Formaldehyde Testing Service for Textiles

Formaldehyde Testing

1、Introduction to Formaldehyde

Formaldehyde is an organic chemical compound with the chemical formula HCHO or CH₂O[1] and a molecular weight of 30.03[2]. It is also known as methanal. It is a colorless, pungent gas that irritates the eyes, nose, and other parts of the body. Its gas relative density is 1.067 (air=1), and its liquid density is 0.815 g/cm³ (-20°C). It has a melting point of -92°C and a boiling point of -19.5°C. It is highly soluble in water and ethanol. The maximum concentration of its aqueous solution can reach 55%, typically 35%-40%, and commonly 37%. This solution is called formalin, also known as formaldehyde water.

Formaldehyde has reducing properties, especially in alkaline solutions where its reducing ability is stronger. It is flammable, and its vapor can form explosive mixtures with air, with a limit of 7%-73% by volume. Its ignition temperature is approximately 300°C.

It can be produced by the dehydrogenation or oxidation of methanol catalyzed by metals such as silver or copper, or separated from the oxidation products of hydrocarbons. It serves as a raw material for phenolic resins, urea-formaldehyde resins, vinylon, dyes, pesticides, and disinfectants. Industrial methanol solutions generally contain 37% formaldehyde and 15% methanol, acting as polymerization inhibitors, with a boiling point of 101°C.

On October 27, 2017, the World Health Organization's International Agency for Research on Cancer listed formaldehyde as a Group 1 carcinogen. On July 23, 2019, formaldehyde was included in the list of toxic and harmful water pollutants (first batch).

2, Application Areas

(1) Chemical Raw Materials

1) Adhesives

Adhesives are the largest consumer sector of formaldehyde in China, accounting for about 40% of total consumption. The main adhesive products produced are urea-formaldehyde resin adhesive, phenolic resin adhesive, and melamine-formaldehyde resin adhesive. These are primarily used in wood processing, molding plastics, coatings, textiles, and paper treatment agents. Among them, adhesives for wood processing account for about 80% of the total adhesive volume. In 2007 and 2008, production volumes were 3.135 million tons and 3.448 million tons, respectively, showing continuous growth and expanding application areas. According to incomplete statistics, there are over 3,500 adhesive and sealant manufacturers in China, but fewer than 100 are large-scale enterprises, with about 3,000 varieties and brands. In terms of application, plywood and woodworking account for the largest share of adhesive usage, about 46.97%, followed by building materials at 26.12%, packaging and labels at 12.14%, footwear and leather at 6.07%, and other uses at 8.7%.

2) Polyformaldehyde

China's demand for POM (polyformaldehyde) has grown rapidly. In 2004, China's demand for polyformaldehyde exceeded the total demand in Western Europe, making it the world's largest consumer of POM. With the rapid development of the domestic electronics, electrical, and automotive industries, the demand for polyformaldehyde, as an engineering plastic with excellent comprehensive properties, will further increase.

3) Paraformaldehyde

Paraformaldehyde is a key raw material for producing herbicides such as glyphosate, acetochlor, butachlor, and alachlor, as well as pesticides like tricyclazole. Additionally, oligomeric formaldehyde shows great potential in replacing industrial formaldehyde. Some pharmaceutical, coating, and resin companies have successfully used low-polymerization-degree paraformaldehyde as a substitute for industrial formaldehyde with good results. For a long time, due to inadequate domestic production technology and unstable product quality, China has lacked large-scale production capacity, unable to meet domestic consumption demand, with about 60% still relying on imports.

4) MDI

MDI (diphenylmethane diisocyanate) is one of the main raw materials for producing polyurethane products. It is widely used in manufacturing PU (polyurethane) rigid foam products. As an essential raw material in leather production, it enhances the softness of leather and provides a realistic simulation effect. Due to the dual advantages of plastics and rubber in its products, MDI has become one of the rapidly developing polymer synthetic materials in the world.

(2) Textile Industry

In fabric production for clothing, formaldehyde is added to auxiliaries to achieve anti-wrinkle, anti-shrinkage, flame retardancy, or to maintain the durability of printing and dyeing, or to improve hand feel. Formaldehyde-based dyeing auxiliaries are more commonly used in pure cotton textiles because pure cotton textiles are prone to wrinkling, and using formaldehyde-containing auxiliaries can enhance the stiffness of cotton cloth. Textiles containing formaldehyde gradually release free formaldehyde during wearing and use, causing respiratory tract and skin inflammation through inhalation and skin contact, and also irritating the eyes. Formaldehyde can trigger allergies and even induce cancer. Some manufacturers use formaldehyde-containing dyeing auxiliaries, especially those using cheap auxiliaries with extremely high formaldehyde content to reduce costs, which is highly harmful to human health.

(3) Preservative Solutions

A 35% to 40% aqueous solution of formaldehyde is commonly known as formalin. It has preservative and sterilizing properties and can be used for preserving biological specimens and disinfecting seeds. However, due to its protein-denaturing nature, it can make specimens brittle. The preservative and sterilizing properties of formaldehyde mainly stem from its ability to react with the amino groups of proteins that constitute living organisms.

