As the properties of the melamine-urea-formaldehyde (MUF) resins were changing during their storage time, this study investigated the impacts of the synthesis method and melamine content of the MUF ...resins on the pH, apparent viscosity, molecular weights, and crystallinity to estimate these properties over storage times of up to 30 days. Melaminesat three addition levels (5, 10, and 20 wt% based on the resin solids) were simultaneously reacted with urea and formaldehyde (MUF-A resins), while those at the same addition levels were first reacted with formaldehyde and then with urea(MUF-B resins). The pH values of the MUF-A and MUF-B resins decreased linearly as the storage time increased; the apparent viscosity increased linearly for the low melamine contents (5% and 10%) but increased exponentially for 20%. As anticipated, the molecular weights (Mw and Mn) increased linearly with the storage time, with a steeper increase in the Mw of the MUF-B resins compared with that of the MUF-A resins. The crystallinity of the two resin types decreased with storage time at higher melamine content. The relationships between these properties and the storage time made it possible to estimate the property changes in these resins synthesized by the different synthesis methods and melamine contents; this could help predict the properties of such resins in the industry during their storage. KCI Citation Count: 6
This study was conducted to investigate the effects of the synthesis method, melamine content, and GPC parameters (such as flow rate, column-detector temperature, and sample injection temperature) on ...the molecular weight of melamine-urea-formaldehyde (MUF) resins. Two different synthesis methods were employed. In the first method, MUF-A resins were synthesized by simultaneously reacting urea, formaldehyde, and melamine (5%, 10%, and 20%) using the reaction of alkaline-acid-alkaline steps under controlled temperature and viscosity. In the second method, MUF-B resins were synthesized by first reacting melamine at the same levels with formaldehyde and then by adding urea. The highest weight average molecular weight (M w ) of MUF-A resins was found at 10% melamine content when the flow rate was 0.3 and 0.8 ml/min; M w decreased slightly at 20% melamine content. The results showed that M w increased with an increase in the melamine content when the flow rate was 0.5 and 1.0 ml/min. In addition, M w was the highest when the flow rate, column-detector temperature, and injection temperature were 0.3 ml/min, 50°C, and 25°C, respectively. On the contrary, MUF-B resins had greater M w and number average molecular weight (M n ) than MUF-A resins. Overall, Mw and M n increased as the melamine content increased. The optimal GPC parameter for MUF resins was determined as follows: a flow rate of 0.5 ml/min, a column-detector temperature of 50°C, and a sample injection temperature of 50°C.
To clarify the effects of drying temperature on the hygroscopicity and mechanical performance of MUF resin-impregnated wood, we investigated the water vapor adsorption capability, modulus of rupture ...(MOR), modulus of elasticity (MOE), and surface hardness of MUF resin-impregnated wood treated at 60, 80, 100, 120, 140 °C. Drying temperature can influence the hygroscopicity of MUF resin-impregnated wood. As temperature increased, hygroscopicity typically decreased, but the resin-impregnated wood hygroscopicity increased after treatment at 60 °C. Drying temperature has shown significant influence on the mechanical performance of MUF resin-impregnated wood (α = 0.01). Increasing the treatment temperature can enhance the mechanical performance of resin-impregnated wood. However, brittleness of the resin-impregnated wood increased after treatment at 140 °C. Characterization of FTIR and
13
C CP/MAS NMR indicate that higher drying temperature led to lower content of hydroxymethyl groups and more substituted reactive sites on the amino group. This refers to more complete dehydration condensation between the resin active groups, thereby increasing the crosslinking density of the resin, increasing the cohesive strength, and decreasing the hygroscopic groups.
In this work, MUF resin was tested by DMA method. It showed that G′ curves and strain curves together could be used to predict the curing behavior of MUF resins. The study showed that sequential ...formulation was preferred for the preparation of MUF resins. Hardener could accelerate the curing of MUF resins. But its addition amount should not be too high to affect the resins' shelf time. MUF showed medium thermal resistance when compared with UF and MF resins.
