Iranian polymer journal
Volume:19 Issue: 2, 2010

One of the known groups of mesoporous materials is MCM-41 that has beenextensively used as support for different types of catalysts. In the present work,rod-like MCM-41 was synthesized to support TiCl4/MgCl2/THF catalyst to formthe bi-supported rod-like-MCM-41/TiCl4/MgCl2/THF catalytic system. Then, ethylene polymerization was performed by this synthesized catalytic system under 8bar ethylene pressure. The formation of rod-like semi-crystalline mesoporous MCM-41with relatively high surface area (~972 m2/g) was confirmed by SEM, XRD, and BETstudies. FTIR spectroscopy was used to confirm the omission of the organic template and water from the synthesized MCM-41. Investigating the specific surfacearea of the prepared catalyst by BETanalysis showed that after loading the catalyst onMCM-41support, the surface area is reduced considerably and it is reached a value ofapproximately 486 m2/g. XRD, SEM, and DSC analyses revealed that the synthesizedPE samples contained nano-fibres as their main morphological units. SEM analysisshowed the formation of dense polyethylene fibres with nanometer sized diameters andlengths of about 1 to more than 20 micrometers. DSC analysis showed the high melting point of 144°C for the synthesized PE samples and their crystal structure wasassigned to be orthorhombic by XRD investigations. Finally a relatively high activity of11×104g PE/mol Ti.h was obtained for the catalytic system.

Moisture absorption behaviour of polymer matrix composites (PMCs) in humidand tropical environments is a complex phenomenon. Moisture diffusion weakens the fibre/matrix interface which leads to deterioration of mechanicalproperties. Hygrothermic ageing of carbon/vinylester, glass/vinylester, carbon/epoxyand glass/epoxy composites were studied for their suitability in marine applications.The specimens were exposed to 50°C, 60°C and 70°C temperatures and humidity of 95% RH for a maximum duration of 170 days. The specimens were periodicallyweighed for moisture absorption and tested for mechanical properties (ultimate tensilestrength, flexural strength and interlaminar shear strength) degradations. The maximum moisture absorption was observed for epoxy/glass composite and the minimum for vinylester/carbon composite. Diffusion mechanism was studied on thebasis of the Fick''s law of diffusion. It was found that diffusion coefficient (D) is at highest for epoxy/glass composite and at the lowest for vinylester/carbon composite.Diffusion coefficient increased with increase in temperature for all the specimens.Comparing vinylester/carbon and epoxy/carbon samples data, although both loweredin properties, the former showed still better results in flexural strength (FS), ultimatetensile strength (UTS) and interlaminar shear strength (ILSS) values than the latter. Asa whole, Vinylester/glass has behaved superior to epoxy/glass with respect to changesin their mechanical properties. The experimental observations are confirmed by SEM.Vinylester based specimens showed greater chemical stability than the epoxy basedspecimens. Even after 170 days of hygrothermic exposure, vinylester/carbon showedlower degree of fibre pulls out compared to other three specimens tested.

Nano-titanium dioxide (TiO2) was surface modified by isopropyl tri(dioctyl phosphate) titanate (NDZ-102 titanate coupling agent) using ultrasonic wetmethod. The modified nano-TiO2(M-TiO2) was characterized by sinkability,rotary viscometry, activation index measurement, and transmission electronmicroscopy (TEM). The results showed that, after being surface modified by NDZ-102titanate coupling agent, the surface property of TiO2changed from hydrophilic tohydrophobic, the M-TiO2showed a good dispersion property and could evenly suspendin liquid paraffin, viscosity reduced to 87.76% of that of the pristine nano-TiO2(P-TiO2)and its activation index was increased up to 100%. On the basis of the above result, P-TiO2/polybutylene terephthalate (PBT) and M-TiO2/PBTcomposite samples wereprepared by melt-blending process and their crystallization behaviours were character-ized and compared together. Scanning electron microscopy (SEM) results showed thatthe M-TiO2of smaller particle size was uniformly dispersed in PBTmatrix. X-ray diffraction (XRD) results showed that TiO2as nucleating agent accelerated the crystallization of PBTwhere PBTand TiO2crystallized separately in the blend system.Polarized light microscopy (PLM) micrographs indicated that the crystal sizes were inthe order of PBT> P-TiO2/PBT> M-TiO2/PBT, while the order of crystal number wasPBT< P-TiO2/PBT< M-TiO2/PBT. Moreover, the crystals of M-TiO2/PBTwere perfectspherulite with a good dispersability and its crystallization behaviour improved greatlycompared to those of PBTand P-TiO2/PBTcrystals.

