How can the formaldehyde content in fabrics be reduced(1)?

Formaldehyde is a nasty and irritating chemical that can cause dermatitis and is potentially carcinogenic. The occupational safety and health care regulations of many countries have made obvious limits on the concentration of formaldehyde in the air. As early as 1974, the Japanese government made regulations on the limit on textiles, but in the following period of time, my country did not pay enough attention, perhaps because the understanding of environmental protection has not reached a certain height, plus Developed countries have not yet used "green barriers" as trade weapons. It was not until the 1990s that the rise of environmentally friendly textiles and the promulgation of relevant national laws and regulations raised the awareness of the restrictions on formaldehyde to the same level as those of banned dyes, and new products that replace auxiliaries that may release formaldehyde have become a domestic concern. hot spot.

1. Ways to reduce or eliminate formaldehyde

There are two main types of formaldehyde used in auxiliary products. One is that formaldehyde and amide generate methylol compounds. Due to the existence of amide bonds, methylol has greater activity and can be cross-linked by itself or with hydroxyl groups in cellulose. The products containing formaldehyde in the auxiliaries are mainly such products. Such as 2D, hexahydroxy resin, self-crosslinking adhesive, hydroxymethyl stearic acid amide softener, etc. The second is to use formaldehyde as a methylene bridge to form polymolecular or polymer compounds. Such as fixing agent Y, M, diffusing agent N, etc. There are three main ways for these products to produce formaldehyde hazard on textiles: ① Unreacted free formaldehyde in the product - due to reactions such as methylolation or acetal, the presence of free formaldehyde in the product is unavoidable. ②After cross-linking with the fabric, the unreacted methylol can continuously release formaldehyde during storage or use. ③ The acetal bonds or imine chains in the molecule formed by cross-linking will regenerate formaldehyde by hydrolysis in humid air, especially under acid and alkali conditions.

People have done a lot of work in reducing or eliminating the harm of formaldehyde. In general, the first two reasons above are solved, such as minimizing free formaldehyde in products, using formaldehyde scavengers or etherifying methylol with lower alcohols. , the harm of formaldehyde cannot be eradicated. Only reduce the amount of formaldehyde released. To completely eradicate the problem of formaldehyde, it is necessary to use products produced without formaldehyde (including products produced without raw materials produced by the reaction of formaldehyde).

2. Ways to reduce the amount of formaldehyde released

There are two main ways to effectively reduce the amount of formaldehyde released: one is to etherify the methylol that may continuously release formaldehyde. The second is to use formaldehyde scavengers.

2.1 Blocked hydroxymethyl

It is an effective way to reduce the amount of formaldehyde released. According to the different timing of sealing, it can be divided into: ① in the production process of the product ② in use during cross-linking.

2.1.1 To produce low-formaldehyde products, when methylol is etherified with lower alcohol, the stability of C-N bond can be improved. At this time, unreacted free formaldehyde can also react with alcohol to form acetal or hemiacetal, thereby reducing formaldehyde free and released amounts. Generally, methanol, ethanol, diethylene glycol, etc. are commonly used. The free formaldehyde in etherified 2D resin and melamine resin products can be reduced to less than 0.3%. Among them, the methyl etherified 2D can reduce the formaldehyde emission of the fabric to 300ppm, and the denaturation of diethylene glycol is lower than 100ppm. Generally, the reactivity of methylol resin modified by etherification is lower than that before modification, and high-efficiency catalyst such as magnesium chloride and citric acid mixed catalyst must be used. There are two kinds of resins of this type: highly etherified and partially etherified. The two-step method has a more obvious effect on reducing formaldehyde than the one-step method. During the reaction, pH value, reaction temperature and reaction time should be strictly controlled.

2.1.2 Adding polyols to the finishing liquid, generally speaking, the principle of adding alcohols to the finishing liquid to reduce formaldehyde is similar to that described in 2.1.1. Because the reaction occurs in the cross-linking and baking stage at a higher temperature, the added alcohols such as the lower boiling point cannot achieve the purpose of etherification.