Interpretation of relaxation and swelling phenomena in lyocell regenerated cellulosic fibres and textiles associated with the uptake of solutions of sodium hydroxide

Abstract

The uptake of solutions of sodium hydroxide by lyocell fibre results in a phenomenon in textiles described as swelling-shrinkage. The response of woven fabrics in a tensile stress-relaxation experiment shows two time-dependent processes, corresponding to different mechanisms of pressure development. Rapid diffusion has been assigned to osmotic swelling through the interconnected pore structure of the fibre (D = 6-15 9 10 @12 m 2 /s), which is influenced by the extent of ionization of hydroxyl groups at the pore surfaces. A ratio for the cellulose and water dissociation constants (K cell /K w ) of 70 provides best agreement with experimental data. A second slower diffusion process (D = 2-10 9 10 @14 m 2 /s) is assigned to transport through the cellulose polymer structure, associated with the Na-cellulose transition. This can be modeled assuming an ion-exchange equilibrium, where the cellulose gel converts reversibly between compact hydrogen and expanded sodium forms, with K = 1.04 9 10 14 , in favour of the hydrogen form. The model successfully predicts the concentration dependence of the transition and the movement to higher concentration with external constraint. The slow diffusion process only becomes apparent at high alkali concentrations, as the pores in the fibre collapse due to the expansion of the gel. Continued gel-diffusion is only possible through the polymer phase, which then dominates over fast pore-diffusion.

Adsorption of chlorhexidine onto cellulosic fibers

“…In order to consider the influence of diffusion process in this situation, that is, low concentration of CHX and room temperature, we have estimated the empirical diffusion coefficient. Values obtained are similar to those obtained by Roger and colleagues with lyocell fibers (Ibbett et al 2008) which were D = 6-15. 10 -12 m 2 s -1 .…”

Changes in the intra- and inter-fibrillar structure of lyocell (TENCEL®) fibers caused by NaOH treatment

“…The modulus of fibers immersed in alkali solution in creep-recovery measurements decreased up to 2.5 M NaOH which was attributed to a reduction in the modulus of the crystalline regions. The modulus value leveled off above 2.5-3 M NaOH solution which was consistent with the existence of a stable Na-cellulose phase in this region (Ibbett et al 2008a). Increases in the crystallite size of NaOH treated lyocell fabrics resulted in a decrease of the molecular mobility of the crystalline region obtained from Solid-state 13 C NMR Spectroscopy (Sakaguchi et al 2002).…”

“…The planes 1 " 10; 110 and 020 are parallel with the C direction and the polymer chain axis, consequently the crystallite sizes represent lateral dimensions across a section of the fiber. Sodium hydroxide causes swelling and separation of the 1 " 10 planes causing this peak to move to lower angles, as also happens although to a lesser degree in the case of the 020 peak, however this is reversed upon washing and drying (Kolpak et al 1978;Ibbett et al 2008a). Figure 6 shows the crystallite size normal to the 110, 1 " 10and 020 planes.…”

“…The position of the 110 diffraction peak does not change, reflecting the strong interaction, probably via hydrogen bonding, between the cellulose glucose rings (Kolpak et al 1978;Ibbett et al 2008a). The short chain material may not be able to interact in this way on the 110 face of a crystallite to form a perfect crystal.…”

“…Wide angle X-ray diffraction (WAXD) (Kolpak et al 1978;Ibbett et al 2008a) Samples were prepared by pressing randomly oriented samples into the form of discs at 50-60°C.…”