Synthesis and application of core–shell particles as toughening agents for epoxies

Poly(butadiene-co-styrene) [P(B-S)] core-poly(methyl methacrylate) (PMMA) shell particles were prepared using a two-step emulsion polymerization. These core-shell particles were used to toughen an epoxy polymer. The role of particle-epoxy interfaces were studied by systematically varying the shell compositions of the core-shell particles such as PMMA, P[MMA-acrylonitrile (AN)], P[MMA-glycidyl methacrylate (GMA)] and P[MMA-divinyl benzene(DVB)]. Therefore, the nature of the particle-epoxy interfaces is varied in terms of physical interactions and chemical bonding. The fracture toughness values of the toughened epoxies were measured using linear elastic fracture mechanics. Results indicate that the morphology of the dispersed particles in the epoxy matrix plays an important role in the toughening of epoxies. This degree of dispersion can be varied by incorporating AN and GMA comonomers in the PMMA shells or by crosslinking the shell. In summary, nanoscale interactions of the rubber-matrix interface do not directly influence fracture toughness, instead, it was found that the nanoscale interactions could be used to control the blend morphology which has a dramatic effect on toughness. © 1995 John Wiley & Sons, Inc.     

Elucidation of the miniemulsion stabilization mechanism and polymerization kinetics

Styrene/hexadecane miniemulsions were polymerized at 50°C using a redox initiator. The miniemulsions and their corresponding latexes were characterized in terms of size, polymerization rate, and surface properties. The resulting data were analyzed to elucidate the miniemulsion stabilization and polymerization mechanisms. It was found that the free surfactant concentration exceeded the critical micelle concentration when large amounts of surfactant (60 mM sodium lauryl sulfate) were used, resulting in simultaneous micellar and droplet nucleation. Most surfactant was on the surface of the droplets (85%) or particles (95%). The fractional surface coverage was proportional to the surfactant concentration to the 0.55 power. Using a particle diameter equation, the number of particles was calculated to be proportional to the surfactant concentration to the 1.35 power. Through direct particle size measurements, a power of 1.38 was confirmed. The rate of polymerization was determined by reaction calorimetry to be proportional to the number of particles to the 0.59 power, in contrast to classical Smith–Ewart kinetics for conventional emulsions (1.0 power). The average number of radicals per particle was estimated from the rate and number data, and varied with the particle diameter to the 0.97 power. The observed kinetic dependencies were validated through an extension of Smith–Ewart theory. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3987–3993, 2003     

Extraction of metals from sulphides using sulphur trioxide in fluidised bed

The kinetics of the reaction of chalcopyrite, iron sulphide, copper sulphide, and nickel sulphide with sulphur trioxide gas were studied using a fluidised bed technique. O₂, N₂, or air was used as a carrier gas for the sulphur trioxide in fluidisation. Binary mixtures of finely ground (0.37–75 μm) samples were reacted with the sulphur trioxide in a Pyrex column at 373–673 K. The reaction products were leached with water and the soluble metals in the solution were determined by atomic absorption spectrometry. The total soluble reaction products were determined gravimetrically. The results obtained showed that a higher yield of soluble salts was obtained when O₂ or air was used as a carrier gas for sulphur trioxide than when an inert gas was used. Higher yields of soluble salts were obtained when the samples were most finely ground. Increase of copper sulphide content in binary mixtures with iron or nickel sulphide led to an increase in the yield of soluble salts. For iron sulphide/nickel sulphide mixtures, the yield of soluble salts increased with the nickel sulphide content. There were maximum values for the soluble metal ratios Ni/Fe and Cu/Ni in the corresponding sulphide binary mixtures and this maximum was at about 50% weight. The soluble Cu/Fe ratio increased with copper sulphide content in mixtures with iron sulphide.     

High PVC film‐forming composite latex particles via miniemulsification,part 1: Preparation

Miniemulsification technology was used to encapsulate TiO₂ particles inside a styrene/n‐butyl acrylate copolymer with high loading levels (11 to 70% PVC (pigment volume concentration)). In this approach, a St/BA copolymer dissolved in toluene in the presence of a costabilizer (hexadecane) was mixed with a dispersion of TiO₂ particles in toluene and sonified, and then emulsified in an aqueous surfactant solution by sonification. The effect of sonification time on both the dispersibility of the TiO₂ particles in the presence of the copolymer and hexadecane and on the encapsulated particle size was investigated. Particle size analysis by dynamic light scattering showed that these composite latexes are quite stable. It was also found that as the TiO₂ loading increased from 11 to 43% PVC, the particle size of the TiO₂ dispersion decreased while the polymer‐encapsulated TiO₂ particle size increased. The effect of surfactant concentration (sodium lauryl sulfate, SLS) on the encapsulated particle size was investigated using four different SLS concentrations in the 11% PVC system. The results showed that as the SLS concentration increased the particle size decreased, as expected. Also it was found that the minimum surfactant concentration that gives stable encapsulated TiO₂ particles is above 10 mM SLS. The role of HD in the recipe was studied for an artificial latex containing no TiO₂ and one prepared at 11% PVC, in terms of particle size before and after solvent stripping, and its effect on the T_g. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4504–4516, 2006     

