Studies on Kinetics of Crystallization of PA6／UFAPR Composites

The influence of Ultrafine Full-Vulcanized Acrylate Powdered Rubber(UFAPR) on the isothermal crys-tallization kinetics and nonisothermal crystallization behavior of PA8 has been studied by means of DSC. The results show that with the introduction of a small amount of UFAPR, the crystallization rate of PA8 can be increased obviously, and the crystallization temperature range can be augmented and the crystallite size distri-bution of the crystal can be narrowed down. The change of free energy perpendicular to the crystal nucleus, which has been calculated according to the Hoffman theory, is consistent with the result of Avrami′s equa-tion. The unit surface free energy of the radial-developing crystal spherulite decreases while the crystalliza-tion rate of PA8 increases with the introduction of UFAPR. Meanwhile, it is shown by means of the polariz-ing microscope(PLM) that the crystal size drops down and the number of the crystal grains augments with the addition of UFAPR, which shows that UFAPR can function as a nucleating agent.     

Mechanical Properties,Water Absorption,and Chemical Resistance of Napier Grass Fiber Strand–Reinforced Epoxy Resin Composites

Napier grass fiber strands were used as reinforcement to obtain composites with epoxy resin as matrix. To improve the surface, these fiber strands were treated with alkali solution. The composites were prepared by means of hand lay-up molding, then the effects of Napier grass fiber strand loading on mechanical properties such as tensile, flexural and impact, interfacial bonding, and chemical resistance were investigated. The composite with 20 wt.% Napier grass fiber strands gives excellent mechanical properties and chemical resistance, showing that it has the best bonding and adhesion of the composites. SEM micrographs of fractured and worn surfaces clearly demonstrate the interfacial adhesion between fiber and matrix. Alkali-treated Napier grass fiber strand–reinforced composites have better resistance to water and chemicals than the untreated fiber strand composites.     

Thermal conductivity behavior of SiC–Nylon 6,6 and hBN–Nylon 6,6 composites

A study was performed to determine the effect of the content and orientation of fillers on the thermal conductivity of a polymeric composite packed with hexagonal boron nitride (hBN) and silicon carbide (SiC) fillers. The thermal conductivity behavior of SiC–Nylon 6,6 and hBN–Nylon 6,6 composites was more dependent on the orientation and shape of the filler than on its thermal conductivity. The thermal conductivity of SiC–Nylon 6,6 composites with 59 % (v/v) isotropic SiC fillers increased from 0.25 to 3.83 W/m K. That of hBN–Nylon 6,6 composites with 62 % (v/v) anisotropic hBN fillers increased from 0.25 to 2.16 W/m K in the perpendicular direction whereas in the parallel direction it increased rapidly to 8.55 W/m K .     

Resole-Type Phenol–Formaldehyde Resin with Neutralized Liquid Products of Fast Pyrolysis of Birch Wood

A method of preparation of a phenol–formaldehyde resin by replacing phenol with liquid products of the fast pyrolysis of wood is described. Strength tests reveal that substituting a pyrolysis liquid for 60% of phenol in the phenol–formaldehyde resin allows strength to be increased by 6% relative to the control sample.     

Preparation of Phenolic Resin/Silver Nanocomposites via in-situ Reduction

Polymer/metal nanocomposites have attracted considerable interest because of their potential application in catalysts, electronics, electromagnetics and nonlinear optics1-3. They have been prepared by blending polymer with nanometer metal particles4, reducing polymer-metal ion complexes with reducing agents5, and reducing metal ions in the polymer matrix by high-energy radial irradiation3. In this paper, we report a new approach to phenolic resin/silver nanocomposites, which have potential a…     

Preparation and Characterization of Polyborosiloxanesand Their Blends with Phenolic Resin as ShapeableCeramic Precursors简

Two polyborosiloxanes(PBSis) with char yield up to 74.13% at 800 °C were synthesized by the direct polycondensation of boric acid with phenyltrimethoxysilane in diglyme. The PBSis were characterized by gel permeation chromatography, IR spectroscopy as well as1H-,29Si- and11B-NMR. PBSi modified phenol-formaldehyde resins(PBSi/PFs) were prepared at different PBSi/PF mass ratios and were cured at 150 °C. The PBSi/PFs were characterized by IR spectroscopy, scanning electron microscopy, thermogravimetric analysis and tensile test. The results revealed that the cured PBSi/PFs had sea-island morphology and higher char yield than the common PF. PBSi/PF blend with PBSi/PF mass ratio of 0.4:1 had char yield up to 70.83% at 800 °C. The PBSi/PFs had tensile strength similar to PF. The ceramization of PBSi/PFs was also studied. The silicon boron oxycarbide(SiBOC) ceramics formed were characterized by IR spectroscopy and elemental analysis. This method provided a valuable way to prepare easily shapeable polymer blends as ceramic precursors.     

