Optimization of experimental parameters for the quantification of polymer additives using SFE/HPLC

Analysis of low concentration additives; for example, antioxidants, in polymeric materials remains a difficult task. In the usual analytical methods, additives are extracted using large quantities of solvents first followed by concentrating the resulting solution for making possible the analysis. The supercritical fluid extraction (SFE) technique eliminates the use of large quantities of solvents and simplifies the analytical procedure. This work has been done with the goal of extracting the antioxidants Irganox 1010 and Irgafos 168 from a polypropylene matrix by using the SFE technique and by subsequent analysis using high‐performance liquid chromatography (HPLC). The experimental parameters; that is, temperatures, pressure, and modifiers have been varied to find the best extraction conditions. The optimum temperature and pressure for extraction of above‐mentioned polymer additives were found to be 120°C and 384 bar, with methanol as the modifier. The quantitative extractions are significantly faster than those reported earlier in the literature. The results point out that the technique used in these experiments—SFE combined with HPLC—is a reliable and environmentally friendly alternative to the commonly used liquid extraction and analytical methods. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 938–946, 2000     

Effects of additives on the performance of two-component waterborne polyurethane coatings

The effects of various additives and solvents on a coating’s performance in a two-component waterborne polyurethane coating system are studied using a statistical experimental design method. Using a blocked arrangement of fractional factorial design matrices, six different independent variables, including the use of different additives, catalysts, as well as solvents at different levels, were examined for their effects on various coating performance parameters, such as gloss, hardness, viscosity, and chemical resistance. Statistical analysis revealed several significant effects of these additives on the coating performances. Most importantly, several two-factor interactions between additives were also found to significantly influence the performance properties of the coating. These interactions could be very difficult to detect using traditional one-at-a-time experimental approaches. The information obtained from this study could be used for designing coating systems with superior performance properties. Presented at the 26th International Waterborne, High-Solids and Powder Coatings Symposium, February 10–12, 1999, New Orleans, LA. Coatings and Colorants Division, 100 Bayer Rd., Pittsburgh, PA 15205-9741.     

The effect of oxide,carbide, nitride and boride additives on properties of pressureless sintered SiC: A review

Properties such as high hardness, low density, and high elastic modulus have made SiC ceramics proper choices for a variety of industrial applications. However, disadvantages such as low sinterability, and low fracture toughness have limited the fabrication of these ceramics. Past researches show that the use of Al₂O₃-Y₂O₃ additives play an important role in improving the sinterability and the properties of the composites. The use of oxide, carbide, nitride and boride additives results in improved sinterability, physical and mechanical properties. The investigations show that the microstructure, porosities, amount of additives, reaction of additives with the matrix, grain size and, finally, the sintering temperature are the most important factors affecting the properties of SiC ceramics. In this paper, the effect of using various additives, the sintering temperature and the annealing heat treatment on sinterability, microstructure and properties of the SiC matrix composites fabricated by pressureless sintering method have been investigated.     

锂离子电池高压电解液研究进展

传统碳酸酯类电解液在高压(>4.3 V, vs. Li/Li+)下易发生氧化分解反应,导致锂离子电池不可逆容量增加、循环性能下降. 为解决这一问题,需从理论和实验两方面对电解液溶剂、锂盐、添加剂及其基本组成等进行针对性设计. 耐高压溶剂是提升电解液稳定性的关键因素之一,既经济又有效,添加高浓锂盐是近年来研究较多的可提升电解液电化学窗口和循环稳定性的新策略. 本工作从耐高压溶剂、高压添加剂和高浓锂盐三方面综述了近几年锂离子电池高压电解液的研究进展.     

Cellulose nanofibres and cellulose nanowhiskers based natural rubber composites: Diffusion,sorption, and permeation of aromatic organic solvents

This article investigates the transport behavior of three aromatic organic solvents, viz. benzene, toluene, and p‐xylene in natural rubber nanocomposite membranes containing cellulose nanofibres (CNFs) and cellulose nanowhiskers (CNWs) isolated from bamboo pulp. The solvent molecules act as molecular probes to study the diffusion, sorption, and permeation through the nanocomposites, and provide information on the nanocomposite structure and matrix–filler interactions. Both the nanocelluloses were found to decrease the uptake of aromatic solvents in nanocomposite membranes, but the effect was more significant in the case on nanofibers compared to nanowhiskers. Furthermore, the uptake decreased with increased penetrant size; being the highest for benzene and the lowest for p‐xylene. Transport parameters such as diffusion coefficient, sorption coefficient, and permeation coefficient have been calculated. Comparison of the experimental values of equilibrium solvent uptake with the predicted values indicated that both the nanocelluloses have restricted the molecular mobility at the interphase and thereby decreased the transport of solvents through the materials; being more significant for nanofibers. The results showed that both the used cellulosic nanomaterials act as functional additives capable of manipulating and tailoring the transport of organic solvents through elastomeric membranes, even at concentrations as low as 2.5 wt %. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Retarding behaviour of organic solvents in permanganate-sulphite-initiated polymerization of acrylamide

