Thermosetting plastics phenol formaldehyde resins

Amino resins are thermosetting polymers made by combining an aldehyde with a compound containing an amino (—NH2) group. Urea—formaldehyde (U/F) accounts for over 80% of amino resins melamine—formaldehyde accounts for most of the rest. Other aldehydes and other amino compounds are used to a very minor extent. The first commercially important amino resin appeared about 1930, or some 20 years after the introduction of phenol—formaldehyde resins and plastics (see Phenolic resins). 

Table 12.3 summarizes the uses of formaldehyde. Two important thermosetting plastics, urea- and phenol-copolymers, take nearly one half the formaldehyde manufactured. Urea-formaldehyde resins are used in particleboard, phenol-formaldehyde resins in plywood. 1,4-Butanediol is made for some polyesters and is an example of acetylene chemistry that has not yet been replaced. Tetrahydrofiiran (THF) is a common solvent that is made by dehydration of 1,4-butanediol. 

What was the first synthetic plastic Although some nineteenth-century experiments should be mentioned, such as the 1869 molding process for cellulose nitrate discovered by John and Isaiah Hyatt, probably the first major breakthrough came in 1910 with Leo Baekeland s discovery of phenol formaldehyde resins (Bakelite ). These are still the leading thermoset plastics made today. The pioneering work of Wallace Carothers at Du Pont in 1929 produced the nylons now used primarily as fibers but known as the beginning of thermoplastic resin technology. 

Elastomeric 1, Natural rubber. 2, Neoprene. 3, Nitrile. 4, Urethane. 5, Styrene-butadiene. Thermoplastic 6, Poly(vinyl acetate). 7, Polyamide. Thermosetting 8, Phenol-formaldehyde. 9, Resorcinol, Phenol-resorcinol/formaldehyde. 10, Epoxy. 11, urea-formaldehyde. Resin 12, Phenolic-poly(vinyl butyral). 13, Polyeser. Other 14, Cyanoacrylate. 15, Solvent. Source Adapted from O Rinda Trauernicht, J. 1970. Plastics Technology, Reinhold Publishing, New York. 

Phenols Formaldehyde. Phenol-formaldehyde resins were the first commercial synthetic plastics. Since their invention in 1908, they have grown and matured into the second most important family of thermoset plastics, with a U.S. market volume of 4 bU-hon Ib/yr (see Table 3.6). 

However, densely cross-linked plastics (thermosets) are sometimes deliberately used. Reasons tend to be nonmechanical increased solvent and swelling resistance, high-temperature resistance, and reduced flammability are cited. The last arises because the polymer chars rather than degrades with concomitant reduction of volatile (and flammable) components. Examples include epoxies, phenol-formaldehyde resins, and some polyurethanes see Section 14.2. 

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... 

The thermoplastic or thermoset nature of the resin in the colorant—resin matrix is also important. For thermoplastics, the polymerisation reaction is completed, the materials are processed at or close to their melting points, and scrap may be reground and remolded, eg, polyethylene, propjiene, poly(vinyl chloride), acetal resins (qv), acryhcs, ABS, nylons, ceUulosics, and polystyrene (see Olefin polymers Vinyl polymers Acrylic ester polymers Polyamides Cellulose ESTERS Styrene polymers). In the case of thermoset resins, the chemical reaction is only partially complete when the colorants are added and is concluded when the resin is molded. The result is a nonmeltable cross-linked resin that caimot be reworked, eg, epoxy resins (qv), urea—formaldehyde, melamine—formaldehyde, phenoHcs, and thermoset polyesters (qv) (see Amino resins and plastics Phenolic resins). 

This group includes many plastics produced by condensation polymerization. Among the important thermosets are the polyurethanes, epoxy resins, phenolic resins, and urea and melamine formaldehyde resins. 

Important thermosetting plastics include the phenolics, melamine-formaldehyde, epoxides and polyester resins used in glass-reinforced plastics. (See also Sections 14.5 and 14.9.)... 

Commonly accepted practice restricts the term to plastics that serve engineering purposes and can be processed and reprocessed by injection and extrusion methods. This excludes the so-called specialty plastics, eg, fluorocarbon polymers and infusible film products such as Kapton and Upilex polyimide film, and thermosets including phenolics, epoxies, urea—formaldehydes, and silicones, some of which have been termed engineering plastics by other authors (4) (see Elastomers, synthetic-fluorocarbon elastomers Fluorine compounds, organic-tetrafluoroethylene copolymers with ethylene Phenolic resins Epoxy resins Amino resins and plastics). 

Thermoset A resin or plastic compound that in its final state is substantially infusible and insoluble. It cannot be repeatedly softened by heating and hardened by cooling. Examples of thermosets are epoxy, phenol-formaldehyde, some types of polyester, some types of... 

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... 

Phenolic plastics. Collective designation for phenolic resin-based plastics. Phenolic resins are produced by condensation of phenol and/or its homologues, such as cresol, with an aldehyde, such as formaldehyde or with an aldehyde-releasing material such as hexamethylenetetramine. Phenol/formaldehyde and/or cresol/formaldehyde resins are used as binding materials in fibre board, laminated paper and fabrics. In phenolic moulding compounds, the proportion of filler (such as wood flour, rock flour, asbestos, stone powder, mica, glass fibre) can be equal to that of the resin. These thermosets can be processed by compression or injection moulding into black or dark-coloured products mainly for the electric industry. 

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