Thermokinetics of Cellulose Fiber Penetration by Physically and Chemically Reactive Liquids and the Structure of Accessible Regions

Abstract

The thermokinetics of the action of water, methanol, ethanol, n-propanol, n-butanol, acetic acid, and concentrated aqueous solutions of NaOH and ethylenediamine on native, mercerized, and regenerated cellulose has been studied by a microcalorimetric method. The penetration rate depends, first of all, on the structure of accessible regions, the dimensions of the penetrant molecule, and the penetrant reaction with hydroxyl groups. If the penetrant molecule has suitable dimensions, the penetration becomes a slow process, making it possible to follow the structural differences in the accessible region even in fibers of the same type. Such liquids are ethanol and acetic acid for native cellulose, methanol and concentrated solutions of ethylenediamine for regenerated cellulose, and concentrated solutions of NaOH (37.5% and 41.5%) for all kinds of cellulose. The accessible phase in cellulose has a discontinuous structure within the spacing of structural elements in the intermicrofibrillar and intermolecular regions. This discontinuity may sometimes be the cause of composite thermograms. Similar thermograms with two characteristic peaks are obtained for some viscose fibers which have at least a two-zone structure of the skin-core type. The intermolecular distances in the accessible regions of microfibrils seem to be of the same order of magnitude as that of the ethanol molecule with reference to native cellulose and the methanol molecule, to regenerated cellulose. The structure of these regions readily undergoes specific changes under the influence of various treatments. This is reflected in the shape of thermograms and magnitude of integral heat effects. The results indicate that the microcalorimetric measurements of the penetration thermokinetics may be a useful tool for investigating the accessible regions