HEAT-RESISTANT,PYRIDINE-BASED POLYAMIDES CONTAINING ETHER AND ESTER UNITS WITH IMPROVED SOLUBILITY

A diamine containing ether and ester units, as basic monomer for the preparation of polyamides, was prepared via three consecutive reactions. Nucleophilic substitution reaction of 1,4-dihydroxy benzene with 4-nitrobenzoyl chloride produced 4-hydroxyphenyl 4-nitrobenzoate （HPNB）. Reduction of nitro groups to amino groups using Fe and HC1 resulted in preparation of 4-hydroxyphenyl 4-aminobenzoate （HPAB）. The diamine was synthesized through nucleophilic substitution reaction of HPAB with 2,6-dichloropyridine. The precursors and diamine were fully characterized by common methods, and the diamine was polycondensed with different diacid chlorides in the presence of an acid scavenger to prepare new polyamides. The polyamides were characterized, and their physical properties including thermal stability and behavior, inherent viscosity and solubility were studied.

Parameters affecting reaction rate and conversion of TiO_2 chlorination in a fluidized bed reactor: Experimental and modeling approach

Pilot scale chlorination of TiO2 was carried out with CO as reducing agent.The experimental analysis and modeling of chlorination process of TiO2 in the presence of CO and Cl2 in a semi-continuous fluidized bed reactor were aimed.Chlorination process was continuously monitored by measuring the amount of produced TiCl4 with time.The effects of different operating parameters including chlorination temperature,feedstock particle size and size distribution,amount of feedstock and Cl2 and CO flow rates on the conversion were systematically investigated.A gradual increase in chlorination temperature led to monotonous increase of conversion rate.Conversion decreased with increased particle size of feedstock.An increase in loaded feedstock led to a decrease in reaction conversion.A model was proposed to predict conversion,particle size distribution and mole fraction of components in gas phase as reaction proceeds.A good agreement between conversions predicted by the model and experimental data under various operating conditions was observed.

Comparative study of kinetic modeling for the oxidative coupling of methane by genetic and marquardt algorithms

Overall kinetic studies on the oxidative coupling of methane,OCM,have been conducted in a tubular fixed bed reactor,using perovskite titanate as the reaction catalyst.The appropriate operating conditions were found to be：temperature 750-775 ℃,total feed flow rate of 160 ml/min,CH4 /O2 ratio of 2 and GHSV of 100·min-1 .Under these conditions,C 2 yield of 28% was achieved.Correlations of the kinetic data have been performed with lumped rate equations for C2 and COx formation as functions of temperature,O2 and CH4 partial pressures.Six models have been selected among the common lumped kinetic models.The selected models have been regressed with the experimental data which were obtained from the Catatest system by genetic algorithm in order to obtain optimized parameters.The kinetic coefficients in the overall reactions were optimized by different numerical optimization methods such as：the Levenberg-Marquardt and genetic algorithms and the results were compared with one another.It has been found that the Santamaria model is in good agreement with the experimental data.The Arrhenius parameters of this model have been obtained by linear regression.It should be noted that the Marquardt algorithm is sensitive to the first guesses and there is possibility to trap in the relative minimum.

CFD modeling of reaction and mass transfer through a single pellet: Catalytic oxidative coupling of methane

In this study a mathematical model of a small scale single pellet for the oxidative coupling of methane（OCM）over titanite pervoskite is developed.The method is based on a computational fluid dynamics（CFD）code which known as Fluent may be adopted to model the reactions that take place inside the porous catalyst pellet.The steady state single pellet model is coupled with a kinetic model and the intra-pellet concentration profiles of species are provided.Subsequent to achieving this goal,a nonlinear reaction network consisting of nine catalytic reactions and one gas phase reaction as an external program is successfully implemented to CFD-code as a reaction term in solving the equations.This study is based on the experimental design which is conducted in a differential reactor with a Sn/BaTiO3 catalyst（7-8 mesh） at atmospheric pressure,GHSV of 12000 h-1,ratio of methane to oxygen of 2,and three different temperatures of 1023,1048 and 1073 K.The modeling results such as selectivity and conversion at the pellet exit are in good agreement with the experimental data.Therefore,it is suggested that to achieve high yield in OCM process the modeling of the single pellet should be considered as the heart of catalytic fixed bed reactor.

