Suspension Agent Research Articles

Development of New Cordierite‐Based Refractory Coatings for Casting Applications

In this study, new refractory coatings based on synthesized cordierite for the casting applications were developed. The investigation included starting raw materials characterization, synthesis of the cordierite, design of the refractory coating as final product, and its application testing. The obtained results pointed out that coating suspension sediment stability was crucial quality parameter. Design and optimization of the coatings composition, with controlled rheological properties included, were achieved by application of different coating components, namely different suspension agents and by alteration of the coating production procedure. Cordierite, used as filler, was obtained by means of synthesis in the solid‐state reaction on the basis of talc, kaolin, and alumina. The investigation showed that the application of these particular types of water/alcohol‐based coatings has positive influence on surface quality and structural and mechanical properties of the castings of aluminum alloys obtained by casting into sand molds by means of evaporable models method, that is, evaporate pattern casting process.

수산화칼슘/인산 현탁제가 스타이렌 기반 현탁중합토너의 특성에 미치는 영향

고품질의 현탁중합토너를 제조하기 위해서는 수상 현탁계의 최적화가 매우 중요하다. 따라서 본 연구에서는 무기현탁제로 사용한 수산화칼슘(<TEX>$CaOH_2$</TEX>)/인산(<TEX>$H_3PO_4$</TEX>)(Ca/P)의 몰비 및 수상의 pH가 스타이렌 기반 현탁중합토너의 특성에 미치는 영향을 중점적으로 조사하였다. 먼저 수상을 중성조건(pH=7.5)으로 고정하고 Ca/P의 몰비를 1.5:1부터 1.76:1까지 변화시켰다. 그 결과 Ca/P의 몰비를 1.73:1로 하였을 때 이상적인 인산칼슘염(하이드록시아파타이트)이 만들어졌으며 이 조건에서 제조된 중합토너는 입도분포, 원형화도 및 대전특성이 우수하였다. 이 결과를 바탕으로 Ca/P의 몰비를 1.73:1로 고정하고 수상을 약산성(pH=5.5) 및 약염기성(pH=9.5) 조건으로 변화시켰다. 그 결과 약산성 조건에서 제조된 중합토너는 더욱 더 우수한 입도분포, 원형화도 및 대전특성을 나타냈으며 인쇄품질도 매우 우수하였다. Ca/P의 몰비와 수상의 pH 조건을 최적화하여 고품질의 현탁중합토너를 제조할 수 있었다. Optimizing a water-phase suspending system is very important to manufacture high-quality suspension polymerized toners. Therefore, in this study, the effects of the molar ratio of calcium hydroxide (<TEX>$CaOH_2$</TEX>)/phosphoric acid (<TEX>$H_3PO_4$</TEX>)(Ca/P), which were used as inorganic suspending agents, and pH of the water-phase on the characteristics of styrene-based suspension polymerized toners were mainly investigated. At first, the water-phase was fixed to neutral condition (pH=7.5) and Ca/P molar ratio was changed from 1.5:1 to 1.76:1. As a result, an ideal calcium phosphate (hydroxyapatite) was prepared at the Ca/P molar ratio of 1.73:1 and polymerized toners prepared at this condition showed good particle size distribution, circularity and charging characteristic. Based on this result, Ca/P molar ratio was fixed to 1.73:1 and pH of the water-phase was changed to weak acidic (pH=5.5) and weak basic (pH=9.5) conditions. As a result, polymerized toners prepared under the weak acidic condition showed very good particle size distribution, circularity and charging characteristic along with excellent printing quality. High-quality suspension polymerized toners could be prepared via optimizing Ca/P molar ratio and pH of the water-phase.