Redox polymerization of acrylamide initiated by a new redox couple, potassium permanganate-sodium sulphite, has been studied under atmospheric oxygen at 35 ± 0.2° C. The rate of polymerization has been found to vary with the half power of the redox components and the first power of the monomer concentration. The energy of activation has been calculated to be 8.29 kcal/(deg. mol.). The effect of various additives such as neutral salts and surface-active agents has been studied qualitatively. The retarding effect of organic solvents on the rate of polymerization has also been studied both qualitatively and quantitatively. An interpretation of the observed results has been proposed.     

基于LiPF6的锂离子电池电解液的发展现状

近年来随着社会的发展和科技的进步,锂离子电池已成为重要的主流动力电池之一。分别从溶剂和添加剂2个方面综述了基于LiPF6的锂离子电池电解液的发展现状,详细介绍了适用于锂离子电池电解液的溶剂和添加剂,应用于锂离子电池电解液的常用有机溶剂有碳酸酯类、醚类和羧酸酯类有机溶剂,添加剂以其作用目的区分,可分为SEI成膜添加剂、导电添加剂、稳定添加剂、控制水分和游离酸添加剂、抗过充添加剂、阻燃添加剂及浸润性添加剂等;展望了锂离子电池电解液的研究方向。     

Insight into the degradation mechanism of cefixime under crystallization condition

The chemical stability of cefixime was determined by high-performance liquid chromatography(HPLC) under different conditions, including factors such as p H, solvents, initial concentration, temperature and additives.The degradation process follows the first-order kinetics. A p H-rate profile exhibits the U-shape and shows the maximum stability of cefixime at pH = 6. The stability in different pure solvents is ranked as acetone N ethanol N methanol N water, while the degradation rate of cefixime exists a maximum at the ratio of 0.6 in water + methanol mixtures. In addition, the degradation rate increases with the temperature increasing and the activation energy of degradation was found to be 27.078 k J·mol~(-1) in acetone + water mixed solvents. The addition of different additives was proven to either inhibit or accelerate the degradation. The degradation products were analyzed using HPLC, LC–MS and infrared spectroscopy, and the possible degradation pathways in acid as well as alkaline environment were proposed to help us understand the degradation behavior of cefixime.     

Effect of ultrasonic wave on the degradation of polypropylene melt and morphology of its blend with polystyrene

A new method using high intensity ultrasonic wave has been developed for the degradation of polymer melt in an intensive mixer. For the effective transfer of ultrasonic energy, experimental apparatus was specially designed so that polymer melt can be in direct contact with the ultrasonic horn. In this research, we observed that the significant degradation of polypropylene (PP) melt in a mixer occurs due to the action of ultrasonic wave without any aid of additives or solvents. To compare the degradation efficiency of ultrasonic irradiation with that of peroxide, additional experiments were performed to practice the peroxide-aided degradation by mixing 1 part of dicumyl peroxide with PP in the mixer. It was also found that the direct sonication on polymer mixture in melt state reduces the domain sizes and stabilizes the phase morphology of the blend. It is suggested that ultrasound assisted melt mixing can lead to in situ copolymer formation between the components and consequently provide an effective route to compatibilize immiscible polymer blends.     

Evaluation of kinetics and transport mechanism of solvents through natural rubber composites containing organically modified gadolinium oxide

The solvent transport properties of the prepared composites were analysed using solvents of varying cohesive energy density and the effect of both modified as well as unmodified filler on the sorption and diffusion behaviour of NR vulcanisates has been investigated. It is found that the equilibrium uptake decreases with increase in filler content, as anticipated owing to the restrictions offered by the filler for solvents to diffuse into the polymer matrix. The mechanism of transport in natural rubber composites was carefully tracked and it was found to exhibit an anomalous mode of solvent transport where the polymer relaxation is in par with the rate of diffusion. Theoretical modelling of the swelling parameters was done and the results were found to be in agreement with existing models. The excellent swelling resistance coupled with the simultaneous improvement in mechanical properties would definitely pave way for the utilisation of these composites as barrier membranes.     

