An evaluation of urea-rubber matrices as slow-release fertilizers

The viability of a urea-rubber matrix (URM) as a slow-release nitrogen fertilizer was assessed by field trials and incubation studies. Encapsulation of urea in the rubber matrix apparently prevented the inhibition of seed germination experienced at high temperatures (> 20°C) following high urea applications. The release of urea from URM increased with temperature and was well described by a diffusion model which allowed for the temperature-dependence of both the diffusion coefficient in water and the saturated concentration of urea. Initial results suggest that the effect of varying the size of URM cuboids on both their release characteristics in moist soil and N-supply to plants is also reasonably well predicted by the diffusion model. In a ryegrass field trial over 24 weeks, the URM gave higher dry matter yields than either prilled urea or (NH₄)₂SO₄ (following a single application at sowing) through efficient matching of nitrogen supply and crop demand.     

Urea-rubber matrices as slow-release fertilizers

The efficacy of a prototype slow-release fertilizer, urea-rubber matrix (URM) was assessed under flooded rice conditions. URM cuboids of size 0.5 × 1.0 × 0.4 cm were applied in comparison with prilled urea at levels of 50, 130 and 200 kg N ha^?1. URM was placed at the soil/solution interface in intimate association with rice seedlings whereas prilled urea was broadcast into the floodwater to simulate the normal application method of South East Asian farmers. URM cuboid sizes of 0.25 × 0.5 × 0.4 cm, 0.5 × 0.5 × 0.4 cm and 1.0 × 1.0 × 0.4 cm were similarly evaluated at a single rate of 130 kg N ha^?1; a broadcast URM treatment was also included. Different methods of prilled urea application including deep placement and split application were also studied at a single rate of 130 kg N ha^?1. It was found that the build-up of floodwater N (urea + NH ₄ ⁺ ) from URM during the 13 days following application was almost negligible irrespective of level or method of application. This was thought to result in low losses of N through ammonia volatilization as shown by higher rice grain yields in comparison with prilled urea at all levels of application. Deep-placed urea gave a comparable grain yield to that of broadcast URM. There was no significant difference in grain yield between URM applied by placement and by broadcast, suggesting that URM can be effectively applied either in intimate association with rice seedlings or by broadcasting to the rice field before, or after, planting. An attempt to predict the release of urea from URM was made using a diffusion-based simulation model. It was found that the model underestimated the actual release of urea from URM within the rhizosphere, probably due to the extensive penetration by rice roots of the URM cuboids.     

Factors affecting N release of urea from reactive layer coated urea

An experimental fertilizer called reactive layer coated urea (RLCU) has been developed by coating urea with a mixture of diisocyanate and polyol in the presence of a catalyst. The hard, durable layer that is formed on the granule conveys slow-release character to the product. A series of soil incubation tests were conducted under simulated upland conditions for periods up to 56 days to study the effect of factors such as temperature, pH, soil moisture, and organic C additions on N release. The N release rate from RLCU was shown to be increased with increasing temperature and decreasing coating thickness. It was unaffected by the addition of lime to raise the pH or organic carbon sources to increase microbial activity. Although a slight effect of soil moisture was noted, it was not pronounced. Urea release tended to be in two stages — a constant diffusive stage in which, it is postulated, urea was still dissolving within the granule and diffusing to the soil at a constant rate and a slower logarithmic stage where the rate of release decreased with time.     

Dependence of soiling and soil release of easy care cotton on factors-controlling the finishing treatment

The conventional pad-dry-cure method was used for effecting crosslinking of cotton with N-methylol finishing agents under different conditions. Factors studied include nature and concentration of finishing agent and softener, type and concentration of catalyst, and curing temperatures. Variation of soiling and soil release characteristics of crosslinked cotton with these factors were investigated. The effect of finishing agent on aqueous soiling followed the order: Carbamate reactant-fabric > Dimethylolethylene urea-fabric > Dimethyloldihydroxyethylene urea-fabric > Untreated fabric > Modified triazinone-fabric ≥ Modified ethylene urea-fabric. On the other hand, the effect of these finishing agents was to enhance the susceptibility of the fabric to oily soiling. Nevertheless, nature of the finishing agent governed the magnitude of this enhancement. Aqueous and oily soil release depended also upon the nature of finishing agent, soiling increased and soil release decreased by increasing finishing agent concentration. Type of catalyst exerted a considerable influence on aqueous and oily soil release without significantly affecting the degree of soiling. For aqueous soil release, the following order was found: Al₂(SO₄)₃ · 18H₂O > MgCl₂ · 6H₂O > urea nitrate > ZnCl₂ · 6H₂O > Zn(NO₃)₂ · 6H₂O > urea phosphate > urea oxalate > NH₄ · H₂PO₄ ≥ NH₄Cl. A reverse order held good for oily soil release. Both aqueous and oily soil release were impaired by increasing catalyst concentration. Similarly, nature and concentration of the softener had no striking effect on soiling while they did on soil release. Raising the curing temperature from 80 to 140°C caused substantial reduction in case of soil removal of urea salts catalyzed-crosslinked cotton samples while having the degree of soiling practically intact.     

