Small angle X-ray scattering studies on lyocell cellulosic fibres: the effects of drying, re-wetting and changing coagulation temperature

Lyocell fibres have been characterised by small angle X-ray scattering as-produced wet (never-dry), after drying and after subsequent re-wetting. In all the fibres, the scattering bodies are long and quite well oriented rods or ribbons. The never-dry fibres have the longest (5000 Å) water-filled voids with a cross-sectional correlation length of 30 Å. On drying the scattering bodies become shorter (1600 Å) and the cross-sectional correlation length increases (50 Å) and on re-wetting the voids become much shorter (400 Å) and smaller in cross-section (28 Å). Dry fibres are the most highly oriented (FWHM 13°) followed by never-dry ones (19°) and on re-wetting there is a loss of orientation (24°). Compared to the never-dry fibres re-wet ones show minor differences in the size of the cellulose containing regions (18–22 Å) and a significant decrease in the size of the water containing regions (52–27 Å). Although the wet fibres give good fits to Porodʹs law, the dry ones do not. The background at higher scattering vectors is relatively high and consistent with scattering from small inhomogeneties or defects. Thus, the wet fibres contain 2 phases, crystalline cellulose and water, and the dry ones 3 phases, crystalline cellulose, large air-filled voids and small defect regions. Increasing the coagulation temperature increases the water content and the size of the water containing regions in all wet samples giving improved dyeablity.