Low capacity and reliability are the challenges in the development of ionosphere communication channel systems. To overcome this problem, one promising and state-of-the-art method is applying a ...multi-carrier modulation technique. Currently, the use of multi-carrier modulation technique is using a single transmission frequency with a bandwidth is no more than 24kHz in real-world implementation. However, based on the range of the minimum and maximum ionospheric plasma frequency values, which could be in the MHz range, the use of these values as the main bandwidth in multi-carrier modulation techniques can optimize the use of available channel capacity. In this paper, we propose a multi-carrier modulation technique in combination with a model variation of Lowest Usable Frequency (LUF) and Maximum Usable Frequency (MUF) values as the main bandwidth to optimize the use of available channel capacity while also maintaining its reliability by following the variation of the ionosphere plasma frequency. To analyze its capacity and reliability, we performed a numeric simulation using a LUF-MUF model based on Long Short Term-Memory (LSTM) and Advanced Stand Alone Prediction System (ASAPS) in Near Vertical Incidence Skywave (NVIS) propagation mode with the assumption of perfect synchronization between transmitter and receiver with no Doppler and no time offsets. The results show the achievement of the ergodic channel capacity varies for every hour of the day, with values in the range of 10Mbps and 100Mbps with 0 to 20dB SNR. Meanwhile, the reliability of the system is in the range of 8% to 100% for every hour of one day based on two different Mode Reliability calculation scenarios. The results also show that channel capacity and system reliability optimization are determined by the accuracy of the LUF-MUF model.
As the properties of the melamine-urea-formaldehyde (MUF) resins were changing during their storage time, this study investigated the impacts of the synthesis method and melamine content of the MUF ...resins on the pH, apparent viscosity, molecular weights, and crystallinity to estimate these properties over storage times of up to 30 days. Melaminesat three addition levels (5, 10, and 20 wt% based on the resin solids) were simultaneously reacted with urea and formaldehyde (MUF-A resins), while those at the same addition levels were first reacted with formaldehyde and then with urea(MUF-B resins). The pH values of the MUF-A and MUF-B resins decreased linearly as the storage time increased; the apparent viscosity increased linearly for the low melamine contents (5% and 10%) but increased exponentially for 20%. As anticipated, the molecular weights (Mw and Mn) increased linearly with the storage time, with a steeper increase in the Mw of the MUF-B resins compared with that of the MUF-A resins. The crystallinity of the two resin types decreased with storage time at higher melamine content. The relationships between these properties and the storage time made it possible to estimate the property changes in these resins synthesized by the different synthesis methods and melamine contents; this could help predict the properties of such resins in the industry during their storage.
Biological oil weathering facilitated by specialized heterotrophic microbial communities plays a key role in the fate of petroleum hydrocarbon in the ocean. The most common methods of assessing oil ...biodegradation involve (i) measuring changes in the composition and concentration of oil over time and/or (ii) biological incubations with stable or radio-labelled substrates. Both methods provide robust and invaluable information on hydrocarbon biodegradation pathways; however, they also require extensive sample processing and are expensive in nature. More convenient ways to assess activities within microbial oil degradation networks involve measuring extracellular enzyme activity. This perspective article synthesizes previously published results from studies conducted in the aftermath of the 2010 Deepwater Horizon (DwH) oil spill in the northern Gulf of Mexico (nGoM), to test the hypothesis that fluorescence assays of esterases, including lipase activity, are sensitive indicators for microbial oil degradation in the ocean. In agreement with the rates and patterns of enzyme activity in oil-contaminated seawater and sediments in the nGoM, we found close correlations between esterase activity measured by means of methylumbeliferyl (MUF) oleate and MUF butyrate hydrolysis, and the concentration of petroleum hydrocarbons in two separate laboratory incubations using surface (<1 m) and deep nGoM waters (>1200 m). Correlations between esterase activities and oil were driven by the presence of chemical dispersants, suggesting a connection to the degree of oil dissolution in the medium. Our results clearly show that esterase activities measured with fluorogenic substrate proxies are a good indicator for oil biodegradation in the ocean; however, there are certain factors as discussed in this study that need to be taken into consideration while utilizing this approach.