Pharmacokinetics after oral and intravenous administration of a single dose of tramadol hydrochloride to Hispaniolan Amazon parrots (Amazona ventralis)

To determine pharmacokinetics after IV and oral administration of a single dose of tramadol hydrochloride to Hispaniolan Amazon parrots (Amazona ventralis). 9 healthy adult Hispaniolan Amazon parrots (3 males, 5 females, and 1 of unknown sex). Tramadol (5 mg/kg, IV) was administered to the parrots. Blood samples were collected from -5 to 720 minutes after administration. After a 3-week washout period, tramadol (10 and 30 mg/kg) was orally administered to parrots. Blood samples were collected from -5 to 1,440 minutes after administration. Three formulations of oral suspension (crushed tablets in a commercially available suspension agent, crushed tablets in sterile water, and chemical-grade powder in sterile water) were evaluated. Plasma concentrations of tramadol and its major metabolites were measured via high-performance liquid chromatography. Mean plasma tramadol concentrations were > 100 ng/mL for approximately 2 to 4 hours after IV administration of tramadol. Plasma concentrations after oral administration of tramadol at a dose of 10 mg/kg were < 40 ng/mL for the entire time period, but oral administration at a dose of 30 mg/kg resulted in mean plasma concentrations > 100 ng/mL for approximately 6 hours after administration. Oral administration of the suspension consisting of the chemical-grade powder resulted in higher plasma tramadol concentrations than concentrations obtained after oral administration of the other 2 formulations; however, concentrations differed significantly only at 120 and 240 minutes after administration. Oral administration of tramadol at a dose of 30 mg/kg resulted in plasma concentrations (> 100 ng/mL) that have been associated with analgesia in Hispaniolan Amazon parrots.

The use of multinuclear solid-state NMR to evaluate polystyrene/silica composites

Organic–inorganic hybrid materials have attracted much interest because of their novel and specific characteristics. One method to obtain these materials is in situ polymerization through free-radical polymerization. In this study, styrene monomers were covalently linked to silica (SiO2) using the suspension polymerization technique. In the reaction process, benzoyl peroxide was used as an initiator; poly(vinyl alcohol) was used as a suspension agent and water was used as the reaction environment. The styrene/silica composites were characterized in relation to chemical structure and microstructure using solution and solid-state nuclear magnetic resonance, and thermal analysis was performed by differential scanning calorimetry to evaluate the thermal transition temperature (Tg). All results showed that styrene/silica nanocomposites were obtained. The material with 2.5 % SiO2 showed the best characteristics.

Effect of Competitive Surface Functionalization on Dual-Modality Fluorescence and Magnetic Resonance Imaging of Single-Walled Carbon Nanotubes.

It is well-known that ionic surfactant coated single-walled carbon nanotubes (SWNTs) possess higher near-infrared fluorescence (NIRF) quantum yield than nonionic polymer functionalized SWNTs. However, the influence of surface functionalization on the magnetic properties of SWNTs for T2-weighted magnetic resonance imaging (MRI) has not been reported. Here, we demonstrate that SWNTs functionalized by nonionic polymers display superior T2 relaxivity for MRI as compared to those coated by ionic surfactants. This difference may indicate that micelle structures formed by ionic surfactants are sufficiently tight to partially exclude water protons from the iron catalysts attached to the ends of SWNTs. On the basis of the different effects of the two types of suspension agents on NIRF and MRI of functionalized SWNTs, we further explore the competitive surface functionalization between ionic surfactants and nonionic polymers by stepwise replacing ionic surfactant molecules in a nanotube suspension with nonionic polymers. The superior NIRF of ionic surfactant coated SWNTs gradually quenches whereas no improvement on T2 relaxivity is observed during this replacement process. This result may indicate that nonionic polymers wrap around the outside of micelle structures to form small nanotube bundles rather than replacing ionic surfactants in the micelle structures to directly interact with the SWNT surface. Finally, we demonstrate the feasibility of dual-modality NIRF and MRI of nonionic polymer functionalized SWNTs in brain cells.