Controlling numbers and sizes of beads in electrospun nanofibers

BACKGROUND: Electrospinning is a powerful and effective method to produce nanofibers. Beads have been observed widely in electrospun products, but effects of solvents, weight concentrations and salt additives on the number and morphology of beads in the electrospinning process have not been systematically studied. RESULTS: Both theoretical analysis and experimental results show that beads strongly depend upon solvents, weight concentrations and salt additives. Either a suitable weight concentration or a suitable salt additive can completely prevent the occurrence of beads in the electrospinning process; solvents can affect the number of beads and the morphology of electrospun fibers. CONCLUSION: Beads are mainly caused by lower surface tension. With a higher surface tension, the size and number of beads in electrospun products are smaller and fewer, respectively. Copyright © 2007 Society of Chemical Industry     

Carbon nanoparticle-filled polymer flow in the fabrication of novel fiber composites

During the fabrication process of advanced composites using nanoparticle-filled matrices, many problems potentially could arise. One such problem is the clogging of the channels of the microfiber matrix used due to strong interactions between the nanoparticle additives and the matrix walls. In the present paper, a two-dimensional simulation model based on an Eulerian multiphase flow approach is introduced to investigate and predict the flow characteristics of carbon nanoparticle-filled fluid around carbon microfiber matrix. The interactions between the microfiber matrix walls and the nanoparticle additives have been studied, and an energy “imbalance” technique has been applied between the fluid and the microfiber walls to prevent any potential sticking of the nanoparticle additives on the microfiber matrix walls during the flow process. The concept of phasic volume fractions is utilized, and the effects of external body forces, lift forces, and virtual mass forces are introduced into the momentum equations. The phase coupled SIMPLE algorithm is employed to solve the model.     

Interfacial adhesion in polyethylene–kaolin composites: Improvement by maleic anhydride-grafted polyethylene

Polyethylene–kaolin composites were investigated with a special emphasis on the control of the interfacial adhesion. Both matrix and filler were modified for this purpose. A stearic acid and maleic anhydride-grafted polyethylene were used as potential interfacial agents and the efficiency of aminosilane-surface-treated kaolin was considered. Tensile strength, elongation, impact strength, and melt index were currently measured in relation to the processing conditions. Enhanced interfacial filler-polymer adhesion progressively results in an decreased melt index. This has been clearly shown by comparing the effect of two polymeric additives to the polymer matrix, i.e., a maleic anhydride-grafted HDPE (MAGPE) and an unmodified HDPE of a similar melt index. Compared to low molecular weight additives, such as stearic acid and aminosilane, MAGPE has proved to be a very efficient additive in improving the impact resistance of HDPE–kaolin composites even at low contents. © 1995 John Wiley & Sons, Inc.     

聚苯乙烯与溶剂体系相容性的计算机模拟

使用推广的 Flory-Huggins理论结合 Monte Carlo法模拟聚苯乙烯与几种不同溶剂的相容性。用 Monte Carlo法从大量分子对中取样 ,计算配位数和相互作用能 ,将数据输入 Flory-Huggins格子模型中 ,估算出体系的混合自由能和相图 ,研究聚合度对聚苯乙烯与溶剂体系相容性的影响。模拟结果表明聚苯乙烯与甲苯等溶剂的相容性较好 ,与水等溶剂的相容性较差 ;随着聚苯乙烯聚合度增大 ,体系相容性变差 ;而且在聚合度较低时 ,相容性变差的程度更显著 ;以上结果与实际情况相符。     

Application of the dynamic SIMS technique to the study of silicone release coatings

Secondary ion mass spectrometry (SIMS) depth profiling has been used to determine elemental compositions of cured silicone release coatings as well as the location of controlled release additives (CRAs) in the cured polymer matrix. The two CRAs examined were found to be uniformly distributed throughout the matrix with no apparent increase at either the air or adhesive interface. As CRAs are required for tight release, this suggests that a minimum concentration at the surface is necessary but this concentration is not greater than that found in the bulk.     

改性高氯化聚乙烯甲板漆的研制

采用成本低而性能好的高氯化聚乙烯（ ＨＣＰＥ） 进行改性，作为主要成膜物，配制附着力好、防腐蚀性优异、耐磨性高的改性ＨＣＰＥ 甲板漆。介绍了该甲板漆及配套底漆的配方及其制漆工艺步骤。比较了不同改性树脂所得甲板漆的性能，以聚氨酯改性ＨＣＰＥ 甲板漆的性能为最佳。也讨论了颜料体积浓度、溶剂、助剂等对涂料性能的影响。     

Electron‐beam‐radiation‐induced grafting of acrylonitrile onto polypropylene fibers: Influence of the synthesis conditions

Electron‐beam‐radiation‐induced grafting of acrylonitrile onto polypropylene fibers was investigated with a pre‐irradiation method. Grafting conditions such as the solvents, additives, monomer concentration, radiation dose, and temperature were varied, and the effects on the degree of grafting were studied. The nature of the reaction medium and additives had a considerable influence on the degree of grafting. The dilution of acrylonitrile with N,N‐dimethylformamide significantly enhanced the degree of grafting in comparison with other solvents. The addition of sulfuric acid to the reaction mixture led to an increase in the degree of grafting and an acceleration of the rate of grafting. The order of dependence of the rate of grafting on the pre‐irradiation dose and monomer concentration was found to be 1.31 and 1.21, respectively, in the presence of sulfuric acid. The activation energy for grafting was calculated to be 21.9 kJ/mol. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Lipase-Catalyzed Esterification

