How can the formaldehyde content in fabrics be reduced(2)?

2.2 Use formaldehyde scavenger

The use of formaldehyde acceptors to reduce the amount of formaldehyde has long been reported. One of them is the compound with =N-H group, because this group can react with formaldehyde to play a scavenging effect, and the compound without carbonyl group is more effective than the one with carbonyl group (the former can be eliminated at 1% concentration). The removal effect of the latter can be achieved by 3 to 4%). However, some compounds are difficult to apply due to their low solubility (eg, benzotriazole) or may cause discoloration (eg, indole). The more valuable of these compounds is carbohydrazide (H2N-NHCONH-NH2) (commercially available), which can reduce the release of formaldehyde to about 10ppm, but it has a greater impact on the D.P grade (down to 1.5). Therefore, it is not suitable for wrinkle-free finishing (non-wrinkle finishing DP-grade shirts should be greater than or equal to 3.2, trousers should not be less than 3.5), and another type of compound that can reduce formaldehyde has active methylene, which is representative of Dimethyl 1,3-acetone dicarboxylate (CH3OCOCH2COCH2COOCH3) is added to the padding bath, which has the effect of controlling the release of formaldehyde below 10ppm, and has little effect on the DP grade (from 3.5 to 3.25).

To be an effective formaldehyde scavenger, it must be water-soluble and can penetrate into the fiber for reaction. In addition, the scavenger must be non-volatile under the baking conditions, and the scavenger must be non-alkaline, so as not to passivate the catalyst, nor to lower the pH value of the fabric, so as to avoid the hydrolysis of the cross-linked resin to release formaldehyde.

3. Alternative product types to eliminate formaldehyde hazards

To completely eliminate formaldehyde, it is required that the product does not contain free formaldehyde and will not be hydrolyzed to release formaldehyde after finishing. Therefore, there are fundamental differences in structure and mechanism between aldehyde-free products and aldehyde-containing (including low-aldehyde) products. In the past two decades, a lot of research and development have been carried out in this field at home and abroad. However, since the application effect of aldehyde-containing products has been generally recognized, the substitutes must be compared with the original products in terms of performance, price and many other aspects, and only the more suitable ones can be accepted by enterprises.

3.1 Alternative products of resin finishing agent

There are many formaldehyde-free resin finishing agents that have been studied, and some of them have even been used in production for a period of time, but not many have been recognized

3.2 Formaldehyde-free self-crosslinking adhesive

In order to achieve self-crosslinking or crosslinking with fibers, the current self-crosslinking adhesives generally add methylol acrylamide to the polymerization monomer, which brings about the problem of formaldehyde. In this type of adhesive, the methylol acrylamide content is generally 2 to 4% of the total monomer. As long as the methylol type crosslinking agent is not added to the slurry, the amount of formaldehyde released will not be too large. Pigment printing should be below 75ppm, while flocking can sometimes reach about 100ppm. The specific formaldehyde emission is related to the content of methylol in the adhesive, the coating area, and the baking conditions.

3.3 Formaldehyde-free color fixing agent

The color-fixing agent with formaldehyde hazard is mainly a resin color-fixing agent (such as color-fixing agent Y.M) which is condensed by dicyandiamide and formaldehyde. Other fixatives generally do not have this problem. The reason why it attracts attention is because the performance-price ratio of these color-fixing agents is relatively good, so my country is used more in cotton spinning and silk. Because there are many types of color-fixing agents, it is not a problem to substitute them. At present, there are more resin-based color-fixing agents which are condensed with polyvinylpolyamine and dicyandiamide and polymerized by dimethyldiallylamine. The materials in this regard have been introduced more recently, and will not be repeated here.

3.4 Substitute products for cross-linking agent hexahydroxy resin

Such products still need further development. In addition to being commonly used as resin finishing and stiffening finishing, hexahydroxy resin is also used as a crosslinking agent in many occasions. For example, adding it to the flocking adhesive can greatly improve the wet fastness of the film of the flocking product; in the oil-repellent finishing, it can produce a synergistic effect with the fluororesin to reduce the amount of the fluororesin; it is also commonly used for cross-linking in some functional finishing. components to improve the durability of product functionality. However, hexahydroxy resin is a product with high release of formaldehyde (up to 1000ppm or more). Even after etherification modification, although the free formaldehyde in the product has been greatly reduced (<0.3%) [1], the processed cloth surface releases formaldehyde. Still unacceptable (if 5% modified hexahydroxy is added to flocking pulp, the final product still reaches 500-600ppm). To replace the hexahydroxy, if a crosslinking agent (such as EH) with active groups at both ends is used, the satisfactory effect is often not obtained. It may be that the low degree of crosslinking affects the wet strength of the film. If the polycarbamyl sulfonate SUW-2 with three cross-linking active groups is used, the effect is obviously improved. Satisfactory wet fastness can be achieved if the polymeric resin NF-2 (developed by Changzhou Printing and Dyeing Institute) with multiple active groups is used. In terms of the replacement of cross-linking components, there is not much work done now, and products are often developed for a certain purpose, and further development and research are needed to fully replace them.