Síntese e caracterização de copolímeros à base de metacrilato de metila e divinilbenzeno com propriedades magnéticas

Neste trabalho, foram sintetizados materiais binários baseados em copolímeros de metacrilato de metila reticulados com divinilbenzeno contendo partículas de ferro com propriedades magnéticas pela técnica de polimerização em suspensão. Foram estudados os efeitos da concentração de ferro adicionado na polimerização, da razão molar MMA/DVB, do tipo de agente de suspensão e da velocidade de agitação na formação do copolímero. Os copolímeros foram caracterizados quanto à morfologia, à estabilidade térmica, ao teor de ferro incorporado, à distribuição de tamanho de partículas, às propriedades magnéticas, à área superficial, ao volume e ao tamanho de poros. Foram obtidas microesferas poliméricas com propriedades magnéticas que apresentaram bom controle morfológico esférico e partículas de ferro aglomeradas por toda a superfície da microesfera. As análises de propriedades magnéticas mostraram que os materiais obtidos não apresentaram ciclos de histerese, estando assim próximos de um material com propriedades superparamagnéticas, com magnetização de saturação entre 8,0 e 13,0 emu.g-1.

抗HIV薬の懸濁時における安定性に関する検討

抗HIV薬の懸濁時における安定性に関する検討

Bismuth tri-iodide nanoparticles synthesized from octadecene suspension

ABSTRACTBiI3 is a semiconductor layered compound of growing interest for direct and digital imaging. This structure determines that bismuth tri-iodide crystals can grow with platelet habit. Thereby, we consider of great importance to study if such structure can determine nanoparticles of this material as well, that means, if such layers can be rolled in order to form nanotubes and/or nanorods. In light of this, the present work reports the synthesis of bismuth tri-iodide nanoparticles by the suspension method.Bi(NO3)3.5H2O, I2 and KI were used as source materials, and 1-octadecene was used as suspension agent. The intermediate and final synthesized compounds were characterized by Xray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM).Results clearly show that BiI3 nanoparticles can be synthesized by the suspension method, which means that the layer structure of these compounds can determine the growth of nanostructures. Nanoparticles of different sizes and morphologies were obtained, depending on the synthesis conditions. There has been not possible to control such conditions in order to obtain uniform size and morphology distributions. The use of these nanostructures may be an interesting way of improving nucleation and further growth of bismuth tri-iodide films.

Scientific paper zircon-based coating for the applications in Lost Foam casting process

In this work, a possibility to develop a new zircon-based refractory coating for casting applications was investigated. Optimization of the coating composition with controlled rheological properties was attained by application of different coating components, particularly by application of a new suspension agent and by alteration of coating production procedure. Zircon powder with particle size of 25x10-6 m was used as filler. The zircon sample was investigated by means of the following methods: X-ray diffraction analysis, diffraction thermal analysis and polarized microscope. The shape and grain size were analyzed by means of the PC program package OZARIA 2.5. It was shown that application of this type of water-alcohol-based coating had a positive influence on surface quality, structural and mechanical properties of the castings of cast iron obtained by pouring into sand molds by means of the expandable patterns method (Lost Foam casting process).

Suspension Polymerization of Styrene Using Zinc Oxide as a Suspension Agent

The advantage of suspension polymerization is that the polymer product can be separated easily from the mixture of reaction product, in the form of small spherical polymer solid. This method is commonly employed in the production of expanded polystyrene. This research has investigated the reaction rate of suspension polymerization of styrene, along with the product characteristics. Classical model on chain polymerization was proposed, to determine the rate of reaction. The experiment was conducted in a three neck flask provided with a stirrer and water bath. The reaction was run at temperature 60 °C-90 °C and pH of 10. Sample was taken regularly from the reaction mixture at certain time, and the remaining styrene monomer in the sample was determined by gravimetric method (i.e. vacuumed vaporization). In the end of experiment, the polymer product (in the form of small sphere) was separated from the suspension mixture, dried and measured its diameter. The molecular weight of polystyrene product was measured by capillary viscometer. The results showed that the proposed reaction rate model fitted well to the experimental data, with its relative error being around 2.38%-10.9%, hence it was good enough to describe suspension polymerization process. The overall polymerization reaction rate constants was around 2.34-45.1 (L/mol) 0.5 , which depends on mainly the reaction temperature. The initiator decomposition rate constant was around 0.0051-0.0091 min -1 . Suspension agent concentration did not influence the styrene conversion. The diameter of polystyrene particle was around 0.1-1 mm, which was influenced by reaction temperature and suspension agent concentration. Viscosity average molecular weight of polystyrene products was between 100,000 to 670,000.

