Molar Ratio Of Urea Research Articles

Influence of Nitrogen-Doped Carbon Dots on H• Radical-Mediated Au-H Formation in the Hydrogenation of 4-Nitrophenol Using NCDs-Au Nanohybrids.

The hydrogenation of 4-nitrophenol using carbon dot-stabilized gold (Au) nanoparticles is well-studied, with Au-H species known to catalyze the reaction. However, the impact of specific nitrogen moieties in nitrogen-doped carbon dots on Au-H formation and catalytic activity remains unexplored. These nitrogen species, acting as surface ligands, may influence the catalytic properties through the generation of Au-H species via H• radicals. In this regard, modulation of the catalytic properties of Au nanoparticles has been explored by conjugating their surface with nitrogen-doped carbon dots (NCDs). Three distinct nanohybrid formulations comprising NCDs and Au nanoparticles (i.e., NCDs-Au) have been prepared, where the NCDs were derived from different carbon sources (e.g., citric acid and l-malic acid) and varying mole ratios of the nitrogen source (i.e., urea). The impact of NCDs on Au nanoparticle-mediated catalysis has been investigated using the model reaction of hydrogenation of 4-nitrophenol (4-NP) in the presence of NaBH4. The fractions of different nitrogen species (such as pyrrolic, pyridinic, and amidic) in the different NCDs-Au nanohybrids were quantified through XPS analysis, and their roles in catalytic performance have been studied. Further, the size, shape, crystallinity, defects, and exposed facets of the NCDs-Au nanohybrids have also been assessed (through XRD, HRTEM, and Raman studies), and their structure-activity relationships have been corroborated. The hydrogenation of 4-NP is proposed to happen through the formation of gold-hydride (Au-H) species facilitated by H• radicals, as confirmed by EPR analysis. The NCDs-Au nanohybrid, synthesized from NCDs derived from a 1:3 molar ratio of l-malic acid and urea (MU13-Au), exhibits superior catalytic efficiency with a rate constant of 1.013 min-1, attributed to its abundant defects and a notably high relative content of catalytically favorable pyridinic nitrogen species compared to other tested nanohybrids.

A formaldehyde-free amino resin alternative to urea-formaldehyde adhesives: A bio-based oxidized glucose – urea resin

Urea-formaldehyde resins (UF) are the most commonly used wood-based panels adhesive in industry. These adhesives are more than 80 % by volume of the wood adhesives market. However, due to formaldehyde toxicicity and extreme volatility UF resins yield panels with formaldehyde emission problem both during wood panels preparation and their in-service use. In order to address this problem, to find an environment friendly replacement for formaldehyde to manufacture novel and safe aminoresins is essential research for wood adhesives. In this article, a bio-based amino resin wood adhesive (OGU) is developed by using oxidized glucose reacted with urea. The research work presented here tests the impact on the adhesive properties of a number of oxidation treatment parameters and of the glucose to urea molar ratio. The molecular structure and thermal properties of the OGU adhesive were studied by different analytical techniques. The results indicate that the bioaldehydes are obtained by glucose under mild oxidation conditions. The bioaldehydes obtained can then be reacted with urea to form a novel oxidized glucose-urea amino resin, suitable to manufacture plywood. Under the specified process conditions at pH 4 and at a urea-to-glucose molar ratio of 1, the OGU adhesive yielded plywood with a dry strength of 0.99 MPa, 24 h cold water soaking wet strength of 0.77 MPa, and 3 h hot water (63°C) soaking wet strength of 0.76 MPa. These results satisfy the requirements of the GB/T 9846–2015 standard. The OGU resin adhesive prepared has then a good market potential to replace the current UF resins used in the industrial production of wood-based panels and as a novel biomass amino resin adhesive.

Deep Eutectic Solvents for Efficient Drug Solvation: Optimizing Composition and Ratio for Solubility of β-Cyclodextrin.

