How to effectively remove formaldehyde


Formaldehyde is a well-known pollutant, there are various methods to remove formaldehyde on the market, many people are difficult to judge the effectiveness, so I consulted many information articles, comprehensive judgment to form this article, hope to explain formaldehyde and treatment more systematically and in depth, as a reference for everyone
  • Formaldehyde concept and hazards

    1. Formaldehyde concept and hazards

      Formaldehyde, colorless pungent odor gas, highly volatile, chemical formula HCHO or CH₂O, slightly heavier than air, formaldehyde in the air is generally concentrated at a height of 0.8-1.5 meters. It can irritate people's eyes and respiratory mucosa, causing tearing, sore throat, sneezing, coughing, difficulty breathing and other symptoms, and also inducing asthma. The World Health Organization's International Agency for Research on Cancer lists formaldehyde as a class of carcinogens.

      When the indoor air formaldehyde concentration reaches 0.06-0.07mg/m³, children will have mild asthma; When it reaches 0.1mg/m³, there is peculiar smell and discomfort; When it reaches 0.5mg/m³, it can irritate the eyes and cause tearing; Up to 0.6 mg/m³, it can cause throat discomfort or soreness. Higher concentrations can cause nausea and vomiting, cough, chest tightness, asthma and even pulmonary edema; When it reaches 30 mg/m³, it will cause immediate death.

    2. Formaldehyde safety concentration standard

      • Chinese Standard:

        <=0.08mg/m3 (Code for the Control of Indoor Environmental Pollution in Civil Construction Engineering GB50325-2012, Class I civil building standard, that is, housing, hospitals, school classrooms, etc., tested after closing doors and windows for 1h), which is suitable for mandatory control specifications for environmental pollutants before the delivery of construction projects.

        <=0.1mg/m3 (Indoor Air Quality Standard GB/T18883-2002, tested after closing doors and windows for 12 hours). This standard refers to the World Health Organization's limit standard for indoor formaldehyde concentration and is the minimum standard for human settlement environment health.

        Personally, I believe that the safety standard of home formaldehyde concentration should be based on family members (such as the elderly in the family, children with poor physical fitness, need to be reduced to less than 0.06 mg/m³) and the time to close doors and windows (such as closing 12 hours measurement and 1 hour measurement standards are different), of course, the lower the better.

      • American Standards:

        US WELL Building Standard: 0.03mg/m³

    3. The smell of formaldehyde

      Some people ask what is the taste of formaldehyde, how is it a pungent taste, after various searches, it is generally believed that formaldehyde has no smell, and when the concentration exceeds the standard (0.1mg/m³), people will not smell the smell of formaldehyde, formaldehyde smell olfactory threshold is 1.07mg/m³, after this concentration, many people will choke the nose, slightly burn the throat irritation.

    4. Whether the formaldehyde exceeds the standard according to the taste of formaldehyde

      No way. If asked about odor, usually formaldehyde and other harmful pollutants have exceeded the standard. And as mentioned earlier, most people can't smell when they just exceed the standard.

      In addition, the formaldehyde released in the decoration is mostly urea-formaldehyde resin in the glue, but the free formaldehyde content of the resin is very low, and in the manufacturing process, the taste is very small, and after the gumming, there is almost no smell of formaldehyde. Therefore, the room smells very stimulating general TVOC (that is, total volatile organic compounds, melting point is lower than room temperature and boiling point between 50 ~ 260 °C volatile organic compounds, toxic and harmful, mainly from paints, coatings and adhesives, the cost includes benzene, alkanes, aromatics, olefins, halohydrocarbons, esters, aldehydes, ketones and others), these are the smell that smells huge and choking.

    5. Whether to choose environmentally friendly materials, formaldehyde will not exceed the standard

      Not necessarily, because if the formaldehyde content of each environmental protection material does not exceed the standard, the indoor may still exceed the standard.
  • Sources of formaldehyde

    There are all aspects of clothing, food, housing and transportation, the main interior decoration has a greater impact, and the main source of formaldehyde in the decoration (in order of predominance):

    1. Glue. There is glue must have aldehyde, no aldehyde is not gum, formaldehyde and urea a certain proportion of mixing reaction to form urea-formaldehyde resin, used for glue, formaldehyde can improve viscosity. The glue contains an incomplete release of formaldehyde. As long as all materials and furniture used in glue have formaldehyde (man-made panels, man-made board furniture, glass glue, wallpaper glue, gypsum board, etc.).

    2. Coatings. Contains formaldehyde additives and auxiliary materials, which can be waterproof and fireproof, improve viscosity, including paint (paint, latex paint), wall base material, coating (wall and floor solid, interface agent, waterproof coating), etc.

