Iranian Journal of Polymer Science and Technology
Year:2007 | Volume:20 | Issue:3 (ISSUE NO. 89)|Papers Count:11

In this article, a complete model for the mixed flow slurry reactor for polymerization of ethylene to high density polyethylene in the presence of Ziegler-Natta catalyst is presented. In addition to the effects of the multiple active sites, the effect of other important parameters such as the catalyst concentration, co-catalyst, hydrogen, monomer, impurities and pressure on the mass-average and number-average polymer product chain length, the average product distribution index and the required residence time for the reactor were investigated. The simulation results show that as the catalyst, hydrogen and solvent concentrations increase, the mass and number-average polymer chain length decrease, whereas with increasing monomer concentration and pressure, the average molecular weight increases. The effects of these parameters on the polydispersity index and residence time do not follow the same trend and their relationship changes in some of these variables.

This is a report on the study of high melt flow, highly isotactic polypropylene homopolymer synthesized in liquid monomer using a fifth generation Ziegler-Natta catalytic system. At highest catalyst productivity, the response of the catalyst to hydrogen as chain transferring agent, is studied. Melt flow rate is controlled by hydrogen from 0.4 to 300 g/10min with changing the amount of hydrogen from 0 to 1400 ppm. Results show that the melt flow rate of homopolymer is increased linearly with increasing the amount of hydrogen in polymerization. The effect of external electron donor on catalyst productivity and stereoregularity of the final product has been studied. The external electron donor on the catalyst caused an increase in polymer isotacticity, but led to decrease in catalyst productivity and its response to hydrogen (i.e., requiring relatively more hydrogen for molecular weight control). This new generation of Z-N catalyst system containing 1, 3-diether as internal electron donor has the ability to produce very high MFR polymers (for thin wall parts) in combination with narrow molecular weight distribution. These reactor grades of polypropylene have many advantages compared to visbroken (controlled rheology) grades such as lower cost and better processability. These resins can be used as homopolymer matrix in sequential polymerization to obtain impact copolymers (heterophasic copolymers).

Utilizing polymeric materials for damping mechanical waves is of great importance in various fields of applications such as military camouflage, prevention of structural vibrational energy transfer, and noise attenuation. This ability originates from segmental dynamics of chain-like polymer molecules. Damping properties of styrene-butadiene rubber containing 10 wt% of monosize polystyrene particles with different diameters (from 80 nm to 500 mm) was investigated in the frequency range of vibration, sound, and ultrasound via dynamic mechanical thermal analysis, normal sound adsorption test, and ultrasound attenuation coefficient measurement. The obtained results indicated that for different systems, containing different sizes of polystyrene particles, the area under the damping curve does not show significant change comparing to the neat SBR in the frequency range studied. However, addition of polystyrene particles, specifically nanosized particles, resulted in emergence of a secondary glass transition temperature which could be attributed to the modified dynamics of a layer of matrix molecules near the surface of PS particles. In the range of sound frequency, 0.5 to 6.3 kHz, the maximum damping was observed for the system containing polystyrene nanoparticles. However the single damping curve of neat SBR was separated into two or even three distinct curves owing to the presence of the particles. The maximum damping in the ultrasound frequency range was found for the system containing 0.5 mm polystyrene particles. This is attributed to different contributions from matrix chains dynamics and the reflection of mechanical waves from particles-matrix interface at different frequency ranges. On other words, the increase in the glass transition temperature of the elastomeric matrix phase with increasing the mechanical wave frequency causes a reduction in the contribution from matrix chains dynamics while the contribution due to diffraction from dispersed phase increases as the particles size approaches the wavelength of the mechanical waves.

Fire behavior of different types of EPS was evaluated with the use of ISO 5660 cone calorimeter test method. Considering the complexity of behavior of EPS against high temperatures, several specimens were tested, so a better judgment on fire behavior of this material could be acquired. The effects of foam density, thickness of specimens and the level of heat flux on fire behavior of foam were examined. The relation between total heat release (THR) and heat release rate (HRR) with the density of the specimens were examined. The increase of thickness showed a two-fold influence on the fire behavior of the specimens. In one side, the mass of fuel increases with thickness, hence the THR and HRR needs to be increased. Contrary to that however, as EPS quickly melts and recedes away the heat source at high temperatures, the incident heat flux on specimen considerably reduces with increase of thickness and as a result the time to ignition will be lengthened with increase of thickness. These observations are discussed in the paper. On the basis of our results the comparison between the fire behavior of fire-retarded and standard types of foam is also discussed in the paper.

Good dispersion of nano-particles in polymer matrices is a crucial parameter in determining the final properties of polymer Nan composites. In this work, the distributions of Cloisite 30B. Cloisite 10A and Cloisite 93A in PTMEG, popular polyols in the polyurethane manufacturing, were investigated in the nano, micro and macro scales. This investigation was carried out using X-ray diffraction, rheometry and visual observation. The X-ray results indicated that the distance "between the layers increased after addition of the polymer but this increase was higher in case of Cloisite 30B than the two other nanoclays. The rheological measurements also showed that Cloisite 30B induces a stronger structure within the suspension. Visual observation of the various suspensions verified the above hypothesis.