Deep eutectic solvents (DESs) show promise in pharmaceutical applications, most prominently as excellent solubilizers. Yet, because DES are complex multi-component mixtures, it is challenging to dissect the contribution of each component to solvation. Moreover, deviations from the eutectic concentration lead to phase separation of the DES, making it impractical to vary the ratios of components to potentially improve solvation. Water addition alleviates this limitation as it significantly decreases the melting temperature and stabilizes the DES single-phase region. Here, we follow the solubility of β-cyclodextrin (β-CD) in DES formed by the eutectic 2:1 mole ratio of urea and choline chloride (CC). Upon water addition to DES, we find that at almost all hydration levels, the highest β-CD solubility is achieved at DES compositions that are shifted from the 2:1 ratio. At higher urea to CC ratios, due to the limited solubility of urea, the optimum composition allowing the highest β-CD solubility is reached at the DES solubility limit. For mixtures with higher CC concentration, the composition allowing optimal solvation varies with hydration. For example, β-CD solubility at 40 wt% water is enhanced by a factor of 1.5 for a 1:2 urea to CC mole ratio compared with the 2:1 eutectic ratio. We further develop a methodology allowing us to link the preferential accumulation of urea and CC in the vicinity of β-CD to its increased solubility. The methodology we present here allows a dissection of solute interactions with DES components that is crucial for rationally developing improved drug and excipient formulations.

Enhanced oxygen reduction and fuel cell performance and durability of ultra-low loading Pt-supported high surface area titanium nitro-carbide

Corrosion resistance, porous structure and high surface area are becoming more and more significant as electrode properties in long-term operation of polymer electrolyte membrane fuel cell. In this work, high surface area, porous titanium-based ceramic compound was synthesized via the facile modified urea glass method (mUGM) and utilized as electrocatalyst support for oxygen resection reaction (ORR) in fuel cells cathodes. The as-prepared compound was found to have surface area and crystallite sizes of the scale of carbon black (CB) with strong dependency on the Ti precursor to urea molar ratio. N–C bonds were found to be involved, as suggested from the X-ray photoelectron spectra, and little to-no residual bulk carbon was found in the samples (X-ray diffraction and Raman spectroscopy). After deposition of Pt metal catalyst, the ceramic-based system demonstrated superior ORR activity and fuel cell performance, alongside superior durability when compared with commonly used commercial Pt/C catalyst, despite the ultra-low loading of deposited Pt (45 μg/cm2). Among all the ceramic-based samples studied in this work, the one synthesized in ratio of 1:10 (Ti:urea) showed the highest overall performance in fuel cell configuration.

Porous Defective Bi/Bi3NbO7 Nanosheets for Efficient Photocatalytic NO Removal under Visible Light

Since conventional techniques are ineffective for NO removal at low concentrations, photocatalysis has become attractive in this regard, recently. However, in practice, photocatalytic NO removal has drawbacks such as limited light absorption and the proclivity of producing toxic by-products. To address these issues, novel defective Bi/Bi3NbO7 structures with good porosity were fabricated by a solvothermal method and used for enhanced photocatalytic NO removal under visible light irradiation. The morphological and structural properties of the prepared materials were comprehensively analyzed. The optimal photocatalytic activity of pore-defective Bi/Bi3NbO7 for NO removal was 60.3%, when the molar ratios of urea and Bi(NO)3•5H2O to pristine Bi3NbO7 were 1:25 and 1:2, respectively, under the following operational conditions: NO concentration of 700 ppb, catalyst dosage of 50 mg and irradiation time of 14 min. The induced defects and the surface plasmon resonance (SPR) effect of Bi nanodots made remarkable contributions to improving the photocatalytic NO removal as well as inhibiting the toxic byproduct NO2. The photocatalytic NO removal pathway over the prepared photocatalysts was further mechanistically clarified taking advantage of EPR results and scavenging experiments. Considering the increased NO generation in the atmosphere, this work may provide novel insights for designing effective porous photocatalysts to treat gaseous toxic pollutants.