Improving the Sound Absorption Properties of Flexible Polyurethane (PU) Foam using Nanofibers and Nanoparticles

Polyurethane foam as the most well-known absorbent materials has a suitable absorption coefficient only within a limited frequency range.The aim of this study was to improve the sound absorption coefficient of flexible polyurethane(PU)foam within the range of various frequencies using clay nanoparticles,polyacrylonitrile nanofibers,and polyvinylidene fluoride nanofibers.The response surface method was used to determine the effect of addition of nanofibers of PAN and PVDF,addition of clay nanoparticles,absorbent thickness,and air gap on the sound absorption coefficient of flexible polyurethane foam(PU)across different frequency ranges.The absorption coefficient of the samples was measured using Impedance Tubes device.Nano clay at low thicknesses as well as polyacrylonitrile nanofibers and polyvinyl fluoride nanofibers at higher thicknesses had a greater positive effect on absorption coefficient.The mean sound absorption coefficient in the composite with the highest absorption coefficient at middle and high frequencies was 0.798 and 0.75,respectively.In comparison with pure polyurethane foam with the same thickness and air gap,these values were 2.22 times at the middle frequencies and 1.47 times at high frequencies,respectively.Surface porosity rose with increasing nano clay,but decreased with increasing polyacrylonitrile nanofibers and polyvinyl fluoride nanofibers.The results indicated that the absorption coefficient was elevated with increasing the thickness and air gap.This study suggests that the use of a combination of nanoparticles and nanofibers can enhance the acoustic properties of flexible polyurethane foam.

ORGANOSOLUBLE,THERMALLY STABLE POLYAMIDES CONTAINING SULFONE AND SULFIDE UNITS

A new diamine containing sulfone,sulfide and amide groups was synthesized via a three-step reaction process. The nucleophilic substitution reaction of 4-aminothiophenol with 4-nitrobenzoyl chloride in the presence of propylene oxide (PO) afforded N-(4-mercaptophenyl)-4-nitrobenzamide(MPNB).The catalytic reduction of the nitro group in MPNB to amino group was accomplished by using Pd/C and hydrazine monohydrate to produce 4-amino-N-(4-mercapto phenyl)benzamide(AMPB).Reaction of two moles of AMPB with bis(4-c...

Preparation and Characterization of Functionalized Polypropylene with Acrylamide and Itaconic Acid

Functionalized polypropylene with acryl amide (AAm) and itaconic acid (IA) were prepared in the molten state in the presence of dicumyl peroxide. The effects of the concentration of both mono- mers on the degree of functionalization and properties of the products were investigated by FT-IR, contact angle measurement and DSC analysis. It was found that the degree of functionalization depends on the initial concentration of both monomers that used in the reaction. The influence of the AAm and IA content on the melting and crystallization temperature of PP was investigated by DSC. The contact angle of water on film surfaces of the functionalized PP (PP-g-AAm and PP-g-IA) decreased with increasing modified polymer content. From FT-IR spectra of functionalized PP a calculation was made of carbonyl index on the films surfaces. It was found that the higher intensity of the carbonyl index, the lower contact angle value and the lower crystallinity confirmed the ex- istence of functionalized AAm and/or IA in PP. It was concluded from the different characteriza- tion methods that the polarity and percentage of functionalized PP were increased up to 3 phr for both monomers, and then it was decreased by increasing the amount of monomers and had a threshold value, due to nucleating agents of monomers in PP.

UV irradiation-H2O2 system as an effective combined depolymerization technique to produce oligosaccharides from chitosan

UV irradiation hydrogen peroxide （H202） system is used as an effective, easy and low-cost combined depolymerization technique to produce oligosaccharides from chitosan. UV-Vis spectroscopic studies explained that with increasing treatment time, the absorption of the depolymerized chitosan solution has increased, indicating the increase in the carbonyl and amino groups in their structure. Fourier transform infrared spectroscopy and nuclear magnetic resonance （1H NMR） analysis showed that the 1,4-β-D-glucoside linkages of chitosan are degraded without important changes in chemical structure of decomposed samples. X-ray diffraction patterns verified the polymerization of chitosan to produce oligomers, changing in structure from crystalline to amorphous. Viscosity-average molecular weight measurements of fragmented chitosan samples and MarkHouwink equation are used to demonstrate the efficiency of this depolymerization method. Finally, the obtained results ascertained that this combined method could produce water soluble chitosan with significant efficiency and no essential change in its chemical structure.UV irradiation hydrogen peroxide （H202） system is used as an effective, easy and low-cost combined depolymerization technique to produce oligosaccharides from chitosan. UV-Vis spectroscopic studies explained that with increasing treatment time, the absorption of the depolymerized chitosan solution has increased, indicating the increase in the carbonyl and amino groups in their structure. Fourier transform infrared spectroscopy and nuclear magnetic resonance （1H NMR） analysis showed that the 1,4-β-D-glucoside linkages of chitosan are degraded without important changes in chemical structure of decomposed samples. X-ray diffraction patterns verified the polymerization of chitosan to produce oligomers, changing in structure from crystalline to amorphous. Viscosity-average molecular weight measurements of fragmented chitosan samples and MarkHouwink equation are used to demonstrate the efficiency of this depolymerization method. Finally, the obtained results ascertained that this combined method could produce water soluble chitosan with significant efficiency and no essential change in its chemical structure.

