• Journal of the Korean Wood Science and Technology
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• v.48 no.2
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• pp.136-153
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• 2020

In this paper, the influence of initial formaldehyde/urea (F/U) molar ratios on the performance of low molar ratio (1.0) urea-formaldehyde (UF) resin adhesives has been investigated. Two initial F/U molar ratios, i.e., the first and second initial molar ratios were used for the alkaline addition reaction. Three levels of the first initial F/U molar ratios (2.0, 3.0, and 4.0) and two levels of the second initial molar ratios (2.0 and 1.7) were employed to prepare a total of six UF resins with an identical final molar ratio (1.0). The basis properties, functional groups, molecular weight, crystallinity, and thermal curing properties of the UF resins were characterized in detail. Higher levels (3.0 and 4.0) of the first initial F/U molar ratio provided the UF resins with better properties (non-volatile solids content, viscosity, gelation time, pH, and specific gravity) than those of the resins prepared with the conventional level F/U molar ratio of 2.0. Statistical analysis suggested that combining the first and second initial molar ratio of 4.0 with 1.7 would result in UF resins with greater adhesion strength and lower formaldehyde emission than those of the resins prepared with other molar ratios. The results showed that higher levels of the first initial molar ratio resulted in a more branched structure, as indicated by GPC, FTIR, DSC, XRD, and greater adhesion strength than those of the other UF resins with an identical final molar ratio of 1.0.

• Journal of Environmental Science International
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• v.32 no.10
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• pp.731-739
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• 2023

In this study, lab-scale phosphorus coagulation/precipitation experiments were performed using three types of polyaluminum chloride (PAC) with different Al contents (10%, 12%, and 17%). The PO₄-P removal efficiencies at various operating conditions, such as initial PO₄-P concentration, initial pH, and Al/P molar ratio, were evaluated, and correlations among the operating factors affecting phosphorus coagulation/precipitation with PAC were derived to optimize the process efficiency. When the initial PO₄-P concentration was 0.065 and 0.161 mmol P/L under an initial pH of 8-10, the optimal PAC dose was 0.126-0.378 and 0.189-0.667 mmol Al/L, respectively. Under these conditions, the Al/P molar ratio was 2.16-6.18 and 1.28-4.30, respectively, and the PO₄-P removal efficiency was in the range of 40.2-92.5%. When the Al/P molar ratio was 2 or less under an initial pH condition of 6-8, the PO₄-P removal efficiency was approximately ≤40% owing to insufficient Al³⁺ ions. However, when the Al/P molar ratio is 3-5, the PO₄-P removal efficiency improved to approximately 80-90%. Thus, the optimal Al/P molar ratio to achieve a PO₄-P removal efficiency of over 90% was determined to be approximately 4 in the PO₄-P coagulation/precipitation process using PAC.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.5
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• pp.669-678
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• 2009

The reduction of excess activated sludge from petrochemical plant was investigated by the electro fenton (E-Fenton) process using electrogenerated hydroxyl radicals which lead to mineralization of activated sludge to $CO_2$, water and inorganic ions. Factors affecting the disintegration efficiency of excess activated sludge in E-Fenton process were examined in terms of five criteria: pH, $H_2O_2/Fe^{2+}$ molar ratio, current density, initial MLSS (mixed liquid suspended solids) concentration, $H_2O_2$ feeding mode. TSS total suspended solid and $TCOD_{cr}$ reduction rate increased with the increasing $H_2O_2/Fe^{2+}$ molar ratio and current density until 42 and $6.7 mA/cm^2$, respectively but further increase of $H_2O_2/Fe^{2+}$ molar ratio and current density would reduce the reduction rate. On the other hand, as expected, increasing pH and initial MLSS concentration of activated sludge decreas TSS and $TCOD_{cr}$ reduction rate. The E-Fenton process was gradually increased during first 30 minutes and then linearly proceed till 120 minutes. The optimal E-Fenton condition showed TSS reduction rate of 62~63% and $TCOD_{cr}$ (total chemical oxygen demand) reduction rate of 55~56%. Molar ratio $H_2O_2/Fe^{2+} = 42$ was determined as optimal E-Fenton condition with initial $Fe^{2+}$ dose of 5.4 mM and current density of $6.7{\sim}13.3 mA/cm^2$, initial MLSS of 7,600 mg/L and pH 2 were chosen as the most efficient E-Fenton condition.

