Mercerized cotton accessibility

Accessibility. The extent of etherification is often determined by the accessibility of a substrate under a given environment. As Segal discussed [8], the extent of methylation with ethereal diazomethane (indicated by methoxyl contents) increased in the order hydrocellulose (5.9%) < cotton (7%) < mercerized cotton (14.9%) < cuprammonium rayon (18.6%) < ball mill-ground cotton (20.6%). Crystallinity of the cellulose was considered to be a significant factor. 

The effect and action of enzymes seems to be very limited because ol the stronger conditions of alkali of mercerizing strength. Enzymatic hydrolysis is accelerated when mercerization is carried out without tension [44]. The greater accessibility and lower crystallinity of cellulose mercerized without tension is a decisive factor in the enzymatic hydrolysis process. Mercerized cotton is generally more prone to enzymatic modification than untreated cotton. 

Crystalline Material (X) and Accessibility (A ) of Cotton and Mercerized Cotton Calculated fran Water Sorption Data ( )... 

Figure 5. Internal water (V.) that is accessible to a solute as a function of molecular weight. Column packings were cotton (X) and mercerized cotton ( ).

The influence of polyethylene morphology on its reactivity has been analyzed in Section 1.3.4.1 this section will be limited to the case of cellulose, which has been the subject of many studies. It has long been known that the reactivity of cellulose depends on its morphology. Thus, when cotton is etherified by diazomethane the extent of conversion of hydroxy group (molar %) is 7.0,14.9,18.6,5.9 and 20.6 for native cotton, mercerized cotton, cupro rayon, hydrocellulose and finely ground cotton respectively it is obvious that these values vary with the accessibility of the material. 

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. 

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. 

Under similar acetylation conditions [153], the acetyl content of cotton (4.3%) was more than twice that of ramie (2.1%) or linen (1.3%) cellulose. Mercerization [8,154,155] greatly enhances the reactivity (or accessibility) of cellulose if it is maintained in a never-dried state. Drying of mercerized cellulose considerably reduced its reactivity to even less than half that of the unmercerized samples [8]. However, its impact, can be alleviated by dehydration through a solvent exchange process. The reactivity of mercerized samples expressed by acetyl content increased from 1.7% to 17.7% if water-washed sample was solvent-exchanged with pyridine and to 29% if washing directly with absolute ethanol and a subsequent pyridine exchange. 

Fiber preparation ordinarily involves scouring to remove foreign material and ensure even access to dye hquor from the dye bath. The textile material generally needs a pretreatment before dyeing. Wool must be washed to remove wax and dirt and sometimes bleached. Cotton must be boiled and bleached to remove pectins and cotton seeds and is mercerized. Sizes and spinning oils must be eliminated [7]. 

The effects of slack and tension mercerization on the morphology and accessibility characteristics of remie, flax and cotton fibres are compared [66], Mercer-... 

FIGURE 9.52 Internal water (Vi) that is accessible to scoured/bleached ( ), caustic mercerized ( ), and cross-linked with 4% DMDHEU (+) cotton cellulose. Ethylene glycols were used as molecular probes. 

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