Oxidative coupling of methane in a fixed bed reactor over perovskite catalyst:A simulation study using experimental kinetic model

The oxidative coupling of methane （OCM） to ethylene over a perovskite titanate catalyst in a fixed bed reactor was studied experimentally and numerically. The two-dimensional steady state model accounted for separate energy equations for the gas and solid phases coupled with an experimental kinetic model. A lumped kinetic model containing four main species CH4, O2, COx （CO2, CO）, and C2 （C2H4 and C2H6） was used with a plug flow reactor model as well. The results from the model agreed with the experimental data. The model was used to analyze the influence of temperature and feed gas composition on the conversion and selectivity of the reactor performance. The analytical results indicate that the conversion decreases, whereas, C2 selectivity increases by increasing gas hourly space velocity （GHSV） and the methane conversion also decreases by increasing the methane to oxygen ratio.

Modeling the oxidative coupling of methane: Heterogeneous chemistry coupled with 3D flow field simulation

The oxidative coupling of methane （OCM） over titanate perovskite catalyst has been developed by three-dimensional numerical simulations of flow field coupled with heat transfer as well as heterogeneous kinetic model. The reaction was assumed to take place both in the gas phase and on the catalytic surface. Kinetic rate constants were experimentally obtained using a ten step kinetic model. The simulation results agree quite well with the data of OCM experiments, which were used to investigate the effect of temperature on the selectivity and conversion obtained in the methane oxidative coupling process. The conversion of methane linearly increased with temperature and the selectivity of C2 was practically constant in the temperature range of 973-1073 K. The study shows that CFD tools make it possible to implement the heterogeneous kinetic model even for high exothermic reaction such as OCM.

Kinetic simulation of oxidative coupling of methane over perovskite catalyst by genetic algorithm:Mechanistic aspects

The reaction kinetics of oxidative coupling of methane catalyzed by perovskite was studied in a fixed bed flow reactor.At atmospheric pressure,the reactions were carried out at 725,750 and 775℃,inlet methane to oxygen ratios of 2 to 4.5 and gas hourly space velocity （GHSV） of 100 min^-1.Correlation of the kinetic data has been performed with the proposed mechanisms.The selected equations have been regressed with experimental data accompanied by genetic algorithm （GA） in order to obtain optimized parameters.After investigation the Langmuir-Hinshelwood mechanism was selected as the best mechanism,and Arrhenius and adsorption parameters of this model were obtained by linear regression.In this research the Marquardt algorithm was also used and its results were compared with those of genetic algorithm.It should be noted that the Marquardt algorithm is sensitive to the selection of initial values and there is possibility to trap in a local minimum.

SPECTRAL AND CHEMICAL MONITORING OF CYCLO-ADDITION REACTION OF CO_2 WITH POLY(MMA-co-GMA) COPOLYMERS

This paper deals with the monitoring cyclo-addition of CO2 to methyl methacrylate （MMA）-glycidyl methacrylate （GMA） copolymers using spectral （IH-NMR and FTIR） and chemical （elemental analysis and titration） methods. Thus, poly（MMA-co-GMA）, was first prepared via solution polymerization. The copolymer was then treated with CO2 gas flow in the presence of cetyltrimethyl ammoniumbromide as a catalyst. In terms of the carbonation reaction time, the terpolymer poly（MMA-eo-GMA-co-2-oxo-l,3-dioxolane-4-yl-methyl methacrylate） was prepared in various yield of CO2 fixation （〉 90%）. The peak intensity changes in the 1H-NMR and FTIR spectra provided excellent demonstrative techniques to monitor the carbonation reaction progression. In a comparative analytical viewpoint, the NMR and elemental analysis were recognized to be the most accurate ways to follow the cyclo-addition reaction progression. However, titration was recognized to be the most preferred method, because it is a very inexpensive, facile and available method with a reasonable cost- accuracy balance.