Characterisation of the interactive properties of microcrystalline cellulose–carboxymethyl cellulose hydrogels

Combinations of microcrystalline cellulose (MCC) and sodium carboxymethyl cellulose (Na-CMC) are commonly used as stabilising agents and suspending agents in pharmaceutical formulations. This paper is based on a study of the interactions that take place during the process of hydrogel formation, break down, and recovery. Also considered is the binding that occurs between the MCC and the Na-CMC. Avicel RC 591, a processed mixture of MCC and Na-CMC, is one of the more commonly used commercial suspending agents for aqueous compositions. Avicel RC 591 is used as an effective, blended stabilising agent. In this study, the contributions made by each of the components of Avicel RC 591 have been rationalised by monitoring the behaviour of the individual components in Avicel RC 591 suspensions or solutions. The hydrogels that are formed by Avicel RC 591 and by their laboratory formulated equivalent, which is spray dried (MCC + Na-CMC), have been characterised by confocal microscopy scanning electron microscopy and by dynamic light scattering. A 3D network structure that is formed by the MCC, in Avicel RC 591 is visualised. This network is supported by hydrogen bonding and by ionic interactions among and between the MCC, the Na-CMC and water. The strength of the network determines the physical properties of the hydrogel system, as seen in the rheological behaviour.

Effects of Surface-coated Carbon on the Chemical Selectivity for Water-Soluble Dispersants of LiFePO4

The effects of additions of dispersants, poly(4-styrene sulfonic acid) (PSSA), poly(ammonium acrylate) (PAA-NH4) and poly(acrylic acid-co-maleic acid) (PAMA), on the dispersion and electrochemical properties of carbon-coated lithium iron phosphate (LiFePO4) cathodes are studied. The influence of the addition of dispersants on the dispersion behaviors of carbon-coated LiFePO4 and conductive agents in aqueous suspensions is explored by analyses of zeta-potential and rheology. The homogeneity of the composition in the LiFePO4 cathode is assessed by scanning electron microscopy observation. The result shows that both PSSA and PAMA can interact with the carbon-coated LiFePO4 and they are efficient dispersants for LiFePO4 cathodes. PAA-NH4, however, is unfavorable to interact with carbon materials, and thus has a restricted efficiency for the dispersion of carbon-coated LiFePO4 cathodes. In addition to the dispersion property, the effect of the addition of dispersants on the rate capability of LiFePO4 cathodes is also examined. Although PSSA improves the dispersion homogeneity of the LiFePO4 electrodes, it is detrimental to the electrochemical property due to its high average molecular weight () of 70,000 g/mol. On the contrary, the PAMA used has a low of 3,000 g/mol, and hence only the positive influence of the improved dispersion of the cathode in terms of an increase in rate capability is observed.

Some physicochemical properties of acetaminophen pediatric suspensions formulated with okra gums obtained from different extraction processes as suspending agent

The purpose of this work was to evaluate the effect of the extraction process and the potential of okra gum as a suspending agent in pharmaceutical oral formulations containing acetaminophen as a model drug. Clarified mucilage of dried okra was either extracted directly with ethanol 96% (F1) or was first treated with base (F2), acid (F3) or heating in the presence of salt (F4) before extraction with ethanol 96%. The samples were used at 0.5% w/v as suspending agents in acetaminophen acetaminophen suspension to deliver 125 mg/5 mL acetaminophen. A binary mixture of F2 and F4 (1:1) was also used. Similar suspensions of acetaminophen containing either hydroxymethylpropylcellulose (HPMC) or tragacanth gum (TRAGA) were produced. Some physicochemical properties of the formulations were evaluated. The rheological properties of acetaminophen-containing treated okra gums (F2-F5) were generally similar. Changes in viscosity with storage were slower in the F2-F5 formulations as compared with F1. Particle size and particle size distribution were different for all formulations, and hysteresis was a function of time and the suspending agent used.The re-dispersion time of the formulations with treated okra gums was generally shorter than that observed with the untreated okra gum. The use of a binary mixture of F2 and F4 resulted in different physicochemical properties from those of either F2 or F4.The physicochemical properties of the formulations were comparable to those with HPMC and TRAGA. It can thus be concluded that treating okra gum with acid, base or salt impacted better physicochemical properties on an acetaminophen pediatric suspension when they were used as suspending agents.

