Some Theoretical Considerations of Cellulose Cross-Linking

Abstract

Much available chemical evidence supports the hypothesis that covalent cross-linking is the best way to improve the resilience of cellulosic fabrics. This paper reviews the theories relating physical properties to cross-linking in rubbery polymers and shows that they apply in some qualitative aspects to cellulose. Particularly, the observed changes in swelling, solubility, modulus, tensile strength, and resilience are consistent with these theories.On the basis of published data, the concentration of intermolecular cross links is estimated ; it is found that at least every twenty-fifth accessible anhydroglucose unit has to be intermolecularly cross-linked when maximum crease recovery values are attained. In rubbery polymers, substantial changes in mechanical properties are obtained at much lower levels of cross-linking. This difference between cellulose and rubbers in response to cross-linking is probably due to the polar nature of cellulose.IT IS widely accepted that cross-linking is the most efficient method to impart high resilience, good crease recovery, and dimensional stability to cellulose fabrics. The cross-linking hypothesis was first advanced by Meunier and Guyot [29] J in 1929 for the formaldehyde-cellulose reaction. It obtained wider attention in 1948 through the work of Cameron and Morton [5], who based their conclusions on the lowered moisture regain, water imbibition, and solubility of rayon samples reacted either with urea-formaldehyde or melamine-formaldehyde precondensates or with formaldehyde or glyoxal alone. It had, however, been known [2, 8, 511 and has reently been confirmed by Reeves et al. [ 36] that wet state treatments of cellulose with formaldehyde . increase the moisture regain and water imbibition. Furthermore, reduction in the solubility of cellulose may also be caused by simple single-ended substituton on the cellulosic hydroxyls. The evidence provided by Cameron and Moron was therefore not unequivocal. , A very powerful argument in favor of the crosslinking hypothesis is the general experience that only difunctional reactants are particularly efficient in improving the resilience of cellulosic fabrics. For example, Steele and Giddings [42,43] found that monomethylol urea increased the crease recovery of cotton to a much lesser extent than dimethylol urea. Most known cellulose cross-linkers are able to polymerize when reacted in the absence of cellulose. It has been argued that these compounds improve resilience by forming polymers within the fiber (25J ] and thus stabilizing the physical entanglements of the molecules ( 28 J . One could imagine that complicated cross-linked structures are obtained by polymerizing difunctional reactants and that the resulting three-dimensional networks are more efhcient in stabilizing the fabric than the linear polymers derived from monofunctional reactants. However, this argument is weakened by the available data indicating that certain reactants do form covalent links with cellulose. This has been shown by Wagner and Pacsu [49] by methylation of...

Performance of durable press finish on cotton with modified DMDHEU, citric acid, BTCA and maleic acid

“…Th e introduction of covalent cross-links into cellulosic fi bres has two important eff ects, i.e. i) it reduces the mobility of chain molecules to move laterally [10], and ii) it extends longitudinally under stress [10,11]. Studies have shown that the unavoidable side eff ect of cross-linking fi nishes is a reduction in elasticity and fl exibility of cellulosic fi bres, next to a considerable decrease in abrasion resistance, tear and tensile strength [12].…”

Effect of Dimethyloldihydroxyethyleneurea on the Properties of Cellulosic Fibers

“…tions may also have increased in length. Gardon and Steele [7] ] have discussed the loss in strength of cotton with application of a crosslinking agent in terms of the effect of crosslinking on the strength of rubberlike polymers. In light of the very high crystallinity cotton is now thought to have, it would appear to be difficult to draw too many analogies between rubber and cotton cellulose.…”

“…It is possible, then, that cotton in the mercerized state can be considered to be equivalent to a highly crosslinked rubber [ 7 ] . The relation between the strength of rubberlike polymers and the degree of crosslinking passes through a maximum as crosslinking is increased.…”

Oxidation of Formaldehyde Cross-Linked Cotton

“…Several different methods have been used to measure the friction (see bibliography given by Moncrieff [12] and see also Flanagan [6], Lyons [9J, Scheier and Lyons [14 ). The capstan method, in which the wool fiber is drawn round a rod of some suitable material, has been and appears likely to remain the most popular, not because it is the best suited to the study of the role of single-fiber friction in any particular set of circumstances, but because it is so easy to use.…”