Abstract
We report here on some aspects of the acetylation in LiCl/N,N-dimethylacetamide, DMAc, of untreated and mercerized sisal cellulose, hereafter designated as sisal and M-sisal, respectively. Fiber mercerization by NaOH solution has resulted in the following changes: 29.9% decrease in the index of crystallinity; 16.2% decrease in the degree of polymerization and 9.3% increase in α-cellulose content. A light scattering study of solutions of sisal, M-sisal, microcrystalline and cotton celluloses in LiCl/DMAc has shown that they are present as aggregates, with (an apparent) average aggregation numbers of 5.2, 3.2, 9.8, and 35.3, respectively. The presence of these aggregates affects the accessibility of cellulose during its functionalization. A study of the evolution of the degree of substitution, DS, of cellulose acetate as a function of reaction time showed an increase up to 5 h, followed by a decrease at 7 h. Possible reasons for this decrease are discussed. As expected, M-sisal gave a higher DS that its untreated counterpart.
Highlights
Derivatization of cellulose, e.g., into esters and ethers is a subject of continuing interest because of the important applications of these products as fibers, filters, dialysis membranes etc.[1]
We report here the acetylation of untreated and mercerized cellulose from sisal, hereafter designated sisal and M-sisal, respectively, in LiCl/DMAc
Standard procedures were employed for the characterization of celluloses; these are described here only briefly: (i) the viscosity-based average molecular weight, MV was determined at 25 °C from the intrinsic viscosity of cellulose solution in Cuen/water (1:1, v/v),[11] by using shear-dilution Cannon-Fenske viscometer (Schott), inserted in Schott AVS 360 automatic viscosity determination equipment; (ii) the a-cellulose content was determined from the dry masses (3 h at 105 oC) of cellulose before and after treatment with 17.5% NaOH solution, at liquor ratio = 1:20, m/v;12 (iii) X-ray diffraction of the cellulose samples was recorded by using Carl Zeiss Jena URD-6 X-ray diffractometer
Summary
A light scattering study of solutions of sisal, M-sisal, microcrystalline and cotton celluloses in LiCl/DMAc has shown that they are present as aggregates, with (an apparent) average aggregation numbers of 5.2, 3.2, 9.8, and 35.3, respectively. The presence of these aggregates affects the accessibility of cellulose during its functionalization. A study of the evolution of the degree of substitution, DS, of cellulose acetate as a function of reaction time showed an increase up to 5 h, followed by a decrease at 7 h Possible reasons for this decrease are discussed.
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