机械活化淀粉制备水凝胶及其尿素的控释性

以机械活化60 min的木薯淀粉、氢氧化钾部分中和的丙烯酸和丙烯酰胺为原料,合成农用淀粉基离子/非离子型复合高吸水树脂(SCSA),采用FT-IR和SEM对样品的官能团和表面形貌进行表征。以SCSA在5.0 mol·L^-1的尿素溶液中平衡溶胀后所得的水凝胶(SCH)为尿素在水溶液中的释放材料,考察合成工艺条件和释放环境对尿素释放过程的影响。结果表明,尿素从SCH中的释放过程符合Fickian扩散机理;SCH的溶胀率越大,尿素的释放速率越慢;释放温度越高,尿素的释放越快。在丙烯酸和丙烯酰胺质量比为3:3,交联剂N,N'-亚甲基双丙烯酰胺溶液用量为1.0 ml(浓度为0.02 mol·L^-1)的条件下制备的SCH对尿素的释放活化能为17.28 kJ·mol^-1。     

Effect of Urea on Dynamic Relaxation Behaviour of Poly(2-hydroxyethyl methacrylate)

Abstract

Effect of urea on the dynamic relaxation behaviour of poly(2-hydroxyethyl methacrylate) (PHEMA) was studied by means of a torsion pendulum in a temperature range from - 196°C to + 130°C. The incorporation of urea decreases the glass transition temperature of PHEMA, whereas the temperature of the secondary (β₁) relaxation of the oxycarbonyl groups does not change appreciably; the extent of the low-temperature (γ) relaxation assigned to the hindered rotation of the hydroxyethyl side groups is reduced. In contradistinction to other low-molecular weight compounds urea does not give rise to a characteristic diluent dispersion in PHEMA. A decrease in the molecular mobility with increasing urea content manifests itself in an increase in the storage modulus below the temperature of the β₁ dispersion (Tβ₁ = 28°C) (antiplasticizing effect). The atypical effect of urea on the relaxation behaviour of PHEMA was tentatively assigned to a strong interaction of the components which is evidenced by densification of the system. The effect of water on the relaxation behaviour of the system PHEMA-urea is analogous to that assessed for PHEMA.     

Preparation of poly(acrylic acid‐co‐acrylamide)/kaolin and release kinetics of urea from it

A series of poly(acrylic acid‐co‐acrylamide)/kaolin [poly(AA‐co‐Am)/kaolin] composites were prepared by aqueous solution copolymerization of partially neutralized acrylic acid and acrylamide in the presence of kaolin nanopowder, which was synthesized to act as a release carrier of urea fertilizer. The superabsorbent composite was swollen in aqueous solution of urea to load urea, and the effect of urea concentration on the swelling was investigated. Furthermore, the effects of the contents of crosslinker, kaolin, and acrylamide, the neutralization degree of acrylic acid, and temperature, pH, and ionic strength of release medium on water absorbency and diffusion coefficient of urea release from poly(AA‐co‐Am)/kaolin were studied systematically. It was found that urea loading percentage could be adjusted by urea concentration of swelling medium, and urea diffusion coefficient could be regulated through the contents of crosslinker, kaolin, and acrylamide, and the neutralization degree of acrylic acid. Additionally, temperature and ionic strength of release medium may also affect the urea release process. The conclusions obtained could provide theoretical basis for urea diffusion behavior in superabsorbent used in agriculture. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Generation of microcellular polymeric foams using supercritical carbon dioxide. II: Cell growth and skin formation

We have generated microcellular polymeric foam structures using a pressure induced phase separation in concentrated mixtures of supercritical CO₂ and poly(methyl methacrylate). The process typically generates a microcellular core structure encased by a nonporous skin, the thickness of which decreases with increasing saturation pressure. This trend can be described by a model for skin formation that is based on the diffusion rate of gas out of the sample. Significant density reductions on the order of 30 to 70% can be achieved by changing the pressure and temperature conditions in the foaming process. There are several ways in which the saturation pressure affects the average cell size, with the net effect that cell size decreases sharply with increasing pressure above 2000 psi, leveling out at higher pressures. Cell size increases with increasing temperature from 40°C to 70°C. A model for cell growth, based on a cell model of Aremanesh and Advani, modified to include the effect of CO₂ on model parameters, reproduces these trends.     

