Cotton cellulose modification

The modification of the properties of fibrous cotton cellulose through free-radical initiated copolymerization reactions with vinyl monomers has been investigated at the Southern Laboratory for a number of years. Both graft and block copolymers are formed. Under some experimental conditions the molecular weight of the polyvinyl polymer, covalently... 

The morphology of the fibrous cellulose graft copolymers depended on the method of initiation of free radical formation, experimental conditions during the copolymerization, chemical modification of the cellulose before reaction, and the type of monomer used (60). Variations in the shape of the fibrous cross section, in layering effects in the fiber, and in the location and distribution of the grafted copolymer in the fiber were observed by electron microscopy (61). Cotton cellulose—poly (acrylonitrile) copolymer was selected to show the possible variations in location and distribution of the grafted copolymer in the fiber. 

The modification of cotton cellulose by treatment with low-temperature, low-pressure ammonia plasma created by passing ammonia gas through a radiofrequency (rf) electric field of 13.56 MHz has been reported (1). Earlier reports (2,3,4) were on the effects of rf plasma of argon, nitrogen or air on a group of polysaccharides that included cotton and purified cellulose. 

The existence of an ordered structure in cellulose is shown conclusively by wide-angle x-ray diffraction (WAXD) and electron diffraction studies (3). The diffraction patterns exhibit reasonably well-definid reflections for which unit cells have been defined. There are four basic recognized crystalline modifications, namely, cellulose I, II, III and IV. By the WAXD method as proposed by Hermans (4,5) it has been found that native celluloses of different biological origin vary in crystallinity over wide limits, from A0% in bacterial cellulose to 60 in cotton cellulose and 70 in Valonia cellulose. 

The methodology of CMA is straightforward and superficially sinple but requirements for control of a multitude of chemical steps in the analysis impose severe demands for precision and reproducibility of results. Nevertheless, there is at present no alternate measurement or series of measurements that provide detailed information concerning the sites of chemical reactions, the types of accessible surfaces, and the order of hydrogen bonding that characterize the cotton fiber and are pertinent to the chemical modification and finishing of cotton cellulose. 

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. 

Benerito, R., Ward, T., Soignet, D.M., Hinojosa, O., 1981. Modifications of cotton cellulose surface by use of radiofrequency cold plasmas and characterization of surface changes by ESC A. Text. Res. J. 51, 224-232. 

Patino, A., Canal, C., Rodriguez, C., Caballero, G., Navarro, A., Canal, J.M., 2011. Surface and bulk cotton fiber modifications plasma and cationization. Influence on dyeing with reactive dye. Cellulose 18,1073-1083. 

Etherification. The accessible, available hydroxyl groups on the 2, 3, and 6 positions of the anhydroglucose residue are quite reactive (96) and provide sites for much of the current modification of cotton cellulose to impart special or value-added properties. The two most common classes into which modifications fall, include etherification and esterification of the cotton cellulose hydroxyls as well as addition reactions with certain unsaturated compounds to produce cellulose ethers (see Cellulose Ethers). One large class of cellulose-reactive dyestuffs in commercial use attaches to the cellulose through an alkali-catalyzed etherification by nucleophilic attack of the chlorotriazine moiety of the dyestuff ... 

It was later determined that the crystallographic form cellulose I was irreversibly chang to the form cellulose II. The unit cell of cellulose II also contained two cellobiose units with axes a = 0.814 nm, b = 1.03 nm, c = 0.914 nm, and fi = 62° (angle between a and c axes). The fibrillar cellulose II is less ordered than fibrillar cellulose I and is about 60% crystalline. This 1840s development, now called mercerization, is probably the most important process for the modification of natural cellulose, particularly cotton cellulosic textile fibers, to current date. Lowe later confirmed these results and showed the effects of mercerization on cotton fibers while under tension. 

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). 

An older method of cellulose fiber modification is mercerization [22,33-36], which has been widely used on cotton textiles. Mercerization is an alkali treatment of cellulose fibers. It depends on the type and concentration of the alkalic solution, its temperature, time of treatment, tension of the material, and the additives used [33,36]. At present there is a tendency to use mercerization for natural fibers as well. Optimal conditions of mercerization ensure the improvement of the tensile properties [33-35,37] and absorption characteristics [33-35], which are important in the composing process. 

Polymers are very large organic molecules that are either made synthetically or are of natural origin, and find use as plastics, rubber, fibers, and coatings. Polymers were first produced commercially in 1860 by modification of cellulose from wood or cotton, followed by a fully synthetic product made from phenol and formaldehyde in 1910. 

Amorphous cellulose, so defined, was reported for two simple but noteworthy modifications of cotton linters. First, linters which had been swollen with cold 10% sodium hydroxide, washed, and dried by solvent exchange prior to thallation and methylation, showed an amorphous content as high as 27 %. Secondly, unswollen linters appeared to contain only 0.25 to 0.50% of amorphous cellulose. Similarly, swollen ramie appeared to contain 18% of amorphous cellulose unswollen ramie, 0.25%. 

Modification of cotton textiles by chemical plating of their surfaces with cobalt (II) or nickel (II) salts produced metallized fibers and fabrics with high electrical conductivity and the capability to transport and dissipate thermal energy (109). The heat capacity of cellulose acetate fibers was increased by treatment with epoxy compounds (110). 

Water vapor adsorption isotherms have been obtained on cotton from room temperature up to 150°C [303,304]. Theoretical models for explaining the water vapor sorption isotherms of cellulose have been reviewed [303]. Only adsorption theories will be discussed here at ambient temperatures. The shape of the isotherm indicates that multilayer adsorption occurs and thus the Brunauer, Emmett and Teller (BET) or the Guggenheim, Anderson and deBoer (GAB) theory can be applied. In fact, the BET equation can only be applied at relative vapor pressures (RVPs) below 0.5 and after modification up to a RVP of 0.8 [305]. The GAB equation, which was not discussed in the chapter in the book Cellulose Chemistry and Its Applications [303], can be applied up to RVPs above 0.9 [306]. Initially as the RVP... 

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