Papers by Keyword: Solvent

Abstract: In this work, the liquid phase exfoliation (LPE) method was investigated to produce a large quantity of 2D MoS₂. The introduction of ultrasound into IPA and IPA/DI solutions containing MoS₂ resulted in fragmentation and exfoliation of the MoS₂. The determination of the layers of LPE-MoS₂ was performed by optical microscopy, atomic force microscopy, non-resonant Raman spectroscopy and XRD. Flakes with few layers were detected by AFM and resonant Raman investigations.

Abstract: Today the prepreg technology for the manufacture of products from polymer composite materials is widely used in the global industry. This technology involves the use of prepregs obtained by preliminary impregnation of the reinforcing materials with binder solutions, which contain up to 50% environmentally sensitive and fire hazardous solvents. However, in many cases no systematic approach is used to solve the issues of choosing the optimal values of the solvent content in the binder solution to ensure its specified viscosity according, as well as the issues of safety of the industrial activity; instead, these issues are solved independently. It results in the unreasonable expense, loss of quality of the composite products and insufficient level of safety of production activity at the relevant workplaces. This study deals with the systematic prediction of the process parameters, taking into consideration the safety of operational procedures during the impregnation of prepregs and permissible range of deviations from their regulated value. The method and the relevant implementing technique for the prediction of optimal process parameters of the binder solutions for impregnation of prepregs in view of safety of the production activity have been developed. Dependences of the viscosity of the binder on its temperature and volume content of one-component, binary and three-component solvents have been obtained, with the tolerance band specified for the volume and weight contents of the solvent in the binder, which provides an acceptable deviation in the solution viscosity for the effective impregnation of prepreg. The paper proposes and substantiates the criterion of content of the binary solvent in the binder being optimal one in terms of process conditions. This criterion provides both the specified quality of impregnation of the reinforcing material and requirements for the safety of production activity. The actual hands-on examples are considered as related to the determination of optimal content of the binary solvent with the components for the specific binder and alcohol-acetone solvent. It is shown that the optimal weight concentration of acetone in the solvent is 0.085, with the solvent weight content in the mixture of 0.279. These parameters provide the maximum allowable concentration of solvent vapors, ensuring the safety of production activity. It should also be noted, that the solvent weight content differs by maximum 5% from the value required when using alcohol only, which provides high safety margin of the production activity.

Abstract: Tetramethylammonium hydroxide (TMAH) and N-methyl pyrrolidinone (NMP) are commonly used in photoresist developing and stripping process, however, both of TMAH and NMP have been confirmed with CMR (Carcinogenic, Mutagenic and Reprotoxic) concerns. With more attention attracted to TMAH and NMP replacements, Huntsman developed a range of new quaternary amines products, including E-GRADE^® Choline OH (Choline Hydroxide), E-GRADE^® THEMAH (Tris (2-hydroxyethyl) methylammonium Hydroxide), XHE-125, XHE-128, XHE-138, XHE-145 and XHE-148, and solvents, E-GRADE^® MEOX (3-Methyl-2-oxazolidinone) and XHE-123, which have been evaluated in comparison with the performance of TMAH and NMP.

Abstract: A new method with limited layer of polymeric solution was used to study the kinetics of precipitation of highly concentrated solutions of PAA in various precipitants; it allows to quickly estimate the rate of formation of the polymer membrane, adequately evaluate its morphology without membrane casting and reduce the experimental time for the preparation of a membrane with required porous structure. It was shown that the rate of precipitation of 18 wt. % PAA solution and the morphology of a layer resulting from the phase separation formed upon contact with water differ significantly in a “limited” layer and in a layer of infinite thickness. It was shown that morphology of a layer formed during phase separation of 18 wt. % PAA solution with water in the “unlimited” layer corresponds to morphology, which is formed in precipitation by 50% NMP-water solution of the same polymer solution in a “limited” layer. This supports the assumption about the strong dilution of the precipitant with a solvent when an “unlimited” layer method is used. In addition, during the investigation of the kinetics of the phase separation by water it was found that the rate of precipitation of highly concentrated polymer solution in a “limited” layer (ν = 8.3 μm/s) is significantly higher than in “unlimited” (ν = 1.7 μm/s). Using this method with “limited” layer, the kinetics of the phase separation of 18 wt. % PAA solution in aliphatic alcohols was also investigated; the rate of precipitation of the polymer solution is inversely proportional to their viscosity. Approximately twofold increase of dynamic viscosity with the chain length for each subsequent alcohol in the homologous series, the rate of precipitation of the PAA solution in them was also reduced by about 2 times