Lipases are versatile catalysts. In addition to their natural reaction of fat hydrolysis, lipases catalyze a plethora of other reactions such as esterification, amidation, and transesterification of esters as well as organic carbonates. Moreover, lipases accept a wide variety of substrates while maintaining their regioselectivity and stereoselectivity. Lipases are highly stable even under adverse conditions such as organic solvents, high temperatures, and so forth. Applications of lipases include production of food additives, chiral intermediates, and pharmaceutical products. Among these, synthesis of various chiral intermediates in pharmaceutical industry and cocoa butter substitutes is being commercially exploited currently.

Lipase-catalyzed esterification and transesterification in anhydrous media (e.g., organic solvents and supercritical fluids) has been an area of major research activity in the past decade or so. Absence of water eliminates the competing hydrolysis reaction. Moreover, substrate specificity, regioselectivity, and stereoselectivity of the enzyme can be controlled by varying the reaction medium. Although organic solvents, which are generally used for lipase-catalyzed reactions, are nearly anhydrous; they contain water in trace quantities. This water content can be controlled over a range and has a profound effect on the activity of lipases. Water not only affects the enzyme but also acts as a competing nucleophile. Enzyme activity has been correlated with thermodynamic activity of water in the medium rather than with the concentration of water. Because lipases are not soluble in most organic solvents, the method of preparation of the enzyme has a strong influence on the enzymatic activity. The major factors are the pH of the aqueous solution in which the enzyme last existed, additives used during preparation, and method of removal of water (e.g., freeze-drying, evaporation, extraction of enzyme into solvent, etc.). Immobilization of lipases allows easy recovery and reuse of the enzyme. Various immobilization techniques have been studied for lipases and some of them have been shown to enhance the activity and stability of the enzyme. Enzyme stability is an important parameter determining the commercial feasibility of the enzymatic process. Various factors, such as temperature, reaction medium, water concentration, as well as the method of preparation, affect the stability of the lipases.

This review deals with fundamental as well as practical aspects of lipase catalysis. A discussion has been presented on various factors affecting lipase activity and stability. Moreover, a brief account of current and potential applications of lipases has been given.     

Die beeinflussung des o/p-Verhältnisses bei azokupplungen mit 1-Naphthylamin in nichtwäßrigen medien

The azo coupling reaction of 1-naphthylamine with diazonium ions under normal conditions in aqueous media occurs predominantly in the 4-position. A study has been made showing how the o/p ratio of this reaction can be influenced in non-aqueous media. It has been found that diazonium ions react with 1-naphthy lamine in solvents with extremely low donor but medium acceptor properties, such as 1,2-dichloroethane and dichloromethane, with higher yields in the 2-position than is the case in solvents with relative high basicity, and also in solvents with both low donor and acceptor numbers, such as carbon tetrachloride. By the addition of carboxylic acids with pK_a values ⩽ 2, such as dichloro- and trichloro-acetic acid, to the solvents with extremely low basicity, the o/p ratio could be clearly increased. Under these conditions, various substituted benzenediazonium tetrafluorborates react with yields of about 90% in the o-position. It has been found that the intermediate formation of 1-naphthylammonium carboxylates plays a decisive role in the surprisingly high selectivity of azo coupling at the 2-position. The reaction proceeds in a similar manner with 1-naphthylammonium dihydrogenphosphate and toluene sulfonate. but not however with the 1-naphthylammonium chloride.     

Solubility and diffusion coefficient of antioxidants in polyethylene

As an aid in assessing the ability of antioxidant additives to persist in polymers and thus remain effective in protecting against oxidation, the solubility and diffusion coefficient of two antioxidants in branched polyethylene have been determined in this work. A method was developed for this purpose by which the diffusion coefficient and solubility could be determined simultaneously. The method consists of analyzing the concentration profile across a stack of polyethylene sheets through which the antioxidant was allowed to diffuse. The concentration of antioxidants in polyethylene was determined by a thermogravimetric technique which relies directly on the ability of the additives to suppress oxidation reaction. The diffusion coefficients determined showed excellent agreement with values in the literature which were obtained by a radiotracer method. The solubility of the antioxidants in three normal hydrocarbon solvents of varying molecular sizes was also determined by a conventional technique at various temperatures and found to correlate well with their solubility in polyethylene determined by the diffusion method. In particular, the dependence of the solubility on the size of solvent molecules and on temperature agrees well with an equation derived on the basis of the regular solution theory of liquid mixtures.