Modifications cellulose

From this standpoint, cellulose modification by grafting is exceptionally promising. Recently, grafting has become a popular method of modifying various high molecular weight compounds1,2. ... 

Cellulose modification dates from 1833 (Braconnot). In 1838 Regnault photo-polymerized vinylidene chloride. A year later Simon observed that heating styrene in the presence of air generated a tough gelatinous material — a low molecular weight PS. Polyoxymethylene (acetal) was discovered in 1859. In 1872 several new polymers were announced, viz., PVC, polyvinyl bromide (PVB) and phenol-formaldehyde (PF). Polymethacrylates were discovered by Kahlbaum in 1880, polymethylene in 1897, one year later polycarbonate (PC) by Einhorn, polyamide-6 (PA-6) in 1907, etc. In the... 

The chemical modifications discussed in this section are historically and scientifically so closely linked to one polymer, cellulose, that although the latter occurs primarily as a fiber and not an elastomer, a discussion of this group of cellulose modifications seems appropriate. Apart from the fact that some cellulose derivatives, like ethyl cellulose, when plasticized, can be quite elastomeric, the effects of modification of a basic polymer are particularly well demonstrable on a substance as stiff and highly crystalline as cellulose. Moreover, in view of the expected hydrocarbon shortage, cellulose may soon gain a new role as a polymeric starting commodity. 

Cellulose. — A comprehensive treatise on the modification of cellulose has appeared.The book is sub-divided into five parts a summary of previous work on modified cellulosics, a discussion of cotton and wood cellulose, a review of the accessibility and reactivity of cellulose, a discussion of modification of cellulose by grafting of vinyl monomers, and a description of additional techniques for cellulose modification. 

Cyclic anhydrides like acetic, phthalic, and succinic anhydride have been widely used in cellulose modifications to produce different cellulose derivatives such as cellulose acetate, cellulose butyrate, cellulose benzoate, cellulose phthalate, and cellulose with or without catalyst, which have several applications such as water absorbents for soil in agriculture, drug delivery system, and as thermoplastic. 

In this chapter, the current state of development in the field of cellulose modification and application is demonstrated. It should be also pointed out that cellulose as a natural product belongs to the polymers, which hold an Impressive future potential... 

Roy D, Semsarilar M, Guthrie JT, Perrier S (2009) Cellulose modification by pol5mer... 

Some interesting approaches to cellulose modification are possible via formations of double bonds in the glucopyranosine unit at the 5,6 positions. This is accomplished by dehydrohalogenat-ing a previously formed 6-iodocellulose ... 

Derivatives of eellulose constitute the most important area of cellulose modification fiom both a technological and commercial viewpoint... 

Many starch derivatives are prepared in a manner similar to cellulose modification. Both heat and alkali ate often used to prepare the starch for chemical addition. As with cellulose, the properties of the starch change with the degree of derivatization. The final characteiisties of the modified gums are controlled by factors which include (a) the amylose/amylopectin content, (b) the degree of modification, (c) the degree of derivatization, and (d) the type of derivatization. This range of factors can result in wide varieties of different gums. 

The S5mthetic approach of in situ activation of carboxylic acids is based on the preliminary reaction of the carboxylic acid with a specific reagent to give an intermediate reactive daivative which can be prepared prior to the reaction with cellulose or converted directly in a one-pot process. This approach opens the way to a broad variety of new esters, because for numwous acids, for example unsaturated or hydrolytically unstable ones, reactive derivatives such as anhydrides or chlorides simply cannot he synthesized. The mild reaction conditions apphed for the in situ activation prevent common side reactions hke pericychc reactions, hydrolysis, and oxidation. Moreover, due to their hydrophobic charactCT, numa-ous anhydrides are not soluble in organic media used for cellulose modification, resulting in unsatisfactory yields and insoluble products. In addition, the conversion of an anhydride is combined with the loss of half of the acid during the reaction. Consequently, in situ activation is much more efficient. 

Simple weight gain measurements showed that approximately 5-6 wt% of BC was deposited onto the surface of these natural fibres. However, the mechanical properties of the natural fibres after bacterial cellulose modification depend on the... 

The practical application of cellulose pulps for different processes is connected with the selection of different methods for modifying this valuable raw material in order to improve its reactivity and solubility. The cellulose modification process can be conducted by chemical (alkalisation), physical (irradiation) " or biochemical (enzymatic transformation) methods. Two major modified strains of Aspergillus nigeP and Trichoderma ree et have been selected as being the best producers of enzymes suitable for biotransformation of softwood- and hardwood-originated pulps. 

The first approach for cellulose modification followed in the Bamer-Kowollik team employs the photoinduced functionalization of photoinitiator-modified substrates with preformed raYrax/cfe-functionalized macromolecules, which are derived from commercially available photoinitiators and nitroxides [DEL 12a]. The approach is based on the generation of radicals at the cellulose surface by mild UV irradiation (5 -max 311 nm) of an immobilized photoinitiator, followed by radical trapping with a nitroxide species. To evaluate the new photochemical grafting method, preliminary studies were carried out based on the nitroxide end functionalization of PEG in solution. Moreover, the light-induced radical technique was used to eouple two synthetie maeromolecular strands. 

Table VI. Percentage of cellulose modifications present and degree of crystallinity (italics in parenthesis) in samples obtained from IR- and NMR-...

Two nonclassical interfacial systems have been developed by Carraher and co-workers (3,10). One utilizes a typical aqueous phase containing a Lewis base (here the dextran) and an added base brought together with a liquid Lewis acid, here a liquid stannane. Thus liquid stannanes such as tributyltin chloride and dibutyltin dibromide can be condensed with aqueous solutions containing the cellulose. Modification was successfully carried out for the majority of liquid stannanes (Table 2). 

Prokhorov, A.V., Calculation of thermodynamic characteristics of some cellulose modifications for predicting its processing conditions, Khimiya Drevisiny, 1981, no. 4, pp. 73-80 (in Latvian). 

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