Recent Developments in the Chemistry of Cellulose which Pertain to the Cross-Linking of Cotton

The distributions of sites of attachment of substituents or cross linkages (a) at the 2–0-, 3–0-, and 6–0-positions of the d-glucopyranosyl units, (b) along the molecular chains of cellulose, (c) on or in the microstructural units, and (d) within the fiber cross sections are reviewed in order to develop perspective for the factors that influence and control these distributions. Among the factors determining the site of attachment in the d-glucopyranosyl unit are: (1) the type of reaction (e.g., reversible or nonreversible), (2) the specific nature of the reagent (e.g., molecular size), and (3) the medium from which the reagent is introduced. Means of controlling this distribution are discussed. There is no available information on the distributions of linkages introduced along the molecular chains of cellulose from reactions that occur without disruption of the crystalline order. It is evident, however, that, even under these conditions, every molecule in the cellulose matrix has one or more accessible segments along its chain. Measurements that are specific to the distribution of substituents among the total d-glucopyranosyl units, but which are applicable, in first-order approximation, to the units along the molecular chain, are discussed in connection with reactions conducted in mercerizing media. Evidence indicative of reactions occurring on the surfaces of highly ordered micro-structural units (microfibrils or bundles of microfibrils) has been obtained from measurement of the distribution of substituents introduced into the d-glucopyranosyl units of cotton cellulose under nonmercerizing conditions. Penetration within these units is evident under mercerizing conditions of reaction. An interrelationship between the site of attachment in the d-glucopyranosyl unit and the site of reaction in the microstructural unit is discussed. At the fiber level of structure, the complex interplay between rate of chemical reaction and rate of diffusion into the fibers is considered. Gross variations of distribution of substituents or cross linkages in the fiber cross section (from peripheral to uniform) result from changes in the two rates noted. In a case examined in some detail, wrinkle-recovery angles benefit from the more uniform distribution of cross linkages.