Decolorization of Chitosan
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DECOLORIZATION OF CHITOSAN
G. GRAHAM ALLAN AND MUTOMBO MUVUNDAMINA1 , University of Washington, Department of Chemical Engineering and College of Forest Resources, Seattle, WA98195.
ABSTRACT The industrial process for extracting chitosan from low cost shellfish waste is well known. It comprises three basic steps: deproteinization, demineralization of the shells to yield chitin, followed by deacetylation of chitin to produce chitosan. However, the product obtained from the process often still contains many impurities. In general, these encompass minerals and carotenoids bonded to chitosan. The treatment of chitosan flakes with aqueous solutions of inorganic polybasic acids permits the removal of the impurities mentioned above. This paper describes an engineering-type procedure which develops a pure, colorless material having a controlled molecular weight. INTRODUCTION Chitosan may be utilized in numerous applications which fall broadly in two categories. First, uses where relatively a low quality and low-priced product is recommended [1-4], and secondly, applications where a high quality chitosan is required but only a small amount of material is needed. This latter class of applications include biomedical and specialty products, and previous work [5-7] has demonstrated that there is a great potential for chitosan in this domain. Although the requirement for the control of molecular weight has been made clear [5, 6], it is certain that there is also a great need for purity, and preferably colorless products, when the material has to be incorporated in biomedical or specialty articles. Previous reports on the purification and molecular weight manipulation of chitosan seems to have been done for scientific purposes only, for example when a pure material with a determined molecular weight was needed to perform a specific experiment [5-9]. Now, it is necessary to move beyond a one-time laboratory purification or fractionation into an engineering-type procedure which can be repetitively, easily and economically carried out. The present effort was undertaken to establish an engineering-type procedure capable of yielding a pure, colorless material with a controlled molecular weight. The strategy of this investigation depends on the permeability of chitosan flakes to facilitate removal of carotenoids from the polymer. EXPERIMENTAL Materials The chitosan used in the study was extracted from king and snow crab shells. A random mixture of samples of chitosan extracted from crab shells of 'Current address: University of Minnesota, Paper Science and Engineering, Department of Forest Products, Saint Paul, MN55108. Mat. Res. Soc. Symp. Proc. Vol. 218. 01991 Materials Research Society
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different origins was also utilized. The characteristics of these samples are given in Table I. All the other chemicals employed were standard stock items. Table I.
Characteristics of chitosan obtained from different sources before decolorization.
Characteristic moisture1 (%) ash content' (%) deacetylation (%) 2 degree of decolorization int
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