Dicarboxylic acids amides as an acceptor of formaldehyde in urea-formaldehyde resins

The possibility of reducing the content of free formaldehyde in urea-formaldehyde resin by introducing into the final resin composition of diphthalic and dimaleic acids amides was studied. It was found that the amides synthesized are able to participate in formaldehyde addition as well as in its polymerization and they are effective acceptor of formaldehyde in urea-formaldehyde resins.     

Study of the structural changes in urea-formaldehyde condensates during synthesis

Chemical constitution of urea-formaldehyde resins in synthesis and in storage was determined using ¹³C NMR spectroscopy. Methylolation, methylene and dimethylene ether bond-forming reactions were discussed. The changes in the content of structural elements with secondary and tertiary amino groups of urea at various stages were followed. The resin synthesis technology was used, which considers the requirement in low free formaldehyde content, connected with somewhat smaller storage stability of resins.     

脲醛树脂胶粘剂及其发展状况

脲醛树脂是目前使用量最大的木材用胶粘剂,文章主要从脲醛树脂的合成、改性、应用及固化机理等方面,综述了近年来脲醛树脂的研究进展。讨论了脲醛树脂的合成工艺,分析了pH值对脲醛树脂合成工艺的影响。针对脲醛树脂释放甲醛、耐水性差的缺点,列举了脲醛树脂常用的各种改性物质及它们的改性效果。并讨论了脲醛树脂在使用过程中使用的助剂和固化剂。     

A zero-discharge procedure for production of urea-formaldehyde resins

A zero-discharge procedure was suggested for preparing urea-formaldehyde resins by poly-condensation of urea, formaldehyde, and dimethylolurea at variable pH, with urea added continuously or in a single portion.     

Lignocellulose - polymer composites

Water hyacinth and its mechanical pulps were used as lignocellulose to produce composites together with polystyrene or urea-formaldehyde resins. The bending strength of the composites increased with increasing concentration of the resin. The temperatures of the treatment of water hyacinth to obtain the pulps affect the strength and densities of the composites. This may be attributed to the behavior of lignin at temperatures higher than 135°C. The composites produced using urea-formaldehyde resins showed slight increase in bending strengths compared with those produced using polystyrene, which may be attributed to the ability of formaldehyde to make crosslinks with the free OH groups of cellulose and hemicellulose. Contrary to water hyacinth, the use of ground palm leaves together with 10% urea-formaldehyde resin produced composite with high density and low bending strength, while the ground water hyacinth failed. The pulp from palm leaves when processed into composites using 10% urea-formaldehyde resin show bending and densities affected by its preparation and by the amount of the composite mixture to be pressed. Hence the type of the substrate defined the type of the polymers or resin used to obtain composites with proper mechanical properties. The effect of the pressure used to produce composites from ground palm leaves or their pulp together with polystyrene was investigated. Linear relationships between the bending strength and pressure were obtained, the bending strength and densities increasing with increasing pressure. Thus, the increased pressures enhance mechanical properties of the composites.     

Zur Analytik von Harnstoff-Melamin-Formaldehyd-Harzen

Summary A method is described for the distinction between urea-formaldehyde and melamine-formaldehyde resins by precipitating the melamine derivates with picric acid. The analysis of this precipitation by urease-decomposition gives information whether urea and melamine are condensed with formaldehyde together or whether the investigated resin is only a mixture of an urea-formaldehyde and a melamine-formaldehyde resin.Moreover, it is possible to prove the formation of cocondensates of urea, melamine, and formaldehyde during the three-component condensation by combination of these two methods.     

酸性条件下脲醛树脂中不稳定结构的研究

通过较强酸性介质中尿素和甲醛的反应, 在不同条件下合成了透明的脲醛树脂溶液, 利用液体13C NMR研究了甲醛与尿素摩尔比对最终树脂中不稳定结构的影响.     

Silicon Dioxide Sol as a Component of Urea-Formaldehyde Adhesive

The possibility of combining an inorganic polymer, silicon dioxide sol, with urea-formaldehyde resins, was studied with the aim to prepare a binding agent for producing nontoxic chip boards. The kinetic characteristics of formaldehyde binding with silicon dioxide during complex binder curing were determined.     

