Changes in Certain Structural and Mechanical Properties of Cotton Cellulose with Progressive Acetylation

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Abstract
Scoured cotton yarns were acetylated by two processes: (1) by a 1:3 mixture of acetic anhydride and acetic acid to give a series of low- and medium-substituted products (PA); and (2) a 1:1 mixture of acetic anhydride and isopropyl acetate to give a series of medium- to highly-substituted products (FA). Perchloric acid was the catalyst in both processes. The products were studied with reference to rate of esterification and changes in gross morphology, density, x-ray fiber diagram, tensile properties, and thermal behavior at various temperatures up to 230° C. Esterification proceeds by what appears to be a diffusion-controlled reaction. Above about DS = 2, the x-ray diffraction pattern disappears. Although the gross morphology, as viewed by electron microscopy, does not change noticeably during reaction, the density decreases progressively with substitution and is independent of method of preparation. On the other hand, breaking strength is influenced by acetylation process and increases somewhat as substitution increases. Thermal studies disclose a plastic region in the products between 125° and 175° C. Above that temperature crystallization of cellulose triacetate I sets in and increases progressively with temperature to about 225° C. The plastic and crystal responses of the fibers are reflected in stiffness, elastic recovery, and resiliency behavior at different temperature regions. The results are interpreted in terms of molcular structure.