• Korean Chemical Engineering Research
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• v.52 no.6
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• pp.775-780
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• 2014

Micellar enhanced ultrafiltration (MEUF) was used to remove cadmium from an aqueous solution using sodium dodecyl sulfate (SDS) as a surfactant. Operational parameters such as initial permeate flux, retentate pressure, initial cadmium concentration, pH solution, molecular weight cut-off (MWCO), and molar ratio of cadmium to SDS were investigated. Removal efficiency of cadmium from an aqueous solution increased with an increase of retentate pressure, pH solution and molar ratio of cadmium to SDS, and decreased with an increase of initial permeate flux. Higher removal efficiency of cadmium from the aqueous solution was achieved using lower MWCO (smaller membrane pore size). Under optimized experimental condition, cadmium removal efficiency reached 74.6 % within an hour. Using MEUF-ACF hybrid process the removal efficiency of both cadmium and SDS was found to be over 90%.

• Journal of Korean Society on Water Environment
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• v.23 no.1
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• pp.138-143
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• 2007

This study goes in for the observation of the characteristics of nitrogen removal from swine wastewater by struvite crystallization. In addition, the struvite formation potential in supernatants after struvite crystallization was investigated. In the study for nitrogen removal by struvite crystallization, the effects of pH and molar ratio of magnesium (Mg) injected using bittern as Mg source were investigated. Also, the potential of struvite formation in the supernatant with amount of Mg added was carefully observed. As the results, the optimum pH in the removal of nitrogen was 8.8 and sludge volume was increased as pH was raised from 7 to 12 under the condition that the molar ratio of $Mg^{2+}$ to ${NH_4}^+$-N to ${PO_4}^{3-}$-P was 1:1:1. An optimum removal efficiency of ammonia-N was observed at 1 molar ratio of Mg to ${NH_4}^+$-N, showing no further increase at over 1 molar ratio and dramatical deterioration at under 1 molar ratio. However, the sludge volume was increased by increasing the molar ratio of Mg. In the experiments for the potential of struvite formation in the supernatants, initial -log([$Mg^{2+}$][${NH_4}^+$][${PO_4}^{3-}$]) value was much lower than $pK_{sp}$ and gradually reached $pK_{sp}$ at 2 days, as the molar ratio of Mg increased over 1.2. At 31 days, -log([$Mg^{2+}$][${NH_4}^+$][${PO_4}^{3-}$]) value was returned to the initial value. In addition, the supernatants had a potential precipitation of hydroxylapatite due to calcium contained in bittern, $K_2Mg(SO_4)_3$ and $K_3Na(SO_4)_2$ resulting from the decrease of sodium and potassium in supernatants formed after struvite crystallization as times go by. Based on the results, it appears that some retention time and proper dosage of Mg may be needed for the prevention of scale in pipe line.

• Membrane Journal
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• v.16 no.3
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• pp.230-234
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• 2006

This study discusses an esterification of trifluoroethanol (TFEA) with methacrylic acid (MA) using acid-resistant PVA pervaporation membrane. The acid-resistant PVA membranes, which were prepared via a thermal cross-linking reaction of PVA and EGDE were adopted in the esterification reaction. The effect of reaction conditions such as temperature, acid catalyst content, and initial molar ratio of TFEA/MA was investigated on the conversion of trifluoroethyl-methacrylate (TFEMA). It was found that TFEMA conversion increased with increasing the reaction temperature, the catalyst content, and the initial molar ratio. The economical conversion of TFEMA more than about 90% was obtained at the following reaction conditions: reaction temperature of $90^{\circ}C$, 2.5 wt% of catalyst and initial molar ratio of 1.7.

• Journal of the Korean Wood Science and Technology
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• v.38 no.2
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• pp.117-123
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• 2010

The objective of this research was executed to investigate the effect of molar ratio of formaldehyde to urea and melamine (F/(U+M)) of urea-melamine-formaldehyde (UMF) resin on bonding high and low moisture content veneers. For that purpose, UMF resin types with 5 different F/(U+M) molar ratios (1.45, 1.65, 1.85, 2.05, and 2.25) synthesized were used in present study. First, their curing behavior was evaluated by differential scanning calorimetry. Second, their adhesion performance in bonding high and low moisture content veneers was evaluated by probe tack and dry and wet shear strength tests. Curing temperature and reaction enthalpy decreased with the increase of F/(U+M) molar ratio. And the dry and wet shear strengthsof plywood manufactured from low moisture content veneers were higher than thoseof plywood manufactured from high moisture content veneers. Also, the maximum initial tack force on the low moisture content veneer was higher than that on the high moisture content veneer.