Even though cure kinetics of melamine–urea–formaldehyde (MUF) resins with low melamine contents (0–20 mass%) and high-temperature curing have been studied, research on the thermal cure kinetics of ...cold-setting MUF resins with relatively high melamine content (20–40 mass%) is limited. Therefore, this study reports thermal cure kinetics of cold-setting MUF resins synthesized with three melamine contents, using differential scanning calorimetry. A model-fitting method (Kissinger), three model-free kinetic methods (Friedman (FR), Flynn–Wall–Ozawa (FWO), and Kissinger–Akahira–Sunose (KAS)), and a nonlinear isoconversional (or Vyazovkin) method were employed to theoretically estimate the cure kinetics of cold-setting MUF resins with high melamine content. The results of Kissinger analysis provided reliable activation energy (
E
a
) which was also comparable with those of isoconversional analysis. As the degree of conversion (
α
) increased, the activation energy (
E
α
) of MUF resins decreased, regardless of melamine content. However, the activation energy (
E
a
), isoconversional activation energy (
E
α
), and the peak temperature (
T
p
) increased as the melamine content increased. Two methods such as KAS and Vyazovkin methods were reliable in estimating their cure kinetics based on
R
2
values and cure kinetic parameters. Analysis of the cure kinetics showed that all melamine contents MUF resins followed an nth-order reaction (OR (
n
> 1)) model.
•Earth-ionosphere geometry is used for MUF estimation with h’F2 replacing hmF2.•Linear regression analysis reduces error in MUF estimation to 2 MHz.•The methodology may be applicable for HF ...communication support.
We report the estimation of the Maximum Usable Frequency of F2-layer for 3000 km circuit (MUF(3000)F2) using Earth-ionosphere geometry. The study is based on the assumption that h′F2 may replace hmF2 to estimate M(3000)F2. The monthly hourly medians of foF2,h′F2, and M(3000)F2 are extracted for Karachi (geog. coord. 24.9° N, 67.3° E) & Multan (30.2° N, 71.5° E) during 1996, 1992, & 1989 representing low, moderate & high solar activity years, respectively. The MUF(3000)F2 estimated using spherical geometry shows large deviation and greater Root Mean Square Error values (RMSE > 4 MHz) on comparison with MUF(3000)F2 observed from ionosonde. In order to reduce the error, linear regression analysis technique is used and applied on independent data set of years 1995, 1993 and 1991 representing low, moderate and high solar activity to compute corrected MUF(3000)F2, respectively. It is found that corrected MUF is in good agreement with observed MUF decreasing RMSE to less than 2.0 MHz for the stations and years under study. The results of this study would be helpful in MUF estimation using h′F2 and also in improving radio services for smooth HF communication.
Rice is a highly consumed staple food all over the world. The economic value of the rice crop can be further increased by producing rice bran oil (RBO) from rice bran which is a by-product of rice ...milling. However, high utilization of RBO is difficult to achieve as lipases present in rice bran cause decomposition of lipids present in the form of triacyl glycerol (TAG) into free fatty acids (FFA). In this work, we selected and systematically analyzed 125 putative lipase gene sequences derived from Oryza sativa ssp. japonica genome using bioinformatic tools. LOC_Os11g43510 was experimentally demonstrated to be highly expressed in rice bran. Further, molecular modeling and protein docking studies suggested that the protein encoded by LOC_Os11g43510, has high affinity for oleic acid and linoleic acid, common components of TAG in rice. The transcript from LOC_Os11g43510 was cloned and expressed as a secretory protein in Pichia pastoris X-33. SDS-PAGE and zymography showed that expressed protein had lipase activity and was glycosylated. These results are consistent with the hypothesis that LOC_Os11g43510 encodes an active lipase that could be involved in TAG breakdown in rice. This study demonstrates an alternative route to identifying lipases in rice bran.
•A total of 125 putative lipase genes were selected from the rice genome and analyzed.•The locus LOC_Os11g43510 was shown to be expressed in the RNA extracted from rice bran.•Expression of LOC_Os11g43510 in yeast led the production of an active triacylglycerol lipase.•The product of LOC_Os11g43510 could be involved in the breakdown of rice bran oils.•This study suggests a new way of screening and studying lipases in plants.
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