Thermosetting plastics , adhesives urea-formaldehyde

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... 

Uses Mfg. of phenolic and thermosetting resins, furan polymers, urea-formaldehyde resins wetting agent foundry sand binders corrosion-resist, resins intermediate for esterification and etherification paints solvent, plasticizer for phenolic resins solvent for dyes and resins nonreactive epoxy resin diluent vise, reducer, cure promoter, and carrier in amine-cured epoxy resins gel retarder in casein/protein glues polymer sealants/cements synthetic flavoring agent in foods and pharmaceuticals cosmetics ingred. in food-pkg. adhesives... 

Thermosetting plastics (e.g., epoxies diaUyl phthalate polyesters melamine, phenol and urea formaldehyde and polyurethanes) are joined either mechanically or by adhesives. Their thermosetting nature prohibits the use of solvent or thermal welding processes however, they are easily bonded with many adhesives. 

For a general introduction, see Wood adhesives - basics. Aminoplastic resins are polycondensation products of the reaction of aldehydes with compounds carrying amine or amide groups. Formaldehyde is by far the primary aldehyde used. The name amino-plastic is traditional, but is a misnomer these are thermosetting, irreversibly hardening resins. Two main classes of these resins exist urea-formaldehyde (UF) resins and melamine-formaldehyde (MF) resins. Today, for wood adhesives, pure MF resins are not used anymore because of cost, and only melamine-urea-formaldehyde (MUF) adhesives are used. The main use of these resins is in composite products such as particle board, plywood, medium density fibreboard (MDF), oriented strand board (OSB), glu-lam/flngerjointing and furniture. 

A number of plastic, adhesive, and coating materials are utilized in a densely cross-linked form known as thermosets. Some of the more important of these include the phenol-formaldehyde resins, urea-formaldehydes, polyimides, epoxies, amino resins, and the alkyds, among others (8). Because these... 

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