Phenolics melamine formaldehyde

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.)... 

PVF resins are generally compatible with phthalate, phosphate, adipate, and dibenzoate plasticizers, and with phenolic, melamine-formaldehyde, urea-formaldehyde, unsaturated polyester, epoxy, polyurethane, and cellu lose acetate hutylate resins. They are incompatible with polyamide, ethyl cellulose, and poly(vinyl chloride) resins. 

Both melamine—formaldehyde (MF) and resorcinol—formaldehyde (RF) foUowed the eadier developments of phenol—, and urea—formaldehyde. Melamine has a more complex stmcture than urea and is also more expensive. Melamine-base resins requite heat to cure, produce colorless gluelines, and are much more water-resistant than urea resins but stiU are not quite waterproof. Because of melamine s similarity to urea, it is often used in fairly small amounts with urea to produce melamine—urea—formaldehyde (MUF) resins. Thus, the improved characteristics of melamine can be combined with the economy of urea to provide an improved adhesive at a moderate increase in cost. The improvement is roughly proportional to the amount of melamine used the range of addition may be from 5 to 35%, with 5—10% most common. 

Resorcinol is to phenol as melamine is to urea. Resorcinol—formaldehyde (RF) is very expensive, produces dark and waterproof gluelines, but will cure at room temperature. As with melamine and urea, resorcinol is often combined with phenol to produce phenol—resorcinol—formaldehyde (PRF) adhesives, thus producing an exceUent adhesive with some of the economy of phenol. These adhesives are the mainstay of the laminated timber industry which generally requites a room-temperature cure with durable, waterproof gluelines. 

Amino and Phenolic Resins. The largest use of formaldehyde is in the manufacture of urea—formaldehyde, phenol—formaldehyde, and melamine—formaldehyde resins, accounting for over one-half (51%) of the total demand (115). These resins find use as adhesives for binding wood products that comprise particle board, fiber board, and plywood. Plywood is the largest market for phenol—formaldehyde resins particle board is the largest for urea—formaldehyde resins. Under certain conditions, urea—formaldehyde resins may release formaldehyde that has been alleged to create health or environmental problems (see Amino RESINS AND PLASTICS). 

Paraformaldehyde is used by resin manufacturers seeking low water content or more favorable control of reaction rates. It is often used in making phenol—, urea—, resorcinol—, and melamine—formaldehyde resins. 

It should be possible to form linear noncross-linked polymers of melamine—formaldehyde or phenol—formaldehyde by reaction of one mole of the patent with one mole of formaldehyde, but this is generally not the case. The melamine crystal itself is very insoluble in water and only becomes soluble as the formaldehyde molecules add on. If much less than 1.5 moles of formaldehyde pet mole of melamine ate used, the aqueous resin solution is very unstable. 

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). 

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). 

Although phenolic resins are too dark for use in the surface layers of decorative laminates these resins are employed in impregnating the core paper. In the.se cases a melamine-formaldehyde resin is used for impregnating the top decorative layer. Phenolic laminates have also been used in aircraft construction and in chemical plant. 

The term aminoplastics has been coined to cover a range of resinous polymers produced by interaction of amines or amides with aldehydes. Of the various polymers of this type that have been produced there are two of current commercial importance in the field of plastics, the urea-formaldehyde and the melamine-formaldehyde resins. There has in the past also been some commercial interest in aniline-formaldehyde resins and in systems containing thiourea but today these are of little or no importance. Melamine-phenol-formaldehyde resins have also been introduced for use in moulding powders, and benzoguanamine-based resins are used for surface coating applications. 

Property Units Urea-formaldehyde Melamine-formaldehyde Melamine- phenolic GP phenolic... 

Decorative laminates have a core or base of Kraft paper impregnated with a phenolic resin. A printed pattern layer impregnated with a melamine-formaldehyde or urea-thiourea-formaldehyde resin is then laid on the core and on top of this a melamine resin-impregnated protective translucent outer sheet. The assembly is then cured at 125-150°C in multi-daylight presses in the usual way. 

Seventy years ago, nearly all resources for the production of commodities and many technical products were materials derived from natural textiles. Textiles, ropes, canvas, and paper were made of local natural fibers, such as flax and hemp. Some of them are still used today. In 1908, the first composite materials were applied for the fabrication of big quantities of sheets, tubes, and pipes in electrotechnical usage (paper or cotton as reinforcement in sheets made of phenol- or melamine-formaldehyde resins). In 1896, for example, airplane seats and fuel tanks were made of natural fibers with a small content of polymeric binders [1]. 

Uses of Formaldehyde. Formaldehyde is the simplest and most reactive aldehyde. Condensation polymerization of formaldehyde with phenol, urea, or melamine produces phenol-formaldehyde, urea formaldehyde, and melamine formaldehyde resins, respectively. These are important glues used in producing particle hoard and plywood. 

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. 

Well-known thermosetting plastics include the phenolics, urea-formaldehyde and melamine-formaldehyde plastics, polyesters and epoxides. 

Aminoplastics In this group, melamine-formaldehyde resins with their good heat resistance, scratch resistance and stain resistance, are usually preferred to urea-formaldehyde resins where chemical resistance is important. Unlike the phenolics these materials are not restricted to dark colours. 

Zone 4 alkyd, fluorinated ethylene-propylene, melamine-formaldehyde, phenol-furfural, and polysulfone. 

Synthetic resins Acrylic Alkyd. Chiorobenzols Chlorodiphenyls Chloro-naphthalenes Chlorophenols Cumaron Epoxies Melamine formaldehyde Phenol formaldehyde Polyesters Sulphonamide formaldehyde Urea formaldehyde Urethane Vinyl Others Enzymes derived from B. subtilis... 

Thermosets differ molecularly from thermoplastics in that their individual chains are anchored to one another through crosslinks. The resulting network creates cohesive materials that demonstrate better thermal stability, rigidity, and dimensional stability than thermoplastics. Some examples of traditional thermosets are melamine-formaldehyde resins, which are used to treat fabrics to make them wrinkle-free, and Bakelite (a phenol-formaldehyde resin), a historically important polymer used in many applications, such as costume jewelry, electrical switches, and radio casings. 

Chlorophenols Cumaron Epoxies Melamine formaldehyde Phenol formaldehyde Polyesters Others Enzymes derived from B. subtilis... 

Phenol-formaldehyde resins (237, 238), urea-formaldehyde resins (239,240), melamine-formaldehyde resins (241), furfuryl... 

Melamine formaldehyde Melamine phenolic Nitrile resins Phenolics Polyamides Nylon 6 Nylon 6/6 Nylon 6/9 Nylon 6/12 Nylon 11 Nylon 12 Aromatic nylons Poly(amide-imide)... 

Other nonfood applications of D-sorbitol result from etherification and polycondensation reactions providing biodegradable polyetherpolyols used for soft pol5mrethane foams and melamine/formaldehyde or phenol resins. Sizable amounts of D-sorbitol also enter into the production of the sorbitan ester surfactants (cf. later in this chapter). 

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