Cellulose modification with acetic

Various details of procedure are known for the esterification of cellulose with acetic anhydride in acetic acid. solvent. The factors of pretreatment, catalyst concentration, acetylation temperature and time of reaction are kept in balance in order that products of satisfactory appearance and the desired range of viscosity will be obtained. Modifications of this general formula usually involve the use of different solvents to replace part or all of the acetic acid. 

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. 

One of the early attempts of in situ activation was the reaction of carboxylic acids with sulphonic acid chlorides that was adopted for the homogeneous modification of cellulose. The exclusion of the base simplified the reaction medium and the isolation procedure [29]. There is an ongoing discussion about the mechanism which initiates esterification of cellulose with the carboxylic acids in the presence of p-toluenesulphonic acid chloride (TosCl). The mixed anhydride of p-toluenesulphonic acid (TosOH) and the carboxylic acid is favoured [30]. However, from H NMR experiments with acetic acid/TosCl, it was concluded that a mixture of acetic anhydride (2.21 ppm) and acetyl chloride (2.73 ppm) was responsible for the high reactivity of this system (Figs 16.2 and 16.3). 

Finally on studies on the determination of nitric oxide, platinum electrodes sealed in glass were mocUfied with Nation and cellulose acetate. Modification with Nation was achieved by placing over a freshly polished electrode a lOpl volume of a 0.5% (w/v) solution of Nation in ethanol and allowing the solvent to dry in air. Modification with cellulose acetate was carried out in a similar fashion with an acetone/cyclohexanone solution (2%) of cellulose acetate and again employing a 10 il volume. Prior to use, the electrode was contacted with a phosphate buffer solution for 30 min. to allow the modifying layers to equilibrate and swell. The determination of NO was carried at +0.90V vs SSCE to ensure that the response was mass transport limited. 

Cellulosics. CeUulosic adhesives are obtained by modification of cellulose [9004-34-6] (qv) which comes from cotton linters and wood pulp. Cellulose can be nitrated to provide cellulose nitrate [9004-70-0] which is soluble in organic solvents. When cellulose nitrate is dissolved in amyl acetate [628-63-7] for example, a general purpose solvent-based adhesive which is both waterproof and flexible is formed. Cellulose esterification leads to materials such as cellulose acetate [9004-35-7], which has been used as a pressure-sensitive adhesive tape backing. Cellulose can also be ethoxylated, providing hydroxyethylceUulose which is useful as a thickening agent for poly(vinyl acetate) emulsion adhesives. Etherification leads to materials such as methylceUulose [9004-67-5] which are soluble in water and can be modified with glyceral [56-81-5] to produce adhesives used as wallpaper paste (see Cellulose esters Cellulose ethers). 

DNA modification of a commercial carbon ink without any electrochemical preconditioning by dry-adsorption was also reported. The surface was modified by covering with dsDNA solution and leaving the electrode to dry overnight. A stable, thin (about 100 p,m) DNA layer was obtained [111, 112]. The dsDNA was also demonstrated to be stably adsorbed when entrapped in a cellulose-acetate-based film on the surface of a carbon-based ink [113]. 

The choice of material for use as inhibitor depends mainly upon the type of propellant, that is, DB, CMDB, Composite and Fuel-rich and also on the ingredients in their formulations. For double-base propellants, cellulosic materials such a cellulose acetate, ethyl cellulose and different filled or unfilled flexible polyesters are used while fuel or binder material filled with inert substances such as asbestos, mica, silica, etc. in fine powder form is used for composite propellants. Since nitroglycerine is present in CMDB propellants also as in DB propellants, the materials used for DB propellants may also be used with minor modifications for the inhibition of CMDB propellants. 

PULP (Wood) PRODUCTION AND PROCESSING. Pulps can be defined as fibrous products derived from cellulosic fiber-contaiumg materials and used in the production of hardboard, fiberboard, paperboard, paper, and molded-pulp products. With suitable chemical modification, pulps can be used in Hie manufacture of rayon, cellulose acetate, and other familiar products. Pulps can be produced from any material containing cellulosic fiber but in North America and several other regions of the world, wood is the predominant source of pulp. This description is confined to the production and processing of wood pulp,... 

---