Kinetics of Reaction Bisphenol-S Epoxy Resin with Methylacrylic Acid

The reaction kinetics of bisphenol-S epoxy resin with methyl-acrylic acid in the presence of quaternary ammonium salt catalyst was studied. The reaction rate constants at different temperatures were determined. The reaction is first order with respect to epoxy group, zero order with respect to methylacrylic acid and 0.71 order with respect to quaternary ammonium salt catalyst, respectively. The mechanism of this reaction was discussed.     

Preparation of Feather Keratin Hydrolyzate‐Gelatin Composites and Their Graft Copolymers

With the aim of utilizing the Keratinous waste material, poultry feather, which is up till now discarded as a waste, was hydrolyzed to form keratin hydrolyzate (FH). As FH does not form a film, it was mixed with gelatin (G) and FH‐G composite was prepared in film form. FH‐G was further graft co‐polymerized with 2‐hydroxyethyl methacrylate (HEMA) to achieve better physico‐chemical properties for the resultant hydrogels. Percentage grafting studies and IR studies confirmed the grafting of PHEMA onto FH‐G. FH‐G‐PHEMA exhibited better mechanical properties compared to FH‐G and FH‐PHEMA. TG studies clearly indicated the grafting of HEMA onto FH and FH‐G. SEM (Scanning Electron Microscopy) pictures of FH‐G and FH‐PHEMA films exhibited brittle nature on their surface, whereas continuity and A smooth surface was observed on for the FH‐G‐PHEMA films.     

Theoretical Study on the Pyrolysis Mechanism and Kinetics of 3-Hydroxy-3-Methyl-2-Butanone

Thethermolysisofpyruvicacid2Ieadstotheeliminationofcarbondioxideandacetaldehydeisformedasanotherproduct.Hong'hasstudiedthemechanismofthereactionintheMINDO/3molecularorbitaltheory.Al-AwadiandEL-Dusouqui'havestudiedthepyrolysisofthe3-hydroxy-3-methyl-2-butanoneinordertoexaminetheinfluenceofthehydrogenatominvolvedintheTransitionStateoftheeliminationprocessandtoassessitscontributiontotherate-controllingstep.TheygaveoutthethermalrateconstantsandhypothesizedthatthereactionmightproceedthroughafO…     

Synthesis,Structures, and Complexation with Phenolic Guests of Acridone-Incorporated Arylene–Ethynylene Macrocyclic Compounds

Acridone units were incorporated into the arylene–ethynylene structure as polar arene units. Cyclic trimers consisting of three acridone-2,7-diyl units and three 1,3-phenylene units were synthesized by Sonogashira couplings via stepwise or direct route. X-ray analysis revealed that the trimer had a nearly planar macrocyclic framework with a cavity surrounded by three carbonyl groups. In contrast, the corresponding tetramer had a nonplanar macrocyclic framework. ¹H NMR measurements showed that the trimer formed a 1 : 1 complex as a macrocyclic host with dihydric phenol guests, and the association constants were determined to be ca. 1.0×10³ L mol⁻¹ for hydroquinone or resorcinol guests in CDCl₃ at 298 K. The calculated structures of these complexes by the DFT method supported the presence of two sets of OH⋅⋅⋅O=C hydrogen bonds between the host and guest molecules. The spectroscopic data of the cyclic trimers and tetramers are compared with those of reference acridone compounds.     

Preparation of Phenolic Resin／Silver Nanocomposites via in—situ Reduciton

Resol type phenolic resin/silver nanocompostie was prepared by in-sinu reduction method,in which the curing of phenolic resin and the formation of silvernano-particles took place simultaneously.The silver ions were reduced completely to silver nanoparticles,which were dispersed homogeneously in the resinmatrix with narrow size distribution.     

Tensile,Electrical Conductivity,and Morphological Properties of Carbon Black–Filled Epoxy Composites

This work investigates the effect of carbon black content on the tensile, electrical, and morphological properties of epoxy matrix. Carbon black–filled epoxy composites were obtained by mixing the desired amount of carbon black from bamboo stem (BS-CB), oil palm empty fruit bunch (EFB-CB), and coconut shell (CNS-CB) with the epoxy resin. Tensile and electrical properties of carbon black from three different sources (BS-CB, EFB-CB, and CNS-CB) used to fill epoxy composite with 5% filler loading were measured and the results indicated improvement in tensile and electrical properties. The diffraction patterns of X-ray diffraction (XRD) indicated nonlinear crystalline amorphous structure of the CB.     