Efficient Thermal Stabilization of Polyvinyl Chloride with Tannin-Ca Complex as Bio-Based Thermal Stabilizer

The potential use of tannin-Ca complex derived from tannins as bio-based thermal stabilizer and antioxidant additive for polyvinyl chloride (PVC) was investigated in this work. For this project, Reapak B-NT/7060 was applied as reference thermal stabilizer. Variable compositions: (1, 2, and 3) part per hundred ratio (phr) of tannin-Ca complex in the presence of 10 phr Dioctyl phthalate (DOP) as plasticizer in all PVC formulations were prepared by melt mixing by internal mixer at 165°C. Tannin-Ca complex was characterized by FT-IR spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) analysis as well as by means of differential scanning calorimetry (DSC). The tannin derivative stabilization efficiency under inert atmosphere was determined by using thermogravimetric analysis (TGA). In addition, its thermal stabilization effect has been assessed in air as oxidizing atmosphere by DSC in dynamic conditions. According to TGA thermograms, the initial degradation temperature (Ti) and optimum degradation temperature (Top?) for the main degradation stage of PVC stabilized with this derivative were about 280°C and 310°C, respectively. While these were about 255°C and 293°C, respectively for PVC stabilized with commercial thermal stabilizer. Global results of TGA, DSC, SEM and EDX show that the tannin-Ca complex provides the best properties and results in stabilizing both against thermal degradation and thermal oxidation degradation of PVC.

Influence of monovalent alkaline metal cations on binder-free nano-zeolite X inpara-xylene separation

The adsorption process was studied for separating para-xylene from xylene mixture on modified nano-zeolite X in a breakthrough system. Nano-zeolitic adsorbent with different ratios of Si O2/Al2O3 was synthesized through hydrothermal process and ion-exchanged with alkaline metal cations like lithium, sodium and potassium. The product was characterized by X-ray diffraction, scanning electron microscopy(SEM), nitrogen adsorption,transform electron microscopy(TEM) and in situ Fourier transform infrared(FTIR) spectroscopy. The influence of nano-zeolite water content and desorbent type on the selectivity of para-xylene toward other C8 aromatic isomers was studied. The optimization of adsorption process was also investigated under variable operation conditions. The isotherm for each isomer of C8 aromatics and the desorbents possess the adsorption characteristics of Langmuir type. The selectivity factor of para-xylene relative to each of meta-xylene, ortho-xylene and ethylbenzene under the optimum conditions obtained to be 5.36, 2.43 and 3.22, in the order given.

Tannin-Ca Complex as Green Thermal Stabilizer Additive for PVC: Viscoelastic Properties

This study investigated the viscoelastic and rheometeric properties of PVC stabilized with tannin-Ca complex as totally bio-based thermal stabilizer. Dynamic mechanical thermal analysis (DMTA) used to characterize the viscoelastic properties of PVC samples obtained by thermal mixing of PVC with three composition percentages (1.0, 2.0, and 3.0) part per hundred ratios (phr) of tannin-Ca complex with this polymer. The torque rheometery test used to monitor the effect of tannins derivative on the thermal stability and mixing properties of PVC formulations during samples processing. For that purpose, PVC sample with 2 phr commercial thermal stabilizer (Reapak B-NT/ 7060) was used for comparison and considered as reference samples. Before the glass transition temperature of PVC at 30°C - 60°C, the DMTA curves show that the values of storage modulus and tan delta of PVC samples stabilized with tannin derivative were very similar with those of PVC sample stabilized with commercial thermal stabilizer. The glass transition temperature (Tg) of PVC stabilized with commercial thermal stabilizer and with tannin-Ca complex occurred at about 76°C. In a sequence, after the glass transition region of PVC samples, the DMTA scans confirmed that the PVC samples with 2 phr tannin-Ca complex have relatively longer flowing stage which occurs at lower temperatures by 18°C per that of PVC sample stabilized with commercial stabilizer. Global results of the torque rheometery which have suitable plateau stages and the DMTA show that the processing thermal stability and thermal flexibility of PVC are clearly increased with the incorporation of tannin-Ca complex. All the PVC formulations with tannins-Ca complex show excellent viscoelastic properties which were found to be slightly best or much closed to those obtained for PVC stabilized with commercial thermal stabilization.

CELL ADHESION AND SURFACE PROPERTIES OF POLYSTYRENE SURFACES GRAFTED WITH POLY(N-ISOPROPYLACRYLAMIDE)

Cell adhesion plays a key role in various aspects of biological and medical sciences. In this study, poly（N- isopropylacrylamide） （PNIPAM） was grafted on polystyrene surfaces using different solvents under UV radiation. Moreover, the relation between surface roughness and cell adhesion were evaluated by gravimetric, SEM, AFM, contact angle measurement and cellular analyses. The gravimetric analysis clearly indicated an increase in the grafting by adding 10% methanol to water. The study of surface topography by AFM images showed an increase in the surface roughness and as a result of which, a decrease in wettablity was observed. At 37 ~C, epithelial ceils were well attached and proliferated on the grafted surfaces, while these cells were spontaneously detached below 32 ℃ in the absence of any enzymes. Moreover, MTT assay and SEM images indicated good cell viability and an increase in cell adhesion caused by the roughness increase. The results of this study reveal the great potential of PNIPAM-grafted polystyrene for being used in the biomedical fields such as drug delivery systems, tissue engineering and cell separation.

