Detailed explanation of MDI adhesive
Guide: With people’s pursuit of quality of life and their concern for health and environmental protection, MDI adhesive seems to have become the “new favorite” of the home decoration industry. What is MDI adhesive? Compared with traditional adhesives such as urea formaldehyde adhesive, what are the advantages of MDI adhesive?
- What is MDI adhesive MDI adhesive is a downstream product of MDI (diphenylmethane diisocyanate), which is used to manufacture various plates. MDI ecological adhesive is used to make boards, which not only solves the over development of forest resources, but also is conducive to people’s home health because it does not contain formaldehyde. 2. The advantage of using MDI adhesive is that no aldehyde is added to the adhesive; Low sizing amount; Excellent plate performance; The hot pressing cycle is short; The adhesive property is stable. 3. MDI adhesive will react with fiber to form a polymer form called polyurea (similar to plastic). This polymer structure has no volatility. Therefore, the environmental protection board made of MDI adhesive can not only achieve zero formaldehyde release of adhesive, but also has better safety and environmental protection than urea formaldehyde resin adhesive. The position of MDI in isocyanates belongs to the low toxicity type (comparison of the parameters of three common isocyanates). Compared with TDI and HDI, MDI has a higher melting point. At room temperature, it does not appear as liquid as TDI and HDI, but as solid, with lower vapor pressure, and is not easy to volatilize. Unlike TDI and HDI, which are prone to cause systemic reactions and respiratory failure, MDI is the most commonly used isocyanate and has the lowest risk. 2 MDI is not easy to volatilize to form gas at room temperature, and its stability is better than that of urea formaldehyde resin glue. Vapor pressure means that under certain external conditions, liquid molecules in the liquid will evaporate into gaseous molecules, while gaseous molecules will also hit the liquid surface and return to the liquid. This is a two-phase change in a single component system. After a certain period of time, equilibrium can be reached. In equilibrium, the content of gaseous molecules reaches the maximum, and the pressure generated by these gaseous molecules on the liquid is called vapor pressure. The higher the vapor pressure is, the greater the escape tendency of molecules in the liquid is, that is, the easier it is to volatilize. (MSDS parameters of MDI) From the MSDS of MDI, it can be seen that the vapor pressure of MDI increases to 0.13Pa at 40 ℃, equivalent to 0.000975mmHg, nearly 200 times higher than that at 20 ℃. Even so, the 40 ℃ vapor pressure of MDI is still far less than that of formaldehyde. Formaldehyde has a melting point of – 92 ℃ and a boiling point of – 19 ℃. Formaldehyde is a gas at room temperature, and its vapor pressure is less than 1 atm (standard atmospheric pressure, equal to 101.325 kPa), which is very volatile. It is concluded that the main component of MDI adhesive is MDI, which is mixed with some other polyphenyl polymethylene cyanates, and its toxicity is close to that of pure MDI. Considering the safety of MDI adhesive, it is superior to urea formaldehyde and phenol formaldehyde resin that release formaldehyde. According to statistics, more than 70% of North American OSB board manufacturers use MDI adhesive to produce, and the trend of switching from urea formaldehyde to phenol formaldehyde is increasingly obvious. According to the application characteristics of MDI adhesive, its main advantages are shown in the following aspects: adhesive formaldehyde free addition MDI is a kind of substance chemically named polyphenylmethane diisocyanate, and is one of the most important raw materials for preparing polyurethane. With the dual advantages of rubber and plastic, polyurethane is widely used in chemical industry, light industry, textile, construction, household appliances, building materials, transportation, medical treatment, aerospace and other fields, and even implanted into human organs in medical treatment. Because MDI adhesive does not contain formaldehyde and has very low volatility, it can greatly avoid the harm of chemicals to human body during the production process. The boards produced by MDI adhesive are solidified at high temperature to form stable chemicals, which will not release formaldehyde and other organic chemicals, thus eliminating environmental pollution during product use. The bonding principle of MDI adhesive with low sizing amount is different from that of traditional tri aldehyde adhesive. Traditional trialdehyde adhesive is physical bonding, while MDI is chemical bonding. The – NCO group in MDI can react with water in wood and – OH in cellulose to form stable chemicals. From the microscopic point of view, it can make the materials form intermolecular crosslinking, thus reducing the traditional “surface bonding” to “point bonding”, greatly reducing the amount of adhesive used. The excellent performance of the board can be easily introduced due to the above chemical bonding characteristics of MDI adhesive, and the performance of the board produced by the MDI adhesive will greatly exceed that of the adhesive based on the traditional physical bonding principle. The micro transformation from van der Waals force to chemical bond force has greatly improved the internal bonding force and waterproof and moisture-proof performance of the board. Some studies have shown that the static bending strength and creep properties of MDI oriented structural board are far superior to those of urea formaldehyde adhesive. Short hot pressing cycle Due to the chemical reaction characteristics of MDI adhesive, it can also accelerate the curing speed of adhesive, reduce the hot pressing time, and improve the production efficiency. From the application experience of OSB manufacturers in North America, the curing speed of MDI is at least 30% faster than that of urea formaldehyde adhesive, and it has more obvious advantages than that of phenol formaldehyde adhesive. In addition, MDI can also provide fast curing special products according to customer needs, so as to help customers achieve higher production efficiency and better product quality.