    3. Dyeing auxiliaries, resin finishing agents, etc. The formaldehyde of the dyeing additive can make the color of the textile bright and bright, and maintain the durability of printing and dyeing; The formaldehyde of the resin finishing agent can make the cotton fabric wrinkle-proof, shrink-proof and flame retardant. Therefore, many textile products have formaldehyde (curtains, mattresses, sofas, various decorative items, etc.), and leather products will also increase formaldehyde additives.

      (Extension: The log itself contains formaldehyde, but the content is less.) In addition to formaldehyde, there are many kinds of indoor pollutants caused by decoration, which can be divided into three categories: organic pollutants, inorganic pollutants and radioactive pollution. At present, the pollutants detected in China mainly include: formaldehyde, benzene, ammonia and TVOC, etc., man-made panels, paints, etc. may release benzene, toluene, xylene, formaldehyde and other harmful substances; Sediment, bricks and cement concrete may contain urea, which releases ammonia at higher temperatures, and some natural stones release radioactive radon gas, causing radon contamination... )

  • Formaldehyde release

    1. Formaldehyde release cycle

      Free formaldehyde and its own bound formaldehyde, in the absence of new volatilization, in the case of good ventilation, less than an hour can all diffuse to the outdoors, the formaldehyde and bound formaldehyde enclosed in the plate coating, etc., with the slow aging of formaldehyde-containing material synthetic resin, the base bond is broken, will be re-released, this cycle is 3-15 years.

    2. Influencing factors of formaldehyde release

      • Indoor temperature: the boiling point of formaldehyde is -19.5 °C, above this temperature, every 1 °C increase in room temperature, the volatilization rate of formaldehyde will increase by 0.4 times, especially in summer or winter heating, the release of formaldehyde is more intense, the release is 20%-30% higher than other seasons. This is the main reason why formaldehyde detection in spring and autumn does not exceed the standard, and formaldehyde detection in summer and winter exceeds the standard.

      • Decoration materials themselves: Generally speaking, the formaldehyde of textile decorations is quickly released completely, and it can be washed with water. The formaldehyde in the paint can be volatilized in 7-15 days. The wallpaper glue needs to be released for more than 18 months. Large core boards need to be released from 15 months to 5 years. MDF is almost more than 3 years, or even more than 10 years.

      • Indoor air circulation: the higher the indoor formaldehyde concentration, the slower the formaldehyde release rate, or even 0, open window ventilation to strengthen indoor air circulation, can allow furniture to continue to release formaldehyde, shorten the formaldehyde release cycle.

      • Indoor relative humidity: board furniture and other moisture, the urea-formaldehyde resin reacts with water to produce formaldehyde and urea, of which formaldehyde is released in the air and then dissolved in the water in the air.

    3. How long after renovation can I move in

      Depending on the degree of pollution when the decoration is completed, the release of formaldehyde in the first 6 months of indoor new decoration is generally fast, and the back is slow, but the pollution is serious, and 6 months is not enough. It can only be said that the average family adopts the standard of 6 months, and it is after the summer (because the summer release is fast), and it is best to measure it if it is accurate.

  • How to remove formaldehyde

    1. Reduce pollution sources. Eco-friendly materials are used during decoration, and the materials for decoration furniture are reduced.

    2. Ventilation (most effective)

      At present, there are three common ventilation methods:

      • Open window ventilation: Studies have shown that when ventilation is good, open the window for ventilation for 10 minutes, and the concentration of formaldehyde in indoor air can be reduced by about 70%~90%.

        Some people say that it is necessary to close the doors and windows for several hours under high temperature and humidity (summer or open air conditioning) and then open the windows for ventilation, which helps to maintain high temperature and humidity and release formaldehyde. However, this method does not work well in practice. Some people have done experiments at 25 °C and 32 °C, the release rate of closed formaldehyde is high 0-3 hours before the stuffy method, and the subsequent speed is greatly reduced until 0, while the release rate of the ventilation method has been stable at a high level. Because the higher the indoor formaldehyde concentration, the more unfavorable it is to formaldehyde release, and stuffiness will keep the indoor formaldehyde concentration at a high level, and the previous release factors also mention this.

        It is recommended that no matter what season to use natural ventilation, winter non-heating area, because the window is opened to lead to too low temperature, formaldehyde release effect is poor, may be appropriate to use the "stuffy method" effect is better, but no experimental data has been found, so I personally think that ventilation is the simplest and most effective.