3. Hazards

(1) Acute Toxicity

Acute formaldehyde poisoning manifests as irritation to the skin and mucous membranes. Inhalation of high concentrations of formaldehyde can cause respiratory irritation symptoms, such as sneezing, coughing, and a burning sensation in the nose and throat. It can also induce bronchial asthma, pneumonia, and pulmonary edema. Ingestion of a large amount of formaldehyde at once can cause digestive tract and systemic toxic symptoms, including corrosive burns to the mouth, throat, and digestive tract, abdominal pain, convulsions, and death. Skin contact with formaldehyde can cause allergic dermatitis, spots, skin necrosis, and other lesions. Ingestion of 10-20 ml of formaldehyde solution can be fatal.

In animal experiments, the oral LD50 of formaldehyde in rats is 800 mg/kg, the dermal LD50 in rabbits is 2700 mg/kg, and the inhalation LD50 in rats is 590 mg/m³.

(2) Chronic Toxicity

Long-term exposure to formaldehyde can reduce respiratory function, impair the nervous system's information integration function, and affect the body's immune response. It also has toxic effects on the cardiovascular system, endocrine system, digestive system, reproductive system, and kidneys. Systemic symptoms include headache, fatigue, loss of appetite, palpitations, insomnia, weight loss, and autonomic nervous system disorders. Animal experiments have confirmed pathological changes in the aforementioned systems.

(3) Mutagenicity

Formaldehyde can cause mutations in Salmonella typhimurium and Escherichia coli, regardless of the presence of a metabolic activation system. After continuous dynamic exposure of mice to formaldehyde concentrations of 0.5 mg/m³, 1.0 mg/m³, and 3.0 mg/m³ for 72 hours, the micronucleus rate in polychromatic erythrocytes significantly increased.

(4) Carcinogenicity

On October 27, 2017, the World Health Organization's International Agency for Research on Cancer listed formaldehyde as a Group 1 carcinogen.

Animal studies have found that rats exposed to 15 μg/m³ of formaldehyde for 11 months developed nasal cancer. A study published by the U.S. National Cancer Institute on May 12, 2009, showed that chemical plant workers frequently exposed to formaldehyde had a much higher risk of dying from blood cancer, lymphoma, and other cancers compared to workers with less exposure. In 2010, it was further discovered that formaldehyde can cause gene mutations and chromosomal damage in mammalian cell nuclei. Formaldehyde has synergistic effects with other polycyclic aromatic hydrocarbons, such as benzo[a]pyrene, enhancing toxicity.

4. Formaldehyde Detection

Formaldehyde detection refers to the quantitative analysis of formaldehyde in air, water, food, clothing, panels, leather, etc., using specific methods or instruments. Stiff or wrinkle-resistant clothing, especially some jeans and garments labeled as 100% anti-wrinkle and anti-shrinkage, or all-cotton non-iron shirts that use glyoxal resin for shaping, contain formaldehyde.

5. Detection Methods

Domestic and international methods for detecting formaldehyde in indoor environments, textiles, and food mainly include: spectrophotometry, electrochemical detection, gas chromatography, liquid chromatography, and sensor methods.

(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 is the most conventional method for detecting formaldehyde in indoor environments, textiles, and food. Related methods include the acetylacetone method, phenol reagent method, AHMT method, Schiff's reagent method, chromotropic acid method, phloroglucinol method, and catalytic spectrophotometry. Each detection method has its preferred application areas, with各自的优点和一定的局限性。

(2) Electrochemical Methods

Electrochemical analysis is based on changes in current (voltammetry), electric charge (coulometry), or potential (potentiometry) during chemical reactions to determine the concentration of analytes for quantitative analysis. For formaldehyde detection, polarography and potentiometry are the two main methods used.

(3) Chromatography

Chromatography has powerful separation capabilities and is less affected by sample matrix and reagent color interference. It is sensitive and accurate for detecting complex samples and can be directly used for the analysis and detection of formaldehyde in indoor environments, textiles, and food. Alternatively, formaldehyde in samples can be derivatized before measurement. Samples from indoor environments, textiles, and food are generally complex with many interfering components and low formaldehyde content. Conventional detection methods require extensive time and effort for separation, concentration, and other pretreatment steps before detection. Chromatography offers high sensitivity, accurate quantification, and strong anti-interference capabilities, making it suitable for direct detection of formaldehyde in these samples. However, chromatography requires advanced equipment, has long derivatization times, and involves繁琐 steps such as extraction, making it unsuitable for rapid on-site detection in general laboratories and households, thus难以满足市场需求。

(4) Sensor Methods

Sensors used for formaldehyde detection include electrochemical sensors, optical sensors, and optochemical sensors. Electrochemical sensors have a relatively simple structure and low cost. High-quality products offer stable performance, with measurement ranges and resolution基本上 meeting the requirements for indoor environmental detection. However, their drawbacks include susceptibility to interference from many substances and a generally short operational lifespan due to the irreversible chemical reaction between the electrolyte and the formaldehyde gas being measured. Optical sensors are more expensive and larger in size, making them unsuitable for online real-time analysis, which limits their widespread use. Although optochemical sensors improve selectivity, factors such as enzyme activity and others lead to sensor instability and lack of practicality. Additionally, the high cost of formaldehyde gas sensors generally makes them difficult to普及。