Effect of carbonization time on the structure and electromagnetic parameters of porous-hollow carbon fibres

A series of polyacrylonitrile-based porous-hollow carbon fibres (PAN-PHCFs) were prepared by carbonizing PAN porous-hollow cured fibres at 1073 K for different times in nitrogen. The effects of carbonization time on the structure, electrical volume conductivity and electromagnetic parameters were investigated. Results indicate that the degree of graphitization increases as carbonization time increases. The electrical volume conductivity increases as the degree of graphitization and carbonization time increase. The real and imaginary parts of the complex permittivity (′ and ″) increase with carbonization time increasing. The values of ′ and ″ of composites of PAN-PHCFs and paraffin are 13.76 and 10.09 when the carbonization time is 240 min, and the electrical volume conductivity of PAN-PHCFs is 190.47 Ω⁻¹ m⁻¹.     

Novel synthesis of -caprolactam from cyclohexanone-oxime via Beckmann rearrangement over mesoporous molecular sieves MCM-48

Vapor-phase synthesis of -caprolactam (-C) from cyclohexanone-oxime (CHO) has been studied at 1 atm and 300–400 °C using SiMCM-48 and AlMCM-48(X) with Si/Al molar ratios X in a fixed-bed, continuous flow reactor. The catalysts were characterized with ICP-AES, XRD, TEM, FT-IR, N₂-adsorption, ²⁷Al and ²⁹Si MAS NMR and TPD of ammonia. An increase of X value in AlMCM-48(X) enhances both the BET surface area and the unit cell parameter but diminishes the acid amount. In the reaction of CHO, benzene, toluene, ethanol and 1-hexanol were utilized as solvents. The CHO conversion increases with the reaction temperature, whereas the -C selectivity exhibits the opposite trend due to side reactions. The catalyst stability is greatly enhanced by using ethanol and 1-hexanol as the solvents due to their production of water vapor via dehydration. Excellent catalytic performance of AlMCM-48(10) is attained at 1 atm, 350 °C and W/Fc 74.6 g h/mol by using 1-hexanol in the feed; the CHO conversion and the -C selectivity exhibit higher than 99% and 90%, respectively, during at least 130 h process time.     

Molecular dynamics in chlorinated butyl rubber containing organophilic montmorillonite nanoparticles

The dynamic mechanical loss tangent (tanδ) of chlorinated butyl rubber (CIIR) shows an asymmetrical double-peak structure with a shoulder on the low-temperature side and a maximum on the high-temperature side, which are attributed to local segmental motion and Rouse modes, respectively. To study the effect of nanoparticles on these two different modes of molecular motion, organophilic montmorillonite nanoparticles (OMMT) were incorporated into CIIR. With the increase of OMMT weight fraction, a filler network is formed and becomes more and more compact in the CIIR matrix, which exerts significant effect on the molecular dynamics of CIIR. The maximum and the shoulder of the tanδ peak are both suppressed by the filler network, but the maximum is suppressed to a higher extent and finally even becomes lower than the shoulder at high filler loading. The temperature position of the maximum is also shifted toward lower temperature with the formation of the filler network, while that of the shoulder remains nearly constant. These phenomena can be interpreted in terms of the different restriction extents of the filler network on the different modes of molecular motion.     