        (Expand, some people say that just after the decoration can not be long-term ventilation, wall paint and plaster roof will crack, regular window ventilation for a few hours can be, you can consult the decoration company, and you can use an industrial fan to blow on the ground after the wall latex paint dries and is set, because formaldehyde molecules are heavier than air, and some of them are close to the ground and are difficult to take away by natural wind)

      • Fresh air system: purify the outdoor air through the fresh fan, and then introduce it indoors to achieve the purpose of indoor and outdoor air exchange, which is equivalent to the optimized version of window ventilation. For the case of good ventilation of the window, because most of the formaldehyde is taken away by the natural wind, the advantages of the new fan are not obvious in this case, and the effect is obvious in the case of closing the doors and windows (there are quite a few cases of closing windows at home, turning on the air conditioner in winter and summer, sleeping at night, etc., it is recommended to install it conditionally).

      • Air purifier: the machine inhales air, and the filter screen intercepts and adsorbs pollutants in the air, and discharges the purified air to the room. It works better when doors and windows are closed. Unlike fresh fans, air purifiers cannot channel fresh outside air into the room, but can only purify the existing air and then re-enter the room. For homes that cannot install new fans, air purifiers are a good choice.

        It should be noted that some people say that empty cleaning cannot remove formaldehyde, because most of the air purifiers on the market mainly remove PM2.5, and there are relatively few effective formaldehyde removals. If you choose to remove formaldehyde from air purification, it is recommended to use a professional air purifier for formaldehyde removal, preferably with PM2.5 and formaldehyde digital display, so that you can intuitively see the filtering effect and use it more assuredly.

        Strictly speaking, air purification formaldehyde belongs to the adsorption method, and its purification active ingredient is high-efficiency activated carbon, which is very different from activated carbon packets, and the air purification actively absorbs polluted air, so it can effectively remove formaldehyde.

    3. Adsorption method (weak effect)

      • Activated carbon package: physical adsorption is mainly (a small amount of chemical adsorption), large specific surface area and porosity are the basis of adsorption, and the physical adsorption force between activated carbon and pollutant molecules is van der Waals force.

        However, the adsorption capacity of the activated carbon package is weak, because it can only passively adsorb formaldehyde in small surrounding areas; Second, it is not specifically for formaldehyde adsorption, but also adsorbs other pollutants and odors at the same time, so it quickly adsorbs saturation; Third, the physical adsorption stability is poor, and it is easy to re-release formaldehyde when temperature, humidity, pressure and other conditions change; Fourth, after adsorption saturation, formaldehyde will be re-released.

        Therefore, it is recommended that the activated carbon package is mainly used for deodorizing in dead corner areas (closed cabinets, etc.) or toilets, sufficient amount (experimental data show that the recommended dosage of activated carbon per unit volume space is 8g/m³, but the reliability of this data is not guaranteed), and replace after adsorption saturation (experimental data show that activated carbon adsorption saturation in 5 hours, but the reliability of this data is not guaranteed, it is determined that family conditions such as high temperature exposure cannot restore the saturated activated carbon, so new activated carbon is needed)

      • Plants: This method passes. Part of the removal principle is adsorption, and part is the absorption of formaldehyde synthetic nutrients due to the defense mechanism; However, the effect of both is very weak, lower than activated carbon, and beyond its ability, it will cause harm to plants.

      • Diatom mud: This method passes. The principle of formaldehyde removal is similar to activated carbon, physical adsorption is the main (a small amount of chemical adsorption), the disadvantages are the same, there are mainly adsorption saturation and environmental changes re-release problems (but it is okay to adjust humidity and other considerations, and diatom mud also needs glue on the wall).

        Some people will apply a layer of photocatalyst on the surface of diatom mud to use, which is equivalent to the role of photocatalyst, and the effect is still weak (photocatalyst will be discussed below).

    4. Chemical purification method (weak effect, passable)

      Chemical purification is mainly to decompose formaldehyde or block formaldehyde, the former has a removal effect on formaldehyde that has been released in the air, and cannot absorb the formaldehyde reaction inside the furniture, unless it has been sprayed in the 3-15 year release period. The latter only seals the formaldehyde to prevent its volatilization, and as the material ages and falls off, the formaldehyde will still be slowly released. Specifically, it is mainly divided into the following types:

      • Photocatalyst:

        The photocatalyst belongs to the early decomposition and late closing. The main component is nanoscale titanium dioxide, which is a catalyst that catalyzes water or oxygen in the air under ultraviolet light into active groups with strong oxidizing ability, which can strongly decompose various organic compounds with unstable chemical bonds and some inorganic substances, and can destroy the cell membrane of bacteria and coagulate the protein carrier of the virus, including formaldehyde (reaction with formaldehyde to produce water, carbon dioxide and other harmless substances).

