Urea-Formaldehyde Condensation

Safety precautions Be oxeth s experiment is carried out, Sect. 2.2.5 must be read as well as the material safety data sheets (MSDS) for all chemicals and products used. 

Caution Because of the formation of gaseous formaldehyde all reactions must be carried out in a closed hood. 

30 g (0.5 mol) of urea are dissolved in 61 g of a 37% aqueous formaldehyde solution (0.75 mol) heated to 50 °C (use a well ventilated hood) in a 250-ml three-necked flask fitted with thermometer,stirrer, and reflux condenser.2.5 ml of concentrated ammonia solution are then added and the temperature is raised to 85 °C. After about 20 min the solution becomes cloudy and the viscosity increase at the same time the pH value falls to about 5. After a total period of 1 h the heating is removed and a small sample is tested to see if the condensation product is still soluble in water. 

Cellulose powder is now stirred into the cooled solution until the mass can still just be stirred.The contents of the flask are then transferred to a large beaker and more cellulose powder is kneaded in by hand (wear rubber gloves ) until a total of 35 g has been added.The crumbled mixture is dried for 24 h at 50 °C in the vacuum oven. Finally, the dried product is finely ground in a mortar, mixed with 1% of ammonium chloride and 1 % of zinc stearate (as lubricant) and crosslinked (cured) by heating to about 160 C for 10 min in a simple press at 300-400 bar. A thin transparent plate is obtained that is no longer soluble in or attacked by water this is more convincing if a small piece is allowed to stand overnight in a beaker of water. 

If a heatable press is not available, one may proceed as follows Two flat iron plates of about 2-cm thickness are heated in an oven to 240 °C and then taken out. One of these plates is laid on the lower jaw of a horizontally mounted vice.lt is allowed to cool until a crumb of the filled condensation product no longer decomposes (colors) when placed 

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Figure 4d represents in situ encapsulation processes (17,18), an example of which is presented in more detail in Figure 6 (18). The first step is to disperse a water-immiscible Hquid or soHd core material in an aqueous phase that contains urea, melamine, water-soluble urea—formaldehyde condensate, or water-soluble urea—melamine condensate. In many cases, the aqueous phase also contains a system modifier that enhances deposition of the aminoplast capsule sheU (18). This is an anionic polymer or copolymer (Fig. 6). SheU formation occurs once formaldehyde is added and the aqueous phase acidified, eg, pH 2—4.5. The system is heated for several hours at 40—60°C.

German patent DE 3442454 (1984), European patent EP0185205, B1 (1986). Process for the preparation of melamine-urea-formaldehyde condensates. Assigned to BASF AG. 

The broadest classification for plastics is the old thermoplastic and thermosetting . Examples of the former group are polyethylene, polystyrene, and poly-(methyl methacrylate) examples of the latter are urea-formaldehyde condensation polymers, powder coatings based on polyesters, epoxy resins, and vulcanized synthetic elastomers. 

TEXAPRET K is a high-molecular urea-formaldehyde condensation product. It is supplied in powder from and is readily soluble in warm or hot water. The 5% solution has a pH of about 8. In contrast to TEXAPRET S, it requires no solubilizer owing to the good liquor stability. 

Rhonite [Rohm Haas]. TM for thermosetting modified and unmodified urea-formaldehyde condensates. Supplied as water-clear solutions and aqueous pastes. Reactive with cotton, various grades producing shrink resistance, crease proofing, or modification of hand. 

Urac [Cytec]. TM forproducts based on urea-formaldehyde condensates used mainly as adhesives for the production of moisture-proof bonds in plywood manufacture, plywood assembly, and furniture manufacture. 

Finally, the overall behavior of urea toward formaldehyde is much different than is the behavior of, for example, formaldehyde with phenol. Mixing phenol and formaldehyde at a ratio of 4 1 in an acidic medium will result in a reaction of impressive vigor. At ratios of 4 1 urea and formaldehyde are not capable of advancing under acidic conditions even with the application of heat. Urea-formaldehyde concentrate, a stable mixture of urea and formaldehyde at a mole ratio of 4.8 1 and concentrations of as high as 85% solids, is a common material of commerce. These observations, taken together, are not consistent with the orderly formation of a urea-formaldehyde condensation polymer. 

