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

摘要

Lyocel1 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 ]ong and quite wel1oriented rods or ribbons. The never-dry fibres have the longest (5000 A) water-fil1ed voids with a cross-sectionalcorrelation length of 30 A. On drying the scattering bodies become shorter ( 1600 A) and the cross-sectional correlation length increases (50 A) and on re-wetting the voids beCome much shorter ( 400 A) and smal1er in cross-section (28 A).Dry fibres are the most highly oriented (FWHM 13deg) followed by never-dry ones (19deg) and on re-wetting there is a loss of orientation (24deg). Compared to the never-dry fibres re-wet ones show minor differences i,nthesize of the cel1ulose containing regions (18-22 A) and a significant decrease in the size of the water containing regions (52-27 A). Although the wet fibres give good fits to Porod's law, the dry ones do not. The background at higher scattering vectors is relatively high and consistent with scattering from smal1 irihomogeneties or defects. Thus, the wet fibres contain 2 phases, crystal1irle cel1ulose and water, and the dry ones 3 phases, crystal1ine cel1ulose, large air-fil1ed 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.