Structure and applications of cellulose regenerated from zinc -cellulose complexes
Abstract
Aqueous zinc chloride solutions dissolve cellulose only when concentrations of zinc chloride are above 64% (w/w). However, studies showed that cellulose solutions with zinc chloride concentration above 64% (w/w) could be slowly diluted with water at an elevated temperature (65°C) to as low as 35% (w/w) without causing precipitation of cellulose. How far the initial cellulose solutions could be diluted without precipitation of cellulose depended on the temperature as well as the initial cellulose concentration. Regenerated cellulose (RC) samples were made at different stages (before and after the solution became turbid) during the dilution process. The supermolecular structures of RC samples have been investigated using wide-angle X-ray diffraction techniques. Two types of regenerated cellulose, RC-II and RC-I, were observed. RC-II was always formed when it was regenerated before the turbid point and RC-I was always formed when it was regenerated after the turbid point. The crystalline patterns of RC-I and RC-II have been confirmed to reflect the patterns of pure cellulose-I and pure cellulose-II, respectively. This is an exciting discovery in cellulose chemistry since most researchers believe that regenerated cellulose with type-I characteristics (RC-I) is thermodynamically impossible. Further analysis on the X-ray diffractograms showed that the cellulose-I characteristics of RC-I samples were imperfect, particularly in the neighborhood of 101, 101¯, and 021 planes, while RC-II resembled cellulose-II very well. The crystallinity of RC-I samples was much lower than starting cellulose-I while the crystallinity of RC-II samples could be as good as mercerized cellulose-II. After propylene (PP) nonwoven fibers were treated with cellulosic solutions and followed by the regeneration of cellulose, a thin layer of cellulose coating on PP could be obtained. This cellulose coating turns the hydrophobic PP fibers into hydrophilic materials, which can be applied to the area of personal hygiene and health care products. Wettability tests showed that cellulose-coated PP fibers performed as well as or even better than surfactant-treated PP fibers, which are commercially used. However, cellulose coating on PP fibers is superior to surfactant treatment in terms of durable wettability.
Degree
Ph.D.
Advisors
Chen, Purdue University.
Subject Area
Food science
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