An Improved Optimization Model to Predict the MOR of Glulam Prepared by UF-Oxidized Starch Adhesive: A Hybrid Artificial Neural Network-Modified Genetic Algorithm Optimization Approach.

The purpose of the present article is to study the bending strength of glulam prepared by plane tree (Platanus Orientalis-L) wood layers adhered by UF resin with different formaldehyde to urea molar ratios containing the modified starch adhesive with different NaOCl concentrations. Artificial neural network (ANN) as a modern tool was used to predict this response, too. The multilayer perceptron (MLP) models were used to predict the modulus of rapture (MOR) and the statistics, including the determination coefficient (R2), root mean square error (RMSE), and mean absolute percentage error (MAPE) were used to validate the prediction. Combining the ANN and the genetic algorithm by using the multiple objective and nonlinear constraint functions, the optimum point was determined based on the experimental and estimated data, respectively. The characterization analysis, performed by FTIR and XRD, was used to describe the effect of the inputs on the output. The results indicated that the statistics obtained show excellent MOR predictions by the feed-forward neural network using Levenberg-Marquardt algorithms. The comparison of the optimal output of the actual values obtained by the genetic algorithm resulting from the multi-objective function and the optimal output of the values estimated by the nonlinear constraint function indicates a minimum difference between both functions.

Comparison of the Estimation Ability of the Tensile Index of Paper Impregnated by UF-Modified Starch Adhesive Using ANFIS and MLR

The purpose of the present study is to offer an optimal model to predict the tensile index of the paper being consumed to make veneer impregnated with different weight ratios of modified starch (from 3.18 to 36.8%) to urea formaldehyde resin (WR) containing different formaldehyde to urea molar ratios (MR, from 1.16:1 to 2.84:1) enriched by different contents of silicon nano-oxide (NC, from 0 to 4%) using multiple linear regression (MLR) and adaptive neuro-fuzzy inference system (ANFIS) and compare the precision of these two models to estimate the response being examined (tensile index). Fourier-transform infrared spectroscopy (FTIR) and transmittance electron microscopy (TEM) were also used to analyze the results. The results of studying the adhesive structure using FTIR analysis showed that as the WR increased to the maximum level and MR increased to the average level (3%), more ether and methylene linkage forms due to cross-linking. TEM analysis also indicated that if an average level of silicon nano-oxide is applied, there will be more cross-linking due to the more uniform distribution and suitable interactions between the adhesive and nanoparticles. The modeling results showed that the ANFIS model estimates have been closer to the actual values compared to the MLR model. It can be concluded that the model offered by ANFIS has a higher potential to predict the tensile index of the paper impregnated with the combined adhesive of UF resin and modified starch. However, the MLR model could not offer a good estimate to predict the response. According to the preferred approach to predict the most effective property of resin coated paper, modelling would be useful to the research community and the results are beneficial in industrial applications without spending more cost and time.

Effect of temperature and composition on density and dynamic viscosity of (lanthanide metal salts + urea) deep eutectic solvents

