Wholly aromatic polyamide-hydrazides I. A viscometrical method for monitoring of condensation polymerization reactions

A simple and practical viscometrical method for monitoring the progress of condensation polymerization reactions was investigated. It consisted of following the reaction mixture capillary flow time as a function of molar ratio of the reacting monomers in a polymerization reaction performed by gradual addition of terephthaloyl chloride (TCI) into solution of p-aminobenzhydrazide (ABH) in N,N-dimethylacetamide (DMA) solvent. The results obtained were compared to those from dilute solution viscometry and light scattering studies. This indicated that the observed increase in the reaction mixture capillary flow time accurately enough reflected the buildup of the molecular weight of growing polymer product during the course of this course of this condensation polymerization reaction and that this viscometrical monitoring method provided an extremely practical tool for controlled preparation of the polymers of high and/or predetermined molecular weights by this synthetic route. A series of para-oriented, wholly aromatic amide–hydrazide polymers from ABH and TCl, was also characterized by viscometry and light scattering in DMA at 20°C, and the following viscosity–molecular weight relationship was determined: [η] = 5.16 × 10^?4M?.     

Determination of the particle interactions,rheology and the surface roughness relationship for dental restorative ceramics

The effect of inter-particle interactions on the slurry properties and the final surface roughness of the dental ceramic restoratives was investigated. A commercial dental ceramic powder, IPS Empress 2 veneer, was used as the raw material.The magnitudes of the particle–particle interactions were computed by the DLVO theory for the ceramic slurries of different electrolyte solutions (0.1 M, 0.25 M, 0.5 M, 0.75 M, 1 M NaCl and CaCl₂). As expected, the energies of particle–particle interactions were influenced significantly by the presence of electrolytes. These computations demonstrated that addition of electrolytes leads to a progressive depression of the repulsive double layer forces. The absence of these forces should inevitably lead to agglomeration caused by the ever-present van der Waals forces.The rheological measurements carried out using the slurries with same solution properties supported the findings of the DLVO computations. It was found that dental ceramic slurries showed a Newtonian behavior in the absence of electrolytes, which is indicative of little or no agglomeration in the slurry. On the other hand, the same slurries displayed a non-Newtonian, shear thinning behavior in the presence of electrolytes which can be attributed to agglomeration or gelation.Roughness of the ceramic surfaces produced from these slurries was studied by SEM analysis and profilometer measurements. Contact angle studies were also carried out on the same surfaces. It was observed that the surface became rougher initially with electrolyte addition to a maximum, most probably due to formation of isolated agglomerates due to a reduction of the repulsive double layer forces. After reaching a maximum, surface roughness decreased to a much lower value with further increase in electrolyte concentration. This was most probably caused by the formation of a relatively homogeneous, gel-like structure within the extensively agglomerated slurry due to a complete collapse of the double layer.     

Multi-time-scale analysis of a power system

A time-scale separation procedure is outlined and applied to a three machine interconnected power system modeled with flux linkage and voltage regulator dynamics. Partial models such as the electromechanical model and single machine-infinite bus model are used to identify the slow and fast states of the systems. Linear simulation results in two- and four-time-scales demonstrate the potential applicability of the singular perturbation approach to long-term dynamic studies of power systems.     

Role of CO2 During Oxidative Dehydrogenation of Propane Over Bulk and Activated-Carbon Supported Cerium and Vanadium Based Catalysts

Catalysis Letters - CeO2, V2O5 and CeVO4 were synthesised as bulk oxides, or deposited over activated carbon, characterized by XRD, HRTEM, CO2-TPO, C3H8-TPR, DRIFTS and Raman techniques and tested...     

Performance Analysis of Interference-Limited Mobile-to-Mobile κ–μ Fading Channel

Wireless Personal Communications - In this paper, a wireless cooperative network, with two sections, operating over multipath mobile-to-mobile interference-limited fading channel is considered. The...     

Efficient catalytic abatement of greenhouse gases: Methane reforming with CO2 using a novel and thermally stable Rh–CeO2 catalyst

2% Rh–CeO₂ catalyst was synthesized using the hard template method and characterized by means of N₂ adsorption/desorption, XRD and H₂-TPR methods. The prepared powdered catalyst exhibited high thermal stability and high surface area with negligible sintering during 24-h exposure to 973 K in an inert atmosphere. During the temperature programmed methane dry reforming reaction between 473 and 1073 K, an increase in the molar H₂/CO ratio from 0.3 at 623 K to as high as 0.96 at 1073 K was observed. Besides H₂ and CO, H₂O was identified among reaction products, originating from the simultaneously occurring reverse water-gas shift reaction. During the isothermal test performed at 923 K, the 2% Rh–CeO₂ catalyst exhibited stable performance and produced syngas with the average H₂/CO ratio equal to 0.62. A relative drop of catalyst activity equal to 11% was observed within 70-h time on stream at 1023 K, with the average H₂/CO ratio at the reactor outlet equal to 0.71.     

Side reactions in the synthesis of triblock copolymers of nylon‐6 with telechelic oligomers

BACKGROUND: The polymerization of hexanelactam (HL) is complicated by numerous side reactions: chain transfer to monomer, termination of the polymer chain, exchange as transamidation and formation of β‐ketoimides and β‐ketoamides. The generation of by‐products and their effect on the anionic polymerization of HL in the bulk in the presence of functionalized tetrahydrofuran oligomers as polymeric activators (PACs) were investigated. RESULTS: In order to consider how side reactions influence the process of HL polymerization, qualitative and quantitative determination of the by‐products obtained and their exhaustion were carried out. An investigation of the polymerization kinetics and the formation of low molecular weight by‐products through the polymerization was performed. The products are further involved in the polymerization process and consumed until an equilibrium level is reached. The mechanism of their generation is discussed. These processes were followed during the first polymerization stage by means of gel permeation chromatography. A mechanism of by‐product formation and consumption is proposed. CONCLUSION: The investigation of the polymerization kinetics and the formation of low molecular weight by‐products through the polymerization has shown that the side reaction yields oligomeric HL‐based products. The products are further involved in the polymerization process and consumed until an equilibrium level is reached. The equilibrium values depend on the HL/PACs ratio. Copyright © 2008 Society of Chemical Industry     

The emerging liquid biofuel market in Argentina: Implications for domestic demand and international trade

While the world's transport energy matrix is still strongly linked to limited and heavily polluting fossil fuels, new markets are appearing for the production and use of alternative transport fuels, such as liquid biofuels. Due to an interconnected global economy, such markets today are developing on a global scale with actors looking to meet local as well as potential international demand. The aim of this paper is to describe and evaluate the emergence of markets for liquid biofuels in Argentina. It reveals that biodiesel production for international supply is likely to emerge in the short run (up to 2010), giving the opportunity to be switched back to local supply in the medium run (post-2010). It also suggests that a bioethanol market (demand and supply) does not seem to be likely in the short run, and it is highly uncertain in the medium run as the most influential actors oppose its development. On the other hand, the current constellations of the biodiesel market appear to leave many uncertainties regarding its sustainability, especially in regard to a limited role of small and medium sized enterprises, and a suitable and diversified biodiesel feedstock. Currently, the focus lies solely on (very) large-scale production of biodiesel derived from soybean oil for the export market.