Fischer-Tropsch Synthesis: Catalyst activation of low alpha iron catalyst

Activation with three different gases (H₂, CO and synthesis gas) over an Fe100/K1.4/Si4.6/Cu2.0 catalyst was conducted to investigate the effects of pretreatment gas on Fischer-Tropsch Synthesis (FTS) activity and selectivity. Catalyst slurry was withdrawn from the reactor at increasing time intervals of FTS for Mössbauer spectroscopic analysis. Activation with CO produced the highest syngas conversion while H₂ generated the lowest; syngas activation produced a slightly lower conversion than CO activation. CO activation transformed the majority of the iron into χ-Fe₅C₂ and Magnetite with only 12% -Fe_2.2C being detected. Unlike the CO activated catalyst, the syngas activated iron catalyst resulted in a lower amount of χ-Fe₅C₂ than -Fe_2.2C. The initial high (64%) content of -Fe_2.2C decreased gradually to below 30% while CO conversion decreased from 83% to 55%. During this period, χ-Fe₅C₂ increased from initial 10% to 33%. Magnetite changed little during the process while the form of carbides interchanged. Hydrogen activation yielded a low CO conversion of 50% and only 8% χ-Fe₅C₂ and 16% -Fe_2.2C was formed while Magnetite was as high as 75% after the FTS reaction rate became constant. Although activation gas type had a significant effect on syngas conversion, hydrogen, syngas and CO activations produced similar H₂ to CO usage ratio, hydrocarbon product distribution, olefin fraction, alpha value and CO₂ selectivity.     

A novel route to α,ω-telechelic poly(-caprolactone) diols, precursors of biodegradable polyurethanes, using catalysis by decamolybdate anion

A new convenient route for the synthesis of poly(-caprolactone) (PCL) with α,ω-telechelic diols' end-groups is presented. Synthesis of α,ω-telechelic PCL diols (HOPCLOH) was achieved by ring-opening polymerization (ROP) of -caprolactone (CL) catalyzed with ammonium decamolybdate (NH₄)₈[Mo₁₀O₃₄] and using diethylene glycol (DEG) as initiator. Obtained HOPCLOH was characterized by ¹H and ¹³C NMR, FT-IR, GPC and MALDI-TOF. Comparative studies demonstrate that ammonium decamolybdate (NH₄)₈[Mo₁₀O₃₄] is better catalyst than Sn-octanoate (SnOct₂) toward CL polymerization in presence of DEG, under the conditions tested. A biodegradable poly(ester-urethane-urea) derivative was efficiently prepared from synthesized HOPCLOH. Obtained polymer shows minor differences with respect to the properties recorded for a poly(ester-urethane-urea) obtained from commercial HOPCLOH.     

Modelling of heat transfer and hydrodynamic with two kinetics approaches during supercritical water oxidation process

Supercritical water oxidation is an innovative and very efficient process to treat hazardous organic waste. In order to better understand the complex physic phenomena involved in this process, and to design more efficient reactors or to insure future efficient scale-up, a simulation with the Computational Fluid Dynamics software FLUENT was carried out for a simple tubular reactor.The turbulent non-reactive flow is well-represented using the k– model. Nevertheless, the k–ω model gives better results when a source term is added to take into account the chemical reaction.Two approaches are used to model the reaction rate: an Arrhenius law and the Eddy Dissipation Concept (EDC) generally used to describe combustion reactions.The results of this simulation using Arrhenius law, are in good agreement with experimental data although a simple thermohydraulic model was used. Moreover, the sensitiveness to the inlet temperature has been demonstrated. It influences the reaction start-up and the shape of the measured wall temperature peak. Equally, the simulated temperature profiles using Eddy Dissipation Concept model are in good agreement with experimental ones. Hence, the two approaches give similar results. Nevertheless, the EDC model predicts more precisely the thermal peak location at the reactor wall.     

Novel synthetic strategy toward shape memory polyurethanes with a well-defined switching temperature

Shape memory polyurethanes (SMPUs) have been synthesised via a novel synthetic methodology, resulting in an improvement of the phase separation in the multi-block structure of the polyurethane and in its shape memory properties. ABA block copolymers based on semi-crystalline poly(-caprolactone) and amorphous poly(propylene oxide) (PPO) were used as precursor for the SMPUs. For their synthesis, poly(-caprolactone) diols have been converted into isocyanate end-capped prepolymers by using a mixture of 3(4) isocyanato-1-methyl-cyclohexylisocyanate isomers, after which a coupling with low-T_g poly(propylene oxide) oligomers is done. The shape memory polymers are obtained by reaction of the ABA block copolymers with hexamethylenediisocyanate and 1,4-butanediol as chain extender. Using this new strategy, a flexible segment (PPO) was introduced between the hard and the switching segments of the SMPU. For comparison, SMPUs without flexible segment have also been prepared with the conventional synthetic route. DSC, isostrain experiments and cyclic shape memory tests revealed narrower switching temperatures for the SMPUs including a flexible segment.     