Urea-formaldehyde condensates show a surprisingly similar behavior to the lignin salts investigated by Terbilcox. The ability to produce a material such as UF concentrate demonstrates the solvent ability of hydrated formaldehyde. It is often seen that a fresh cook of a UF is clear, and will remain so for a short period of time. UF resins above a mole ratio of 1 2.5 (U F) are relatively easy to produce as a clear liquid. Typically resins which are produced at the very low F U ratios are the most difficult to make clear and are the least stable. 

Two-Package Coatings with Aminoformaldehvde Cure. One component consists of a hydroxyl-terminated urethane prepolymer while the other component is an alkyl ether (usually methyl or butyl ether) of a methylolmelamine or methylolurea derivative (melamine- or urea-formaldehyde condensation products or derivatives thereof) (140, 141). Various catalysts may be employed to accelerate the heat cure (. 125 C) and to lower the curing temperature. Curing results by splitting off of the respective alcohol, as shown ... 

Furthermore, some cross-linking reactions were studied. The gum is easily cross-linked in the solid state with formaldehyde, when hydrochloric acid is used as catalyst. The acid causes some hydrolysis of the glycosidic linkages. The products obtained are completely insoluble in water. It is believed that, especially between primary hydroxyl groups of different molecules, methylene bridges are formed. Cross-linking with urea-formaldehyde condensation products was useful in preparing water-resistant films. 

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),... 

These resins are quite similar to urea-formaldehyde condensates and, probably for that reason, find similar applications. Melamine reacts with formaldehyde under slightly alkaline conditions to form mixtures of various methylolmelamines ... 

Glyoxalin Glyoxaline. See,Imidazole Glyoxaline-5-alanine. See L-Histidine Glyoxaline-5-alanine monohydrochloride. See Histidine hydrochloride monohydrate Glyoxal/urea/formaldehyde condensate CAS 27013-01-0... 

Glyoxal/urea/formaldehyde condensate Glyoxal/urea polymer insolubilizer, textile finishing agents Zirconium butoxide insolubilizer, vinyl polymer Methacrylatochromic chloride instrument housings Phenol-formaldehyde resin instrument indicator fluid Mercury... 

The can and coil coatings, generally, are cross-linked with phenol, melamine, or urea-formaldehyde condensation products at elevated temperatures (150-200°C) with acid catalysts. Normal epoxy-amino resin weight ratios are epoxy-urea, 70 30 epoxy-benzoguanamine, 70 30 epoxy-melamine, 80 20, and 90 10. Increasing cross-linker levels give improved thermal and chemical resistance at the sacrifice of coating flexibility and adhesion. 

Pizzi A 1979 The chemistry and development of tannin/urea-formaldehyde condensates for exterior wood adhesives. J Appl Polym Sci 23 2777-2792... 

The formulation of more recent APP-based systems also seems to be based on phosphorus-nitrogen synergism. Co-additives are polymeric in nature such as poly(triazine-piperazine) materials, essentially substituted melamine rings linked by piperazine groups, and poly(ethylene-urea-formaldehyde) condensates. The sequence of reactions leading to char formation in these systems is poorly understood. It is likely that both water and ammonia are evolved at certain stages, some phosphorus and probably some nitrogen remain incorporated in the char structure, and some phosphorus ends up as polyphosphoric acid. 

The development of synthetic adhesives paralleled the development of plastics which began in 1845 with the nitration of cellulose to give cellulose nitrate, the first semi-synthetic plastic, whose ethereal solution was used by the shoe industry in 1910 for bonding leather. The products discovered in 1872 by Adolf Baeyer by polycondensation of phenol with formaldehyde were the basis for the first firlly synthetic plastic, Bakelite, which was obtained by Bakeland in 1909 by thermally curing reactive phenolic pre-condensates. But it was not until 1930 that phenol-formaldehydes and urea-formaldehyde condensates developed by C. Goldschmidt in 1896 (Kaurit) were used widely as adhesives. 

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