Talking about the Control of Formaldehyde Content in Plywood
China Quality News Network
Formaldehyde is a highly toxic chemical that ranks second in the priority list of toxic chemicals in China. Formaldehyde has been identified by the World Health Organization as a carcinogenic and teratogenic substance. It is a recognized source of allergies and one of the potential strong mutagens. At present, many countries and regions in the world, such as the European Union, the United States, and Japan, have limited formaldehyde emission, and China’s national mandatory standards, “Limited Release of Formaldehyde in Interior Decoration Materials, Wood-based Panels and Products” (GB18580-2001), apply to formaldehyde. The amount of release is also limited. The standard provides for formaldehyde emission from plywood (artificial panel): E1 level ≤ 1.5 mg/L, E2 level ≤ 5.0 mg/L. E1 grade standards can be used directly for interior decoration. Only conforms to the E2 standard and must be finished before use. Therefore, how to control the formaldehyde content of plywood is an urgent need to discuss and solve the problem.
To control the formaldehyde content of plywood, it is first necessary to clarify the cause of excessive formaldehyde content in the plywood. In order to analyze the causes of excessive formaldehyde in plywood, it is necessary to clarify the source of formaldehyde.
There are four main sources of formaldehyde in plywood: one is the free formaldehyde in the adhesive, and the other is a part of the unstable structure of the adhesive in the hot-pressing process, such as ether bonds, methylol groups, and methylene groups. During the use of plywood, the cured structure decomposes to release formaldehyde. Fourth, some woods also contain natural aldehyde and ketone chemicals. Therefore, there are four reasons for excessive formaldehyde content in plywood, namely: improper formulation of adhesives, excessive amount of glue, unreasonable production process, and neglect of wood species selection.
Therefore, the control of formaldehyde content of plywood should start from the three aspects of raw materials, production and finished product testing.
First, raw material control. Plywood commonly used plastic urea-formaldehyde resin (UF), phenolic resin (WBP), melamine modified urea-formaldehyde (Mel). Urine aldehyde rubber is processed from formaldehyde and urea as the main material. Free formaldehyde content is usually between 1% and 2%. To control formaldehyde, suppliers must use a low molar ratio of formaldehyde to urea to effectively control the release of free formaldehyde. The amount is less than 0.2%; phenolic glue is processed with formaldehyde and phenol or resorcinol as the main material, due to the role of phenol and resorcinol in the benzene ring, can reduce the release of free formaldehyde; melamine modified urea-formaldehyde adhesive to Formaldehyde and urea as the main material, melamine as a modifier can effectively absorb free formaldehyde, free formaldehyde can achieve the required requirements in the glue.
Therefore, it is extremely important to strengthen the control of free formaldehyde in plywood production glue. If the manufacturer uses self-made glue, it must strictly follow the formula and process flow. The glue should be sent to the authoritative department for testing to ensure that the free formaldehyde content is controlled. If the glue is purchased, the purchased glue must be approved by an authoritative department. Whether self-made or purchased glue, the free formaldehyde content must reach the E2 level before use.
In addition, a few woods such as poplar wood contain aldehydes and ketones, and formaldehyde may be released during processing. Therefore, the factory should also pay attention to the choice of wood species when selecting raw materials.
Second, the control of the process. According to the different glue characteristics, the corresponding process flow is formulated, including the gluing process (adding amount and action time of various catalysts in different glues and different temperatures) and the hot pressing process (hot pressing temperature, hot pressing time). Shortening the hot-pressing time and reducing the hot-pressing temperature will reduce the formaldehyde emission. Regular training is required for plastics and hot-press process personnel, and the staff involved in these two processes are required to strictly implement the technological process to ensure that the unstable structure during the hot-pressing process is decomposed to release formaldehyde at the minimum. The factory inspection personnel should strictly inspect according to regulations. , Found that the defective glue should stop production immediately, found that unreasonable process should be corrected immediately.
When controlling the process, it is also important to note that the factory cannot omit the health process. Sometimes the delivery time of the factory is urgency, artificially eliminating this process, and in fact, the slow release of free formaldehyde takes some time.
Third, finished product testing control. The factory shall establish a physical and chemical laboratory, and carry out formaldehyde testing for each batch of products according to the relevant standards (sampling in the workshop). If the result is unqualified, the production department shall be notified immediately to stop the production, identify the cause, re-treat the unqualified product, re-treat and test again, and only the qualified product can be stored in the warehouse.
In addition, it is necessary to strengthen logo management, and indoor and outdoor panels should be clearly identified.
In summary, the key to producing low-formaldehyde emission plywood is to use a one-time glue with low free formaldehyde content, and adopt scientific process and strictly control the time and temperature of hot-pressing. At the same time, we must strengthen the detection and control of finished products. And pay attention to the choice of wood species. If you can do the above points, you can effectively control the amount of formaldehyde released from plywood.