• Journal of the Korean Ceramic Society
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• v.11 no.1
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• pp.10-18
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• 1974

The hydration at $23^{\circ}C$ between $Ca(OH)_2$ and siliceous materials with various compositions of silica gel and quartz were studied in paste state, and also diatomite was empolyed as another form of silica. The effect of the structural state of silica on the pozzolanic reactivity was investigated by X-ray, DTA, electron microscopy, and chemical analysis. The results obtained were as follows. (1) The molar ratio of $Ca(OH)_2$ to silica gel(C/Sg) being changed in 0.49, 0.81 and 1.22, the free $Ca(OH)_2$ was disappeared within six hours, three days and two weeks respectively and ill-crystallized CSH(I) was formed. However, in the case fo molar ratio of C/Sg=2.45, almost lime was remained uncombinedly after twenty four weeks yet. (2) Though the molar ratio C/Sg of diatomite was 0.71, the hydration was stabilized at three weeks and the result exhibited very peculiar characteristics from silica gel. (3) Pozzolanic reactivity of quartz was negligible, but $\alpha$-cristobalite in diatomite showed appreciable reactivity. (4) The thermal curves showed the exothermic peaks in the range 830 to $930^{\circ}C$ and lower broad peaks at high temperature in the initial steps of hydration, transfered to lower temperature with sharp peaks by proceeding of hydration. (5) The samples containing more silica gel exhibited higher pozzolanic reactivity and martar strength, but the diatomite gave remarkable result for them and they were matched to the strength development rate.

• Elastomers and Composites
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• v.40 no.4
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• pp.249-257
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• 2005

Polyurethane(PU) prepolymers were prepared from polyol and diisocyanate. Unionized PU prepolymers were synthesized from poly(propylene glycol)(PPG, MW: 1000), 2,2-bis (hydroxymethyl) propionic acid(DMPA), and isophorone diisocyanate(IPDI) by prepolymer syhthesizing process. After PU prepolymers were dispersed into water, the physical properties were investigated by changing the molar ratio of polyol and diisocyanate. The results showed a stable state with the best physical properties when the prepolymer was composed of PPG/DMPA with hard segment=40%, NCO%=3.43%, [NCO]: [OH]=1.5: 1.0 in molar ratio, and was dispersed into water with 30% solid content. PU prepolymers also were synthesized with various molar ratio of PPG and DMPA. Upon higher molar ratio of DMPA, particle size of polyurethane dispersion(PUD) gradually decreased. PU-prepolymers prepared from the various blocking agents represented characteristic initial deblocking temperatures that depended on the blocking agents, and the beginning of deblocking occured within 30 mins on all the blocking agents used.

• Journal of Ceramic Processing Research
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• v.20 no.6
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• pp.655-659
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• 2019

Calcium phosphates such as HA (hydroxyapatite), β-TCP (tricalcium phosphate) and biphasic HA/β-TCP, were synthesized by wet chemical precipitation in aqueous solution combined with ball milling process. Nanosize powders of the calcium phosphates were synthesized using Ca(OH)2 and H3PO4. The effects of initial precursor Ca/P ratio (1.30, 1.50 and 1.67), ball milling process and post heat-treatment on the phase evolution behavior of the powders were investigated. The phase of resulting powder was controllable by adjusting the initial Ca/P ratio. HA was the only phase for as-prepared powders in both cases of Ca/P ratios of 1.50 and 1.67. The single HA phase without any noticeable second phase was obtained for the initial Ca/P ratio of 1.67 in the overall heat-treatment range. Pure β-TCP and biphasic calcium phosphate (HA/β-TCP) were synthesized from precursor solutions having Ca/P molar ratios of 1.30 and 1.50, respectively, after having been heat-treated above 700 ℃. The β-TCP phase has appeared on the pre-existing DCPD (dicalcium phosphate dihydrate) and/or HA phase. Dense ceramics having translucency were obtained at a considerably lower sintering temperature. The modified process offered a fast, convenient and economical route for the synthesis of calcium phosphates.