Nowadays, environment-sensitive smart drug delivery systems have found diverse applications in pharmaceutical science and technology. These systems can respond to the environment stimuli such as temperature, pressure, pH, light, electrical and magnetically fields and etc. They can release the proper amount of drug in human body. Among these systems, special attention and much research works have been devoted to temperature responsive systems. Smart polymeric materials and hydrogels are widely used in production of temperature responsive systems. The temperature responsive polymeric materials and their based smart drug delivery systems are not just responsive to temperature, as other stimuli may induce them as well. Therefore, in practical cases, their performances may be disordered and the drug release may not occur in an anticipated manner. Furthermore, the mathematical relations of drug release in these systems are very complicated. Therefore, in this work, a novel temperature responsive smart drug delivery system is introduced in which the drug release would only be a function of temperature and its mathematical relations are also considerably simple. This system is composed of three individual layers. The modeling of this system is performed by analyzing the heat and mass transfer equations at pseudo-steady state and the effects of system parameters on the performance of the system are investigated. The obtained results show that the performance of the system is drastically related to the types of materials of the system and also their physical and chemical properties. By using the obtained results in this work, we can design the temperature responsive smart drug delivery systems and optimize their performance in practical cases.

Pulling force is one of the most important variables in pultrusion process which determines the capacity of the pultrusion machine. One of the characteristics of a desired pultrusion process is a low pulling force and a high line speed. Among the important factors affecting the pulling force are the internal mold release agent (IMR) and the content and particle size of the filler in resin formulation. In addition to facilitating the part separation from the die, IMR also affects the curing kinetics and in turn the pulling force. In this research, a commercial IMR has been used in a range 1-5phr. DSC and DMTA Analyses showed that the presence of IMR in concentrations above 3 phr reduces the heat of curing reaction and also the curing rate. This results in an increase in pulling force. Study of filler effect showed that the increase in filler content from 4 to 8 phr reduces the pulling force but beyond that it is increased. Also, decreasing the filler particle size in line speed lower than 30 cm/min reduces the pulling force but increases it at higher line speed.

Copolymerization of ethylene and propylene was investigated using a 4th generation phthalate Ziegler-Natta catalyst in normal hexane in a Buchi reactor. The effects of different mole fractions of [Al]/[Ti], [Si]/[Al] and various amounts of hydrogen on productivity and weight percent of ethylene on the product, were studied. In the copolymerization reactions, tri-isobutyl aluminum (TiBAl) was used as cocatalyst instead of triethyl aluminum (TEAl) because TiBA1 produced a more amorphous copolymer. In molar ratio [TiBAl]/[Ti]=480 the catalyst activity was at maximum and ethylene content in this ratio was at minimum. Cyclohexyl-methyldimethoxy silane was used as external donor. In molar ratio [Si]/[TiBAl]= 0.05, the copolymer showed more amorphous behavior. In this molar ratio, the external donor decreased the productivity of the catalyst and a further increase of external donor concentration increased the productivity. Hydrogen increased the productivity of the catalyst and decreased the ethylene content of the copolymer in low concentration. In high concentration, however, hydrogen decreased the productivity and increased the ethylene content of the copolymer. Hydrogen as a chain transfer agent decreased the viscosity average molecular weight.

Composites materials are widely used because of their high specific stiffness and strength. Although the methods and techniques of designing these materials are well developed, however, the research on the behavior of these materials under impact and dynamic loadings are still under progress. In this article the crushing and energy absorption of composite tubes under axial dynamic loadings are studied. In order to calculate the absorbed energy and the crushing load, composite tubes with circular and tubular cross-sections are modeled using LS-DYNA software. In order to simulate the crushing behavior of the tubes the laminated-composite material model is utilized. Also the effects of fiber orientation on the energy absorption are studied. The results show that the energy absorption of the tubes with tubular cross-section is less than those of the circular cross-section. The results show that for [q/-q] configuration, the minimum energy is absorbed for q=15°. The results of simulation for the tubular cross-sections are compared with the experimental results and a very good correlation is achieved.

In this study, based on a biomimetic approach, novel 3D biodegradable porous hybrid scaffolds consisting of chitosan, gelatin, and tricalcium phosphate were developed for bone and cartilage tissue engineering. Macroporous chitosanlgelatin/b- TCP scaffolds were prepared through the process of freeze-gelation/solid-liquid phase separation. The results showed that the prepared scaffolds are highly porous, with porosities larger than 80%, and have interconnected pores. Biocompatibility studies were successfully performed by in vitro and in vivo assays. Moreover, the attachment, migration, and proliferation of chondrocytes on these unique temporary scaffolds were examined to determine their potentials in tissue engineering applications.