Cellulosic substrates

The hydrogen abstraction from —SH groups is faster than from —OH groups. Hebeish et al. [9] and Misra et al. [10,11] reported the chain-transfer method of initiation of graft copolymerization onto cellulosic substrates with azobisisobutyronitrile (AIBN) and benzoyl peroxide (BPO) as initiators. 

Chitosan samples with degrees of deacetylation of 65,73,85, and 92% were almost completely adsorbed onto the surfaces of cellulosic fibers, especially onto the surfaces of fines in a variety of cellulosic systems used in industrial operations. Adsorption increased as the degree of deacetylation of chitosan increased. The aggregation of the fine cellulosic particles was maximum at a dosage of about 10 mg/kg. The interactions between chitosan and the cellulosic substrates were dominated by a bridging mechanism at about pH 7 [32]. 

Cellulase enzyme complexes consist of three major types of proteins that synergistically catalyze the breakdown of a cellulosic substrate. Because the enzymes are strictly substrate-specific in their action, any change in the structure or accessibility of the substrate can have a considerable influence on the course of the hydrolysis reaction. A pretreatment method based on exposing cellulosic substrate to phosphoric acid solution [9] and addition of the nonionic... 

In view of the immense commercial importance of phthalocyanines as pigments, it is perhaps surprising that only a few are of importance as textile dyes. This is primarily due to the size of the molecules they are too large to allow penetration into many fibres, especially the synthetic fibres polyester and polyacrylonitrile. An example of a phthalocyanine dye which may be used to dye cellulosic substrates such as cotton and paper is C. I. Direct Blue 86 (96), a disulfonated copper phthalocyanine. In addition, a few blue reactive dyes for cotton incorporate the copper phthalocyanine system as the chromophoric unit (Chapter 8). 

Economic factors play a major part in the selection of sizes. For this reason, starch sizes and their mixtures continue to be the most widely used, particularly on cellulosic substrates. Nevertheless, more costly size polymers may be economically justifiable if this can be offset by higher productivity in weaving. High productivity generally demands high elasticity and... 

Carboxymethylcellulose, an excellent film-former, is a highly effective size on cellulosic substrates but has poor adhesion to synthetic fibres. It is easily desorbed, hot water generally being sufficient, although surfactant and alkali are usually added to increase the efficiency of... 

Certain researchers have preferred soluble salts such as iron(III) nitrate [236] to represent deliberate contamination, whilst others have used insoluble forms. However, even iron (III) oxide in the form of rust is found to vary in catalytic activity depending on physical form. Although uniform distribution of the contamination, at least below a relatively low concentration, has been claimed to be less troublesome than localised concentrations, there is not even agreement on this. A further complication is that different studies have been carried out in either the absence or the presence of a cellulosic substrate. With these provisos in mind, the catalytic behaviour of trace metals and the effects of some preventive agents will be outlined. 

Oxidative bleaching of wool is invariably carried out with hydrogen peroxide. The active species involved is likely to be the same as on cellulosic substrates but specific reactions with wool amino acid residues must be considered. The primary reaction is oxidation of cystine disulphide bonds leading to the formation of cysteic acid residues (Scheme 10.41). The rupture of disulphide crosslinks, with attendant increase in urea-bisulphite and alkali solubility values, adversely affects fibre properties. As the severity of bleaching conditions increases, the urea-bisulphite solubility remains little changed but the relationships between alkali solubility and cysteic acid (Figure 10.36) and between cystine and cysteic acid (Figure... 

Many other products of a variety of structures have been patented for the brightening of cellulosic substrates. The reader is referred to the reviews mentioned earlier for further information. 

These will be considered first in relation to batchwise application, followed by variations pertinent to continuous dyeing and printing. The discussion relates solely to cotton, by far the most important substrate for these dyes application to other cellulosic substrates follows generally similar principles, the main difference being in product concentrations. 

Hrmova, M., Farkas, V., Lahnstein, J., and Fincher, G.B. (2007) A barley xyloglucan xyloglucosyl transferase covalently links xyloglucan, cellulosic substrates, and (l,3 l,4)-D-glucans. J. Biol. Chem. 282, 12951-12962. 

Cellulose phosphate(s), 5 401 8 29 20 459 flame resistant, 8 27 paper, 5 408 solubility of, 5 402 Cellulose propionate manufacture of, 5 418 moisture properties, 5 416t Cellulose propionate valerate, 5 421 Cellulose propionate isobutyrate, 5 421 Cellulose substrates, dyeability of, 9 482-483... 

Ionisation of the hydroxy groups in cellulose is essential for the nucleophilic substitution reaction to take place. At neutral pH virtually no nucleophilic ionised groups are present and dye-fibre reaction does not occur. When satisfactory exhaustion of the reactive dye has taken place, alkali is added to raise the pH to 10-11, causing adequate ionisation of the cellulose hydroxy groups. The attacking nucleophile ( X ) can be either a cellulosate anion or a hydroxide ion (Scheme 7.8), the former resulting in fixation to the fibre and the latter in hydrolysis of the reactive dye. The fact that the cellulosic substrate competes effectively with water for the reactive dye can be attributed to three features of the reactive dye/ cellulosic fibre system ... 

Because the pKa of the cellulosic substrate is lower than that of water, reaction with the fibre according to Scheme 7.8 is favoured [20]. 

The Ce + initiation of grafting and the products obtained from polysaccharides has been reviewed repeatedly5>6. Only some studies of the optimal grafting conditions for grafting of cellulose substrates will be treated here2°>29 30> The reactants should be added to the cellulose suspension in the order CeI,+ initiator and then vinyl monomer to increase the yield of grafted polymer. The optimum conditions are not only related to the pH of the reaction medium but to the relations between the Ce + concentra-... 

Figure 3. Schematic for the degradation of cellulosic substrates by a microbial consortium.

Cotton and Other Cellulosic Fibres. The dominant natural cellulosic fibre is cotton, the other natural cellulosic fibres, or bast fibres, include flax, linen, jute and ramie. The so-called regenerated fibres, which include viscose, modal fibres and lyoceU (Tencel), are made by various chemical treatments of cellulosic substrates. The dyeing and printing of cellulosic fibres and materials is carried out using, in decreasing order of scale and importance, reactive, direct and vat dyes. ... 

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