5. These last two factors are dependent upon the precise manufacturing method that is used. Requirements: Urea, formaline, 1M NaOH, Universal Indicator, ammonia, Round bottom flask, Reflux condenser. The addition of formaldehyde to urea takes place over the entire range of pH. The resulting resin is a water-soluble, colourless transparent liquid having a solids content of 58% which is suitable for use in the production of fibreboard and particle board. Reagent-grade formaldehyde (37%), sodium hydroxide, formic acid, and hydrochloric acid were purchased from Shanghai Chemical Reagent Ltd., China. These advantages can be achieved with no loss of strength in the resin. Urea-formaldehyde resins are used mostly as adhesives for the bonding of plywood, particleboard, and other structured wood products. © 2004-2020 FreePatentsOnline.com. A voluminous white solid mass appears in the beaker. Whilst maintaining the reflux, aqueous sodium hydroxide solution (9 ml; 10% w/v NaOH) is added to give a neutral solution (pH 7). Softwood core chips (1530 g), dried to a moisture content of 2%, are blended with a mixture comprising the resin described in Example 6 (201 g), ammonium chloride solution (12 g; 15% NH4 Cl), a commercial wax emulsion (12.5 g; 65% wax) and water (47 g). When properly catalyzed with acids or acid salts, it can be used in many Like the previous process described, this process is difficult to control, especially on an industrial scale, and unless careful control is maintained over the reaction the resin will gel during the condensation stage if the conditions that are described are strictly followed. Urea-formaldehyde resins are used mostly as adhesives for the bonding of plywood, particleboard, and other structured wood products. The % free formaldehyde is calculated as: 4. This shape obtained after cooling is permanent, meaning that the substance will not liquify on re application of heat. The resultant chipboard (particle board) has a thickness of 19 mm. Additionally, solid-state 13 C CP/MAS nuclear magnetic resonance (NMR) techniques were used to investigate the structure of cured UF … Such conventional resins usually have a F:U molar ratio within the range 1.3 to 2.3:1. The dehydration step (d) can be carried out in a conventional spray drier to form the particulate resin. (i) mixing an aqueous formaldehyde solution containing more than 50% by weight of formaldehyde with urea at a formaldehyde:urea molar ration of 2 to 3:1 and at pH 6-11. Q3. Tetramethylolurea is apparently not produced, but atleast not in a detectable quantity. By using different conditions of reaction and preparation a more or less innumerable variety of condensed structures is possible. This reaction is i a series of reactions which lead to the formation of mono-, di-, and trimethylolureas. Resins having a F:U molar ratio as low as 1:1 have been described in British Patent Specification No. An aqueous solution of sulphuric acid (5.3 ml; 15% H2 SO4) is added. Urea-formaldehyde is also called urea-methanal and is named so for its common synthesis pathway and overall structure. (iii) optionally, adding more urea so that the final molar ratio is within the range 1-2.75:1. Hello, this is Payal Das working in Ruva Customer Services Pvt. In this process resins having a F:U molar ratio within the range 1.0 to 1.2:1 are prepared as follows: (i) formaldehyde solution is acidified to pH 0.5-2.5. the ratio of formaldehyde to urea when used in its manufacture), the type and proportion of the various linkages within the resin structure, and the proportions of high and low molecular weight material. By means of the process of the present invention, resins having remarkably good washdown properties can be prepared, so that apparatus which has been used for the uncured resin may be cleaned easily with a jet of hot water, as can any spillages. Urea-formaldehyde resins which may be cured to give products having a low total extractable formaldehyde content are prepared by the following process: 156/331.3, 524/35, 524/593, 524/597, 525/399, 528/232, 528/239, 528/242, 528/259, 528/230, 528/232, 528/239, 528/242, 528/259, 525/399, 525/593, 525/597, 525/843, WENDEROTH, LIND & PONACK, L.L.P. This is allowed to cool to 40° C., urea (164 g) is added, giving a F:U molar ratio of 1.4:1, and the mixture is stirred for 30 minutes. In general, the temperature below which the reaction mixture should not be allowed to fall depends on the formaldehyde:urea