Urea, resins from

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. 

Propylene Urea Resins. In similat fashion to ethyleneurea, dimethyl-olpropyleneurea [3270-74-4] [l,3-bis(hydroxymethyl)tetrahydro-2-(m)-pyrimidinone] is the basis of propyleneurea—formaldehyde resin [65405-39-2], Its preparation is from urea, 1,3-diaminoptopane [109-76-2] and formaldehyde. 

The recovery of fiber from broke (off-specification paper or trim produced in the paper mill) is compHcated by high levels of urea—formaldehyde and melamine—formaldehyde wet-strength resin. The urea resins present a lesser problem than the melamine resins because they cure slower and are not as resistant to hydrolysis. Broke from either resin treatment may be reclaimed by hot acidic repulping. Even the melamine resin is hydrolyzed rapidly under acidic conditions at high temperature. The cellulose is far more resistant and is not harmed if the acid is neutralized as soon as repulping is complete. 

Recently, Raju et al.6 reported an attractive method for the preparation of unsymmetrical ureas on solid-phase resins, employing nitrophenylcarbamates as the key intermediates. They used this method to synthesize ureas derived from simple amines. Here, we report that unsymmetrical ureas can be formed in high yield and purity using MicroTubes as the solid supports. 

Figure 7.24 Formation of urea-formaldehyde resins from 1,3-dihydroxymethylurea.

As shown in the infrared absorbance spectrum of the condensation polymer (See Fig. 1), bands characteristic of absorbance of the urea resin at 3,400 cm-1, 3,000 cm-1, 1,680 cm-1, 1,540 cm-1, 1,380 cm-1, 1,100 cm-1, 1,020 cm-1, 780 cm-1, and characteristic absorbance of acrylami demethyl base at 800 cm-1 are present judging from this data, it is considered that N-methylacrylamide is connected with the end group of urea resin main chains and the imino group. The nuclear magnetic resonance (See Fig. 2) spectrum of the oligomer shows a resonance value of 6.48 ppm based on CH2= and a resonance value of 5.74 ppm based on -CH=. 

Unicellular foams are used for insulation, buoyancy, and flotation applications, while multicellular foams are used for upholstery, carpet backing, and laminated textiles. Expanded PS (Styrofoam), which is produced by the extrusion of PS beads containing a volatile liquid, is used to produce low-density moldings such as foamed drinking cups and insulation boards. Foamed products are also produced from PVC, LDPE, urea resins, ABS, and PU. PU foams are versatile materials, which range from hard (rigid) to soft (flexible). These are produced by the reaction of a polyol and a diisocyanate. 

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... 

Some report that over 50 percent of the urea-formaldehyde resins consumed went into particleboard. This is brought out because there may be a shift away from urea resin for certain types of oriented particleboard used in structural plywood constructions. Historically, particleboard has been used for inner plies as previously mentioned in some hardwood plywood. There is now one plant in production in Idaho which produces mechanically oriented strand particleboard for use specifically as core for softwood plywood production. It is anticipated that this trend to some degree will increase in the future, and phenolic resins appear to be the mechanism with which this particleboard will be bonded. 

Fig. 9.26. Mechanism of the formation of a urea/formalde-hyde resin from methylol urea (R1 = H in formula A possible preparation Figure 9.25) or dimethylol urea (R1 = HO—CH2 in formula A possible preparation Figure 9.25). The substituents R1, R2, and R3 represent the growing —CH2—NH— C(=0)—NH—CH2— chains as well as the derivatives thereof that are twice methylenated on N atoms.

Figure 100. Fundamental Reactions in the Formation of Resins from Urea and Furfural.

Note As this table shows, the largest outlet for amino resins by far is their use as adhesives or binders for reconstituted wood products made from sawdust and wood chips. Urea-formaldehyde resin is most commonly used. Melamine-formaldehyde resin can provide improved water resistance and may be combined with the urea resin to provide an improved product. Molding compounds are about the next most important outlet for amino resins. It is approximately evenly divided between urea and melamine. The primary use for urea moldings is in the electrical field, while the most important area for molded melamine plastic is dinnerware. 

Figure 14 Synthesis of linear ureas 23 from resin-bound amino acids.

Similarly, excess amines could be extracted with acidic ion exchange resins as exemplified by the same group in the synthesis of ureas starting from isocyanates and amines. ... 

Synonyms Eormaldehyde copolymer with urea Eormaldehyde/urea condensate Eormaldehyde/urea copolymer Eormaldehyde/urea polymer Eormaldehyde/urea precondensate Eormaldehyde/urea prepolymer Eormaldehyde/urea resin Formalin/urea copolymer Methylolurea resin Paraformaldehyde/urea polymer Paraformaldehyde/urea resin Polynoxylin Polyoxymethylene urea (INCI) UF Ure ormaldehyde adduct Urea/formaldehyde condensate Urea/formaldehyde copolymer Urea/formaldehyde oligomer Urea/formaldehyde polymer Urea/ formaldehyde precondensate Urea/formaldehyde prepolymer Urea, polymer with formaldehyde Classification Amino resin thermosetting resin Definition Thermosetting resin formed from condensation reaction of formaldehyde with urea formu/a (CH,N20 CH2O),... 

Three laboratory UF resins with different degrees of condensation according to recipes described in the literature [63, 64] were provided by DUKOL Ostrava, s.r.o. (Ostrava, Czech Republic). The degree of condensation (DOC) increases as a consequence of the duration of the acidic condensation step from resin UF 1 (lowest DOC) to resin UF 111 (highest DOC). This determines the viscosity of the resin if the solid content is the same. The viscosity of the three resins increased due to the larger molecules present in the resin from 218 mPa s for UF 1 to 281 mPa s for UF II and eventually to 555 mPa s for UF III, measured within two days after the synthesis of the resins (Table 1). The molar ratio of formaldehyde to urea (F/U) of all resins was 2.0 no urea was added after the condensation step. 

Formaldehyde is one ofthe most important basic chemical compounds [1]. Aqueous formaldehyde solutions are used as disinfection and conservation agents. It is an educt for the production of resins from phenol, urea, and melamin. Water-free formaldehyde is the raw material for polyoxymethylene, a dimensionally stable polymer. 

Amino coatings n. Made from amino resins which include resins from reacting urea, thiourea, melamine or allied compounds, usually with formaldehyde. 

Urea resins n. A synthetic resin made from urea and an aldehyde. 

Because of their colorability, solvent and grease resistance, surface hardness, and mar resistance, the urea resins are widely used for cosmetic container closures, appliance housing, and stove hardware. The production of high-quality dinnerware from cellulose-fdled compounds is one of the largest uses for the melamine resins. 

---