tailieunhanh - Thermal Properties of Green Polymers and Biocomposites Part 6

Tham khảo tài liệu 'thermal properties of green polymers and biocomposites part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chapter 4 POLYSACCHARIDES FROM PLANTS Recently functional properties of polysaccharides have received particular attention due to the possibility of application in a wide range of fields 1-9 . Among a large number of terraqueous plants cellulose and lignin are dominant in nature. In this book Chapters 3 and 5 are devoted to the two major components of terraqueous plants. In this chapter thermal properties of a selected number of carbohydrate polymers obtained from plants either terraqeuous or aquatic and bacteria will be described. Formation of hydrogels and liquid crystals of polysaccharides will be focused on from the view point of structural change of water via polysaccharide-water interaction. In order to consider practical applications hydrogels obtained by chemical modification will also be described. 1. GELATION Various kinds of polysaccharides such as agarose 10 11 carrageennan 12 - 15 gellan gum 16 - 20 konjac glucomannan 21 22 etc are known to form physical gels in aqueous media and a there are large number of papers devoted to the gelation mechanism of polysaccharides 23 - 25 . In this section thermal properties of representative polysaccharide hydrogels are described. 132 Chapter 4 Gelation of alginic acid Gel formation of alginic acid via divalent cations Alginic acid is a copolysaccharide consisting of manuronic and guluronic acid which is extracted from seaweed brown masse algae 26 27 28 . Chemical structures of both components are shown in Figure 4-1. Sodium alginate NaAlg is water soluble and has been used in a wide range of industrial fields. It is known that NaAlg forms water insoluble gels when Na ion of aqueous solution of NaAlg is replaced by Ca ions in an aqueous media such as CaCl2 aqueous solution 29 . It is thought that guluronic components enclosing Ca ions coaggregate and act as junction zones. On this account the size of junction zones depend on manuronic guluronic M G ratio of the sample. When NaAlg aqueous solution is .

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