molar ratio employed, lower ratios requiring higher temperatures to be maintained. The effects of the addition of triethanolamine to the polymerization process on some physical properties of the synthesized copolymer were evaluated. This is allowed to cool to 40° C., urea (211.8 g) is added, giving a F:U molar ratio of 1.25:1, and the mixture is stirred for 60 minutes. The mixture is neutralised and urea is added to adjust the F:U molar ratio to within the range 1.8 or less: 1. Typical acids that may be used include trichloroacetic, toluene-p-sulphonic, hydrochloric, sulphuric, sulphamic and phosphoric acids. (d) dehydrating the mixture to form a solid particulate resin. Whilst maintaining the reflux, aqueous sodium hydroxide solution (10% w/v NaOH) is added to give a neutral solution (pH 7). generation, Hydrolytically stable urea-formaldehyde resins and process for manufacturing them, Process for the preparation of urea-formaldehyde resins, Process for the preparation of thermosettable urea-formaldehyde resins and method for use thereof, Process for producing aqueous urea-formaldehyde, Curable resorcinol terminated urea-formaldehyde resins, <- Previous Patent (Process for the prep...). Accordingly, the invention also provides a modification of the process as hereinbefore described which comprises. In this test small rectangular blocks sawn from air-dried particle board or fibreboard are extrated with toluene, the toluene is washed with water, and the water measured iodometrically for formaldehyde. This means that pipework, pumps etc. Aqueous formaldehyde solution (531.9 g; 55% HCHO) is mixed with aqueous sodium hydroxide solution (10% w/v NaOH) and urea (254.3 g), the amount of sodium hydroxide solution being sufficient to give a mixture of pH 9. The fibreboard or particleboard can formed in a conventional press, using conventional curing conditions. (i) mixing an aqueous formaldehyde solution containing more than 50% by weight of formaldehyde with urea at a formaldehyde:urea molar ratio of 2 to 3:1 and at pH 6-11. To prepare Urea-formaldehyde (U-F) resin. Products made using this resin, such as fibreboard and particleboard, generally have the strength which could be expected from products made with a conventional resin having the same solids content and F:U molar ratio. fillers such as wood flour and china clay, to give a storage-stable composition known as a "one-shot" composition which can be activated by the addition of water. The latter liberation of formaldehyde can be a serious problem since it limits the use to which, for example, particle boards or fibreboards may be put. (vi) adding urea to the mixture at a temperature up to 45° C. until the formaldehyde:urea molar ratio is within the range 0.8-1.8:1. Another process for preparing adhesive resins with low formaldehyde content is described in U.S. Pat. A low‐formaldehyde‐emission methylol urea/triethanolamine composite was synthesized through in situ esterification of formaldehyde with triethanolamine and subsequent copolymerization of the synthesized polyester with methylol urea. In the second step, the two precondensates were mixed and condensed using a heterogeneous catalyst in a tube reactor at 90°C. the so-called amino-plastic resins. In our previous paper of this series, 1,2) we reported that a new curing method for urea-formaldehyde (UF) resins had been developed using dihydrazide compounds and hydrazide polymers as curing agents. Your email address will not be published. To determine viscosity of lubricant by Red Wood Viscosity (No. The acidified solution is heated under reflux for 25 minutes. After adding the urea, the mixture is usually stirred for 30 to 90 minutes. Place about 5 ml of 40% formaldehyde solution in 100 ml beaker. These resins are used in adhesives, finishes, particle board, medium-density fibreboard (MDF), and molded objects. Heating of the reaction mixture in steps (ii), (iv) and (v) may be carried out under pressure, in which case the reflux temperature is, of course, higher and the respective heating time can generally be reduced. The optional heat-activated hardener can be any conventional heat-activated hardener for urea-formaldehyde resins, such as an acid salt which liberates an acid on heating, preferably ammonium chloride. The second stage of urea-formaldehyde resin production includes the condensation of the methylolureas to low molecular weight polymers. 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