Synthesis and properties of BCDA‐based polyimide–clay nanocomposites

Bicyclo[2.2.2]oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride (BCDA)‐based polyimide–clay nanocomposites were prepared from their precursor, namely polyamic acid, by a solution‐casting method. The organoclay was prepared by treating sodium montmorillonite (Kunipia F) clay with dodecyltrimethylammonium bromide at 80 °C. Polyamic acid solutions containing various weight percentages of organoclay were prepared from 4,4′‐(4,4′‐isopropylidenediphenyl‐1,1′‐diyldioxy)‐dianiline and BCDA in N‐methyl‐2‐pyrrolidone containing dispersed particles of organoclay at 20 °C. These solutions were cast on a glass plate using a Doctor's blade and then heated subsequently to obtain nanocomposite films. The nanocomposites were characterized using Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal mechanical analysis, dynamic mechanical analysis, polarizing microscopy, scanning electron microscopy, transmission electron microscopy, wide‐angle X‐ray diffraction (WAXD) and thermogravimetric analysis. The glass transition temperature of the nanocomposites was found to be higher than that of pristine polymer. The coefficient of thermal expansion of the nanocomposites decreased with increasing organoclay content. WAXD studies indicated that the extent of silicate layer separation in the nanocomposite films depended upon the organoclay content. Tensile strength and modulus of the nanocomposite containing 1% organoclay were significantly higher when compared to pristine polymer and other nanocomposites. The thermal stability of the nanocomposites was found to be higher than that of pristine polymer in air and nitrogen atmosphere. Copyright © 2007 Society of Chemical Industry     

Organocatalytic Application of Direct Organo-Functionalized Mesoporous Catalysts Prepared by Microwave

The organic functional groups such as primary and quaternary amine, sulfonic acid, and amino acid, especially l-proline, have been tried to immobilize onto mesoporous materials by the direct synthesis method using microwave. Microwave induced direct functionalization enabled to get well ordered mesoporous structures and stable organic tethered groups with enhanced hydrothermal stability due to more hydrophobic surfaces as well as enhanced activity. The method is also useful for overcoming several shortcomings in the post-synthesis grafting method which suffers from pore blocking at the aperture, and difficulties in controlling the as obtained from the direct co-condensation method had their functional groups spatially loadings, as well as the dispersion of active sites. The organo-functionalized mesoporous silica dispersed on the surface which could play roles as single site catalysts. Direct tethering of organic functional groups was preferably synthesized by microwave, gave morphological control and illustrated superiority in some organocatalytic application such as Knoevenagel and Henry reactions base catalytic reaction, Claisen–Schmidt condensation, and diethyl malonate addition reactions.     

Comparison of the morphology and structure of WO3 nanomaterials synthesized by a sol-gel method followed by calcination or hydrothermal treatment

Tungsten (VI) oxide (WO₃) nanomaterials were synthesized by a sol-gel method using WCl₆ and C₂H₅OH as precursors followed by calcination or hydrothermal treatment. X-Ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) equipped with energy dispersive X-ray spectroscopy (EDX) were used to characterize the structure and morphology of the materials. There were significant differences between the WO₃ materials that were calcinated and those that were subjected to a hydrothermal process. The XRD results revealed that calcination temperatures of 300°C and 400°C gave hexagonal structures and temperatures of 500°C and 600°C gave monoclinic structures. The SEM images showed that an increase in calcination temperature led to a decrease in the WO₃ powder particle size. The TEM analysis showed that several nanoparticles agglomerated to form bigger clusters. The hydrothermal process produced hexagonal structures for holding times of 12, 16, and 20 h and monoclinic structures for a holding time of 24 h. The SEM results showed transparent rectangular particles which according to the TEM results originated from the aggregation of several nanotubes.     