十二烷基苯磺酸钠辅助尿素共沉淀制备超细铜铬黑颜料

以十二烷基苯磺酸钠为表面活性剂,采用尿素共沉淀法合成超细尖晶石型铜铬黑颜料。以铬和铜硝酸盐为原料,系统研究了沉淀剂、煅烧温度和表面活性剂等条件对铜铬黑颜料晶型、形貌和粒度的影响;并探讨了合成条件对铜铬黑颜料着色力的影响。研究表明,尿素和十二烷基苯磺酸钠可有效地控制形貌、颗粒大小及均匀性;在尿素用量为理论量4倍、表面活性剂添加量为5%、煅烧温度800℃的条件下制备出了形貌为六面体、平均粒径为300 nm、粒径分布均匀、着色力优异的超细铜铬黑颜料。     

Dissolution of a South African calcium based material using urea: An optimized process

The rate at which limestone dissolves is very important in wet flue gas desulfurization process (FGD). High dissolution rates provide better alkalinity, which is important for sulfur dioxide (SO₂) absorption. This study investigates the use of urea to improve the dissolution rate of limestone. The dissolution characteristics have been studied by using a pH-Stat method. The dissolution rate constant was measured according to the shrinking core model with surface control, i.e. (1−(1−X)^1/3)=k _r t. The effect of experimental variables such as temperature, amount of urea, solid to liquid ratio and stirring speed on the dissolution rate of limestone were investigated. Using a central composite design (CCD) of experiments variables, a mathematical model was developed to correlate the experimental variables to the dissolution rate constant. The experimental value was found to agree satisfactorily with predicted dissolution rate constant. The model shows that high temperature and low solid to liquid ratio improves the dissolution rate. The dissolution rate increased slightly with increase in the stirring speed. In the presence of urea the dissolution rate constant increased by 122%. The dissolution reaction follows a shrinking-core model with the chemical reaction control as the rate-controlling step.     

Temperature dependence of mechanical properties of aluminum titanate ceramics

Aluminum titanate (Al₂TiO₅: AT) is a synthetic ceramic material of potential interest for many structural applications. A critical feature, which greatly limits the mechanical properties of polycrystalline AT, is the considerable intergranular microcracking, which occurs due to the large thermal anisotropy of individual grains during cooling after sintering. This study discusses the temperature dependence of mechanical properties, and presents observations on the microstructure morphology. Both the fracture strength and fracture toughness increased considerably with increasing temperature. The critical frontal process zone (FPZ) size was estimated from the mechanical properties. A decrease in FPZ size was observed with increasing temperature in the first thermal treatment. These phenomena were explained on the basis of the stress redistribution and unique microscopic feature on the fracture surface of AT ceramics. The experimental results revealed that further thermal treatment increased the fracture strength and reduced the fracture toughness, while it had almost no effect on the FPZ size.     

Greenhouse evaluation of phosphorus availability from compacted phosphate rocks with urea or with urea and triple superphosphate

The possible effect of urea hydrolysis on the availability of phosphorus (P) from phosphate rock (PR) was evaluated in two greenhouse experiments with maize, using two sources of PR — Pesca (Colombia) and Bayovar (Peru) — representing low and high chemical reactivity, respectively.In Experiment I, on a neutral Josephine silty clay loam (pH 6.2) (Typic Haplozerult), Bayovar PR compacted with urea (Bayovar PR + urea) performed better than Bayovar PR compacted with NH₄Cl (Bayovar PR + NH₄Cl) in increasing dry-matter yield at a rate of 100 mg P kg^–1 but not at rates of 50 and 200 mg P kg^–1. It was also found that the dry-matter yield obtained with compacted Bayovar PR products was significantly higher when the N ratios of urea: NH₄Cl were 1:1 or higher than when the ratios were below 1:1. Although Bray I–P can overestimate available P from PR with respect to that from TSP, a good relationship was observed between Bray I–P and dry-matter yield from various compacted Bayover PR products with a small particle size (–0.43 + 0.15 mm).In Experiment II an acid Bladen sandy loam (pH 4.5) (Typic Albaquult) was used. Finely ground Bayovar PR (– 0.07 mm) was about 66% as effective as TSP in increasing dry-matter yield, whereas Pesca PR was ineffective. When Pesca PR was partially acidulated with H₃PO₄ at 20% level (PAPR), it became 70% as effective as TSP. Granulated PAPR and Pesca PR compacted with TSP (Pesca PR + TSP) were found to be equally effective in increasing dry-matter yield when both products had the same particle size and the same water-soluble and citrate-soluble P as percent of total P, and when prilled urea was used as the N source. However, when urea was compacted with Pesca PR and TSP, the product's effectiveness was further increased by 30% and to the same level as TSP.In summary, the results tend to support the suggestion that urea hydrolysis can be beneficial in increasing the availability of P from PR to plants in soils having medium to high organic matter contents.     

