Cotton accessibility

Fig. 8. Internal volume (FQ that is accessible to sugars as functions of the cotton molecular diameters (33). (a) Batting A, greige , scoured—bleached , caustic mercerized H, Hquid ammonia treated, (b) Fabric 0> scoured—bleached V> cross-linked.

Scouting and bleaching slightly increase the accessible internal volume, Hquid ammonia treatment of the scoured—bleached cotton decreases it slightly, caustic mercerization substantially enhances accessibiHty, and cross-linking to impart durable press properties reduces this accessible internal pore volume substantially. 

Etherification. The accessible, available hydroxyl groups on the 2, 3, and 6 positions of the anhydroglucose residue are quite reactive (40) and provide sites for much of the current modification of cotton ceUulose to impart special or value-added properties. The two most common classes into which modifications fall include etherification and esterification of the cotton ceUulose hydroxyls as weU as addition reactions with certain unsaturated compounds to produce ceUulose ethers (see Cellulose, ethers). One large class of ceUulose-reactive dyestuffs in commercial use attaches to the ceUulose through an alkaH-catalyzed etherification by nucleophilic attack of the chlorotriazine moiety of the dyestuff ... 

Accessibilities of Cellulose in Original and Modified Wood Pulps and Cotton Linters20... 

Mercerization apparently causes an appreciable increase in the amount of accessible cellulose in cotton while unsubstituted rayons appear to contain a greater proportion of intercrystalline cellulose than either type of cotton. The dye affinities and moisture-regain capacities of these fibers generally seem to be in the order of increasing accessibilities. 

Table 5.1 Effect of swelling on the surface area of cotton as measured by chemical (thallation) and physical (N2 adsorption) methods. (Source G.A. Roberts, Accessibility of Cellulose , in Paper Chemistry , ed. J.C. Roberts, ch. 2, Blackie, Glasgow, 1991).

A new model of the cotton-dust analyzer was constructed to overcome some of the shortcomings of the prototype. It was more compact and easier to operate than the original machine. The sizing-screen arrangement in the new model was more accessible than in the original machine to facilitate the evaluation of various screen sizes. It was also equipped with an air regulator to maintain a constant air pressure on the spray bar for Improved airflow characteristics. Also, a high-efficiency particulate air... 

The development of natural resistance in corn (Zea mays) to the corn earworm (CEW) Helicoverpa zea) received many contributions. The CEW is a major insect pest of maize and other crops (cotton, soybeans, etc.) the eggs are laid on the silks, and the larvae access the ear by feeding through the silk channel. 

The side chain Cotton effect in the 270-290-nm region clearly arises from the tyrosine residues. This effect disappears on denaturation. However, whether the effect is owing to the surface, accessible tyrosines, or... 

Results with newsprint are roughly intermediate between those for wood and cotton linters. Hydrolysis of the delignified chemical pulp component (about 20% of the total newsprint furnish) and of the accessible carbohydrates of the groundwood component is accomplished with about 4 days of digestion. Further hydrolysis of the groundwood carbohydrate is then stymied by lignin as in the case of red oak and Douglas fir. 

Most experiments were performed with cotton or cotton linters as highly crystalline celluloses. Table I shows conditions leading to complete dissolution. A minimum amount of an acid which forms a cellulose ester (sulfuric or trifluoromethylsulfuric acid) (Entries 5 7-14) is necessary for the reaction. The dissolution is accelerated by a temperature increase (Entries 10-12 13, 14) and leads to water-soluble cellulose acetate hydrogensulfate. Whereas this primary hydrolysis can be achieved within 1-5 min, the deesterification and complete hydrolysis of the soluble cellulose derivative proved to be much more difficult. This is in contrast to the generally accepted view that the main resistance to the hydrolysis of cellulose lies in the crystalline nature or low accessibility determining the heterogeneous first step of the reaction. 

An important parameter influencing the mode of action of cellulases is the accessibility of the cellulose to the enzymes. The molecular weights of cellulases range between 30 and 80 kDa. A comparison of the size of cellulase (3-8 nm) and the pore size of cotton swollen in water (1-7 nm) shows very clearly that cellulases can penetrate the cellulose to a limited extent only. In addition, the enzyme reaction takes place preferentially on amorphous cellulose because the more compact, crystalline cellulose structures do not offer any space for such macromolecules. Thus - provided of enzyme and process parameters have been selected correctly -cellulases act mainly on the textile surface. In this way interesting effects on cellu-losic fibers can be achieved. 

Electronic Circular Dichroism In contrast to most organic compounds in which CD measurements are limited to the ultraviolet region, most metal complexes possess d-d absorption bands in the more accessible visible and near-infrared regions, allowing for relatively easier application of electronic circular dichroism (ECD) measurements. In fact, the first observation by Cotton of optical rotation measurements through an absorption band and interpretation in terms of differential absorption of the circularly polarized beam was performed on solutions of L-tartrate chromium(III) and copper(II) complexes.100... 

Household textiles such as bed linens or towels can occur at a crime scene— for instance, a body bundle wrapped in a cotton-polyester duvet cover and deposited in a wood (see case study in Section 7.4.6.1). Biodegradation of the duvet cover will depend on a number of factors including the surface the bundle is placed on, the composition of the fabric, the degree of deterioration of fabric prior to deposition, and whether body decomposition products have access to the textile. 

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