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◉ Introduction of Formaldehyde in Leather
In the leather production process, formaldehyde is an important chemical raw material. It is mainly used in the preservatives, fungicides, aldehyde-containing tanning agents, finishing agents, fixatives, etc. used in the leather processing and production process. These auxiliaries may contain Or generate free formaldehyde, it will inevitably bring formaldehyde into leather products, so there will be a certain amount of formaldehyde residue in leather products more or less.
Formaldehyde is a colorless, poisonous gas with a pungent odor. When the content of formaldehyde in the air is greater than 0.08mg/m³, it will cause harm to human health, which is manifested as sensitization, genotoxicity, induced dermatitis and asthma, and potential carcinogenicity. And studies have shown that even with low doses of long-term exposure, formaldehyde can cause chronic respiratory diseases, skin allergies, physical decline, persistent headaches, insomnia and other symptoms, and even lead to problems such as reduced physical fitness and chromosomal abnormalities in newborns. Therefore, various countries have stricter restrictions on formaldehyde in leather products for children.
◉ Sources of Formaldehyde in Leather
In leather, formaldehyde is an effective cross-linking agent, and its effect is unmatched by other aldehydes. As a main raw material for leather chemical synthesis, formaldehyde is difficult to be replaced in a short time. In fur, in addition to the synthesis of fur-specific chemicals, formaldehyde is still sometimes used as a tanning agent due to its low price and high quality fur. This also leads to higher levels of formaldehyde in some fur products
(1) Preprocessing
Preservatives and fungicides used before tanning may contain formaldehyde, which is why formaldehyde is detected in wet blue leather; wet blue leather pre-tanning materials usually contain free formaldehyde or release free formaldehyde over time, such as Oxazolidine, phosphonate tanning agents, etc., increase the formaldehyde content in leather.
(2) Tanning and retanning
The use of aldehyde-containing tanning agents is one of the main sources of formaldehyde in tanning and retanning processes, such as aldehyde tanning agents, amino resin tanning agents and aromatic synthetic tanning agents. Formaldehyde tanning agents, modified glutaraldehyde tanning agents, oxazolidine tanning agents and organophosphine tanning agents are aldehyde tanning agents or aldehyde derivative tanning agents. In the synthesis process of amino resin tanning agents and aromatic tanning agents, formaldehyde is often used as a condensing agent and is one of the main raw materials of such products. The aldehyde tanning process is mainly based on the nucleophilic addition reaction of the amino group or imino group on the collagen molecule and the carbonyl group on the formaldehyde molecule to achieve cross-linking. However, this chemical reaction is generally reversible, and formaldehyde will be re-released under certain conditions. With the increase of the amount of retanning agent, the formaldehyde content in leather keeps rising. When the amount of amino resin retanning agent used is 2%, the formaldehyde content in leather has exceeded the standard of formaldehyde residue in leather products directly in contact with the skin stipulated in my country; the amount of aldehyde retanning agent and aromatic tanning agent used is less than 4%. %, it complies with this standard.
In fur tanning, formaldehyde, as a common tanning agent, still has certain applications. The fur after formaldehyde tanning has white quilt, soft leather, and has the functions of alkali resistance and oxidant resistance at the same time, and the cost is low. Due to the addition of formaldehyde in tanning, the formaldehyde content in tanned fur has far exceeded the EU standard and my country's ecological leather requirements. In addition, the use of formaldehyde-aluminum combined tanning, formaldehyde-oil combined tanning, and formaldehyde-synthetic tanning combined tanning is also the main reason for the generation of formaldehyde. Synthetic tannins used in tanning have high free formaldehyde content. Formaldehyde is a raw material for the preparation of synthetic tannins. It is a highly reactive substance. If it does not fully react with other components, there will be free formaldehyde in the final product [6]. In addition to the influence of tanning and retanning agents on the formaldehyde content in leather, chemical materials such as aldehyde-containing fatliquors and modified protein fillers will also undergo structural degradation due to the influence of temperature, pH and moisture during storage and use. And slowly release free formaldehyde, increasing the formaldehyde content in leather.
(3) Finishing
Finishing agent is a multi-component mixture, and its film formers, colorants, and auxiliaries may also generate free formaldehyde. Most acrylic and protein finishes and most polyurethane finishes may also be crosslinked with formaldehyde. However, formaldehyde has a strong stimulating effect on human mucous membranes and is also highly toxic. It will cause damage and pollution to operators and the environment during the finishing operation, and formaldehyde and R1-NH-R2 will form cross-links at a very slow speed. Formaldehyde is released. Due to the restrictions on formaldehyde in leather in various countries, formaldehyde is extremely restricted in the finishing process.
(4) Scalding and straight hair of sheep sheared fur
The purpose of sheep shearing straight hair is to elongate and straighten the curved hair in the same direction, so that the wool quilt has a good mercerized feeling. The β-sheet structure of keratin produced in the process of straight hair is an unstable structure. After the loss of external force, keratin spontaneously returns to the α-helix structure. Therefore, when the hair is straightened by ironing and stretching, it is necessary to fix the straightened hair so that it is no longer deformed. The most commonly used fixative and the best fixative at present is formaldehyde. Formaldehyde can generate new cross-linking bonds between the broken disulfide bonds and free amino groups, so that the straight state of the hair can be fixed. Formaldehyde can be volatile at high temperature, and the volatile gas has a strong irritating odor, which is extremely harmful to the human body. Therefore, low-aldehyde or no-aldehyde fixation is the direction of development.
◉ Test Method for Formaldehyde Content in Leather
(1) Spectrophotometry
Spectrophotometry is a qualitative and quantitative analysis method based on the selective absorption of electromagnetic radiation by substances with different molecular structures. It involves ethylene acetone method, phenol reagent method, AHMT method, magenta-sulfurous acid method, chromotropic acid method, phloroglucinol method, catalytic spectrophotometry, etc. Its advantages and certain limitations.
(2) Liquid chromatography
Chromatography has strong separation efficiency, is not easily interfered by the color of sample matrix and reagents, and is sensitive and accurate for the detection of complex samples, and can be directly used for the analysis and detection of formaldehyde in rooms, textiles, and food. The formaldehyde in the sample can also be derivatized and then measured. The sample components in the room, textiles, and food are generally complex, with many interfering components and low formaldehyde content. In conventional detection methods, it takes a lot of time and energy to perform pretreatment such as separation and concentration before detection. The chromatographic method has high sensitivity, accurate quantification and strong anti-interference, and can be directly used for the detection of formaldehyde in rooms, textiles and food. However, chromatography requires high equipment, long derivatization time, and cumbersome extraction and other steps and operations.
◉ Compliance Services
As a professional third-party testing technology service provider, Jiayu Testing boasts qualifications such as CMA, CNAS, CBTL, and CPSC. Additionally, we have obtained laboratory accreditation from multiple authoritative certification bodies both domestically and internationally. Our laboratory is constructed and managed in strict accordance with standards, equipped with advanced instruments and equipment, and staffed by a skilled and professional technical team. With rich industry service experience and robust testing technical capabilities, we are proficient in various regulatory standards. We assist enterprises in actively responding to regulatory requirements and effectively enhancing product compliance. Welcome to contact us. Jiayu Testing's consultation hotline is: 400-9269-886!
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