Chemical Structure and Curing Behavior of Phenol–Urea–Formaldehyde Cocondensed Resins of High Urea Content

Phenol–urea–formaldehyde cocondensed (PUF) resins of high urea content were prepared by adding different forms of urea to the reaction system. The structure, curing behavior, and water resistance of the PUF resins were investigated, and their relations were also discussed by liquid ¹³C nuclear magnetic resonance (NMR) and different scanning calorimetry (DSC). The liquid ¹³C-NMR analysis showed that urea added in the form of methylolureas was well incorporated into the cocondensed resins by reacting with phenolic methylols to form cocondensed methylene bridges, and that the PUF resins had no free formaldehyde with any form. Unreacted urea and low molecule monosubstituted urea of PUF resins play a dominant role in the curing behavior and water resistance of resins. The peak temperature, curing time, and curing enthalpy (ΔH) value correspondingly increased, however, the water resistance of PUF resins decreased when urea content in PUF resins increased. The PUF cocondensed resin with up to 89.4 % (W _U/W _P) urea has relatively low cost, and moreover can pass the requirements of China Industry Standard for the exterior grade of structural plywood after 4-h cyclic boiling test.     

Urea Manufacturers Enjoyed Good Result

PetroChina is the largest ureamanufacturing company inChina, with a capacity of 3.6million t/a, accounting for8.5% in the total. SinopecCorp. followed with 2.6 mil-lion t/a. But here CCR is dis-cussing the 2004 operatingresults of those urea manu-facturers who are listed in     

Bond Strength–Disbonding Behavior and Dimensional Stability of Walnut and Poplar Impregnated with Some Chemicals and Bonded with PVAc,VTKA and Urea Formaldehyde

The aim of this study, is to describe the effects of adhesives (PVAc-Desmodur VTKA and Urea formaldehyde) on wooden materials (walnut and poplar) cut tangentially and radially impregnated with Protim Solignum, CCA and Celcure AC 500 and exposed to: humid–water–heat resistance; heating; and cooling tests. All these tests show a decreased in bonding strength. The conclusion is that poplar wood cut tangentially and impregnated with CCA, bonded with D-VTKA adhesive can be used as a material in damp conditions where good bond strength is required.     

Urea Price Faced with Temporary Containment

Reporter:The relevant departments ofChinese government have recentlymade a decision that to ensure the needof fertilizers for spring plough,an ex-port tariff of RMB260 per ton will beimposed on the urea export for 3months starting from Jan.1,2005 as a     

Chitianhua Corporation:Benefited from Urea Price Rise

In 2004 Guizhou Chitianhua Corporation(600227)accomplished a main-businessrevenue of RMB732 million,an increaseof 24% over the previous year,a net profitof RMB106 million and a per-share earn-ing of RMB0.62,an increase of 48%.     

Urea–formaldehyde resin prepared with concentrated formaldehyde

The characteristics of UF resin prepared with concentrated formaldehyde were studied in this paper. With the molar ratio F/U = 1.1, the UF resin prepared with concentrated formaldehyde showed better mechanical properties than that with formalin. The ¹³C-NMR and FTIR results indicated that there were more methylene groups, ether groups and urons in a UF resin system prepared with concentrated formaldehyde than those in a normal UF resin. The differential scanning calorimetry and DMA results showed that the curing temperature of UF resin with concentrated formaldehyde was lower than that of a normal UF resin. UF resin with concentrated formaldehyde showed worse thermal stability and higher thermal decomposition temperature.     

Spherical Resorcinol‐Formaldehyde Performance Testing with Hanford Tank Waste

The efficacy of a new spherically engineered form of resorcinol‐formaldehyde (RF) resin was tested for cesium removal on two actual Hanford tank wastes. Small‐scale processing was conducted according to the River Protection Project‐Waste Treatment and Immobilization Plant flowsheet in a lead‐lag column format. The RF resin processed 95 bed volumes (BVs) of high potassium‐bearing waste (AP‐101) and >200 BVs of a high complexant‐bearing waste (AN‐102) before reaching 50% cesium breakthrough. Elution with 0.5 M nitric acid was effective and complete after processing 16 BVs. Cesium and other analyte fractionations to the process stream effluent and eluate were evaluated. The RF resin resulted in very little metal and radionuclide fractionation, other than cesium, to the eluate. The spent resins were measured for most analytes relevant to land‐disposal requirements. The actinide concentrations on the spent resins were <3% of the transuranic waste limit; the residual cesium concentrations were <4 mCi/kg; chromium was the only metal, regulated by the Resource Conservation Recovery Act, that was measured in quantities significant to land‐disposal regulations.     

