Melamine dehydration

Urea is dehydrated to cyanamide which trimerizes to melamine in an atmosphere of ammonia to suppress the formation of deamination products. The ammonium carbamate [1111-78-0] also formed is recycled and converted to urea. For this reason the manufacture of melamine is usually integrated with much larger facilities making ammonia and urea. 

Combined condensation of melamine and of the acid residue is also shown by the phosphate and borate. In these cases however, the polymeric dehydrated compound derived from the acid is thermally stable up to above 500 C allowing chemical reactions with melamine condensation products simultaneously formed. The resulting material is stable to 950 C (phosphate, ca 30% of original salt) or to above 1100 C (borate, ca. 20% of original salt). 

Another use of urea is for resins, which are used in numerous applications including plastics, adhesives, moldings, laminates, plywood, particleboard, textiles, and coatings. Resins are organic liquid substances exuded from plants that harden on exposure to air. The term now includes numerous synthetically produced resins. Urea resins are thermosetting, which means they harden when heated, often with the aid of a catalyst. The polymerization of urea and formaldehyde produces urea-formaldehyde resins, which is the second most abundant use of urea. Urea is dehydrated to melamine, which, when combined with formaldehyde, produces melamine-formaldehyde resins (Figure 96.2). Melamine resins tend to be harder and more heat-resistant than urea-formaldehyde resins. Melamine received widespread attention as the primary pet food and animal feed contaminant causing numerous cat and dog deaths in early... 

Figure 96.2 Dehydration of urea produces melamine, ammonia, and carbon dioxide.

Melamine diborate (MB), known in the fire-retardant trade as melamine borate, is a white powder, which can be prepared readily from melamine and boric acid. It is partly soluble in water and acts as an afterglow suppressant and a char promoter in cellulosic materials. Budenheim Iberica79 claims that, in a 1 1 combination with APP, MB (10%-15%) can be used for phenolic bound nonwoven cotton fibers. In general, melamine borate can be used as a char promoter in intumescent systems for various polymers including polyolefins or elastomers. However, its low dehydration temperature (about 130°C) limits its application in thermoplastics that are processed at above 130°C. Melamine borate is also reported to suppress afterglow combustion in flame-proofing textiles with APP or monoammonium phosphate to meet the German DIN 53,459 and Nordtest NT-Fire 002.80... 

A munber of nitrogen derivatives of phosphoric and polyphosphoric acid (ammonium polyphosphate, melamine pyrophosphate) are used for improving the flame retardance of polyurethanes and other polymers. In thermal decomposition these compounds produce ammonia and the corresponding phosphoric acids which catalyze dehydration and other reactions, causing polymer dehydration during combustion. The coke produced in this process is more or less foamed. Ammonium polyphosphate and melamine pyrophosphate are added to compositions of intumes-cent coatings used for fire protection of various structural elements in construction... 

Use Preparation of esters, especially butyl acetate solvent for resins and coatings plasticizers dyeing assistant hydraulic fluids detergent formulations dehydrating agent (by azeotropic distillation) intermediate butylated melamine resins glycol ethers butyl acrylate. 

The current standard process route to melamine uses urea as a starting material. Urea is heated in the presence of ammonia at 250—300°C and 4—20 MPa. The reaction probably involves the simultaneous dehydration and hydration of urea to form cyanamide and ammonium carbamate trimerization of the cyanamide then leads to melamine [10]. 

Epoxy resins have provided excellent corrosion resistant primers for appliances. These can be made from epoxy resins esterified with dehydrated castor oil fatty acids and cured with melamine. Excellent detergent resistance and corrosion resistance are obtained from this type of resin system. 

Waterborne poly(ester amide) resins based on dehydrated castor oil and niger seed oil have been prepared from fatty amides of oils with isophthalic acid, followed by neutralisation with varying percentages of triethylamine. The neutralised polymers were dispersed in water. These water dispersible resins were cured with hexamethoxymethyl melamine in varying proportions at a high temperature. ... 

Reaction of dehydrated melamine-aldehyde condensate with fatty acid in the presence of a lower molecular weight alcohol [95]. 

Keywords fire, combustion, coating, char, pyrolysis, polyhydric compound, amide, amine, inorganic acid, blowing action, foam, dehydration, phosphorylation, dehydrocellulose, intumescence, melamine, piperazine. 

Water-repellent finishes for films and fibers Antistatic coatings for photographic films Melamine-formaldehyde resin modifier K salt and rubber coatings Decarboxylated resin Acid polymer dehydration Hair waving formulations Decarboxylated resins Imide copolymers for nonflammable foams Thermosetting resins... 

Melamine was synthesized early in the history of organic chemistry but remained a chemical curiosity until it was found to react with formaldehyde to form a useful amino resin. Melamine was first manufactured from dicyan-diamide, but it is now made from urea, a much lower-cost starting material. In this process the urea is dehydrated to cyanamid which terminates to melamine. The reaction is carried out at high pressure in the presence of ammonia to suppress the formation of deamination products. Ammonium carbamate is also formed in the reaction and must be recycled to convert it back to urea. 

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