• Lanthanide metal-based type IV deep eutectic solvents (DESs) are prepared. • Density of type IV metal DESs are higher compared to the other urea-based DESs. • Dynamic viscosities of these DESs are lower compared to other urea-based DESs. • Viscosity of the DESs exhibits Vogel − Fulcher − Tammann (VFT) temperature dependence. • Density and viscosity both decrease with increase in mole ratio of urea. Deep eutectic solvents (DESs) are rapidly becoming solvent media of prominence due not only to their unique properties but also to their promising environmentally-benign nature. For effective utilization of these neoteric media, assessment of their physical properties is essential. Density and dynamic viscosity of a class of DESs constituted of a hydrated lanthanide salt and urea at varying composition in the temperature range 293.15 to 363.15 K are presented. Specifically, different possible eutectic mixtures of lanthanum nitrate hexahydrate: urea (named La : Urea), cerium nitrate hexahydrate: urea (named Ce : Urea) and gadolinium nitrate hexahydrate: urea (named Gd : Urea) are investigated. DES (Gd : Urea) at 1: 2 mole ratio exhibits the highest density (1.98783 g.cm −3 at 293.15 K) of all the DESs investigated; density is found to decrease with increasing urea. Density of these DESs decreases linearly with increasing temperature. Dynamic viscosity of these DESs also decrease with increasing urea content. The temperature dependence of the dynamic viscosity follows Vogel − Fulcher − Tammann (VFT) expression. While the activation energy of viscous flow ( E a,η ) for these (lanthanide salt : Urea) DESs is closer to those of (choline chloride + H-bond donor) DESs, their viscosity-temperature dependence is similar to that of common imidazolium ionic liquids.

Ce–Zr-Sm ternary oxides synthesized via a template free urea-hydrothermal method

Nano-crystalline Ce0.9Zr0.1-xSmxO2-δ (0 ≤ x ≤ 0.10) mixed oxides were synthesized for the first time by a urea-hydrothermal method without the use of template or structure directing agents. The use of a high molar ratio of urea to metal cations and temperature reaction ensures the formation of a single-phase homogeneous ternary solid solution. The (NH4)2Ce(NO3)6 precursor, in a greater proportion, together with urea acts as a structure directing agent towards the completion of a self-assembly shuttle to dumbbells to sphere sequence. The analysis of the obtained morphologies has demonstrated that the physicochemical nature of the doping precursor in solution has a strong influence on the final morphology without losing morphological control. Thus, the ZrO(NO3)2 precursor favors the formation of cauliflower-type particles whereas Sm(NO3)3 favors the formation of spheres. As a result, the morphology of the samples evolves from cauliflowers to spheres as Sm content increases in the mixed oxides, with a great effect on the high specific surface area (80–115 m2.g−1) and total pore volume (0.109–0.315 cm3.g−1) obtained in all cases. Solids reduce in three stages reaching high reduction percentages (≈50%).

Preparation of Thermochromic Microcapsules of Bisphenol A and Crystal Violet Lactone and Their Effect on Coating Properties.

Thermochromic microcapsules were prepared with a thermochromic compound as core material and urea formaldehyde as wall material. The molar ratio of urea and formaldehyde, the mass ratio of core material to wall material, the concentration of emulsifier, and rotating speed were selected to make a four-level and three-factor L9(34) orthogonal test. It was found that the molar ratio of urea and formaldehyde had the greatest influence on the coating rate of microcapsules. The effects of molar ratio of urea and formaldehyde on the discoloration temperature and coating rate of microcapsules were studied. When the molar ratio of urea to formaldehyde was 1:1.6, the core material: wall material ratio was 4:7, the concentration of emulsifier was 5.0%, and the rotating speed was 1600 rpm, the performance of the microcapsules was the best. When the microcapsule content was 20.0%, the color difference of the paint film was the largest, the gloss and hardness of the paint film decreased with increasing microcapsule content, and the impact resistance of the paint film first increased and then decreased with increasing microcapsule content. The adhesion of the paint film remained unchanged, and was grade 1. When the microcapsule content was 20.0%, the performance of the paint film was at its best. This provides a basis for the application of thermochromic coatings.

Synthesis and flash sintering of zirconium nitride powder

AbstractZirconium nitride (ZrN) is a transition metal nitride of great interest due to its excellent physical and chemical properties. This study aims to synthesize ZrN fine powders by a facile and low‐cost urea route that avoids the use of any solvent. ZrCl4 and urea mixtures were heat‐treated at up to 1600˚C in nitrogen gas. The products were characterized by X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, and thermogravimetric analysis. The effects of different processing parameters such as metal to urea molar ratio, heat treatment temperature, and dwelling time on the product phase and stoichiometry were studied to understand the synthesis method. In addition, synthesized ZrN powder was consolidated into near fully dense single‐phase bulk ceramic with a homemade flash sintering setup. A constant DC electrical field of ∼80 V/cm and pressure of ∼14 MPa at room temperature triggered flash sintering without pre‐heating, and the entire process finished in 200 s. The composition, microstructure, density, hardness, and oxidation properties of the sintered pellet were also characterized.