Urea and urotropine conversion in the preparation of microspherical metal oxide particles by internal gelation

The results of studies on urea and urotropine product distribution in solutions formed in microspherical nuclear fuel preparation by internal gelation are presented. It is shown that urea, urotropine and formaldehyde, the urotropine hydrolysis product, undergo various conversions in solutions, resulting in methylolurea and urea-formaldehyde resins formation. Results on the influence of acidity on the process as a function of time are presented. The organic content in the resulting solutions and microspheres has been determined.     

Hantzsch reaction in urea-formaldehyde resins

The effect of acetylacetone and ammonia in urea-formaldehyde resins on the reactions occurring in their presence was examined. The formation of 2,6-dimethyl-3,5-diacetyl-l,4-dihydropyridine in urea-formaldehyde resins was confirmed by ¹H NMR spectroscopy.     

脲醛树脂合成反应过程的FTIR研究

利用傅里叶变换红外(FTIR)光谱研究了脲醛树脂合成中不同结构形成和变化情况. 对FTIR谱图解析和分析的结果表明, 在脲醛树脂预聚物合成过程中, 随着甲醛与尿素反应的进行, 红外谱图特征峰发生有规律的变化, 酰胺II带特征峰波数逐渐低移, 有更多羟甲基、醚键和—NHCH2—结构基元形成, 固化反应使上述结构基元相应减少. 着重分析了不同甲醛与尿素摩尔比(nF/nU)下尿素与甲醛反应产物结构的变化, 随nF/nU的增加, 酰胺II带特征峰波数逐渐低移, 碱性条件下醚键和—NHCH2—结构基元明显增加, 在较强酸性条件下Uron环、亚甲基桥和羟甲基显著增加, 而—NHCH2—结构基元含量下降.     

木质素对木质素-脲醛共聚树脂的影响及反应机理

通过调控甲醛与尿素摩尔比, 降低脲醛树脂胶黏剂中游离甲醛的含量, 以生物质玉米芯为原材料, 用碱液提取得到的碱木质素溶液与甲醛和尿素进行三元逐步共聚, 弥补降低醛脲比带来的胶合强度的快速下降问题. 以降低游离甲醛含量同时兼顾胶合强度为原则进行探索, 得到最佳实验条件为甲醛与尿素摩尔比(F/U)为0.91∶1, 木质素添加量为20%(质量分数), 在此条件下木质素-尿素-甲醛共聚树脂(LUF)胶合强度为0.99 MPa, 游离甲醛含量为0.26%. 对共聚树脂进行了结构表征, 表明木质素参与到反应中, 并能提高树脂的热稳定性和耐水性, 同时对反应的机理进行了讨论.     

Thermal behavior of modified urea–formaldehyde resins

The thermal stability of pure urea–formaldehyde resin (PR) and modified urea–formaldehyde (UF) resins with hexamethylenetetramine-HMTA (Resin 1), melamine-M (Resin 2), and ethylene urea (EU, Resin 3) including nano-SiO₂ was investigated by non-isothermal thermo-gravimetric analysis (TG), differential thermal gravimetry (DTG), and differential thermal analysis (DTA) supported by data from IR spectroscopy. Possibility of combining inorganic filler in a form of silicon dioxide with UF resins was found investigated and percentage of free formaldehyde was determined. The shift of DTG peaks to a high temperature indicates the increase of thermal stability of modified UF resin with EU (Resin 3) which is confirmed by data obtained from the FTIR study. The minimum percentage (6%) of free formaldehyde was obtained in Resin 3.     

Use of latex systems for controlling the properties of urea-formaldehyde resins

The influence of latex formulations and a filler, Vulkasil, on the processing and physicochemical properties of urea-formaldehyde resins was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 10, 2004, pp. 1725–1728.Original Russian Text Copyright © 2004 by Glazkov.     

Synthesis of urea-formaldehyde oligomers without a solvent

A urea-formaldehyde oligomer comparing well with commercially avaliable KF-MT and KF-M resins in the adhesive power was prepared from solid paraform and urea without a solvent.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 9, 2004, pp. 1555–1557.Original Russian Text Copyright © 2004 by Bezbozhnaya, Zamashchikov, Lutsyk.     

