Formaldehyde-treated wool

TABLE II. Change In Properties of Formaldehyde-Treated Wool Compared to Untreated Wool... 

Scanning Electron Microscopy. Samples of unweathered and weathered untreated and formaldehyde-treated wools were mounted or specimen stubbs using conducting silver paint and coated with two thin layers of silver. Scanning electron micrographs of the samples were prepared and examined for changes In the fiber surface (Fig. 1). 

Figure Id. Weathered formaldehyde-treated wool at 2500X magnification.

Dyeing of unweathered and weathered control and formaldehyde-treated wools with three representative acid dyes (Acid Violet 7, Green 41 and Red 97) showed that the face and back of the weathered wools dyed very differently than the corresponding unweathered wools (Tables IV-VI). Unweathered control wool dyed to somewhat deeper shades than unweathered formaldehyde-treated wools. When the weathered wool samples were dyed, the face and back of the wool dyed to very different shades and depths of shade compared to the unweathered fabrics. The face of the weathered wools dyed to much lighter shades than the back side of the wool fabric demonstrating that weathering had markedly reduced the... 

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. 

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. 

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. 

Wool with dark pigmented fibers is treated with ferrous sulfate, sodium dithionite, and formaldehyde before it is bleached with hydrogen peroxide. The ferrous ions are absorbed by the dark pigments where they increase the bleaching done by the peroxide. 

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... 

Djenkolic acid residues are formed from cysteine residues when reduced wool is treated with formaldehyde. 

The bleaching process also has peculiarities depending on the type of fibre which is treated. The most common and environmentally friendly bleaching agent used for fibres is hydrogen peroxide. Cotton is also partly bleached while scouring, under the action of sodium chlorite. Some yellow wools or bast fibres may require a harsher bleaching, for which reason sodium dithionite or sodium formaldehyde sulphoxylate (for wool) and sodium chlorite (for bast fibres) are also used. 

Coatings. Urea-formaldehyde resins (5 percent) are used to treat paper to give it wet strength. They are also used (2 percent) to treat cotton and wool cloth to produce permanent press and increase strength, shrink resistance, and wrinkle resistance. 

Yakima and Shivrina report that woolen te.vtiles may be rendered resistant to bacterial degradation by soakir in aqueous formaldehyde, washing and d.rying. Wool treated in this w-ay stands up well on use in paper machines. R istance of treated samples was measured by treating with 0.4 per cent solution of trypsin in a solution buffered to pH 8.3-S.5. 

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