Green Synthesis, Structural Characterization and Biological Activity of Diclofenac-Urea Co-Crystal

Co-crystals have become an area of research interest for pharmaceutical drug improvements due to their characteristic nature in modifying the physico-chemical properties of active pharmaceutical ingredients (APIs) with the aid of a co-former. Co-crystals improve the solubility, dissolution rate, melting point, and stability of the API without changing the chemical identity nor diminishing the biological activity or the therapeutic effect of the API. This work reports the green synthetic approach to synthesize Diclofenac-Urea (DUREA) co-crystal using a benign solvent and stirring at room temperature, all in an environmentally friendly manner. The synthesis of DUREA was accomplished by reaction of a 1:1 molar ratio of diclofenac potassium and urea and the product gave a white crystalline compound with an excellent yield (91%). The product (DUREA) was structurally characterized using melting point, UV/VIS, and FT-IR spectrophotometry. The antimicrobial activity of the co-crystal was tested against Salmonella typi and Proteus mirablis.

Modeling the Bending Strength of MDF Faced, Polyurethane Foam-Cored Sandwich Panels Using Response Surface Methodology (RSM) and Artificial Neural Network (ANN)

The present study evaluates and compares predictions on the performance and the approaches of the response surface methodology (RSM) and the artificial neural network (ANN) so to model the bending strength of the polyurethane foam-cored sandwich panel. The effect of the independent variables (formaldehyde to urea molar ratio (MR), sandwich panel thickness (PT) and the oxidized protein to melamine-urea-formaldehyde synthesized resin weight ratio (WR)) was examined based on the bending strength by the central composite design of the RSM and the multilayer perceptron of the ANN. The models were statistically compared based on the training and validation data sets via the determination coefficient (R2), the root mean squares error (RMSE), the absolute average deviation (AAD) and the mean absolute percentage error (MAPE). The R2 calculated for the ANN and the RSM models was 0.9969 and 0.9960, respectively. The models offered good predictions; however, the ANN model was more precise than the RSM model, thus proving that the ANN and the RSM models are valuable instruments to model and optimize the bending properties of the sandwich panel.

Structural properties and stability of the Betaine-Urea natural deep eutectic solvent

This work focuses on the stability and supramolecular structure of the betaine-urea-water (B:U:W) natural deep eutectic solvent. Solutions spanning a range of molar ratios of betaine, urea, and water were prepared, varying the temperature and preparation times, and were analyzed by attenuated total reflection Fourier-transform infrared spectroscopy and Nuclear Magnetic Resonance. Density Functional Theory and the Natural Bond Orbital analysis were employed to obtain the most stable conformations for each mixture. The experimental results show that, in non-anhydrous conditions, betaine:urea (1:1), a minimum of two moles of water are needed to form a metastable transparent liquid, and a minimum of three moles of water is required to have a stable NADES. Comparison of the 13C NMR spectra of B:U:W 1:1:2 and 1:1:3 shows for the latter that the carbonyl groups of betaine and urea form stronger hydrogen bonds with water, and that the CH3 group of betaine becomes more deprotected by the addition of the extra water molecule, making 1:1:3 a more stable solution. Our experimental and computational results show that water is of crucial importance to the NADES supramolecular structure and stability. A better understanding of the structural characteristics of NADES can lead to better envisage applications for these green solvents.

