultaneous measurement of both the SAXS and WAXS data in a single exposure, the key aspects of the fibre microstructure was probed. SAXS was used to identify the evolution of the mesophase/porous structure during processing while WAXS measurements provided a quantitative measure of the PAN crystallographic structure.

During coagulation the low level of fibre processing, elongation was revealed by nearly perfectly isotropic scattering data. For these fibres, ~40mm in diameter, the microstructural features were randomly oriented. As the draw ratio was increased down the fibre line (hot water stretch) strong levels of anisotropy were observed in the scattering data. At this point the fibre diameter reduced to ~20mm and the preferred level of crystallographic orientation (FWHM) was ~45o. This evolution in the microstructure was further refined at each subsequent processing point. Ultimately for the final PAN fibre, diameter ~12 mm the preferred orientation was reduced to ~20o. By precise measurement of the (100) WAXS data, it was shown that the crystallite size more than doubled from the coagulation bath to the final PAN fibre. Interestingly, the d-spacing information remained largely unchanged across each sample point, indicating that the increase in fibre density (decrease in fibre diameter) did not impact on the observed elastic lattice strain in the PAN microcrystals but rather the decrease in fibre diameter was driven primarily by collapsing of the microporous structure.

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Conference: CAMX 2019

Publication Date: 2019/09/23

SKU: TP19-0861

Pages: 11

Price: $22.00