Abstract: In this work an original installation (manipulator) has been created that allows one to obtain up to 30 samples of hollow fiber membranes in one molding cycle, while simultaneously varying the molding conditions in a wide range (polymer concentration, nature of solvent and precipitant, exposure time in air and in a precipitant environment, post-processing and washing modes samples, diameter of the carrier needle). This installation makes it possible to move to a fundamentally higher level of accumulation of experimental data on the relationship "the composition of the spinning solution - the structure of the hollow fiber membrane - the separating properties of the membrane." It will also make it possible to involve in these studies new laboratory samples of polymers whose synthesis volumes are insufficient for the existing methods of obtaining laboratory samples of hollow fiber membranes. The principle of operation of the manipulator was worked out when obtaining mini-samples of hollow fiber PSF membranes from 24 wt. % PSF solution in NMP with the addition of 19 wt. % PEG-400 blowing agent on a carrier needle with external deposition. Mini-samples were obtained for studies of morphology, mechanical, transport and separation properties in one molding cycle of the manipulator. The properties of mini-samples of hollow fiber PSF membrane were compared with the properties of a membrane made by the method of “dry-wet” molding with internal deposition from a solution of the same composition. It was found that the porous structures of the membranes differ significantly from each other. In a hollow fiber PSF membrane obtained on a manipulator, the porous structure was spongy with separate macrovoids of various shapes. However, in the membrane obtained by the “dry-wet” method, a dense selective layer was formed on the inner side of the backing layer of elongated finger-shaped pores. It is the formation of spongy pores along the entire perimeter of the fiber wall that led to a decrease in the permeability of the hollow fiber PSF membrane obtained on the manipulator. Thus, not only the composition of the solution, but also the molding method makes a significant contribution to the properties of the membrane.

Abstract: Calcium hydroxide (Ca(OH)₂ has been recently synthesized from natural Indonesian limestone to be used as an intracanal medicament for root canal infection. Ca(OH)₂ is applied into the infected root canal in a non-setting paste form to release calcium and hydroxyl ions which elevates the pH and provide an antimicrobial effect to pathogenic bacteria. To form an injectable paste, Ca(OH)₂ powder has to be mixed with a proper solvent to produce optimal consistency, ion dissociation, and maintain its property as a non-set material. Solvent is an important factor affecting ion dissociation and preserving its non-setting paste condition. The aim of this study is to synthesize Ca(OH)₂ powder from Indonesian limestone, and evaluate the setting time of Ca(OH)₂ paste from mixture of Ca(OH)₂ powder synthesized from Indonesian limestone (limestone Ca(OH)₂) with various solvent, to evaluate which solvent serve best to prevent the Ca(OH)₂ paste from setting, to form an ideal paste be used as an intracanal medicament. This study consists of 5 groups (n=5); commercially Ca(OH)₂ paste (Calcipex II) as positive control, Ca(OH)₂ powder (Merck) + distilled water as negative control, limestone Ca(OH)₂ powder + natrium carboxy methylcellulose (Na CMC) as group 1, limestone Ca(OH)₂ powder + propylene glycol (PG) as group 2, and limestone Ca(OH)₂ powder + polyethylene glycol (PEG) as group 3. Setting time evaluation was measured according to ISO 9917 by vicat needle in 37°C to mimic the physiological body condition. Results were analyzed by One Way Anova test and Post Hoc Tukey test. The result of this study showed that the setting time of Ca(OH)₂ paste mixed with Na CMC solvent was 1:04 hours, PG 72:15 hours, and PEG did not harden until 7 days of observation. PEG is a hygroscopic high viscosity solvent, resulting in low and steady molecule interaction, thus prolonged its setting time. From this study it can be concluded that PEG inhibit Ca(OH)₂ setting reaction up to 7 days and might be used as solvent for Ca(OH)₂ paste as intracanal medicament.