Dense Al2O3/ZrO2 Particulate Composites by Free Sintering of Coated Powders

Composite powders, prepared by coating coarse ZrO₂ particles with fine Al₂O₃ powder using a chemical precipitation technique, were compacted and sintered freely at a constant heating rate of 4°C/min to ∼1600°C. Composites containing up to ∼30 vol% inclusions were sintered to nearly full density under the same conditions used for the unreinforced matrix. Furthermore, the sintering kinetics were not influenced significantly by the inclusion volume fraction. The sinterability of the composites formed from the coated powders was significantly better than that for similar composites formed from mechanically mixed powders. The present data provide a further demonstration that the use of coated powders may have widespread applicability for the fabrication, by free sintering, of dense ceramic particulate composites.     

HColonies: a new hybrid metaheuristic for medical data classification

Medical data feature a number of characteristics that make their classification a complex task. Yet, the societal significance of the subject and the computational challenge it presents has caused the classification of medical datasets to be a popular research area. A new hybrid metaheuristic is presented for the classification task of medical datasets. The hybrid ant–bee colonies (HColonies) consists of two phases: an ant colony optimization (ACO) phase and an artificial bee colony (ABC) phase. The food sources of ABC are initialized into decision lists, constructed during the ACO phase using different subsets of the training data. The task of the ABC is to optimize the obtained decision lists. New variants of the ABC operators are proposed to suit the classification task. Results on a number of benchmark, real-world medical datasets show the usefulness of the proposed approach. Classification models obtained feature good predictive accuracy and relatively small model size.     

Rheological behaviour of polysaccharide aqueous solutions

Several data relative to the viscosity of water-soluble polysaccharide solutions were collected from the literature and processed by different rheological models. Some relationships between the viscosity of these polymer solutions, their molecular weight and their solution concentrations, were established and their validity checked. Thus, an accurate equation correlating the viscosity and both the shear rate and the solution concentration of different water soluble polysaccharides (xanthan, hyaluronan, carboxymethylcellulose) was deduced on the basis of Cross' model which suggests two domains in which the viscosity is constant, i.e. very low and very high shear rate ranges. Then, an expression relating the zero-shear viscosity (A) and the concentration of their solutions was proposed. Finally, an alternative equation to that of Mark–Houwink correlating the molecular weight and the intrinsic viscosity of the water-soluble polysaccharides studied in this paper was found.     

Arylidene polymers. XVIII. Synthesis and thermal behavior of organometallic arylidene polyesters containing ferrocene derivatives in the main chain

A new interesting category of organometallic polyesters based on diarylidenecycloalkanones containing ferrocene derivatives in the polymer main chain has been prepared by interfacial polycondensation of 1,1′-dichlorocarbonyl ferrocene or 1,1′-dichlorocarbonyl-4,4′-diiodoferrocene with 2,5-bis(p-hydroxybenzylidene)cyclopentanone, 2,5-divanillylidenecyclopentanone, 2,6-bis(p-hydroxybenzylidene)cyclohexanone, 2,6-divanillylidenecyclohexanone, and 2,7-bis(p-hydroxybenzylidene) cycloheptanone. The resulting polyesters were characterized by elemental analyses, infrared spectroscopy, solubility, and viscometry measurements. The thermal behavior of the synthesized polymers was evaluated by thermal gravimetric analysis and correlated with their structures. The crystallinity of all polymers were examined by x-ray diffraction analysis. Moreover, the electrical conductivity of a selected example of polymer was investigated above the temperature range (300–500 K) and showed that it followed an Arrhenius-type equation with activation energy 2.09 eV. © 1993 John Wiley & Sons, Inc.     

Studies on the pulping of egyptian cotton linters by the nitric acid process

Egyptian cotton linters were pulped by the nitric acid process. In order to reduce the high ash and silica contents of the resulting pulps it was found necessary to apply hot refining with sodium hydroxide solution. Different conditions of concentration, temperature, and pressure in the refining step were investigated. Refining before and during bleaching were compared.