Melamine is an organic chemical intermediate with a nitrogen content as high as 66%. It appears as a white monoclinic crystalline powder. For decades, its most important industrial use has been to react with formaldehyde to produce melamine-formaldehyde resin (MF), which is then used to manufacture melamine ware (also known as “mimic ceramic” or “Mela” tableware) and other food contact materials. This article starts from the fundamental properties of melamine as a monomer and systematically explains how it is chemically transformed into safe, durable tableware material, while addressing the safety concerns that consumers care most about.
The chemical formula of melamine is C3H6N6. Its molecular structure contains three amino groups (-NH2) and a triazine ring, which give it high reactivity and thermal stability. At room temperature, melamine is a solid powder, slightly soluble in water but readily soluble in alkaline solutions and hot polar solvents such as ethylene glycol.
Industrially, melamine is mainly produced by high-temperature condensation of urea. The process is as follows: urea is pyrolyzed at 380–400 °C under an ammonia atmosphere to form cyanic acid, which then polymerizes further to yield melamine, with ammonia and carbon dioxide as by_products. Globally, about 90% of melamine is used to produce melamine-formaldehyde resin. Although the proportion used for food contact materials (especially melamine ware) is smaller than that for wood-based panels, it is the application closest to ordinary consumers and attracts the most public attention.
Melamine cannot be used directly to make tableware. It must undergo a polycondensation reaction with formaldehyde to form a stable, three_dimensional network polymer – melamine-formaldehyde resin. The reaction occurs in two steps:
Hydroxymethylation stage: Under slightly alkaline conditions (pH≈8.5), the three amino groups of melamine undergo an addition reaction with formaldehyde to generate a mixture of mono_, di_, and tri_methylol melamine. The reaction temperature is generally controlled at 54–80 °C.
Polycondensation and cross‑linking stage: The methylol derivatives are further dehydrated and condensed in the presence of heat (130–150 °C) and a small amount of acid catalyst, forming an insoluble, non‑meltable three‑dimensional network. The final product is melamine-formaldehyde resin, which is colourless, transparent, hard, heat‑resistant (can be used long‑term below 120 °C), water‑resistant, oil‑resistant, and self‑extinguishing.
For compression moulding, the resin is usually mixed with α‑cellulose (wood pulp), lubricants, colourants, etc., to produce melamine moulding compound. The α‑cellulose acts as a filler to reduce shrinkage and improve impact strength, while the melamine‑formaldehyde resin gives the finished product a glossy surface and scratch resistance.
Many people worry: since melamine was involved in illegal food adulteration incidents, is it safe to use tableware made from it? The answer is: cured melamine-formaldehyde resin and free melamine monomer are completely different substances. In compliantly manufactured melamine ware, the residual content of free melamine monomer is extremely low, and its migration under normal use conditions is far below the safety limits set by various countries.
China’s national standard GB 4806.6-2016 “National Food Safety Standard – Plastic Resins for Food Contact” explicitly states that melamine-formaldehyde resin can be used to produce food contact materials and articles, but shall not be used for microwave heating. The standard sets a specific migration limit (SML) for melamine of 2.5 mg/kg and for formaldehyde of 15 mg/kg. For articles intended to come into contact with infant food, the SML for melamine is tightened to 1 mg/kg.
Similar regulations are found in the European Union (EU) No 10/2011 and the US FDA 21 CFR §177.1460. These limits are based on extensive toxicological tests and dietary exposure assessments – melamine itself has certain nephrotoxicity and can cause bladder stones, but health hazards occur only when the migration amount exceeds the above limits over a long period. The actual migration from compliant products is usually far below the limits, indicating very low risk.
Melamine-formaldehyde resin is made into tableware mainly by compression moulding. The core steps are as follows:
Preheating: Weigh the melamine moulding compound according to the required weight of the tableware and preheat it uniformly in a high‑frequency preheater to agglomerate the powder.
Unprinted forming: Put the preheated agglomerate into a mould and press at 130–150 °C under a pressure of about 10–20 MPa. The high temperature further cross‑links the resin while making the surface smooth.
Decal application and glossing: If a coloured pattern is required, stick the decal paper onto the unprinted tableware, sprinkle gloss powder, and press again so that the pattern is embedded into the resin layer.
Trimming and polishing: Remove burrs and polish to obtain a glossy, porcelain‑like surface.
During the entire production process, the reaction conditions (temperature, time, pH, efficiency of removing free monomers) directly determine the residual contents of melamine and formaldehyde in the finished product. Reputable manufacturers use post‑treatments such as secondary curing, water washing or hot‑air blowing to minimise free monomers.
Even melamine ware that meets factory standards may, if used improperly, accelerate the migration of melamine and formaldehyde. Experimental studies show that the following factors significantly increase migration:
High temperature: When the temperature exceeds 100 °C (e.g., boiling, microwave heating), the incompletely cross‑linked part of the resin may hydrolyse and release monomers. Therefore, national standards explicitly prohibit microwave use. The normal use temperature should be below 120 °C.
Acidic media: A pH ≤ 4 environment (e.g., vinegar, lemon juice, carbonated beverages) catalyses the acidolysis of melamine-formaldehyde resin, leading to higher melamine migration. Do not store acidic foods for long periods.
Surface abrasion: Using steel wool or hard cleaning tools destroys the dense resin layer on the surface, exposing the insufficiently cross‑linked interior, which increases migration in subsequent use. Studies show that after abrasion, melamine migration can increase by 2‑3 times.
Service life: The recommended service life of melamine ware is 2‑3 years. With repeated washing and heat exposure, the resin gradually ages, cross‑linking bonds break, and the migration risk increases.
In the market, a small number of inferior products are made from urea-formaldehyde resin (UF) or mixed materials and sold as melamine-formaldehyde resin tableware. UF resin is also made from urea and formaldehyde, but its heat and water resistance are much lower than those of MF resin, and it easily releases free formaldehyde under humid and hot conditions. Consumers can identify authentic products by the following methods:
Check the label: Compliant products should bear the mark “MF” (melamine-formaldehyde resin), together with the QS production licence mark. If it is marked “UF”, it must not be used for holding food.
Observe the texture: Products made from pure MF resin have a smooth, porcelain_like surface, feel heavy, and give a crisp sound when tapped. Inferior products look dull and feel light.
Simple hot_water test: Put the tableware in boiling water for 2_3 minutes, then take it out and smell it. Compliant products should have no pungent formaldehyde odour.
Choose light_coloured inner surfaces: The inner surface that contacts food should preferably be white or light_coloured, to avoid possible heavy metal migration from coloured glazes.
As an industrial raw material, melamine provides a solution that combines aesthetics, light weight, durability and cost_effectiveness for food contact materials, provided it is used in compliance with regulations and under proper conditions. From a chemical perspective, it is precisely the triazine ring structure and high cross_linking ability of melamine that give melamine ware its superior heat resistance and surface hardness compared with ordinary plastics. Globally, hundreds of thousands of tonnes of melamine are converted each year via resin into products that reach our dining tables.
Consumers need not panic at the mere mention of “melamine” . Instead, a scientific understanding should be established: the monomer is different from the polymer; compliant use is different from illegal adulteration; correct use is different from abuse. By choosing products from reliable sources, looking for the MF mark, avoiding high temperatures and acidic environments, and replacing old or worn tableware in a timely manner, melamine can safely serve our daily lives.
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