Cross-linking with formaldehyde

Plastics materials may be produced from casein by plasticising with water, extrusion and then cross-linking with formaldehyde (formolisation). The resultant products have a pleasant horn-like texture and are useful for decorative purposes. The amount of casein produced has decreased since World War n but was still one of the preferred materials for use in the decorative button industry until quite recently. 

The fluid loss and thickening time characteristics of the cement slurry is altered, either by increasing the molecular weight of the lignin by cross-linking with formaldehyde or epichlorohydrin or by adding agents such as sodium sulfite, sodium metasilicate, sodium phosphate, and sodium naphthalene sulfonate. 

Stamm, A.J. (1959b). Dimensional stabilisation of wood by catalysed heat treatment and cross-linking with formaldehyde. Tappi, 42(1), 44—50. 

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. 

I Btersen, H. A.. Cross-linking with formaldehyde-containing reactants, in Handhook of Fiber Sciente and Technology. Vol. 2 Chemical processing of fibers and fabrics.- Functional Finishes, Part A, Lewin, M. and Sello,... 

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. 

Column 125 x 4 bovine serum albumin on silica, cross-linked with formaldehyde... 

In the case of thermosets, deliberate and extensive orientation is virtually unknown. This appears to be the result of the practical difficulties involved, rather than from any theoretical obstacle. For example, it is possible that the fibre Kynol produced by the Carborundum Corporation is oriented to some extent. This is produced from a melt-spun Novolak phenol-formaldehyde resin, which is later further cross-linked with formaldehyde. It is, of course, legitimate to consider carbon fibres as extreme examples of thermosets. Formed by the cyclisation and subsequent graphitisation of polyacrylonitrile (or other suitable precursors), they are highly oriented. 

Poly(vinyl alcohol) has many applications as sizing for nylon and rayon fibers, as an emulsifier and protective colloid, e.g., for polymerizations, as a component in printing inks, toothpastes, and cosmetic preparations, and for fuel oil pipes. In Japan, a fiber is produced by spinning, annealing, and cross-linking with formaldehyde, but the fiber has a somewhat wiry feel. A flameproof fiber is obtained by coextruding poly(vinyl alcohol) with poly-(vinyl chloride). Insoluble photocopy layers are produced by exposure to light in the presence of alkaline dichromate. 

Casein wool is prepared similarly to artifical horn. Casein is precipitated by dilute sulfuric acid at 20° C, then washed and pressed. The alkaline casein solution is subsequently spun at 50° C into an acid precipitation tank and the fiber is cross-linked with formaldehyde. 

Ideally, formals should be formed in the cross-linking with formaldehyde ... 

Polyvinyl Alcohol and Acetals. Polyvinyl alcohol fibers are solution-spun, and then cross-linked with formaldehyde (Fig. 3.72) to make them resistant to water. Polyvinyl formal is cross-linked with phenolic resole to make baked coatings on electrical wire. Polyvinyl butyral is cross-linked with phenolic resin to make extremely tough bullet-proof helmets. 

Active immobilized enzymes were obtained when a cellulose isothiocyanate reacted with glucoamlyase and when cellulose cross-linked with formaldehyde and treated with 2-chlorotriethylamine reacted with D-glucose isomerase. Alcohol dehydrogenase and lactate dehydrogenase have been immobilized, without loss of the enzymic activities, on s-triazinylated DEAE-cellulose. 

The first stationary phases were prepared by packing columns with polymeric particles where benzo- or dibenzocrown ethers were cross-linked with formaldehyde in formic acid. The single crown ether molecules are bridged by methylene groups [71]. Dibenzo-18-crown-6 is a preferred starting material. Igawa et al. [76] also developed a polyamide crown ether resin to separate inorganic anions. 

The immobilization of crown ethers on these support materials may take place in different ways. If silica beads are impregnated with a solution of dibenzo-18-crown-6 in formic acid, a substrate that is stable to hydrolysis is obtained when cross-linking with formaldehyde (see Figure 3.86a). 

---