Direct measurement of surface adhesion between thin films of nanocellulose and urea–formaldehyde resin adhesives

When applying an adhesive to wood, the chemical heterogeneity of the wood cell walls makes it difficult to understand the contribution they make to the interfacial adhesion between the adhesive and the wood as the adhesion is a very complex physical and chemical phenomenon. This study, for the first time, directly measured the surface adhesion between cellulose, a major component of wood, and urea–formaldehyde (UF) resin adhesives. The adhesion between thin, smooth nanocellulose films, such as cellulose nanofibrils (CNFs), carboxymethylated nanofibrils (CM)–CNFs, and carboxylated cellulose nanocrystals (C–CNCs), and UF resins with two formaldehyde to urea (F/U) molar ratios of 1.0 and 1.6 was measured using two approaches: (1) direct measurement of the adhesion force between nanocellulose films and liquid droplets of the UF resins, and (2) calculation of the work of adhesion between films of the nanocelluloses and UF resins using the contact angle and the van Oss–Chaudhury–Good method. The results show that the total surface free energies, either between the different nanocelluloses or between the two UF resins are somewhat similar, indicating the similarity in their surface properties. However, the adhesion force and work of adhesion of 1.6 UF resins with different types of nanocellulose are higher than those of 1.0 UF resins, which shows that van der Waals forces are dominant in their molecular interactions. These results suggest that the adhesion between 1.6 UF resins and nanocellulose is stronger than that when 1.0 UF resins are used because the 1.6 UF resins have a more branched structure, smoother surface, and higher surface free energy.

Direct thermal decomposition of FeCl3.6H2O in oleic acid forms hematite cube and nano octahedron structure with quasicrystalline and supercell symmetries for enhanced photoelectrochemical functionality

The direct formation of hematite nanostructures by the thermal decomposition of precursor salt in the oleic acid is discussed here. The obtained nanostructures show interesting structural properties with the unique presence of quasicrystalline and supercell symmetries. The quasicrystalline symmetry obtained is of 2- fold and 3-fold icosahedral symmetries. HRTEM study of the single nano octahedron each faces reveals different axis of symmetry along with the presence of 2-fold icosahedral quasicrystal. The synthesis route results well distributed hematite nano octahedron, where urea plays a role in controlling its distribution as confirmed by FESEM studies. Next, a mechanism is proposed for how 24 h aged Hematite nano octahedron decays with increased acidity of the reaction medium in the presence of urea? It is found that the Urea deprotonated first and keep the nano octahedron morphology stable depending on the salt to urea molar ratio. Finally, the photoelectrochemical properties of the hematite nano octahedron film is studied, and a photocurrent density of 200 μA/cm2 is obtained for non -Urea mediated one (24 O. A.). From the XRD comparison of both films (24 h and 24 O.A.), it is found that (110) Bragg plane diffracted intensity increases without Urea, which helps in the enhancement of the photocurrent density due to a well-established electronic conductivity of Hematite along (001) Basal plane.

Density, dynamic viscosity, conductivity and refractive index for mixture D-glucose and deep eutectic solvent (choline chloride + urea) at different temperatures

ABSTRACT To convert carbohydrates into platform compounds, the deep eutectic solvent (DES) based on choline chloride and urea (molar ratio 1:2) was adopted as a green solvent. The physical properties of density, dynamic viscosity, conductivity and refractive index were determined for the mixture of D-glucose and DES including neat reline at a temperature from 293.15 K to 363.15 K at 101.3 kPa. The measured data of density, dynamic viscosity, conductivity and refractive index were correlated, respectively. Meanwhile, the molecular volume, standard molar entropy, lattice energy and free volume were calculated. The spectra of FTIR indicates that the hydrogen bond was changed in the mixture with increasing the content of D-glucose.