Effect of controlled-release fertilizer on nitrous oxide emission from a winter wheat field

A 2-year field experiment was conducted to study effects of application rate of controlled-release fertilizer (CRF) and urea on N₂O emission from a wheat cropping system. Two kinds of N fertilizers, CRF and urea, and four application rates (0, 100, 200 and 270?kg?N?ha^?1) were used. Results indicate that the application of either urea or CRF, increased total N₂O emission during the wheat growing period linearly from 32 to 164?%, with increasing N rate (p?<?0.05), compared to the zero N control, and the increase was less significant in CRF than urea treatments. Compared with urea, CRF significantly reduced N₂O emission by 25?C56?% during the wheat growing period (p?<?0.05), and the effect was more significant when N rate was higher. Grain yield increased in a power pattern from 24 to 43?% in urea treatments and from 30 to 45?% in CRF treatments with increasing N rate (p?<?0.05). Specific N₂O emission (N₂O emission per unit of yield) increased linearly from 31 to 114?% in urea treatments (p?<?0.05), and from 2 to 50?% in CRF treatments (p?<?0.05), with increasing N rate. Compared with urea, CRF significantly inhibited specific N₂O emission (p?<?0.05), and the effect increased with increasing N rate. Peaks of N₂O emission did not occur immediately after fertilization, but did immediately after rainfall events. CRF released fertilizer-N slowly, prolonging nitrogen supply and reducing peaks of N₂O fluxes stimulated by rainfall. The application rate of CRF could be reduced by 26?C50?% lower than that of urea for mitigating N₂O emission without sacrificing grain yield. We would not risk any significant loss of wheat yield while achieving economic and environmental benefits by reducing urea or CRF application rate from 270?kg to 200?kg?N?ha^?1.     

Direct synthesis of hydrogen peroxide from H2/O2 and oxidation of thiophene over supported gold catalysts

Direct synthesis of hydrogen peroxide from H₂ and O₂ was performed over supported gold catalysts. The catalysts were characterized by means of UV–vis, H₂-TPR, TEM and XPS. Based on the results we conclude that metallic Au is the active species in the direct synthesis of hydrogen peroxide from H₂ and O₂. During preparation process of catalyst by deposition–precipitation with urea, the pH value increased and the gold particle size decreased with increasing the urea concentration. The catalyst prepared with higher urea concentration showed a higher activity and its stability also was efficiently improved. Gold nanoparticles, supported on TiO₂ or Ti contained supports, gave a higher catalytic activity. Thiophene can be efficiently oxidized by hydrogen peroxide synthesized in situ from H₂ and O₂ over Au/TS-1.     

Effect of hole size on the incorporation of C60 molecules inside single-wall carbon nanohorns and their release

We created holes in single-wall carbon nanohorns (SWCNH) by oxidation (SWCNHox) and investigated how the hole size affected the incorporation of C₆₀ in SWCNHox and their release from it. The incorporation of C₆₀ inside SWCNHox first occurred when the holes were opened by oxidation at 475 °C. It was followed by a steep increase in the incorporation quantity with increasing oxidation temperature. The release rate of C₆₀ from inside SWCNHox was slower than that of C₆₀ crystallites located outside, and did not depend on the oxidation temperature (475-550 °C), indicating that the release rates were not influenced by the hole sizes.     

Removal of NO from flue gas by wet scrubbing with NaClO2/(NH2)2CO solutions

The experiments were performed in a countercurrent packed column in a continuous mode to study the absorption of nitric oxide in sodium chlorite/urea solutions. Sodium chlorite mainly works as an agent to oxidize NO to NO₂. A combined SO₂/NO removal system was also tested. On the basis of high SO₂ removal efficiency, the NO removal efficiencies under various experimental conditions were emphatically measured. Among the operating variables such as initial NaClO₂ concentration, urea concentration, temperature and initial pH value, the pH value of the absorbing liquid was found to have a great impact on both NO removal efficiency and NO₂ concentration. NO removal efficiency was increased with increasing NaClO₂ concentration and temperature. Urea almost has no negative effect on NO removal efficiency, however it aids the abatement of NO₂ greatly. The anions in the spent scrubbing liquor were analyzed by ion chromatography.     

