Flame retardation of polypropylene: Effect of silane treated antimony compounds

Flame retardation of polypropylene was accomplished by blending with antimony compounds (Sb₂O₃ and SbPO₄) in conjunction with polyvinyl chloride (PVC) or ferric oxide. The compatibility and dispersion of antimony compounds in the polymer matrix was enhanced by using silane coupling agents, viz., vinyltriethoxysilane (A-151) and γ-aminopropyltriethoxysilane (A-1100). Rheological properties of filled polypropylene were studied in the temperature range 180 to 220°C at shear rates of 29.5 to 119.5 sec^?1. An increase in the melt viscosity was found in the filled polypropylene as compared to virgin polymer. Silanation of antimony compounds also influenced the melt rheology of flame retardant polypropylene. Incorporation of 6 phr Sb₂O₃ and 19 phr PVC raised the oxygen index of polypropylene to 22.9 and this sample was found to be self extinguishing in 65 s with a burning rate of 0.06 mm/s as compared to 1.1 mm/s for unfilled polypropylene. Though silanation of antimony compounds slightly reduced the oxygen index of flame retardant polypropylene, yield strain and flexural rigidity of injection molded samples was improved over unsilanated flame retardant polymer.     

The aeronomy experiment

The experiments described here were flown onAryabhata and were mainly designed to study the global distribution of suprathermal electrons, ionosphere-magnetosphere coupling, theF-region anomaly and the hydrogen geocorona. The experiments consisted of a retarding potential analyser and two ultraviolet ion chambers. The former was designed for the measurement of the flux of suprathermal electrons in the earth’s atmosphere while the latter was for measuring the intensity of the resonantly scattered hydrogen Lyman alpha (1216 Å) and photoelectronically excited OI (1304 Å) emissions.     

Steady flow simulation in irrigation canals

A mathematical model is developed for the analysis of spatially varied steady flow in irrigation canals. The model accounts for canal seepage and effect of control structures at the upstream and downstream ends of the canal. Two computational methods developed to solve the spatially varied steady flow equations for the irrigation canals are presented here. The governing differential equations are solved iteratively using fourth order explicit Runge-Kutta method. The model results are verified with experimentally observed water surface profiles available in literature. The effects of bed seepage, canal condition and backwater curves on the discharge carrying capacity and variation of flow depth are studied through model application on a canal reach. It is found, that in most of the situations the backwater curves spread sufficiently upstream and significantly affect the performance of the control structure at the upstream end. In many situations, it may not even be possible to operate the canal at design discharges.     

Anomalous Poole-Frenkel effect observed in some polyenes in sandwich cell configuration

Both the dark- and photo-current-voltage characteristics of zeaxanthin and lutein is ohmic in the lower field regime followed by non-ohmic behaviour in the higher voltage regime, which has been satisfactorily explained by the anomalous Poole-Frenkel effect. A single dominant donor level is the major contributor to the dark-current while a single dominant trap level is the major contributor to the photo-current, both levels have been identified from Arrhenius type plots. Photo-action spectra suggest that the predominant mechanism of charge carrier generation is the same both in dark and illuminated conditions.     

Poly(3- hydroxybutyrate)/Bioglass(®) composite films containing carbon nanotubes

Poly(3hydroxybutyrate) (P(3HB))/Bioglass(?)?composites incorporating multiwalled carbon nanotubes (MWCNTs) have been successfully prepared by the solvent casting technique. The microstructure, electrical properties and bioactivity of the composites were characterized using scanning electron microscopy, x-ray diffraction and current-voltage measurements. Different concentrations of MWCNTs were used to determine their effect on the electrical properties of the composites. MWCNTs and Bioglass(?) particles were found to be homogeneously dispersed throughout the P(3HB) matrix. The electrical resistance of the composite samples decreased on increasing the MWCNT concentration, as expected. An in vitro degradation study in simulated body fluid (SBF) was carried out on composite samples. The formation of hydroxyapatite on the surfaces of P(3HB)/Bioglass(?)/MWCNT composite films was confirmed after two months of immersion in SBF. This hydroxyapatite layer was not formed on the neat polymeric films and on composites containing MWCNTs only (without Bioglass(?)). It was found that the presence of MWCNTs did not hinder the bioactivity of the Bioglass(?) particles, as confirmed by SEM and XRD studies on composite samples.     