Preparation of Suspended Liquid Hardener for No-Bake Phosphate Binder Sand

In order to solve the problem that powder hardeners for no-bake phosphate binder sand cause powder pollution, preparation of suspended liquid hardener has been studied in this paper. Orthogonal array L9(34) was selected to arrange the experiment. Under every factor and level an experiment was done, and suspension rate after four hours of the suspended liquid hardener was taken as experimental target. Results show that the addition of suspension agent and interaction between vector and suspension agent are significant factors at significance level α = 0.05. The best scheme is the one which contents 500g powder magnesia, 500g industrial alcohol vector and 20g SN suspension agent.

Evaluation of Yam (&lt;i&gt;Dioscorea sp.&lt;/i&gt;) Starch and Arrowroot (&lt;i&gt;Maranta arundinacea&lt;/i&gt;) Starch as Suspending Agent in Suspension

The aim of our study was to evaluate the applicability of yam (Dioscorea sp.) starch and arrowroot (Maranta arundinacea) starch as suspending agents in suspension. Paracetamol was used as a model drug because of its low solubility. It was found that the optimal concentration as suspending agent in paracetamol suspension was in the range of 7-8% for yam starch and 5-6% for arrowroot starch. All formulations were stable within the period of study with pH of 5.4-6.9. These results were comparable to those obtained from the sodium carboxymethyl cellulose (sodium CMC) which is a common suspending agent. It could be concluded that yam starch and arrowroot starch showed suspending activity in paracetamol suspension and could be applied as commercial suspending agent.

The Application of Oily Sludge in Chinese Oilfield

Using industry wastes for conformance control has recently attracted significant interest—in particular, when using oily sludge for in-depth fluid diversion. About 500 tons of oily sludge is generated from oil production, transportation, and refining each year. Oily sludge is mainly composed of oil, water, o/w emulsions, and solids and is quite difficult to separate and reuse. The accumulation of oily sludge has posed a serious environmental problem. Additives such as suspension agents, dispersion agents, and viscosity thickeners are often added into oil sludge as conformance control agents to extend particle suspension time, increase plugging efficiency, disperse oily drop, and increase penetration depth. The advantages of oily sludge as conformance control agents include: (1) good compatibility with formation; (2) high temperature resistance; (3) high salinity resistance; (4) low costs; and (5) environmental protections. This method has been used by most oilfields in China, with better results.

Preparation and characterization superporous hydroxypropyl methylcellulose gel beads

Stearic acid monoglyceride as suspension agent, divinylsulfone (DVS) as the crosslinker, cyclohexane as the continuous organic phase and nano-calcium carbonate as the porogen were used to produce hydroxypropyl methylcellulose (HPMC) porous gels in bead form by inversing phase suspension crosslinking. Effects of porogen dosage on the gel surface and inner morphology, density, porosity, swelling kinetics have been studied. Results show that the interpenetrate pores can be formed in gel beads when the porogen dosage reached 70 wt% of the dry HPMC. The equilibrium swelling ratios of the gel beads increased from 30.1 (g/g) to 37.4 (g/g) when the fraction of CaCO 3 dosage increased from 0 to 100 wt% of the dry HPMC and the equilibrium swelling time of the gels decreased from about 400 to 20 min. The results also show that the gel re-swelling capability is related to the porous structure.

