Mercerization crystalline alkali-cellulose

Sarko, A., Nishimura, H., and Okano, T., Crystalline alkali-cellulose complexes as intermediates during mercerization, in The Structures of Cellulose, Atalla, R.H., Ed., ACS Symposium Series, No. 340, American Chemical Society, Washington, D.C., 1987, p. 169. 

Crystalline Alkali-Cellulose Complexes as Intermediates During Mercerization... 

The most important alternative crystalline form is cellulose II. This form can result from treatment of cellulose in concentrated alkali, such as 23% NaOH, followed by rinsing in water. This is also the main form that results from crystallization of dissolved cellulose, such as regeneration of rayon. Supercritical water can also effect the transformation [216]. The treatment of cotton in milder alkali, for industrial mercerization, amounts mainly to disruption and decrystallization rather than transformation to crystalline II. Cellulose II can occur as the native state when the normal biosynthesis and subsequent crystallization is disrupted [217-219]. 

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. 

When crystalline cellulose I is treated with aqueous alkali solutions of sufficient strength, a process known as mercerization takes place. As a result of it, cellulose I is converted to cellulose II, the most stable or the four crystalline cellulose polymorphs. The conversion proceeds in the solid state, without apparent destruction or change in the fibrous morphology of the cellulose. As our diffraction analysis indicates, however, it is accompanied by a reversal of the chain packing polarity—from the parallel-chain cellulose I to the... 

Strong basic solutions, such as sodium hydroxide, penetrate the crystalline lattice of a-cellulose producing an alkoxide called alkali or soda cellulose. Mercerized cotton is produced by aqueous extraction of the sodium hydroxide. 

Cellulose crystallinity is not uniform. A simple experiment of immersing cellulose in cold concentrated alkali, a process used for enhancing the dye-absorbing quality of cotton fabrics called mercerization, was found already in the 1930s on the basis of X-ray diffraction to produce a cellulosic allomorph with different unit cell dimensions [13,14]. This was given the... 

The mercerizing is based on the action of cold strong alkali (usually NaOH) solution and concomitant application of a stretching force, followed by neutralization. As is shown in Figure 9.6.4, this allows cellulose fibre to pass from the meta-stable natural crystalline structure I to the stable cellulose II form. The mercerization produces effluents with very high pH, requiring further acidic treatment for discarding. 

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