Poly(Urethane–Urea) Varnishes Containing Tributyltin Groups

New poly(urethane–urea) varnishes containing tributyltin groups were prepared by the reaction of dibenzyldiisocyanate in excess with a macrodiol (PEGA-2000), trimethylolpropane, diethylene glycol and a bisalcohol maleimide monomer containing tributyltin carboxylate group. Tributyltin maleimide monomers were obtained from 4-{3,4-bis[(2-hydroxyethyl)sulfanyl]-2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl}benzoic acid and bis(tributyltin) oxide. Structure of monomers and polymers was confirmed by the IR, NMR spectroscopy and elemental analysis. The polymer films were characterized by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), X-ray diffractions, thermogravimetric (TGA) and stress–strain measurements.     

Rheology Study of Sugar Cane Bagasse Lignin-Added Phenol–Formaldehyde Adhesives

The rheological properties of sugar cane bagasse lignin–phenol formaldehyde (PF) (30% lignin – PF) resins were studied using oscillation tests. The bagasse lignin was introduced in the classic adhesive formulation in order to supply a part of PF. Rheological qualities of optimal lignin–PF (30% lignin – PF) resins and commercial PF resin were assessed by using a rotary rheometer (ARES). Dynamic rheological measurements, performed at low strain in the linear range, are useful to characterize the network properties of resins.

The results obtained showed that the time sweep indicates excellent structural stability of optimal lignin–PF (30% lignin–PF) resins and commercial PF resin. The elastic modulus is greater than the viscous one showing a remarkable elastic character of the resins, and the performed frequency sweeps show a typical spectrum of a “weak gels” structure. The time dependence at 125°C shows that the optimum cure time is 7.5 min.     

Acetone—Formaldehyde—Phenol based IPNs for Glass Fibre Reinforced Composite Applications

Abstract

Three component IPNs Glass fibre reinforced composites (GRC) have been prepared from acetone-formaldehyde-phenol (AF-P) resin, Diglycedyl ether of bisphenol-A (DGEBA) (a commercial epoxy resin) and methyl methacrylate (MMA) (a vinyl monomer). The curing catalyst hexamethylene tetramine (HMTA) for AF-P, radical initiators 2,2′-azobisisobutyronitrile (AIBN) for MMA and curing catalyst 4,4′-diamino diphenyl methane (DDM) for epoxy resin were employed. All the IPN GRCs were characterized in terms of their resistance to chemical reagents, thermal behaviour (DSC, TGA) and mechanical properties.     

Urea/LiTFSI深共融电解液在锂金属电池中的应用

锂金属电池由于具有高能量密度一直受到广泛的关注。然而,目前传统的电解液由于挥发性高,并且与锂金属负极反应产生锂枝晶等问题,使其不能很好的应用于锂金属电池。尿素基深共融体系具有高的离子电导率,良好的热稳定性以及不易燃等优异的特性,目前已经被应用于锂离子电池。基于此,本文尝试将尿素基电解液(Urea/LiTFSI)应用于锂金属电池,并取得了优异的电池循环性能。     

Brönsted Acidic Ionic Liquids as Efficient and Recyclable Catalysts for the Carbonylation of Formaldehyde

Abstract  

Methyl glycolate (MG), as a precursor to ethylene glycol (EG), was synthesized by an efficient and eco-friendly procedure of one-pot, two-step, sequential reaction, including carbonylation and esterification from HCHO with Br?nsted acidic ionic liquids (BAILs) as catalysts. MG was obtained in high yield under mild conditions. In addition, the catalyst could be recycled eight times after separating the unreacted materials and products from the reaction system by distillation under vacuum and no significant decrease in catalytic activity was observed.     

Antimicrobial Polychelates: Synthesis and Characterization of Transition Metal Chelated Barbituric Acid–Formaldehyde Resin

A monomeric Schiff base was prepared by the condensation reaction of salicylaldehyde and semicarbazide, which further react with formaldehyde and barbituric acid-formed polymeric Schiff base. Its metal polychelates were then formed with Mn(II), Co(II), Ni(II), Cu(II), and Zn(II). All the synthesized compounds were characterized by elemental analysis, magnetic moment, FTIR, ¹HNMR, and electronic spectroscopies. The elemental analysis data show the formation of 1:1 [M: L] metal polychelates. Thermogravimetric analysis was carried out to find the thermal behavior of all the synthesized polymeric compounds and thermal data revealed that all the metal polychelates are more thermally stable than their parent polymeric Schiff base. All the synthesized polymeric compounds were screened for antimicrobial activity against some clinically important microorganisms, such as Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, Staphylococcus aureus, Staphylococcus typhi, Candida albicans, Microsporum canis, and Aspergillus niger. In vitro antimicrobial activity was determined by the Agar Well Diffusion method and the result shows that all the metal polychelates exhibited better antimicrobial activity than their parent polymeric Schiff base.     

