Gel-Permeation Properties of Cellulose

The gel-permeation technique has been applied to the characterization of cotton cellulose fibers from fabrics cross-linked with formaldehyde in wet-cure and in bake-cure reactions and reduced to a sufficiently small particle size by Wiley-milling. Measurements of total internal water contents, internal solvent volumes, and permeability limits are indicative of the nature and extent of changes in pore structure resulting from the cross-linking. Cross-linked compositions were examined at progressively higher levels of formaldehyde which were obtained under the various reaction conditions. The wet-cure processes Forms W and W' involving water-swollen cotton produced only limited alterations of the cellu lose pore structure at the maximum levels of cross-linking attainable by these treatments. Changes in the values obtained for the gel-permeation parameters were small, but the trends show that a larger reduction of internal pore volume is pro duced under the Form W process than under the Form W' process. Reaction with the less concentrated Form W reagents caused a smaller decrease in the permeability limit than Form W'. Large changes in pore structure resulted from cross-linking the cotton in a collapsed state by the hake-cure, Form C. process. The internal pore volumes of both the total and of the effective solvent water contents were reduced with cross- linking over the range from 0.47% to 2.20% methyleneoxy contents of the samples. The permeability limit was reduced from a molecular weight of 2430 for untreated cotton to approximately 1250 at the lowest level of cross-linking. No further decrease of this parameter was produced by cross-linking up to the maximum methyleneoxy content of 2.20%. In all three forms of reaction, the changes produced in total internal water contents followed trends similar to the values for water of imbibition determined by centrifuging. The latter values were larger than those measured chromatographi cally by 34-100%, the discrepancies being larger for the smaller true volumes of internal water calculated from column- volume measurements. The centrifugal technique of determining water of imbibition is a simple procedure for estimating relative changes of internal pore volumes of cottons.