Mercerization, effect swelling

Typical one-step commercial mercerization of cotton yam with caustic or liquid ammonia causes only partial conversion to cellulose II or cellulose III. Cotton cellulose is partially converted to cellulose II by repeated mercerization, the swelling of cellulose in strong alkali (eg, 23% NaOH), followed by rinsing and drying. Cellulose III results from treatment of cellulose with liquid ammonia (ammonia mercerization) or amines. Cellulose III can be made from either cellulose I or II. When treated with water, cellulose III can revert to its parent stmcture. Cellulose IV can be prepared by treating cellulose I, II, or III in glycerol at temperatures 260°C. Conversion of the crystal form in cotton fibers to cellulose IV can be effected by heat treatment of ethylamine-treated cotton cellulose in either saturated steam or formamide with minimal fiber degradation (86). Like cellulose III, cellulose IV preparations can revert to their parent stmctures. 

The effect of the swelling depends not only on the reagent but on the cellulose. For example, the LODP of Pima S-5 cotton before and after mercerization is 168 and 87, respectively vrtiereas the LODP of Deltapine Smooth Leaf cotton before and after mercerization is 153 and 62, respectively (41). The large fall in LODP after mercerization is noteworthy and needs to be borne in mind when attempts are made to elucidate the supramolecular structure of celluloses. 

Grafting to cellulose in the absence of solvent (87) is initiated by y-rays by means of a °Co source. The polymer-to-monomer ratio has only a minor effect on the PVF content, which is in the range of 2-5 wt%. In the presence of solvents that cause swelling of cellulose (mercerization), the PVF content increases dramatically. At a radiation of 30 kGy (3 Mrad) in the presence of dimethylformamide, the PVF content of the graft copolymer is 26.6% in its absence it is 4.1%. 

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