Reactivity and electrokinetical properties of different types of regenerated cellulose fibres

Comparative investigations between new lyocell, conventional viscose and modal fibres were made in order to explain the reasons for the differences in the reactivity and electrokinetic properties of these fibres. Lyocell fibres are a new generation of regenerated cellulose fibres produced using environmentally friendly process, which account for the main differences in the fine structure of each fibre despite having the same chemical composition. Analyses of the structural characteristics of lyocell fibres and their comparison with viscose and modal fibres were performed. The molecular (density ρ, degree of polymerisation DP, molecular mass M) and the fine structure (crystallinity index CrI, molecular orientation f_Δn, void volume V_p) of cellulose fibres were investigated. Differences in the molecular and fine structure between various types of regenerated cellulose fibres cause different reactivity, sorption and electrokinetic properties. Differences in the reactivity of investigated regenerated cellulose fibres were analysed using various methods for determining water adsorption (moisture sorption, water retention, swelling in water) and adsorption of different types of surfactants (spectroscopic determination of the surfactant adsorption). The accessibility of free adsorption places in the less ordered regions of cellulose fibres was investigated by determining of electrokinetic properties. The zeta potential (ζ) was determined using streaming potential measurements as a function of the pH and structure/concentration of surfactants in the liquid phase. The structure analyses show that the new lyocell fibres have a greater degree of crystallinity and molecular orientation, and the voids structure is similar to that of viscose fibres (T. Kreze, Dissertation, University of Maribor, 1999). The adsorption phenomena in the aqueous medium and the reactivity of fibres depend, with the exception of the portion and orientation of amorphous regions, predominantly on the void system i.e. diameter, volume and inner surface of voids. The voids of modal fibres are the smallest. The voids of lyocell fibres are similar than those of viscose fibres, and so are their swelling and adsorption properties in aqueous medium (T. Kreze, S. Strnad, K. Stana-Kleinschek, V. Ribitsch, Mater. Res. Innovations, 4(2/3) (2001) 107-114). There exists an excellent correlation between structure, adsorption and electrokinetic properties.