Abstract: Prepreg manufacturing process is one of the most important preparatory technological processes, quality of which has the decisive influence on the physical, mechanical, processing and operational characteristics of the finished composite product. However, manufacturing of prepregs is associated with a number of harmful factors, negatively affecting the participants in the technological process and the environment. Consequently, significant additional costs are required in order to ensure specified maximum permissible levels and concentrations of the harmful products released by the components of polymeric composite materials in the product manufacturing process. The paper deals with the study of peculiarities and efficiency of impregnation of the heated reinforcing material using solvent-free binder. The method for predicting the optimal process parameters of binder solutions for impregnation of prepregs, taking into account the safety of production activity, has been developed. The problem of thermal conductivity from the heated reinforcing material to the binder, which allowed establishing the law of temperature distribution over the depth of the impregnating bath, depending on the duration of continuous impregnation, has been solved. It is found that the binder, with the duration of impregnation even within one working shift, heats up to the temperatures excluding the formation of centers of exothermic polymerization reaction in it. It indicates the availability of the effective regimes of impregnation using the method under study. The paper proposes the practical ways of improvement of the investigated method of impregnation by varying the wavelength, programmed change of the temperature of the reinforcing material at the entry to the bath, and setting of the optimal coordinates of the binder supply as it is drawn in the process of continuous impregnation of the reinforcing material.

Abstract: Among all the solar cell system dye sensitized solar cell is the third-generation solar cell that contains working electrode coating with semiconducting material, dye sensitizer, counter electrode and the efficiency of dye sensitized solar cell is reliant on the material which is absorbing light and converting it as energy. In this respect, dye sensitizer is the most substantial component in dye sensitized solar cell. Though organic and natural dye has been used in solar cell but due to the deleterious effect of organic dye, its application has been suppressed by the natural dye which is environment friendly and accessible. Ample of natural dyes has been applied in solar cell as sensitizer, while their way of application is different especially in case of dye extraction process. In this theoretical analysis, various research work related to dye sensitized solar has been included and explained the working principle of dye sensitized solar cell (DSSC), also summarized the extraction process of natural dye from different along with their photovoltaic parameters of various natural dye sensitized solar cell. Moreover, this study also compares the performance of natural dye sensitized solar cell according to presence of chromophore group in natural pigment.

Abstract: Suitable scaffolds for tissue engineering should promote several features that enable regeneration of the damaged tissue in vivo. In general, nanoto microfibrous meshes resemble extracellular matrix and support cell adhesion; three dimensional scaffolds, together with interconnected pores, promote cell migration into the volume of the scaffolds. Furthermore, the scaffold should be biodegradable with no harmful byproducts and easy to produce. Centrifugal spinning is an alternative method, to widely used electrospinning method, to produce 3D scaffolds suitable for use in tissue engineering. In this study, we tested different molecular weights and solvent systems of poly-ε-caprolactone (PCL) that were produced by the centrifugal spinning method. The produced scaffolds were characterized and seeded with Saos2 osteosarcoma cell line to verify their biocompatibility. We concluded from the results that group 4 scaffold, produced from a mixture of two molecular weights of PCL dissolved in acetic acid/formic acid, supported cell adhesion, proliferation and metabolic activity the most out of all the tested scaffolds. The other PCL scaffolds were prepared either from one type of molecular weight of PCL or chloroform was solely used to produce the scaffolds.

Abstract: Although there are currently different applications for gallium in microelectronics, literature is sparse about its applications in the area of conductive inks. The important characteristics to consider from the ink are viscosity, corrosion and surface tension. The importance of viscosity is a critical parameter in the printing ink mixture, which requires a metal to fulfill the function of conductor, such as gold, copper, and silver. Gallium as a conductor replacement is proposed due to the high cost of such metals currently used. The valence electrons are discussed in this paper due to the direct relation that has with metal conductivity, to provide a justified analysis about gallium application in conductive ink. The application of gallium could mean a significant change in conductive ink elaboration process. Thus, the aim of this research is to analyze the application of gallium as conductive ink, which is done by a literature review on gallium as a semi-conductor because of his valence electrons. Results about gallium as a potential conductive ink show that there is evidence that gallium shares similar properties as the current of materials conductive inks being adopted. This first literature review has some implications on the potential use of gallium as a conductive ink, requiring further experimental research to better test for conducting efficiency.