Electrochemical Synthesis of Fe–Cu Composites Based on Copper(II) Ferrite and Their Electrocatalytic Properties

Russian Journal of Electrochemistry - Copper(II) ferrite is synthesized by the co-precipitation method in the absence and in the presence of polyvinyl alcohol which is followed by thermally...     

Kinetics and mechanism of formation of gehlenite,Al–Si spinel and anorthite from the mixture of kaolinite and calcite

The kinetics and mechanism of formation of gehlenite, Al–Si spinel phase, wollastonite and anorthite from the mixture of kaolinite and calcite was investigated by differential thermal analysis under the heating rate from 283 to 293 K min⁻¹ using Kissinger equation. The changes in the phase composition of the sample during the thermal treatment were investigated via simultaneous TG-DTA, in situ high-temperature x-ray diffraction analysis and high-temperature heating-microscopy. The crystallizations of gehlenite and Al–Si spinel phase show apparent activation energy of (411 ± 5) kJ mol⁻¹ and (550 ± 9) kJ mol⁻¹, respectively. The value of kinetic exponent corresponds to the process limited by the decreasing nucleation rate for gehlenite while constant nucleation rate is determined for Al–Si spinel phase. Anorthite crystallizes from the eutectic melt and the process shows the apparent activation energy of (1140 ± 25) kJ mol⁻¹. The process is limited by the constant nucleation rate of a new phase.     

Pyrolysis of Ethane and Propane in a Temperature Range of 773–1023 K

Kinetics and Catalysis - The thermal pyrolysis of ethane and propane at a pressure of 1–3 atm was experimentally studied in a through-flow reactor. Kinetic modeling of the process under these...     

Kinetics of the reactions of catechins with hypochlorite,peroxynitrite, and amino acid–derived peroxyl- radicals

Catechins, one of the class of flavonoids, are known as very efficient antioxidants. Here we investigated the kinetics of the reactions of three catechins, namely, catechin, epigallocatechin, and epigallocatechin gallate (EGCG) with some oxidants, which are formed in vivo under oxidative stress, hypochlorite, peroxynitrite, and amino acid peroxyl radicals. Stopped-flow spectrophotometry and pulse radiolysis technique with absorption detection were used to observe the formation of intermediate products of oxidized catechins. We found that catechins react with hypochlorite with the rate constant of the order of 10⁵–10⁶ M⁻¹ s⁻¹ at pH 7.4. Experimental kinetic traces of the reaction of EGCG with valine peroxyl radicals were fitted using chemical simulation, and the rate constant of this reaction was found to be 5 × 10⁵ M⁻¹ s⁻¹. The rate constants of the formation of unstable catechin quinones in the reaction with peroxynitrite were comparable to that of spontaneous peroxynitrite isomerization, which indicates that catechins are oxidized indirectly by peroxynitrite. Biological consequences of these reactions are discussed.     

Structure and Electrocatalytic Properties of Copper-Containing Aniline–Melamine–Formaldehyde Polymer Composites

Mixed aniline–melamine–formaldehyde polymer was synthesized by parallel polycondensation of the monomers with formaldehyde. Copper(II) chloride and copper oxides (CuO, Cu₂O) were introduced in situ the process. X-ray diffraction analysis revealed the presence of crystalline CuO phases at introducing CuCl₂ into the polymer and the appearance of copper particles in all the synthesized composites after using them as catalysts in electrohydrogenation of o-nitroaniline, which is caused by electrochemical reduction of copper cations from copper oxides. The use of the synthesized composites for the cathode activation in electrohydrogenation of o-nitroaniline increases the process rate by a factor of 1.5–2.5 compared to electrochemical reduction, and with 100% conversion to o-phenylenediamine.     

Kinetics of coal and char oxycombustion studied by TG–FTIR

Coal and char oxycombustion is a complex process because of very high reaction rate of oxygen with coals and chars carbon. Very important process during oxycombustion is diffusion of O₂ to surface of coal and char grain. This process can be minimized using small samples and high flow of the gas, but it is also dependent on temperature. For this reason, it is impossible to eliminate diffusion processes which cause significant impact on calculated kinetic parameters. This paper describes the results of thermogravimetric studies of oxycombustion process with evolved gas analysis by FTIR. Ultimate and proximate analysis of coal and char were made. Thermogravimetric experiments of coal and its char oxycombustion were conducted using five heating rates, namely 2.5, 5, 10, 20 and 40 K min^?1, and gas mixture composed of 20 % O₂ in CO₂. Activation energies of coal and char oxycombustion were calculated by isoconversional methods: integral Vyazovkin and differential Friedman. Activation energies for three ranges of heating rates were calculated. This paper shows influence of heating rate on calculated activation energy. The reason of this phenomenon is due to change of the mechanism of coal and char oxycombustion from the chemical kinetic control regime to mixed chemical kinetic–diffusion control regime.