Characterization of cellulose gels by small angle light scattering

Abstract

An experimental evaluation of the light scattering from two water‐swollen cellulose gels and the corresponding solvent‐exchanged cellulose gels has been made. The two gels were prepared from a commercial viscose by methods which gave different degrees of swelling. The solvent exchanged gels were finally imbibed with silicone fluids whose refractive indices (n) covered the range 1.40–1.59. The Debye‐Bueche theory for scattering from a heterogeneous solid was applied to the data. The observed scattering could be interpreted in terms of refractive index or density fluctuations which were less for the sample with lover degree of swelling. The average periodicity of the density fluctuations increased as n of the imbibition fluid in the solvent‐exchanged samples approached the value, na, for the amorphous regions and maximized in this region. Comparative lateral order distribution information could be derived from the data. From the results it could be shown that the water‐swollen gel is more homogeneous then after solvent exchange but the difference was less for the less swollen system. The evidence collected supports the idea that cellulose gels are, to a first approximation, three‐phased systems involving high order and low order regions as well as micropores. Electron micrographs of thin sections of the solvent‐exchanged gels served to confirm this hypothesis.

New Insights into Fibre Swelling, Interfibre Bonding and Wet Strength

“…1 diagrams to define five different ways in which free water can be immobilised in materials systems which are frequently referred to as gels. (2, 3) Fig. 1-Models of water immobilising systems at the molecular and colloid level; (a) crosslinked macromolecular network, `hydrogel' ; (b) partially crystalline two phase system with crystallite `pseudocrosslinks' and swollen amorphous phase : (c) partially crystalline three phase system, the third phase being pure solvent ; (d) colloidal particles forming random `house of cards' structure ; (e) paracrystalline structure with swelling agent between regularly spaced rods organised in domains Diagram (a) is the classical crosslinked network where a swelling limit is imposed by a balance between the thermodynamic forces due to polymersolvent interaction and the entropic force of coiled polymer chains .…”