Novel hyperbranched waterborne polyurethane‐urea/silica hybrid coatings and their characterizations

Thermally resistant and mechanically stable novel hyperbranched waterborne polyurethane‐urea/silica hybrid coatings were prepared by using 3‐aminopropyltriethoxysilane as a coupling agent with SiO₂ as a crosslinker. The extent of hydrogen bonding was investigated to show a dependence on SiO₂ concentration, which increased the glass transition temperature of the polymers with increasing SiO₂ concentration. Thermal decomposition profiles and the corresponding stability data suggest two‐step decomposition for the hybrids; further, their stability increased with increasing concentration of SiO₂.Copyright © 2011 Society of Chemical Industry     

Adsorption thermodynamics of CO2 on nitrogen-doped biochar synthesized with moderate temperature ionic liquid

The purpose of this work was to investigate the thermodynamic characteristics of carbon dioxide (CO₂) adsorption on a promising nitrogen-doped biochar at constant temperature and isopiestic pressure. The biochar was prepared as a CO₂ adsorbent based on catalytic pyrolysis of pristine coconut shells using urea as the nitrogen source and moderate temperature ionic liquid as a catalyst. The results showed that CO₂ adsorption on the biochar was a spontaneous, dominantly physical, exothermic, and entropy decrement process that could be well described by the slip model and the dual-site Langmuir model. Those thermodynamic parameters, including interface potential, exhibited a series of interesting tendencies with the changes in adsorption temperature and pressure. Under the conditions of 273 K and 100 kPa, the adsorption capacity and the interface potential were 4.6 mmol/g and −16.7 J/g, respectively. And the site energy ranged from 2.57 to 5.13 kJ/mol in the test conditions, which became narrow with increasing temperature. The temperature exhibited positive effects on interface potential, enthalpy change, entropy change, enthalpy change, internal energy change but negative effects on adsorption capacity, Gibbs free energy change, and Helmholtz free energy change. Interestingly, the pressure exhibited the opposite effect trends. The peak pressure with maximum temperature effect at a given temperature and the peak temperature with maximum pressure effect at a given pressure were found to exist for some thermodynamic parameters. These exhibited a different but significantly beneficial perspective to understand the mass and energy transfer during CO₂ adsorption on the biochar at constant temperature and isopiestic pressure, which have rarely been reported before.     

The effect of carbon dioxide during the desulfurization of flue gas with Mardin–Mazıdagı phosphate rock

The effects of temperature, CO₂ concentration and particle size on simultaneous calcination/sulfation of Mardin–Maz?dag? phosphate rock in fluidized-bed reactor were investigated. For this, a raw sample was exposed to calcination and sulfation processes in a fluidized-bed reactor to determine the effects of parameters by using a model gas mixture similar to the flue gas composition. The calcination ratio increased with increasing temperature and decreasing particle size, but decreased with increasing CO₂ concentration. In sulfation process, however, sulphate conversion ratio increased with increasing CO₂ ratio and decreased with decreasing particle size. The sulfation reaction is well represented by the shrinking core model and can be divided into two regions with different rate controlling step. For low conversions, the controlling step was found to be chemical reaction at the interface, but the diffusion through the product layer for high conversion. The activation energies for the chemical reaction at the interface and diffusion through the product layer cases were calculated as 100 and 296 kJ mol^?1, respectively.     

Preparation of poly(L-lactic acid) submicron particles in aerosol solvent extraction system using supercritical carbon dioxide

The aerosol solvent extraction system process (ASES), which is one of the supercritical anti solvent processes (SAS), was used to produce poly(L-lactic acid) (PLLA) into the submicron particles. Dichloromethane (DCM, CH₂Cl₂) and carbon dioxide were selected as a solvent and as an antisolvent for PLLA, respectively. The objective of this study was to investigate the effect of the various process parameters such as temperature, pressure, and solution concentration on PLLA particles. With increasing temperature and pressure, particle size was increased. Also, higher PLLA concentration led to larger particle size and broader particle size distribution. A scanning electron microscope (SEM) was used to observe the morphology and size of PLLA particles recrystallized by ASES process. The mean particle size and its distribution of processed particles were measured by using a laser diffraction particle size analyzer (PSA).