Effect of tocopherols,tocotrienols, β-carotene,and chlorophyll on the photo-oxidative stability of red palm oil

Effect of tocols, β-carotene, and chlorophyll on photo-oxidative stability of red palm oil (RPO) were studied. Model systems of triacylglycerols+tocols, triacylglycerols+β-carotene, triacylglycerols +tocols+β-carotene, and triacylglycerols+tocols+β-carotene+chlorophyll were exposed to fluorescent light at intensities of 5,000, 10,000, and 15,000 lux for 7 h at 30±2°C. Changes in concentrations of tocopherols, tocotrienols, β-carotene, chlorophyll, and peroxide values were evaluated every hour. Light intensity accelerated degradation of tocols in the triacylglycerols+tocols system and β-carotene in the triacylglycerols+β-carotene system. Gamma-tocotrienol showed the highest degradation rate and β-carotene was the most sensitive compound to changes in light intensity, indicated by the lowest light intensity coefficient (z_i) value. The presence of tocols and β-carotene together showed protective effects for the photo-oxidative stability of RPO. The presence of chlorophyll increased the rate of photo-oxidation at high light intensities. Interactions between tocols and β-carotene contributed to the photo-oxidative stability of RPO.     

A literature review on MHE selection problem: levels,contexts, and approaches

This paper presents a review on selection problem of material handling equipment (MHE) and general equipment used in industry area. The issue on MHE is widely paid attention since MHE has contribution on material, good and product accomplishment. Few methods and softwares have been proposed and developed to select the most appropriate MHE for a complex selection problem. Today’s high diverisity of MHE categories and types influence the generation of many possible choices which leads to the complexity. In this paper, a further discussion in terms of MHE and equipment including three major points namely level of selection, the context of selection problem and the approaches are served to highlight the complex MHE selection according to the number of possible choices provided, to analyse the consideration for the problem context, and to reveal the superior method for complex MHE selection. Forty-two papers collected from the past study are presented asscociating each point of the discussion.     

Variability of geotechnical parameters of lateritic gravels overlying contrasted metamorphic rocks in a tropical humid area (Cameroon): implications for road construction

Bulletin of Engineering Geology and the Environment - The variability of the geotechnical properties of lateritic gravels developed on metamorphic rocks from the same clay protolith and of a nearby...     

Synthesis of short-channeled amino-functionalized SBA-15 and its beneficial applications in base-catalyzed reactions

Amino-functionalized-SBA-15 catalysts with nanostructured hexagonal platelet morphologies were synthesized directly by using microwave synthesis from the hydrolysis and co-condensation of aminopropyltriethoxysilane (APTES) and sodium metasilicate under a strong acidic condition with the Pluronic P123 triblock copolymer as a structure-directing agent. The amino-functionalized-SBA-15 catalysts were proven by SEM and TEM techniques to have very short channels in the range of 200–300 nm perpendicular to the hexagonal platelet morphologies. These short-channeled catalysts were proven to be effective heterogeneous catalysts in liquid-phase reactions such as Knoevenagel and Claisen-Schmidt condensations as well as in Henry reaction. They exhibited greatly improved catalytic activities over the typical fibrous type SBA-15 catalyst having long channels. Obviously, the easy diffusion and rapid mass transfer of substrate into the short channel mesopores played important roles in the significant improvement in the catalytic activities.     

Tangible nanocomposites with diverse properties for heart valve application

Cardiovascular disease claims millions of lives every year throughout the world. Biomaterials are used widely for the treatment of this fatal disease. With the advent of nanotechnology, the use of nanocomposites has become almost inevitable in the field of biomaterials. The versatile properties of nanocomposites, such as improved durability and biocompatibility, make them an ideal choice for various biomedical applications. Among the various nanocomposites, polyhedral oligomeric silsesquioxane-poly(carbonate-urea)urethane, bacterial cellulose with polyvinyl alcohol, carbon nanotubes, graphene oxide and nano-hydroxyapatite nanocomposites have gained popularity as putative choices for biomaterials in cardiovascular applications owing to their superior properties. In this review, various studies performed utilizing these nanocomposites for improving the mechanical strength, anti-calcification potential and hemocompatibility of heart valves are reviewed and summarized. The primary motive of this work is to shed light on the emerging nanocomposites for heart valve applications. Furthermore, we aim to promote the prospects of these nanocomposites in the campaign against cardiovascular diseases.