• Journal of the Korean Wood Science and Technology
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• v.35 no.5
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• pp.67-75
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• 2007

As a part of abating the formaldehyde emission of urea-formaldehyde (UF) resin adhesive by lowering formaldehyde to urea (F/U) mole ratio, this study was conducted to investigate properties of UF resin adhesive with different F/U mole ratios. UF resin adhesives were synthesized at different F/U mole ratios of 1.6, 1.4, 1.2, and 1.0. Properties of UF resin adhesives measured were non-volatile solids content, pH level, viscosity, water tolerance, specific gravity, gel time and free formaldehyde content. In addition, a linear relationship between non-volatile solids content and sucrose concentration measured by a refractometer was established for a faster determination of the non-volatile solids content of UF resin. As F/U mole ratio was lowered, non-volatile solids content, pH, specific gravity, water tolerance, and gel time increased while free formaldehyde content and viscosity were decreased. These results suggested that the amount of free formaldehyde strongly affected the reactivity of UF resin. Lowering F/U mole ratio of UF resin as a way of abating formaldehyde emission consequently requires improving its reactivity.

• Current Research on Agriculture and Life Sciences
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• v.30 no.1
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• pp.41-50
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• 2012

As a part of abating formaldehyde emission of urea-formaldehyde resin, this study was conducted to investigate the rmalcure kinetics of both neat and modified urea-formaldehyde resins using differential scanning calorimetry. Neat urea-formaldehyde resins with three different formaldehyde/urea mol ratios (1.4, 1.2 and 1.0) were modified by adding three different additives (sodium bisulfite, sodium hydrosulfite and acrylamide) at two different levels (1 and 3wt%). An isoconversional method at four different heating rates was employed to characterize thermal cure kinetics of these urea-formaldehyde resins to obtain activation energy ($E{\alpha}$) dependent on the degree of conversion (${\alpha}$). The $E{\alpha}$ values of neat urea-formaldehyde resins (formaldehyde/urea = 1.4 and 1.2) consistently changed as the ${\alpha}$ increased. Neat and modified urea-formaldehyde resins of these two F/U mol ratios did show a decrease of the $E{\alpha}$ at the final stage of the conversion while the $E{\alpha}$ of neat urea-formaldehyde resin (formaldehyde/urea = 1.0) increased as the ${\alpha}$ increased, indicating the presence of incomplete cure. However, the change of the $E{\alpha}$ values of all urea-formaldehyde resins was consistent to that of the Ea values. The isoconversional method indicated that thermal cure kinetics of neat and modified urea-formaldehyde resins showed a strong dependence on the resin viscosity as well as diffusion control reaction at the final stage of the conversion.

• Journal of the Korean Wood Science and Technology
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• v.26 no.4
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• pp.92-97
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• 1998

Four urea-formaldehyde (UF) resins were synthesized as a particleboard (PB) binder with the four different initial formaldehyde/urea mole ratio and the final mole ratio of 1.15. The UF resins were characterized according to the standard method of resin adhesive analysis. PBs were manufactured using liquid UF resins at 5 minutes press time and 6% resin solids levels on an ovendry particle weight basis. A total of 20 PBs was fabricated for 5 panel replication per UF resin types. The panels were tested for physical strength properties per the procedure ASTM D 1037. The formaldehyde emission levels from the PBs bonded with the UF resins were tested according to 2-hour desiccator test method ASTM D 5582. There were no significant differences among UF resin types for internal bond strength of PBs. But there were significant differences among UF resin types for formaldehyde emission level of PBs. The results showed that the formaldehyde emission level was influenced by the UF resin types without reducing the adhesive performance.

• Journal of the Korean Wood Science and Technology
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• v.35 no.5
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• pp.76-86
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• 2007

This study was conducted to investigate the effects of formaldehyde to urea (F/U) mole ratio on thermomechanical curing of UF resin adhesives with different F/U mole ratios. Thermomechanical curing of these UF resin adhesives was characterized using parameters of dynamic mechanical analysis (DMA) such as the gel temperature, maximum storage modulus, and peak temperatures of storage and loss modulus. As the F/U mole ratio decreased, the gel temperature of UF resin adhesives increased. The maximum storage modulus as an indicator of the rigidity of UF resin adhesives decreased with decreasing F/U mole ratio. The peak temperature of tan $\delta$ increased with decreasing F/U mole ratio, indicating that the vitrification occurred faster for high F/U mole ratio of UF resin adhesives than for the one of lower F/U mole ratio. These results partially explained the reason why UF resin adhesives with lower F/U mole ratio resulted in relatively poor adhesion performance when they were applied.

• Journal of the Korean Wood Science and Technology
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• v.36 no.2
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• pp.63-72
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• 2008

As a part of abating formaldehyde emission of urea-formaldehyde (UF) resin adhesive, this study was conducted to investigate chemical structures of UF resin adhesives with different formaldehyde/urea (F/U) mole ratios, using carbon-13 nuclear magnetic resonance ($^{13}C$-NMR) spectroscopy. UF resin adhesives were synthesized at four different F/U mole ratios such as 1.6, 1.4, 1.2, and 1.0 for the analysis. The analysis $^{13}C$-NMR spectroscopy showed that UF resin adhesives with higher F/U mole ratios (i.e., 1.6 and 1.4) had two distinctive peaks, indicating the presence of dimethylene ether linkages and methylene glycols, a dissolved form of free formaldehyde. But, these peaks were not detected at the UF resins with lower F/U mole ratios (i.e., 1.2 and 1.0). These chemical structures present at the UF resins with higher F/U mole ratios indicated that UF resin adhesive with higher F/U mole ratio had a greater contribution to the formaldehyde emission than that of lower F/U mole ratio. Uronic species were detected for all UF resins regardless of F/U mole ratios.

