Thermosetting Melamine Resins

Similar to urea (see Section 13.2), melamine can react with formaldehyde forming a thermosetting resin. Melamine is a trimer of cyanamide and contains three amino groups that offer six possible points of reaction. Since melamine can be considered a triamine of 1,3,5-triazine, this group of resins can be included in the class of polymers with heterocycles in their structure. The first stage of the reaction of melamine with formaldehyde can be written as follows  

Both triazine- and urethane-linked networks are highly resistant to paraffin and silicone oils. Triazine-linked networks are resistant to a wide range of organic liquids, whereas urethane-linked networks are attacked by polar organic solvents. Both types are easily attacked by fluorinated species [1]. 

The polymer has CAS 68002-20-0 and Mr, = 511. The pyrolysis was done at 600° C in He at a heating rate of 20° C/ms. The separation was done on a Carbowax column in conditions described in Table 4.2.2. The peak identification for the chromatogram was done using MS spectral library searches only, and it is given in Table 15.3.1. 

Results from Table 15.3.1 indicate that among the main decomposition products of these polymers are methanol, CO2, formaldehyde, and dimethoxymethane. A few nitrogenous compounds also are detected. Some of the decomposition products may be too polar to be detected in the experimental conditions used for the analysis. 

Heatley, C. Price, C. Booth, Prog. Rubber Plast, Technol., 11 (1995) 94. 

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MIL-P-15037E Thermoset Melamine Resin Sheet, Glass Reinforced MIL-P-15047B Thermoset Phenolic Resin Sheet, Nylon Reinforced MIL-I-15126F Insulation Tape, Electrical, Pressure Sensitive and Thermoset Adhesive... 

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... 

Thermosetting urea or melamine resin. Arochlor—chlorinated diphenyl. 

Melamine resins are used from this group of thermosets for the manufacture of food contact materials. The melamine can be used in mixtures with urea and in some applications with phenol (< 1 %). The polymerization process is catalyzed in the presence of organic acids (e.g. acetic acid, lactic acid, tartaric acid, citric acid), hydrochloric acid, sulfuric acid, phosphoric acid, sodium and potassium hydroxide, ammonia, calcium or magnesium hydroxide as well as salts of these substances (total < 1 %) which cause the elimination of water and lead to a cured resin system. Stearic acid can be used as a lubricant as can zinc, calcium and magnesium salts, esters of montanic acid with ethandiol and 1,3-butandiol, as well as silicone oil (total < 1 %). 

Plastics can be placed into two main categories, thermoplastic and thermoset. Thermoset plastics are irreversibly formed into a permanent shape often by applying heat. Thermosets caimot be softened and remoulded on heating and have few applications in food packaging, except for the iimer linings used for can coatings and many adhesives, as used, for example, in multilayer materials. A limited range of food contact materials is made from thermosets, predominantly melamine resins and unsaturated polyesters used in tableware and utensils. 

Thermosetting phenolic resins form a separate class of polymers containing aromatic rings and aliphatic carbon groups in the polymeric network. These resins are formed from the reaction of phenol (or substituted phenols) with formaldehyde. The fully crosslinked macromolecule is insoluble and infusible. Other thermosetting resins are known in practice, some derived from the reaction of melamine or of urea with formaldehyde. Because these have a different chemical structure, containing nitrogen, they are included in a different class (see Section 15.3). 

For example, U.S. Pat. No. 3,367,917 [15] describes a thermosetting melamine-formaldehyde-benzoguanamine resinous molding composition containing a hbrous hller, such as a-cellulose pulp, in an amount between 25 and 42% by weight. 

U.S. Pat. No. 6,702,969 [27] discloses a composite material prepared by mixing a thermoset resin, such as phenolic resin, urea resin, melamine resin, epoxy resin, urethane resin, and mixture thereof, to bind wood pieces and a filler, such as natural and synthetic graphites, metal, carbon, and other similar compounds and then-mixtures. 

Melamine is a strong organic base, which is used primarily to produce melamine resin, which when combined with formaldehyde produces a very durable thermoset plastic. This plastic is often used in kitchen utensils or plates (often sold under the brand name Melmac), and is the main constituent of Formica and Arborite . Melamine tile wall panels are known as whiteboards. Melamine is also used to make decorative wall panels and is often used as a laminate. Melamine is produced from urea, mainly by either of two methods catalyzed gas-phase production or high-pressure liquid-phase production. 

C3N3(NH2)3) a white solid organic compound whose molecules consist of a six-membered heterocyclic ring of alternate carbon and nitrogen atoms with three amino groups attached to the carbons. Condensation polymerization with methanal or other aldehydes produces melamine resins, which are important thermosetting plastics. 

Thermoset composite systems of phenol and formaldehyde, some of which can he substituted for a number of structural applications can also be considered as engineering plastics and they have been in use for a very long time. In recent applications, improved urea - melamine resins have been used as matrices more and more for composite systems, because of their non-melting, high thermal and chemical resistances, hardnesses, mechanical-dimensional stabilities and low flammabilities. 

Uses Crosslinking agent in melamine resin coating systems, general industrial finishes, coil-coating enamels, appliance finishes, useful with alkyd, polyester, thermosetting acrylic, epoxy, and cellulose resins Properties Gardner 2 max. clear, vise, liq. limited water-sol. dens. 10.0 Ib/gal vise. (G-H) X-Z2 flash pt. > 180 F 98% NV Cymel 350 [Cytecind.j... 

Chem. Descrip. Partially methylated melamine resin in isobutanol Uses Crosslinking agent for thermoset coatings Features Fast, low temp, cure, high crosslink efficiency Properties APHA30 max. color dens. 9.4-9.6 Ib/gal vise. (Gardner-Holdt) Z,.Z, flash pt. (PMCC) 31 C 80-84% solids Resimene 730 [Solutia]... 

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