Iranian polymer journal
Volume:13 Issue: 5, 2004

The effects of tetrahydrofuran and acetonitrile bases on activity of homogeneous Cp2ZrCl2/MAO catalyst system towards ethylene/propylene copolymerization were investigated. The possibility of increasing polymer molecular weight through increasing the electron density of the Zr atoms of the metallocene-based catalyst was studied by means of conducting a semi-continuous polymerization system at atmospheric pressure. Both catalytic activity and viscosity average molecular weight were increased upon addition of acetonitrile into the polymerization system. Although addition of tetrahydrofuran increased the molecular weight slightly small traces of this base, however, lowered the activity of the catalyst. Active centre determinations were carried out using 14CO-tagging technique. The rate enhancement which was observed with acetonitrile addition was suggested to be due to site activation rather than to an increase in the concentration of active centres.

Coating offers a wide variety of methods by which one can process textile and film webs for various end uses. The materials to be processed, the coating, the required properties of the finished product, and the cost-effectiveness of manufacture often dictate in choosing the best method. A best system is ultimately the one that produces the relevant product, manufactured by the most economical method. In this research work major coating techniques used in coating fabrics were briefly mentioned and their rheological requirements were outlined. Coating pastes need to have very specific rheological properties because of the methods in which they are applied. In this study, rheological measurements of paste using DOP and DOA plasticizer and PVC-E with three K values (69, 70 and 75) were studied. The results indicated that the PVC Kvalue and plasticizer type could influence the rheological behaviour. Under studied condition the coating pastes were non-Newtonian pseudoplastic to Newtonian behaviour. The information presented here could help the right selection of coating and laminating method.

In this paper three different types of polyethylene, high density (HDPE), medium density (MDPE) and linear low density (LLDPE), have been used to prepare composites with ultra high molecular weight polyethylene (UHMWPE) fibres. Thermal behaviour of the matrices, the fibre and the prepared hot-pressed composites were investigated by differential scanning calorimeter (DSC) analysis. PE/PE Microcomposites were prepared from the above materials and their crystalline morphology of the fibre and matrice’s interfaces were studied by a polarizing microscope. The hot-pressed samples and microcomposites were cooled by using different processing conditions, i.e. isothermal crystallization (ISO), air cooling (AC) and ice water quenching (IWQ). The DSC studies revealed that only HDPE had a crystallization condition similar to the melted fibres. The microscopic images showed a big difference between those samples prepared by HDPE matrix that cooled by ISO and IWQ methods. The ISO cooled sample contained a regular transcrystallinity (TC) region having 25 μm thickness and consist of compact needle-like crystals set vertically on the fibre surface, while the IWQ cooled sample had a two-layer TC region with irregular thickness. In the microcomposites prepared by MDPE and LLDPE as matrix and cooled by ISO method, a sever irregular TC region appeared and there was no similarity with the microcomposites prepared by HDPE as matrix. With regards to the surface melting of fibres, it is probable to consider a three-layer region around the fibre core where the crystallization of interface begins from the internal layer, which is UHMWPE melt, and continues through the external layer that is matrix melt. The middle layer seems to be composed of a blend of UHMWPE and PE matrix chains

With the development of composite manufacturing processes, such as low-pressure compression moulding of sheet moulding compounds (SMC), resin transfer moulding (RTM) and vacuum infusion moulding processes, low-shrinkage resin which can be processed at low temperatures have attracted considerable interest in composite industry. In this paper the effect of polyvinyl acetate (PVAc) as a low profile additive (LPA) on shrinkage control of an iso unsaturated polyester resin has been investigated and cure behaviour, morphology and mechanical properties of this system has been studied. Our studies show that the maximum exothermic temperature and the rate of cure decreases with increasing the PVAc concentration. The PVAc content has a significant effect on the resin viscosity. It was found that there are two transitions for UP resin containing PVAc cured at low temperatures. The PVAc content is effective for shrinkage control only in a concentration between these two transitions. Experimental results showed that the mechanical properties of this system decreases by increasing the PVAc content.