        This method is used by many formaldehyde removal companies, and a layer of photocatalyst can be sprayed on the surface of furniture such as cabinets.

        However, this method is used well in industrial scenes, but the effect at home is poor. Because experiments have shown that to achieve a good formaldehyde removal effect requires sufficient ultraviolet intensity and suitable indoor chemical pollutant concentration (above the safety standard concentration is not good), the actual home light ultraviolet intensity is low, and if the indoor pollution concentration is high, the effect can be imagined.

        The photocatalysts that claim that they can remove formaldehyde with visible light are added to titanium dioxide with elements such as silver, copper or iron, which can use blue light and even some green light to decompose formaldehyde. However, this photocatalyst generally absorbs less than 5% of blue light.

        In the actual effect of the household, it will initially partially decompose the formaldehyde that has been released from the plate, etc. (as mentioned earlier, these formaldehyde ventilation is quickly emitted), and then more becomes a protective film, sealing formaldehyde (as a catalyst it does not react itself, so it will not be consumed), just like the edge banding process of the furniture manufacturing process, and then as the material ages and falls off, formaldehyde continues its 3-15 years of slow release, and the photocatalyst continues to weakly decompose to release formaldehyde.

      • Amino acid aldehyde removal spray:

        It belongs to the decomposition formaldehyde type, which is a product with high efficiency in removing aldehyde in the current spray products, but it cannot eradicate formaldehyde. Amino acids will chemically react with formaldehyde to form hydroxymethyl derivatives, the effect of which is described in the previous decomposition class.

        Secondly, the amino acid solution cannot penetrate into the plate, because most of the surface of the plate has a waterproof resin decorative layer.

        In addition, dust and microorganisms in the environment can easily make amino acids ineffective, and frequent sweeping, mopping, and scrubbing tables and chairs will also accelerate the loss of amino acids. (Extension: amino acids also have no removal effect on most VOCs)

      • Biological enzyme dehyde removal spray:

        Belongs to the type of decomposition of formaldehyde, biological enzymes are produced by living cells, on the one hand, can be used as a catalyst to decompose formaldehyde, on the other hand, biological enzymes are essentially composed of proteins, etc., containing active amines that can react with formaldehyde, which is no different from amino acid aldehyde removal spray. The effect is described in the decomposition class above.

        The environmental conditions for the catalytic decomposition of formaldehyde by biological enzymes are very harsh, and changes in temperature and humidity, microbial reproduction, dust, etc. in the daily environment will seriously reduce the catalytic effect of biological enzymes.

      • Chlorine dioxide dehyde removal spray:

        Belongs to the decomposition of formaldehyde type, chlorine dioxide is a strong oxidant, can oxidize formaldehyde, benzene and other VOCs in the air, the effect is described in the previous decomposition class. At the same time, the inhalation of chlorine dioxide is toxic, and chlorine dioxide will decompose when seen in the air, and it cannot remove formaldehyde for a long time.

    5. Others (mixed effect)

      • Wash and dry (effective for furniture textiles)

        Before moving in, wipe the wooden furniture inside and out with a wet rag (formaldehyde is easy to water) and then dry it (high temperature is also conducive to the release of formaldehyde), which is effective for the initial release of formaldehyde, and the slow release of formaldehyde in the later stage does not change accordingly; The release cycle of formaldehyde in textiles is only a few weeks, and more water can be washed and dried.

      • Heating and humidification method (effective)

        Specifically, steam mops are used to mop wooden floors, and the principle of high temperature and humidity is used to increase the rate of formaldehyde release.

      • Folk soil transmission method (effect none)

        Put tea residue, grapefruit peel, onion slices, pineapple chunks, etc. in the newly decorated room or fumigate the whole room with white vinegar, this method can only cover the taste, will not adsorb formaldehyde. In addition to these things, some people also like to use perfume and air fresheners, which is not advisable because the chemical raw materials in perfumes and air fresheners may react with substances in the air, resulting in secondary pollution.

      • Ozone decomposition (weak effect)

        Ozone has strong oxidation and can oxidize and decompose formaldehyde, and the effect is the same as that of chemical agents to purify and decompose formaldehyde. Ozone reaction conditions are high (confined space, higher concentration and below 23 °C), poor effect on formaldehyde removal in households, mainly used for disinfection.

      • Negative ions (effect none)

        Negative ions, also known as negative oxygen ions, refer to the acquisition of 1 or more electrons with negative charge oxygen ions, negative ions are recognized as an effective means of killing bacteria and purifying air. The ability of negative ions to purify the air mainly refers to the particulate matter in the air, and there is no obvious purification ability for chemical pollutants in the air such as formaldehyde and TVOC.