Formaldehyde cross-linking, cellulose

Formaldehyde cross-linking is used extensively on a commercial basis, and the pore structures of formaldehyde-cottons have been characterized. Formaldehyde cross-linked cellulose appears to have some application as a medium for gel filtration of carbohydrates, and an Escherichia coli lipopolysaccharide cross-linked with glutaraldehyde has been used in the isolation of anti-polysaccharide antibodies. ... 

Formaldehyde is an important constituent of many textile finishes, especially finishes for cellulosic textiles. As the main chemical route to cross-linking cellulose, formaldehyde or a reactant made from formaldehyde is found in a variety of finishes, ranging from durable press agents to water repellents. 

The simplest compound which cross-links cellulose is formaldehyde, and the literature relating to the interactions which take place between these materials has been thoroughly reviewed. ... 

The effects of diffusion control on the rate of radiation-initiated graft polymerization of cellulose have been studied theoretically. The effects of such variables as the initiator concentration, temperature, and monomer polymer ratio on the graft copolymerization of acrylamide and 0-methylcellulose have been investigated. The thermal properties and behaviour of graft copolymers of formaldehyde-cross-linked 0-cyanoethylcellulose and acrylates have been studied. Copolymerization of periodate-oxidized cellulose (aldehydocellulose) with glycidyl methacrylate in the presence of an enzyme e. peroxidase) afforded a means of immobilizing the enzyme without loss of activity. ... 

Reaction with a derivative of formaldehyde-cross-linked DEAE-cellulose beads... 

The thermoplastic or thermoset nature of the resin in the colorant—resin matrix is also important. For thermoplastics, the polymerisation reaction is completed, the materials are processed at or close to their melting points, and scrap may be reground and remolded, eg, polyethylene, propjiene, poly(vinyl chloride), acetal resins (qv), acryhcs, ABS, nylons, ceUulosics, and polystyrene (see Olefin polymers Vinyl polymers Acrylic ester polymers Polyamides Cellulose ESTERS Styrene polymers). In the case of thermoset resins, the chemical reaction is only partially complete when the colorants are added and is concluded when the resin is molded. The result is a nonmeltable cross-linked resin that caimot be reworked, eg, epoxy resins (qv), urea—formaldehyde, melamine—formaldehyde, phenoHcs, and thermoset polyesters (qv) (see Amino resins and plastics Phenolic resins). 

All wet strength agents are bi- or multi-functional molecules with the capability to cross-link with each other or with cellulose. The choice of chemistry depends to a large extent on pH. In acid systems, the main wet strength agents are urea-formaldehyde (U/F) and melamine-formaldehyde (M/F) resins, whereas in neutral and alkaline systems polyamine-polyamide-epichlorohydrin resins are more effective. However, these are not the only systems in use, and a summary of these and other available methods is provided in Figure 7.22. 

Kamogawa, and Sekiya (54) studied the graft polymerization of acrylamide onto cotton fabric using ceric ammonium nitrate as the catalyst. Similarly to Kulkarni et al. (35) the authors performed subsequent cross-linking with formaldehyde amd methylol compounds. From precipitation studies by acidification of cuprammonium solutions on mixtures of polyacrylamide and cellulose on the one hand and polyacrylamide-cellulose grafts on the other the authors conclude that chemical bonds must exist between the two polymers in the grafted product. 

The first synthetic plastics were the phenol-formaldehyde resins introduced by Baekeland in 1907 [1], Melamine and urea also react with formaldehyde to form intermediate methylol compounds which condense to cross-linked polymers much like phenol-formaldehyde resins. Paper, cotton fabric, wood flour or other forms of cellulose have long been used to reinforce these methylol-functional polymers. Methylol groups react with hydroxyl groups of cellulose to form stable ether linkages to bond filler to polymers. Cellulose is so compatible with these resins that no one thought of an interface between them, and the term reinforced composites was not even used to describe these reinforced systems. 

After impregnation of the cellulose substrate with an aqueous solution containing urea-formaldehyde precondensates and subsequent short heating at 130°-160°C, cross-linking takes place ... 

The most important cotton etherification treatments are those that produce wrinkle resistance in fabrics [331,333,334]. The aldehydes, formaldehydes, and glyoxals, react with the OH groups of two cellulose chains as well as those of one chain. Reaction in which a bond is established between the two cellulose molecules is called cross-linking and is the basis for profound changes in the cotton fiber. Cross-linking produces resiliency in the fiber to give the needed dimensional stabilization, wrinkle resistance, and crease retention for modern durable-press cellulosic fabrics. Cross-links based on etherification reactions traditionally have been used because of their durability to repeated laundering and wear. 

Although formaldehyde is inexpensive, readily available, highly reactive, and ideally would be the simplest ether cross-link between cellulose chains, there has been only limited successful usage of this reagent to produce wrinkle resistant cotton. A treatment based on gaseous- or vapor-phase application of formaldehyde to cotton under rigidly controlled conditions has gained some acceptance. 

The high-temperature cross-linking of cotton cellulose by polycarboxylic acids, having three to four carboxyls per molecule, has been extensively investigated as a method of formaldehyde-free durable-press finishing. In 1963, Gagliardi and Shippee [383] showed... 

Levin M, Handbook of Fiber Science and Technology Vol. II. Chemical Processing of Fibers andFabrics. Functional Finishes Part A,Chnpters 1 (Cross-linking of cellulosics) and 2 (Cross-linking with formaldehyde-containing reactants). New York, Marcel Dekker, 1983. 

Formaldehyde treatment causes wood to become brittle. This embrittlement may be caused by the short inflexible cross-linking unit of the -O-C-O- type. If the inner carbon unit were longer, there would be more flexibility in this unit, and the embrittlement should be reduced. Most of the loss in wood strength properties is probably caused by the hydrolysis structural cellulose units with a strong acid catalyst. 

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