Wool, formaldehyde treatment

The reaction of aqueous solutions of formaldehyde with wool keratin has been Investigated by a number of workers (1-7). Introduction of crosslinks Into wool by formaldehyde treatment was postulated In these studies, but little direct evidence for crosslinking was found. Mason ( ) has presented physical evidence for formation of crosslinks as methylene groups In wool. 

Trezl and coworkers (12,13) studied vapor phase formaldehyde treatment of wool under vacuum. Treatments were conducted at 60 to 100 C using no catalyst or formic acid, trlmethylamine, trlethylamlne, 15-crown-5-ether and 18-crown-6-ether as catalysts. In their system, the presence of water vapor was found to Inhibit the rate of formaldehyde uptake. They found that more sites were attacked by formaldehyde vapor Chan by aqueous formaldehyde. Optimum reaction rates were observed at 70 to 80°C, and formic acid was found to be the most effective catalyst of those used. Scanning electron microscopy (SEM) did not reveal any scale damage to the wool. The treated wool was more thermally resistant, and no change In hand or dyeability of the wool was found. The treated wool had Improved tensile strength and Initial modulus with little change in elongation at break. 

These dyeing studies demonstrate that weathering of the face of the wool fabric was much more severe than noted by degree of yellowing alone and that formaldehyde treatment tended to moderate the degree of weathering. 

Formaldehyde treatment also cross-links wool. Many pairs of amino side-chains are capable of reacting with formaldehyde, but it has proven difficult to determine which are actually involved. For example, formaldehyde may react with lysine side-chains. 

Formaldehyde Treatment of Wool. The impioved resistance of formaldehyde treated wool to the action of boiling Yate, alkalis, alkali sulfides, etc., may be utilized to protect wool in processes such as bleaching, dyeing, washing, etc., which in% olve exposure to these agents. In a process patented by Kaon in 1905, it is stated that satisfactory resistance of woolen fibers can be developed by treatment with foimaldehyde apors or dilute neutral or weakly acid solutions containing as little as 0.03 per cent formaldehyde. Ciood results ai e reported when a hot 4 per cent formaldehyde solution is employed. 

Since formaldehyde treatment also increases the resistaiice of wool to certain dyes, pattern ef ects may be secured by making use of this fact in the dyeing process. Both formaldeh de and condensation products of fomialdehyde with cresoliSuKonic acid may be employed for this purpose according to a German patent. Dyed woolen fabrics ha e been claimed to. show gi eatei fastness and stability after treatment with formaldehyde alone or in combination with tannic acid . 

Polymers. AH nitro alcohols are sources of formaldehyde for cross-linking in polymers of urea, melamine, phenols, resorcinol, etc (see Amino RESINS AND PLASTICS). Nitrodiols and 2-hydroxymethyl-2-nitro-l,3-propanediol can be used as polyols to form polyester or polyurethane products (see Polyesters Urethane polymers). 2-Methyl-2-nitro-l-propanol is used in tires to promote the adhesion of mbber to tire cord (qv). Nitro alcohols are used as hardening agents in photographic processes, and 2-hydroxymethyl-2-nitro-l,3-propanediol is a cross-linking agent for starch adhesives, polyamides, urea resins, or wool, and in tanning operations (17—25). Wrinkle-resistant fabric with reduced free formaldehyde content is obtained by treatment with... 

A number of chemical treatments have been suggested to reduce the photo-yellowing of bleached and whitened wool. Tetrakishydroxymethyl phosphonium chloride, thiourea (alone or as a formaldehyde condensate) and some mercaptans and reducing agents [20,21 ] and the reaction of wool with sulfamic acid [22] have been shown to offer some protection against photo-yellowing, particularly on wet wool. 

Such crosslinks would be expected to Increase the Internal viscosity within the fiber, thereby decreasing the rate at which setting Is lost In hot water. This hypothesis was tested by Caldwell et al. ( ) who compared the crease recoveries of wool fabrics treated with aqueous formaldehyde or formaldehyde vapors with those of untreated fabrics. They found that the treatments enhanced the set through Introduction of crosslinks that Inhibited the rearrangement of disulphide bonds In the wool. Kann (9,10) noted that formaldedye treatment protected wool against alkali... 

Treatment of wool with a FWA, followed by post-treatment with thiourea/formaldehyde by a pad/cure method, confers a high level of protection against photoyellowing and also improves the initial fabric whiteness (134). Unfortunately, this process is not commercially viable, partly because of environmental concerns about thiourea and formaldehyde and also because much of the benefit is lost after laundering. An alternative approach is to physically separate the FWA from the wool fiber by incorporating the whitener into a suitable polymer that can be applied as a surface treatment to wool fabrics (135). The photostability of the treated fabrics is somewhat better than for conventional FWA treatments (being similar to bleached wool) but the initial whiteness is significantly lower than that of FWA-treated wool. 

These regenerated proteins are obtained from milk (casein), soya beans, corn, and peanuts. More or less complex chemical separation and purification processes are required to isolate them from the parent materials. They may be dissolved in aqueous solutions of caustic, and wet-spun to form fibers, which usually require further chemical treatment as, for example, with formaldehyde. This reduces the tendency to swell or dissolve in subsequent wet-processing operations or final end uses. These fibers are characterized by a wool-like feel, low strength, and ease of dyeing. Nevertheless, for economic and other reasons they have not been able to compete successfully with either wool (after which they were modeled) or with other manufactured fibers. 

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