The molecular model of melamine is weakly alkaline (pKb=8), which can form melamine salt with hydrochloric acid, sulfuric acid, nitric acid, acetic acid and oxalic acid. Under neutral or weak alkaline conditions, all kinds of hydroxymethyl melamine are condensed with formaldehyde, but under weak acidic conditions (pH 5.5 ~ 6.5), they are condensed with hydroxymethyl derivatives to produce resin products. When hydrolyzed with strong acid or strong alkali aqueous solution, amino groups are gradually replaced by hydroxyl groups and become cyanuric acid diamide, which is further hydrolyzed to form cyanuric acid monoamide, and finally cyanuric acid is generated.
The main use of structural melamine Melamine is a basic organic chemical intermediate product with a wide range of uses, mainly used as a raw material for producing melamine formaldehyde resin (MF). Melamine can also be used as flame retardant, water reducer and formaldehyde cleaner. The hardness of this resin is higher than that of urea-formaldehyde resin, and it is nonflammable, water-resistant, heat-resistant, aging-resistant, arc-resistant and chemical-resistant. It has good insulation performance, luster and mechanical strength, and is widely used in wood, plastics, coatings, paper-making, textile, leather, electric power, medicine and other industries. Its main uses are as follows:
(1) Decorative board: it can be made into fire-proof, earthquake-resistant and heat-resistant laminated board, bright-colored, high-strength and heat-resistant decorative board, used as veneer for airplanes, ships and furniture, as well as fire-proof, earthquake-resistant and heat-resistant building decorative materials.
(2) Coatings: After etherification with butanol and methanol, it can be used as the base material of advanced thermosetting coatings and solid powder coatings, and can be used to make metal coatings and advanced amino resin decorative paints for automobiles and electrical appliances.
(3) Molding powder: Melamine plastic can be made by mixing, granulating and other processes. It is non-toxic and stain-resistant, and can still maintain good electrical properties when wet. It can be made into white and fall-resistant household utensils, sanitary ware, porcelain-like tableware, electrical equipment and other advanced insulating materials.
(4) Paper: It can be used as a paper treatment agent after etherification with ether to produce high-grade paper such as anti-wrinkle, shrink-proof and non-perishable banknotes and military maps.
(5) Melamine formaldehyde resin can be mixed with other raw materials to produce fabric finishing agent, leather tanning agent, polishing agent and waterproof agent, rubber adhesive, combustion improver, high-efficiency cement water reducer, steel desalter, etc.
At present, melamine is considered to be slightly toxic, and the lethal dose to rats is above 3 g/kg body weight. According to an experimental report of 1945, rats, rabbits and dogs were fed with large doses of melamine, and no obvious poisoning phenomenon was found. Long-term intake of melamine in animals will cause damage to reproductive and urinary systems, bladder and kidney calculi, and further induce bladder cancer. 1994 Volume III of the International Handbook of Chemical Safety and the International Chemical Safety Card jointly edited by the International Chemical Safety Agency and the European Commission only show that long-term or repeated intake of melamine may affect the kidneys and bladder, leading to stones. However, the preliminary investigation of pet food pollution in the United States in 2007 showed that wheat protein powder mixed with melamine ≤6.6% was the cause of pet food poisoning, which put a question mark on the above conclusion of slight toxicity. However, for safety reasons, melamine tableware will be marked "Do not use in the microwave oven".
On September 12, 2008, the Ministry of Health of the People's Republic of China issued the "Diagnosis and Treatment Plan for Urinary Calculi of Infants Related to Eating Contaminated Sanlu Infant Formula Milk Powder", which can be used for reference by relevant parties.
It is pointed out in the plan that most stones involve bilateral collecting system and bilateral ureters, which is different from the clinical manifestations of adult urinary calculi, and the probability of multiple stones affecting renal function is high. Because most children do not have the ability to complain about symptoms, parents need to strengthen the observation of related children, and relying on abdominal B-ultrasound and/or CT examination is helpful for early diagnosis. In terms of treatment, there is no specific antidote for the toxic effect of melamine at present, and clinical treatment mainly depends on symptomatic support. If necessary, surgical intervention can be considered to reduce the risk of long-term damage to children's renal function. Early diagnosis and treatment is the key to a child's early recovery.
Melamine is a low toxic chemical raw material. The results of animal experiments show that it is metabolized quickly in animals and will not remain, which mainly affects the urinary system.
There is an obvious dose-effect relationship between the dose of melamine and clinical diseases. The maximum tolerance of infants to melamine is per kilogram of milk powder 15 mg. Experts' risk assessment of contaminated infant formula shows that, taking an infant weighing 7 kg as an example, assuming daily intake of 150 g of milk powder, its safety preset value is 15 mg/kg of milk powder.
According to the standards of the US Food and Drug Administration, the daily tolerable intake of melamine is 0.63 mg/kg body weight per day. (It is harmful to human body and should not appear in food) Due to the defects of protein content detection methods in food and feed industries, melamine is often used as a food additive by unscrupulous businessmen in food detection to improve the protein content index, so melamine is also called "protein essence".
Protein is mainly composed of amino acids. The average nitrogen content in protein is about 16%, while the nitrogen content of melamine is about 66%. The common protein test method "Kjeldahl method" estimates the content of protein by measuring the content of nitrogen. Therefore, adding melamine will make the protein content of food high, so that inferior food can pass the inspection of food inspection agencies. It is estimated that the content of test protein in plant protein powder and feed will increase by one percentage point, and the cost of using melamine is only 1/5 of that of real protein raw materials. Melamine, as a white crystalline powder, has no smell and taste, and it is not easy to be found after doping.
Milk powder incident: the protein content of all brands of milk powder is 15-20% (and it is marked as 10-20% on the supermarket package at night), and the average nitrogen content in protein is 16%. If the protein content of a qualified milk is 2.8% and the nitrogen content is 0.44%, the protein content of a qualified milk powder is 18% and the nitrogen content is 2.88%. The nitrogen content of melamine is 66.6%, which is 15 1 times that of milk and 23 times that of milk powder. Adding 0. 1g melamine to every 100g milk can theoretically increase protein by 0.625%.
Slightly soluble means that the solute 1g(ml) can be dissolved in the solvent 100 ~ less than 1000ml, and melamine is slightly soluble in water. The solubility in oil-in-water emulsion of milk has not been found in experimental data, so it should be better than that in water, which needs to be verified.
Detection scheme: In the existing national standards for milk powder detection, protein, fat and bacteria are mainly detected. Melamine is a chemical raw material, which is not allowed to be added to food, so the existing standards will not have corresponding content. In other words, there is no national standard for melamine testing at present. So, Germany Rhine t? In group V, the quantitative method of HPLC-UV of American Food Chemical Code (FCC) was referred to, and the baby food, pet food, feed and its raw materials (including starch, rice protein, corn protein, gluten, grain and oil) could also be detected by HPLC/MS (laboratory method). ), and the test results are authoritative.
Another explanation of false protein in Sanlu milk powder is that the enterprise added urea, and the raw milk directly turned into milk powder at high temperature, which dehydrated the urea to produce melamine, so there was melamine in the final milk powder.