Electrospinning is one of the most popular techniques for generating fibres withthe diameters ranged from tens of nanometers to several micrometers. Theproperties of as-spun nanofibres including crystallizability, mechanical performances, and biofunctioning are controlled and affected by several parameters,e.g., electrospinning solvent, temperature, humidity, and polymer characteristics. Inorder to re-verify the theory that the morphology of electrospun nanofibres is influencedby solvents used to dissolve polymer, the present study was carried out in which polymethyl methacrylate (PMMA) was chosen as the solute and processed into nano-fibres by means of electrospinning. Seven solvents were separately used to dissolvePMMAat the concentration of 0.06 g/mL. As a result, ring-like, bead-like, ultrafine, andnano-porous nanofibres were generated from PMMAsolutions by electrospinning.Because all solvents used in this study dissolved PMMAreadily, the different morphologies were not due to their abilities to dissolve PMMA, but rather due to otherproperties such as boiling points, molecular weight, and molecular structure. Therefore,ring-like PMMAfibres was obtained due to the high boiling point (110°C) and stereo-hindrance effect of toluene. Bead-like nanofibres were generated fromPMMA/chloroform and PMMA/dichloromethane solutions. Moreover, two kinds of ultrafine nanofibres were produced through electrospinning of PMMA/1,1,1,3,3,3-hexafluoro-2-propanol, and PMMA/2,2,2-trifluoroethanol solutions.

Aseries of novel chitosan-g-poly(acrylic acid)/muscovite (CTS-g-PAA/MVT) granular superabsorbent composites were synthesized by free-radical graft polymerization in aqueous solution. The effects of different ion-exchanged MVTon equilibrium water absorbency, swelling rate and swelling behaviour in variouscationic saline solutions and different pH solutions of superabsorbent composites weresystematically investigated under the same preparation conditions. The superab-sorbents doped with different ion-exchanged MVTwere characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray fluorescence spectrometry (XRF) andscanning electron microscopy (SEM). FTIR spectroscopy confirmed that AAhas beengrafted onto CTS and -OH groups of MVTseem to have participated in this reaction,simultaneously. These composites show good dispersion and favourable compatibilityof inorganic and organic phases observed in SEM photographs. The introduction of ion-exchanged MVTinto chitosan-g-poly(acrylic acid) polymeric network could improvewater absorbency and swelling rate compared to those of the MVT. It is found that theswelling behaviour of these composites depends on the concentrations of NaCl, CaCl2,and FeCl3solutions; as by increasing the concentration from 0.01 to 10 mM leads togradual decrease in the swelling rates. All prepared composite samples demonstratesimilar swelling behaviour at different pH, while the equilibrium water absorbency of thesamples is kept roughly constant in pH range 4-10.

The polymer melt flow in the conveying region of an intermeshing co-rotating twinscrew extruder (TSE) was studied by using a mathematical model. In this modelthe mixed finite element scheme was combined with generalized Newtonian rheological model to solve governing equations of continuity and momentum in a 3DCartesian coordinate system. Because of the complex geometry of the intermeshing co-rotating TSE, tetrahedral elements have been used in order to mesh for a completemodelling. The Picard''s iterative procedure was used to handle the non-linear nature ofthe derived equations. The modelling is based on a quasi-steady state approach andtherefore, several sequential geometries were selected to demonstrate a completescrew rotation cycle. In order to find the best optimum size and distribution of the elements, two mesh configurations were used with different degrees of refinement. Theaccuracy of finite element approximations improved when the mesh refinement wasused for intermeshing and screws tip regions. The applicability of this model has beenverified by comparison of experimentally measured data and simulation results of highdensity polyethylene (HDPE) melt. This comparison showed that there is a good agreement between the experimental data and model predictions.