• Applied Biological Chemistry
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• v.34 no.2
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• pp.110-116
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• 1991

As the model compounds, citral and n-octanol which possess similar characteristics and structures of low molecular weight insect pheromones and $({\pm})-5-hydroxy-4-methyl-heptan-3-one$ which shows the aggregation pheromones activity of the rice weevil and the maize weevil were microencapsulated with low molecular weight polyethylene(LMPE) and urea-formaldehyde resin as wall materials. The core materials were microencapsulated as small particles in LMPE and urea-formaldehyde resin polymers and the microencapsulated polymers were white powders. And the polymer made from urea-formaldehyde resin was better than that from LMPE as wall material. The slow releasing effect and the releasing patten of the microencapsulated core materials were examined by solvent extraction method and headspace sampling method. Citral and n-octanol and $({\pm})-5-hydroxy-4-methyl-heptan-3-one$ were release more than 40 days and 15 days, respectively. The releasing pattern of urea-formaldehyde resin microcapsules showed rather smooth decrease than that of LMPE and was maintained at steady level longer.

• Journal of the Korean Applied Science and Technology
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• v.26 no.1
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• pp.18-23
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• 2009

Curing behavior and structural property of an inorganic compound added urea-formaldehyde(UF) and urea-melamine-formaldehyde(UMF) were studied. In addition, tensile strength and formaldehyde emission of plywoods made of those resin binders were studied. Curing temperature and structure were not changed, but tensile strengths of plywoods manufactured both with a UF resin and a UMF resin were decreased slightly as increased amount of inorganic compound. Formaldehyde emissions from plywoods were reduced as increased amount of inorganic compound. Wheat flour as an extender was helped to reduce of formaldehyde emission. From the result of this study it might be estimated that using appropriate amount of inorganic compound and proper resin system can be strengthened bond strength and reduced formaldehyde emission.

• Korean Journal of Agricultural Science
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• v.36 no.1
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• pp.11-18
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• 2009

The purpose of this study is to examine a proper amount of addition and a proper point for addition of titanium dioxide for the manufacture of E0 type of urea-formaldehyde resin (UF). The reduction of free formaldehyde from UF resin treated particle board was also investigated. $TiO_2$ content was 0.5%, 1% and 3% on the dry basis of UF resin. UV light was used to initiate reaction. The results of this study are as follows: 1. During UF resin manufacturing process, the second adding step of urea was proper point for $TiO_2$ addition. 2. 1 % addition of $TiO_2$ gave good values for the Eo type urea-formaldehyde resin. 3. There was no significant difference between physical properties of particle board, but the higher the adding content of titanium dioxide resulted in the lower the mechanical properties.

• Textile Coloration and Finishing
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• v.5 no.4
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• pp.79-91
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• 1993

The purpose of this study is to prepare the newer, more comfortable of urea-formaldehyde resin finished fabrics. The methods of this study are by making examinations and comparisons the relations between the thickness, fabrics counts, weight, moisture regain and crease recovery of cotton and viscose rayon fabrics caused by condition of urea-formaldehyde resin finishing and warm retaining ability and warm-cool sense. The analytic results of thermal character in state of fabrics material finished with urea-formaldehyde are as follows: 1. The warm retaining ability has no correlation with mixing ratio of resin but the increase of the warm retaining ability has correlation with the increase of concentration of urea-formaldehyde resin. 2. The result pf multiple regression analysis for effect of physical property according to the concentration of resin to the warm retaining ability revealed as below. As the weight, thickness and density increase and moisture regain decreases, the warm retaining ability increases. 3. The qmax value has no correlation with mixing ratio of resin but the increase of the qmax value has correlation with the increase of resin concentration. In the end, the effect of it promotes cool sense. 4. The result of multiple regression analysis for effect of physical property according to the concentration of resin to the qmax value revealed as below. As he weight and thickness increase, the qmax value decrease. But, as the density and crease recovery increase, the qmax value increase.

• Journal of the Korean Wood Science and Technology
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• v.27 no.1
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• pp.72-78
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• 1999

To accelerate the curing and to improve the bonding properties of urea-melamine-formaldehyde (UMF) resin adhesives for plywood, the effects of resin compositions and additives on gelation time and bonding strength were discussed. The gelation time of UMF resin prepared by simultaneous reaction with urea(U), melamine(M) and formaldehyde(F) at M/U molar ratio 0.2 was shortened as the molar ratio of formaldehyde to urea was increased. However, at F/U molar ratios higher than 2.5, the amounts of free fomaldehyde of resin could not satisfy with KS standard, Therefore, it was difficult to increase the amount of formaldehyde in resin composition for the purpose of fast gelation time. With increasing the molar ratio of melamine to urea(M/U) from 0.3 to 0.6 at constant F/U molar ratio 3.4, the gelation time of UMF resin was slightly decreased, while gradually increased at M/U molar ratio higher than 0.6. The gelation properties of UMF resin and bonding strength of UMF-bonded plywood could be enhanced by using ammonium chloride and p-toluene sulfonic acid as a curing-agent together with wheat flour and corngluten powder as a extender.