Cure rate of Phenol–Formaldehyde (PF) resol resins catalyzed with MgO

One of the main drawbacks that has prevented a wider use of phenol–formaldehyde (PF) resins in the manufacture of impregnated paper and wood composite panels is their relatively slow cure rate. In this study, the curing characteristic of PF resol resins catalyzed with MgO was studied with various formaldehyde (F)/MgO/phenol (P) ratios at various pH values. The results indicated that the pH value, nature of pH regulator and synthesis parameters, including the F/P ratio and MgO content, all influence the rate of cure. The pH value played an important role in affecting both the cure rate and cure time. The cure rate was fast when pH was below 7.5. The cure time decreased as the pH value decreased at all F/MgO/P ratios. The MgO/P ratio had a definite influence on the cure rate, the cure time decreased with the increase of MgO/P molar ratio, and the F/P ratio had no significant influence on the cure rate. Differential scanning calorimetry (DSC) results showed that MgO catalyzed PF resin can cure at a low temperature.     

PVA/P(AA-AM)/Urea半互穿高吸水树脂的合成及性能

以聚乙烯醇(PVA)、丙烯酸(AA)、丙烯酰胺(AM)、尿素(Urea)为原料,过硫酸钾(KPS)为引发剂,N,N'-亚甲基双丙烯酰胺(MBA)为交联剂,采用水溶液聚合法合成了具有尿素缓释功能的PVA/P(AA-AM)/Urea复合高吸水树脂。通过FTIR、TG、DSC、SEM对树脂的结构进行了表征,并从吸水倍率、吸水速率、尿素释放率等方面对树脂进行了性能测定。通过单因素实验探讨了PVA用量、AM用量、KPS用量、MBA用量、尿素用量、AA中和度对树脂吸水倍率的影响。结果表明:在最佳工艺条件(AA 10.0 g,以AA质量为基准加入10%AM、15%PVA、0.4%KPS、0.05%MBA,尿素10.0 g,AA中和度为70%)下,合成的吸水树脂吸水倍率可达到505 g/g,吸盐水倍率可达到88 g/g;此条件下合成的高吸水树脂初始吸水速率可达86.58g·min/g;将树脂在湿度10%、温度25和40℃的烘箱中静置4h,释水率分别为40.9%和68.0%;树脂中的尿素在蒸馏水中可持续缓释13 d左右,弱酸性和中性环境有利于尿素持续释放。     

On the Synergy Effect in MoO3–Fe2(MoO4)3 Catalysts for Methanol Oxidation to Formaldehyde

Methanol oxidation to formaldehyde was studied over a series of Fe–Mo–O catalysts with various Mo/Fe atomic ratio and the end compositions Fe₂O₃ and MoO₃. The activity data show that the specific activity passes through a maximum with increase of the Mo content and is the highest for Fe₂(MoO₄)₃. The selectivity to formaldehyde, on the other hand, increases with the Mo content in the catalyst. A synergy effect is observed in that a catalyst with the Mo/Fe ratio 2.2 is almost as active as Fe₂(MoO₄)₃ and as selective as MoO₃. Imaging of a MoO₃/Fe₂(MoO₄)₃ catalyst by SEM and TEM shows that the two phases form separate crystals, and HRTEM reveals the presence of an amorphous overlayer on the Fe₂(MoO₄)₃ crystals. EDS line-scan analysis in STEM mode demonstrates that the Mo/Fe ratio in the amorphous layer is ~2.1 in the fresh catalyst and ~1.7 in the aged catalyst. The enrichment of Mo at the catalyst surface is confirmed by XPS data. Raman spectra give evidence for the Mo in the amorphous material being in octahedral coordination, which is in contrast to the crystalline Fe₂(MoO₄)₃ bulk structure where Mo has tetrahedral coordination. X-ray diffraction (XRD) analysis gives no support for the formation of a defective molybdate bulk structure. The results presented give strong support for the Mo rich amorphous structure being observed on the Fe₂(MoO₄)₃ crystal surfaces being the active phase for methanol oxidation to formaldehyde.     

Effect of Some Chemicals on Thermal Conductivity of Impregnated Laminated Veneer Lumbers Bonded with Poly(vinyl acetate) and Melamine–Formaldehyde Adhesives

Thermal conductivity is a very important parameter in determining heat transfer rate and is required for the development of drying models and for the industrial operations such as adhesive cure rate. The objective of this research was to investigate the effects of impregnation on the thermal conductivity of six-layered laminated veneer lumber (LVL) made of beech and pine. Boric acid, zinc chloride, and ammonium sulfate were used as impregnation chemicals and poly(vinyl acetate) (PVAc) and melamine-formaldehyde (MF) adhesives as bonding agent were used to produce LVLs. The veneers were impregnated by using the vacuum-pressure method. The thermal conductivity test was performed based on ASTM C 1113-99 hot-wire method. Results showed that the impregnation chemicals increase the thermal conductivity. As impregnation chemicals the highest values were obtained with boric acid and zinc chloride. In addition, the thermal conductivity of LVL made of beech was higher than that of LVL made of pine. The thermal conductivity of LVL bonded with PVAc was absolutely higher than LVL bonded with MF in both wood species.