Preparation and Properties of Vinylester Resin/Clay Nanocomposites

Summary: Vinylester resin matrix composites were fabricated with 1, 3, 5 and 10 wt.‐% loadings of organoclay. The composite samples were subjected to various characterization techniques like X‐ray diffraction, flexural testing, dynamic mechanical analysis, thermogravimetric analysis, and scanning electron microscopy. The clay samples as well as the clay–resin composites were investigated by X‐ray diffraction. From the shift in the peak positions and the change in d‐spacing values, it was evident that there was intercalation in the 10 wt.‐% composites, whereas exfoliation occurred in the 1, 3, and 5 wt.‐% composites. The flexural strength and the breaking energy of all the composites were decreased compared with the unfilled resin, but there was an increase in flexural modulus value by 13%. From the dynamic mechanical analysis of the 3 and the 5 wt.‐% composites, it was observed that the loss modulus value was higher in the 3 wt.‐% composites, but the glass transition temperature was slightly higher in the 5 wt.‐% composites. Thermal degradation behavior was also improved in the 5 wt.‐% composites compared with the 3 wt.‐% composites.

Fracture surface of 3 wt.‐% clay filled vinylester resin matrix composite in different magnifications.     

Recent advances in biodegradable nanocomposites

There is growing interest in developing bio-based products and innovative process technologies that can reduce the dependence on fossil fuel and move to a sustainable materials basis. Biodegradable bio-based nanocomposites are the next generation of materials for the future. Renewable resource-based biodegradable polymers including cellulosic plastic (plastic made from wood), corn-derived plastics, and polyhydroxyalkanoates (plastics made from bacterial sources) are some of the potential biopolymers which, in combination with nanoclay reinforcement, can produce nanocomposites for a variety of applications. Nanocomposites of this category are expected to possess improved strength and stiffness with little sacrifice of toughness, reduced gas/water vapor permeability, a lower coefficient of thermal expansion, and an increased heat deflection temperature, opening an opportunity for the use of new, high performance, lightweight green nanocomposite materials to replace conventional petroleum-based composites. The present review addresses this green material, including its technical difficulties and their solutions.     

Secondary electromagnetic radiation during plastic deformation and crack propagation in uncoated and tin coated plain-carbon steel

This paper presents some new results on the emission of electromagnetic radiation (EMR) during plastic deformation, crack initiation and propagation, and fracture of uncoated and tin–coated 0.15% carbon steel sheets. Intermittent EMR emissions have been observed even at stationary loading, which we term as secondary EMR emissions. These results are expected to provide an insight into the micro-mechanism of dislocation relaxation dynamics in metallic materials.     

Parametric study of the effect of phase anisotropy on the micromechanical behaviour of dentin-adhesive interfaces.

A finite element (FE) model has been developed based upon the recently measured micro-scale morphological, chemical and mechanical properties of dentin-adhesive (d-a) interfaces using confocal Raman microspectroscopy and scanning acoustic microscopy (SAM). The results computed from this FE model indicated that the stress distributions and concentrations are affected by the micro-scale elastic properties of various phases composing the d-a interface. However, these computations were performed assuming isotropic material properties for the d-a interface. The d-a interface components, such as the peritubular and intertubular dentin, the partially demineralized dentin and the so-called "hybrid layer" adhesive-collagen composite, are probably anisotropic. In this paper, the FE model is extended to account for the probable anisotropic properties of these d-a interface phases. A parametric study is performed to study the effect of anisotropy on the micromechanical stress distributions in the hybrid layer and the peritubular dentin phases of the d-a interface. It is found that the anisotropy of the phases affects the region and extent of stress concentration as well as the location of the maximum stress concentrations. Thus, the anisotropy of the phases could effect the probable location of failure initiation, whether in the peritubular region or in the hybrid layer.