Curing adhesives of urea-formaldehyde type with collagen hydrolysates of chrome-tanned leather waste

Condensation of dimethylol-urea (DMU) mixed with urea (U) and collagen hydrolysate (H), obtained through enzymatic hydrolysis of chrome-tanned leather waste, without added acid curing agents in the solid phase was studied through DSC and TG techniques in a temperature interval up to 220°C. Among both techniques TG proved be more useful.While the DMU+U mix produced methylene-oxide (-CH₂-O-CH₂-) and methylene (-CH₂-) bridges at a ratio of approx. 1:1, urea substituted for collagen hydrolysate increased the proportion of more stable methylene bridges to methylene-oxide bridges to a ratio of approx. 2:1. Methylene-oxide bridges are considered to be the main potential sources of formaldehyde emissions from cured urea-formaldehyde type adhesives, and thus the use of collagen hydrolysate in preparation of urea-formaldehyde adhesive types is a suitable way how to make such adhesives more environmental friendly.This revised version was published online in November 2005 with corrections to the Cover Date.     

Study of viscosity behavior and retanning properties of sulfonated glutaric dihydrazide formaldehyde condensate under different reactant ratios

Sulfonated glutaric dihydrazide formaldehyde condensates with less than 0.05% free formaldehyde were prepared through controlled reaction of glutaric dihydrazide, sodium metabisulfite, and formaldehyde in three processing steps. Mole ratio of sodium metabisulfite/glutaric dihydrazide (S/GDH) was varied from 0.1 to 0.5 and that of formaldehyde/glutaric dihydrazide (F/GDH) from 1 to 3. The effects on viscosity and fluidity of resins were observed with varying degrees of sulfonation and changeable mole ratio of formaldehyde/glutaric dihydrazide. Viscosity of resins showed increasing trend with increasing mole ratio of formaldehyde/glutaric dihydrazide and decreasing trend with increasing mole ratio of sodium metabisulfite/glutaric dihydrazide. Increase in viscosity of resins was due to increase in molecular weight of polymer chains. After gaining a critical molecular weight during condensation, resins turned into gel form. The resins were comparatively applied on chrome tanned cow hide against commercial sulfonated urea formaldehyde powder resin (Resin UFT).     

Phenolic resins bearing maleimide groups: Synthesis and characterization

Novel phenolic novolac resins, bearing maleimide groups and capable of undergoing curing principally through the addition polymerization of these groups, were synthesized by the polymerization of a mixture of phenol and N‐(4‐hydroxy phenyl)maleimide (HPM) with formaldehyde in the presence of an acid catalyst. The polymerization conditions were optimized to get gel‐free resins. The resins were characterized by chemical, spectral, and thermal analyses. Differential scanning calorimetry and dynamic mechanical analysis revealed an unexpected two‐stage curing for these systems. Although the cure at around 275°C was attributable to the addition polymerization reaction of the maleimide groups, the exotherm at around 150 to 170°C was ascribed to the condensation reaction of the methylol groups formed in minor quantities on the phenyl ring of HPM. Polymerization studies of non‐hydroxy‐functional N‐phenyl maleimides revealed that the phenyl groups of these molecules were activated toward an electrophilic substitution reaction by the protonated methylol intermediates formed by the acid‐catalyzed reaction of phenol and formaldehyde. On a comparative scale, HPM was less reactive than phenol toward formaldehyde. The presence of the phenolic group on N‐phenyl maleimide was not needed for its copolymerization with phenol and formaldehyde. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 641–652, 2000     

Influence of Process Factors on the Structure of Urea-Formaldehyde Resin

The influence of preparation conditions on the structure of low-toxic urea-formaldehyde resins and the possibility of preparing resins of linear-branched structure and resins containing urone rings were examined.     

Melamine–formaldehyde resins: Constitutional characterization by fourier transform 13C-NMR spectroscopy

The random chemical structures of melamine–formaldehyde resins, including methylated melamine–formaldehyde resins and urea–melamine formaldehyde resins, were investigated by ¹³C-NMR spectroscopy (Fourier transform). All the combined formaldehydes, methylol and methyl ether groups, methylene structures, and dimethylene ether structures were assigned. A ¹³C chemical shift of methylene carbon occurred by substitution of other constituents of the methylene group for a proton of the adjacent monosubstituted nitrogen atom, as shown in a ¹³C-NMR spectrum of urea–formaldehyde resins. It was found that the chemical shift of each corresponding carbon of both melamine resins and urea–melamine resins was almost superimposed with that of urea resins.