The object of this study was to investigate the relaxation time (λk) and the viscosity index (ηk) of a tyre tread compound. The rheological behaviour of the sample was studied using a parallel plate rheometer and the rheological material functions, such as complex shear viscosity (ηk), elastic shear modulus (G’), and viscous shear modulus (G”) were measured in frequency sweep test (FST). The study has focused on a method for calculating λk, and the ηk using generalized Maxwell model (GMM) over a limited range of frequency and temperature. Time sweep test, stress sweep test and frequency sweep test were carried out using a parallel plate rheometer. The stable zone (or steady state region) which is suitable for measuring the rheological material functions was obtained from time sweep test results at various temperatures and frequencies. Stress sweep test was then carried out to determine linear viscoelastic zone of the compound at a given temperature and frequency. The critical stress, which determines the linear- nonlinear transition point, was obtained from stress sweep test results at each temperature and frequency. The complex shear viscosity (η*), elastic shear modulus (G’), and viscous shear modulus (G”) were measured in frequency sweep test and the relaxation time was then calculated. The results showed that the rheological behaviour of the compound followed the GMM. The relaxation time was also found to be a decreasing function of both temperature and frequency.

Low molecular weight polyetherketones were prepared from m-chloroanisole, 1,4-phenylenedioxy diacetylchloride (1,4-PDC), chloroacetyl chloride (CAC), 1,2-dichloroethane (DCE) and dichloromethane by Friedel-Crafts reaction using anhydrous AlCl3 as a catalyst and CS2 as a solvent. The polyetherketones were characterized by IR spectra and gel permeation chromatography (GPC). The kinetic parameters for the thermal decomposition reaction were evaluated by the methods of Broido and Doyle. All the polyetherketones were tested for their biological activity against bacteria, fungi and yeast strains. The results show that most of the polyetherketones can be used as antibacterial and antifungal agents.

The preparation of ethylene propylene diene terpolymer (EPDM)/organoclay nanocomposites was studied by melt blending method. The maleic anhydride modified EPDM oligomer (EPDM-MA) was used as a compatibilizer. The effect of organoclay on structure of nanocomposites was evaluated by X-ray diffraction (XRD). The absence of basal plane peak in XRD results and homogeneously dispersed clay platelets in EPDM matrix, which is shown by TEM photograph suggests that the EPDM clay nanocomposits are exfoliated. The mechanical and thermal properties of nanocomposites were examined to evaluate the influence of the organoclay on the physical properties. The results show remarkable improvement relative to that of EPDM without clay. To prepare EPDM-clay nanocomposites by a straightforward method, a second process was implemented. It was found that the properties of nanocomposites prepared by both methods are nearly the same; however the second method has lower cost and it is industrially more practical.

Anew outlook on a preparative process of superabsorbing hydrogels is presented in this paper. The hydrogels based on acrylic acid (AA), acrylamide (AM) and potassium acrylate (KA) were prepared through polymerization of concentrated solution of the acrylic monomers. Ammonium persulphate/sodium metabisulphite redox pair initiating system was used for the free radical terpolymerization and methylenebisacrylamide was used as a cross-linker. Some certain process variables (cross-linker and initiator concentration) affecting either swelling capacity or swelling rate were thoroughly investigated. Temperature variations of the polymerization mixture were also studied. The synthetic method was found to be an efficient and facile approach for making superabsorbents with quantitative yield under atmospheric conditions. Meanwhile, by swelling measurements in both water and saline media, power law relationships between crosslinker content and swelling capacity were found.

Biodegradable polymers such as chitosan have been used extensively in biomedical fields in the form of sutures; wound dressing and as artificial skin. Colonic drug delivery for either local or systemic effects has been the subject of much research over the last decade. Chitosan exhibits poor solubility at pH values above 6 that prevent enhancing effects at sites of absorption of drugs. In the present work, N-diethyl methyl chitosan (DEMC) was prepared based on a modified two-step process via a 22 factorial design to optimize the preparative conditions. DEMC Polymer with different degrees of quaternization for pharmacological and pharmaceutical experiments was achieved. The reaction was optimized using different amounts of reactants. pH-metric titration and infrared methods predetermined the degree of deacetylation of the starting chitosan. DEMC Chloride was characterized using FTIR and 1H NMR spectroscopies. Based on NMR calculation, high degree of quaternization was achieved through the optimized twostep process. Under our optimized conditions, (i.e. the second step, chitosan 1.5%, ethyl iodide 30%, NaOH 3.1%, 60°C, 6h), the prepared DEMC comprised a degree of quaternization of 79%. The prepared N-diethyl methyl chitosan chlorides were rapidly and completely dissolved in water at room temperature.