Development of mesoporous Al,B-MCM-41 materials: Effect of reaction temperature on the catalytic performance of Al,B-MCM-41 materials for the cyclohexanone oxime rearrangement

A series of aluminum–boron–silicate MCM-41 mesoporous materials and their counterparts treated with NH₄F aqueous solution were synthesized and characterized by using XRD, MAS NMR, nitrogen physisorption, DRIFT, TG-DTA, TP/MS and pyridine adsorption. All of the samples showed typical MCM-41 structural and textural properties. ²⁷Al MAS NMR showed that the aluminum environment was mainly four-coordinated and six-coordinated aluminum for non-fluorinated samples and fluorinated ones, respectively. Boron was in the trigonal framework environment at ca. catalytic reaction temperatures and the NH₄F treatment did not affect the boron environment in our Al,B-MCM-41 materials. All of the Al,B-MCM-41 materials studied contained both Brønsted and Lewis acid sites. However, the strong acid Brønsted/Lewis ratios decreased in the fluorinated catalysts. Moreover, the influence of temperature was studied on the cyclohexanone oxime conversion and the product selectivity in the 623–798 K range. Results indicated that temperatures lower than 748 K favored Beckmann rearrangement to -caprolactam, whereas, at higher temperatures the main reaction was cyclohexanone oxime hydrolysis to cyclohexanone. The aluminum–boron–silicate MCM-41 mesoporous materials treated with NH₄F improved both the selectivity to -caprolactam (related mainly to boron content) and their life span (related to their lower ratios of strong Brønsted/Lewis acid sites).     

Preparation of poly(-caprolactone) grafted titanate nanotubes

This work reported for the first time the surface functionalization of titanate nanotubes (TNTs) with biodegradable poly(-caprolactone) (PCL). A “grafting from” approach based on in situ ring-opening polymerization of -caprolactone from TNTs with a special surface modification was adopted to prepare the PCL-g-TNTs. The thickness of the grafted PCL shell can be controlled by increasing reaction time. After grafted with PCL, both the dissolubility and flexibility of the tubes were greatly improved. The obtained PCL-g-TNTs can easily disperse in several organic solvents, and the dispersal stability depends on solvent polarity and PCL shell thickness. Furthermore, the PCL immobilized on the surface of TNTs still possessed a good biodegradable capacity and could be completely decomposed in the presence of Pseudomonas (PS) lipase. The PCL-g-TNTs reported here are promising in biotechnology applications due to good dissolubility, flexibility, biocompatibility and the tubular nano-structure.     

Viscoelastic changes in chlorinated butyl rubber modified with graphene oxide

The glass–rubber transition region in multiple component systems is significant for studying the slow relaxation processes in amorphous polymers. It is the first time that graphene oxide (GO) is added into chlorinated butyl rubber (CIIR) to study the effect of GO on different relaxation processes of CIIR. We aimed to give a possible insight to the molecular relaxation behaviors of CIIR/GO nanocomposites. In this study, GO was synthesized by a revised Hummers method, and it was incorporated with CIIR at different contents of 0, 1, 2, 3 and 5 phr (parts per hundred rubber). The structure of GO and CIIR/GO nanocomposites was studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), attenuated total reflectance-Fourier transform infrared (ATR-FTIR), scanning electron microscopy (SEM) and transmission electron microscope (TEM).Bound rubber was adopted to study the interfacial interaction between GO and CIIR. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were also performed. Since there were many conflicting results on the effect of nanoparticles in relation to the glass transition temperature (T _g) of polymer matrixes in correlative literature, we investigated the effect of GO on that of CIIR. The T _g determined by DSC shows slight shifting. However, the maximum and the shoulder of tan δ both shift to low temperatures. In addition, GO increases the coupling effect of CIIR, resulting the shoulder merged with the maximum. A mechanism, though still needs to be further refined, has been proposed to interpret the contradictory results in our case.