Synthesis and characterization of poly(methyl methacrylate) polymerized by microwave energy or conventional water bath

AbstractIn this work, the influence of three different suspension agents (agar, sodium alginate, and gelatin) in the synthesis of poly(methyl methacrylate) (PMMA) particles is reported. Sodium alginate was the best suspension agent, obtaining characteristics closer to commercial denture base resins. Synthesized particles and two commercial acrylic resins (Acron MC and Lucitone 199) were characterized by light microscopy, scanning electron microscopy, characteristic X‐ray energy dispersive spectroscopy, thermogravimetric analysis, and molecular weight measurements. Mechanical tests (transverse deflection behavior) were done using two heat‐polymerizing techniques. The results indicated that both the PMMA particles and the commercial acrylic resins have similar characteristics. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Pitfalls in efficacy testing – how important is the validation of neutralization of chlorhexidine digluconate?

BackgroundEffective neutralization of active agents is essential to obtain valid efficacy results, especially when non-volatile active agents like chlorhexidine digluconate (CHG) are tested. The aim of this study was to determine an effective and non-toxic neutralizing mixture for a propan-1-ol solution containing 2% CHG.MethodsExperiments were carried out according to ASTM E 1054-02. The neutralization capacity was tested separately with five challenge microorganisms in suspension, and with a rayon swab carrier. Either 0.5 mL of the antiseptic solution (suspension test) or a saturated swab with the antiseptic solution (carrier test) was added to tryptic soy broth containing neutralizing agents. After the samples were mixed, aliquots were spread immediately and after 3 h of storage at 2 – 8°C onto tryptic soy agar containing a neutralizing mixture.ResultsThe neutralizer was, however, not consistently effective in the suspension test. Immediate spread yielded a valid neutralization with Staphylococcus aureus, Staphylococcus epidermidis and Corynebacterium jeikeium but not with Micrococcus luteus (p < 0.001) and Candida albicans (p < 0.001). A 3-h storage period of the neutralized active agents in suspension resulted in significant carry-over activity of CHG in addition against Staphylococcus epidermidis (p < 0.001) and Corynebacterium jeikeium (p = 0.044). In the carrier test, the neutralizing mixture was found to be effective and non toxic to all challenge microorganisms when spread immediately. However, after 3 h storage of the neutralized active agents significant carry-over activity of CHG against Micrococcus luteus (p = 0.004; Tukey HSD) was observed.ConclusionWithout effective neutralization in the sampling fluid, non-volatile active ingredients will continue to reduce the number of surviving microorganisms after antiseptic treatment even if the sampling fluid is kept cold straight after testing. This can result in false-positive antiseptic efficacy data. Attention should be paid during the neutralization validation process to the amount of antiseptic solution, the storage time and to the choice of appropriate and sensitive microorganisms.

A Novel Time-Controlled Release System Based on Drug-Resin Complexes and Elementary Osmotic Pump

A novel time-controlled system based on elementary osmotic pump tablet containing a drug-resin complexes (DRCs) core is presented. In the traditional osmotic pump tablets (OPTs), the lag time was always minimized. On the contrary, in the DRCs osmotic pump tablet (DRCOPT), the lag time was increased to achieve time-controlled delivery. The system led to a zero-order drug release after an initial lag time. Polyethylene oxide (PEO) N80 was used as suspension agent and NaCl was applied as ion-exchange, osmotic pressure (electrolyte supplementary) agent, respectively. To examine the mechanism of this system, drug release behaviors were investigated under conditions of various osmotic pressures. A new method of combination of conductivity and HPLC was applied to determine the different fractions of NaCl in producing osmotic pressure, ion-exchange and electrolyte supplement. The pharmacokinetic studies conducted in beagle dogs showed that a steadier and controlled drug release behavior was obtained compared with the traditional formulations. On the basis of prescription of the DRCOPT, a good in-vitro-in-vivo correlation (IVIVC, R(2)=0.9541) was achieved. In addition, a lag time of 4 h was observed in in vivo experiment, which indicated that the DRCOPT can be used in therapeutic regimens with the characteristics of chronotherapy.