Theoretical and experimental investigation of CO2 capture through choline chloride based supported deep eutectic liquid membranes

The supported liquid membranes (SLMs) provide a feasible solution to global warming by combining their high CO2 interaction with stripping in a continuous and single step process. Herein, deep eutectic solvents (DESs), possible substitutes to ionic liquids (ILs), were used as material to synthesize novel SLMs. The DESs were prepared from choline chloride and urea using three different mole ratios 1:2, 1:1, and 2:1 respectively. The prepared DESs were impregnated into the pores of polyvinylidene fluoride microporous membrane support to form novel DES-SLMs. The DESs-SLMs were tested using pure and mixed gas CO2 permeability as well as CO2/N2 and CO2/CH4 separation experiments. Density functional theory calculations were performed to get an insight into the interaction of DES with CO2 over N2/CH4. The complexation energies (Ec) of the DES with CO2, N2, and CH4 were in the order of −29.3, −9.9, and −13.0 kJ/mol, respectively which reflected the high interaction of CO2 with DES over CH4 and N2. The DES with choline chloride to urea molar ratio of 2:1 showed the highest CO2 permeability of 45.6 Barrer and corresponding CO2/CH4 and CO2/N2 selectivity of 61.62 and 78.62, respectively. Finally, a comparison with the supported ionic liquid membranes (SILMs) literature showed that the DESs-SLMs presented comparable CO2 permeability and a significantly high CO2/CH4 selectivity which enabled them to surpass the well-known Robeson’s upper bound proving their commercial potential. This reflects that the DES-SLMs are a green strategy for carbon capture which can replace the SILMs in practical applications.

Crystallinity of Low Molar Ratio Urea-Formaldehyde Resins Modified with Cellulose Nanomaterials

Inherent crystalline domains present in low formaldehyde to urea (F/U) molar ratio urea-formaldehyde (UF) resins are responsible for their poor adhesion in wood-based composite panels. To modify the crystallinity of low molar ratio (LMR) UF resins, this study investigates the additional effect of cellulose nanomaterials (CNMs), such as cellulose microfibrils (CMFs), cellulose nanofibrils (CNFs), and TEMPO-oxidized CNFs (TEMPO-CNFs) on the crystallinity of modified LMR UF resins. First, two modification methods (post-mixing and in situ) were compared for modified LMR UF resins with TEMPO-CNFs. The modified UF resins with TEMPO-CNFs decreased the nonvolatile solid contents, while increasing the viscosity and gel time. However, the in situ modification of UF resins with TEMPO-CNFs showed lower crystallinity than that of post-mixing. Then, the in situ method was compared for all CNMs to modify LMR UF resins. The modified UF resins with CMFs using the in situ method increased nonvolatile solid contents and viscosity but decreased the gel time. The crystallinity of UF resins modified with TEMPO-CNFs was the lowest even though the crystalline domains were not significantly changed for all modified UF resins. These results suggest that these CNMs should be modified to prevent the formation of crystalline domains in LMR UF resins.

Crystalline Lamellar Structure of Thermosetting Urea–Formaldehyde Resins at a Low Molar Ratio

Reducing formaldehyde emission from cured urea–formaldehyde (UF) resins forced us to synthesize UF resins at a low formaldehyde to urea (F/U) molar ratio (≤1.0), resulting in low emission and poor adhesion by forming crystalline domains instead of building a three-dimensional network in cured resins. For the first time, we report a crystalline lamellar structure of thermosetting UF resins at a low molar ratio and compare it with highly amorphous UF resins at a high F/U molar ratio (1.6). Films of crystalline and amorphous UF resins were prepared using a spin-coater and characterized using atomic force microscopy. In addition, transmission electron microscopy, gel permeation chromatography, and X-ray diffraction were also employed for their characterization. The results showed that 1.0 UF resins had a low molecular weight with a lamellar structure of the crystalline domain, whereas 1.6 UF resins exhibited a high molecular weight with an amorphous structure and had a lower surface roughness. Fourier transform infrared and carbon-13 nuclear magnetic resonance spectroscopy also proved that linear molecules and hydrogen bonding were responsible for the formation of crystalline lamellar structures in thermosetting UF resins at a low molar ratio.