Birefringence, density, and tensile characteristics of oxycelluloses

Abstract

SynopsisInvestigations have been carried out on the changes in the characteristics such as refractive index, density, single fiber breaking strength, and moisture regain of cotton fibers brought about as a result of oxidation with sodium metaperiodate and potassium dichromateoxalic acid. The study has also been extended to sodium chlorite-treated and sodium borohydride-reduced oxycelluloses obtained from these oxycellulose products. Results indicate that in case of sodium metaperiodate oxidation, birefringence and density first increase, reach a maximum and then decrease sharply as oxidation is continued, while breaking strength decreases in the initial stages, reaches a minimum, and then increases in the later stages. With dichromateoxalic acid oxidation, birefringence increases sharply during the initial stages of oxidation and after reaching a maxima, decreases as oxidation progresses, while there is a rapid increase in the values of density during the initial stages followed by a slow rise as oxidation is continued. In case of dichromahxalic acid oxycelluloses, breaking strength decreases continuously with the progress of oxidation. Results are interpreted in terms of changes in gross morphology and fine structure of cotton as a result of oxidation and subsequent chlorite and borohydride treatments.Changes due to chemical modifications in gross and fine structure of cotton and regenerated cellulosic fibers in relation to physical characteristics have been studied by such different techniques as x-ray diffraction, plane and polarized light microscopy, electron microscopy, infrared spectroscopy, etc. As compared with the considerable information available in the literature regarding the fine structure of cellulosic fibers, useful data in the case of chemically modified cellulose obtained by employing optical techniques are rather limited. Kanamaru' has studied the changes in the refractive indices of cellulose oxidized with sodium hypochlorite and potassium permanganate, whereas Pate12 has carried out optical investigations on oxycelluloses obtained as a result of the action of s3dium metaperiodate-sodium chlorite, dichromate-sulfuric acid, and sodium hypobromite on ramie cellulose. Tensile strength characteristics of oxycelluloses have been studied by Clibbens and Ridge13 Davidson,l and Nevell and Zeronian.6 In the present study, systematic investigation has been undertaken regarding changes in the gross morphology and fine structure of cotton fibers 1437

Viscosity Measurements on Chemically Modified Celluloses

“…Rogovin et al (1949) and Davidson (1941) had observed that nitration of dialdehyde celluloses of a higher degree of oxidation gave poorly soluble nitrates and high viscosity values, which has been attributed to acetal cross linkages formed during the nitration between the individual cellulose molecules (Sihtola, 1960;Sihtola et al, 1958;Virkola, 1958). Acid and alkali stability of dialdehyde cellulose formed by periodate oxidation and stabilization caused by conversion into dicarboxylic and dialcoholic celluloses on further treatment with sodium chlorite and sodium borohydride have been studied (Betrabet et al, 1965;Meller, 1951Meller, , 1956Rutherford et al, 1942). Ellefsen (1963) had suggested a treatment for pulp samples with sodium borohydride to get comparable DP values in CED and on nitration.…”