R. T. Milner elected president of A.O.C.S. for 1947–48

Journal of the American Oil Chemists' Society -     

New hydroxyapatite–hydrotalcite composites I. synthesis

The synthesis and characterization of original materials, composed by hydrotalcite and hydroxyapatite, is discussed. All the syntheses were carried out in presence of microwave irradiation during the crystallization step. The interactions between the two compounds depend on the synthesis procedure. If hydroxyapatite is incorporated to hydrotalcite, the first compound is encapsulated by hydrotalcite. Instead, if hydroxyapatite is first prepared, the resulting solid is essentially a hydrotalcite with interlayered hydroxyapatite. When the composite material is synthesized by a simultaneous coprecipitation, the small clusters of hydroxyapatite and hydrotalcite are homogeneously dispersed. Consequently, the specific surface area and the particle size vary.     

Hybrid PP–EPR–GF composites. Part 1 – Deformation mechanisms

Abstract

The modification of polypropylene (PP) with a combination of ethylene/propylene rubber (EPR) and glass fibres (GF) is a well known route to improving its mechanical properties. This is because the reductions in stiffness and strength due to the presence of rubber particles are more than compensated by the addition of short glass fibres. This study has focused on the combined effects of glass fibres and rubber particles on the mechanical properties and mechanisms of deformation in PP–EPR–GF hybrid composites. Several composites with different amounts of rubber and short glass fibres were examined. To study possible synergistic effects, the total combined weight fraction of rubber and fibres was kept constant at 20%. The results of tensile tests show that the addition of glass fibres to PP–EPR blends promotes yield strength and modulus while reducing elongation at break. Optical microscopy shows that, in the damage zones of all specimens, deformation bands, which appear similar to crazes, are visible after stretching. Scanning electron microscopy shows crazelike features including some voids, which tend to deviate from in plane propagation near the ends of glass fibres. The dominant mechanism of deformation in PP–EPR–GF observed in this work appears to be a crazelike type of damage, which is believed to be highly localised dilatational shear banding, propagating via repeated cavitation.     

Preparation of Li–Mn–O thin films by r.f.-sputtering method and its application to rechargeable batteries

Spinel-LiMn₂O₄ thin films were fabricated on stainless steel substrate by the r.f.-sputtering method. They were annealed within the range 400–700 °C for 1 h in O₂ and their electrochemical performance was compared to that of as-deposited film. The thin films were characterized by X-ray diffractometry and electron spectroscopy for chemical analysis (ESCA). Charge–discharge tests were carried out in an LiClO₄/propylene carbonate solution. The films heat-treated at 400–700 °C exhibited excellent cyclability over a wide potential region from 2.0 to 4.3 V vs Li/Li⁺.     

Determining flammability limits by analyzing diffusive-thermal flame instability. methane–air–diluent mixture

This paper describes the method for determining flammability limits with the use of equations for diffusive-thermal stability boundaries. The key parameter responsible for the existence of flammability limits is the thermal effect produced by the combustion of gas mixtures. The thermal effect and the equation for diffusive-thermal stability boundaries are used to determine a minimum flame temperature below which combustion is impossible. Flammability limits are significantly affected by the heat capacity of components of the mixture if it is strongly dependent on temperature. For upper and lower flammability limits, a minimum flame temperature is generally different and dependent on the relative concentration and properties of the diluent. The theoretical methods for calculating flammability limits are tested according to the experimental data on the combustion of a methane–air–diluent mixture.     

NOVEL LOW-COST JUTE–POLYESTER COMPOSITE. II. SEM OBSERVATION OF THE FRACTURED SURFACES

The scanning electron micrographs (SEM) were taken at different magnifications with respect of the fractured surfaces of the polymer composites prepared from unsaturated polyester resin and jute sliver with 60% fiber loading by weight. The composite specimens were prepared using both untreated (control) and chemically modified (bleached) jute fibers by solution impregnation and hot curing methods and are designated as JPH-60(C) and JPH-60(B), respectively. The method of preparation of the composite specimens have been discussed. The specimens were subjected to tensile and flexural tests and the fractured surfaces were observed under SEM as stated. The fiber surface morphology was also studied from the SEM photographs in the case of the control and bleached jute filaments. The SEM photographs of the fractured surfaces of the composites showed varied extents of fiber pull-outs under both tensile and flexural failure modes. The nature of interfacial adhesion has been discussed on the basis of the SEM study. A good correlation between the SEM study and the mechanical strength properties of the composites could be established. Exceptionally high flexural strength of the composites JPH-60(B) compared to JPH-60(C) could be explained from the SEM study.