SOLUBLE POLYIMIDES FROM A SEMI-ALIPHATIC DIAMINE CONTAINING ESTER,AMIDE AND ETHER GROUPS

A diamine was synthesized by two successive reactions. Nucleophilic reaction of 4-hydroxybenzoic acid with terephthaloyl chloride yielded terephthaloyl bis（4-oxybenzoic） acid. Then reaction of this compound with 1,8-diamino-3,6- dioxaoctane via Yamazaki method resulted in preparation of diamine named terephthalic acid bis（4-{2-[2-（2-amino ethoxy）ethoxy]ethyl carbamoyl}phenyl） ester. After fully characterization it was used to prepare new polyimides through polycondensation with different dianhydrides using trimethylchlorosilane. Characterization of polymers was achieved by common methods and their physical properties including inherent viscosity, thermal behavior, thermal stability, crystallinity and solubility were studied. Prepared polyimides showed improved solubility and good thermal stability.

The Influence of Bridge Type on the Activity of Supported Metallocene Catalysts in Ethylene Polymerization

Ethylene polymerization was carried out by immobilization of rac-ethylenebis（1-indenyl）zirconium dichloride （Et（Ind）2ZrCl2） and rac-dimethylsilylbis（1-indenyl）zirconium dichloride （Me2Si（Ind）2ZrCl2） preactivated with methylaluminoxane （MAO） on calcinated silica at different temperatures. Polymerizations of ethylene were conducted at different temperatures to find the optimized polymerization temperature for maximum activity of the catalyst. The Me2Si bridge catalyst showed higher activity at the lower polymerization temperature compared to the Et bridge catalyst. The highest catalytic activities were obtained at temperatures about 50 ~C and 70 ~C for Me2Si（Ind）2ZrC1JMAO and Et（Ind）zZrCI2/MAO catalysts systems, respectively. Inductively coupled plasma-atomic emission spectroscopy results and polymerization activity results confirmed that the best temperature for calcinating silica was about 450 ℃ for both catalysts systems. The melting points of the produced polyethylene were about 130 ℃, which could be attributed to the linear structure of HDPE.

Effects of polyethyleneimine-functionalized MCM-41 on flame retardancy and thermal stability of polyvinyl alcohol

Hyperbranched polyethylenimine （PEl）-functionalized mesoporous silica （MCM@PEI） was synthesized and used to produce poly（vinyl alcohol） （PVA） nanocomposites. The modified nanofiller was charac- terized with infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and N2 adsorption. When compared with pure meso- porous silica （MCM）, the MCM@PEI nanoparticles exhibited better dispersion in the PVA matrix. The effects of MCM@PEI on the thermal and flame properties of PVA nanocomposites were also studied. Improvement in the thermal properties was confirmed by enhanced thermal stability and char yield. Incorporation of MCM@PEI in PVA led to a significant drop in the heat release rate and the total heat release.

Preparation and Characterization of DGEBA/EPN Epoxy Blends with Improved Fracture Toughness

The physical and mechanical properties of blends composed of two kinds of epoxy resins of different numbers of functional groups and chemical structure were studied. One of the resins was a bifunctional epoxy resin based on diglycidyl ether of bisphenol A and the other resin was a multifunctional epoxy novolac resin. Attempt was made to establish a correlation between the structure and the final properties of cured epoxy samples. The blend samples containing high fraction of multifunctional epoxy resin showed higher solvent resistance and lower flexural modulus compared with the blends containing high fraction of bifunctional epoxy resin. The epoxy blends showed significantly higher ductility under bending test than the neat epoxy samples. The compressive modulus and strength increased with increasing of multifunctional epoxy in the samples, probably due to enhanced cross-link density and molecular weight. Morphological analysis revealed the presence of inhomogeneous sub-micrometer structures in all samples. The epoxy blends exhibited significantly higher fracture toughness（by 23% at most） compared with the neat samples. The improvement of the fracture toughness was attributed to the stick-slip mechanism for crack growth and activation of shear yielding and plastic deformation around the crack growth trajectories for samples with higher content of bifunctional epoxy resin as evidenced by fractography study.