Iranian Journal of Polymer Science and Technology
Year:2008 | Volume:20 | Issue:6 (ISSUE NO. 90)|Papers Count:8

Using controlled drug delivery devices is one of the novel methods of drug delivery which is used to perform drug therapy with the minimum side effects. Mucoadhesive polymers are one of these devices. Chitosan is a natural polymer which is a suitable candidate for this purpose due to it is biocompatibility, bioadhesion and high capability to adsorb peptide drugs. Since GI tract has both acidic and basic pH, in this study the interaction between mucin and chitosan as well as swelling of chitosan were investigated in two different media (pH= 5.5 and 7.4). The amount of surface adsorbed mucin was obtained by using spectroscopy. The results have shown that interaction intensity and swelling were pH dependent and reversible.

In the current work, ethylene polymerization was investigated from a mathematical modeling point of view. The initiation (activation), propagation, termination, and deactivation reactions were taken into account and the relevant equations used in the modeling were obtained from the elementary reactions. Some assumptions including neglecting the transfer and deactivation reactions were considered to simplify the modeling. According to the results obtained, these assumptions were only applicable to the initial stages of the polymerization reaction, namely the first 20 min of the reaction. Finally, transfer to monomer and deactivation reaction was also included in the improved version of the model and a new equation acceptably matching the experimental results was developed for the rate of the polymerization.

The final treatment for diabetes is transplantation of islets of Langerhans. One of the new proposed methods for immunological preservation of transplanted cells is coating of cell surface by polyethylene glycol. In this study, the surface of islets of Langerhans was coated by cyanuric chloride activated methoxy polyethylene glycol. The effect of polymer coating, at two different reaction times and polymer concentrations, by immunological and morphological tests on the cells, was studied. A decrease of 47-76.5% in the immunological response against the coated cells, in comparison to control samples, was observed. Also, morphologically, these coated cells were more stable.

In this investigation, the mechanical properties of the blends of blown bitumen110/10, heavy vacuum slops (H.V.S), bitumen 60/70 penetration grade and isotactic polypropylene (iPP) were studied for the first time. Our results showed that modulus varies non-linearly and at certain asphaltenes contents a peak appears. Considering these phenomena it is revealed that in the absence of iPP, interactions between the asphaltenes control the modulus of the blends. These interactions are dependent on the H.V.S and soft bitumen contents. The asphaltenes establish strong interactions with other asphaltene groups during dissolution in H.V.S or bitumen 60/70 (called solubility limit). At low percentages of iPP and high concentrations of asphaltenes a segregated network of asphaltenes is formed. Formation of this network increases the modulus of blends. At higher percentages of iPP and low asphaltenes concentration an inter diffusion-coalescence network is established. This network creates transition structures and increases the blend modulus. Finally, it is found that incorporation of iPP improves the modulus of bituminous blends.

Conventional processes of food dewatering, such as thermal, have undesirable and destruction effects on vitamins, aromatic compounds and pigments. In addition, they are accompanied with some technological complications and energy consumption. Thus, food concentration processes are directed to non-thermal techniques or methods with reduced heat effects. Superabsorbents are highly hydrophilic polymer networks which can absorb water and aqueous solutions some hundred times of their weights and retain them. These materials are subgroups of hydrogel family that are transformed into gels after absorbing water. In the present research, the possibilities of yoghurt dewatering using superabsorbents have been investigated for the first time in Iran and some remarkable results are obtained for this vital product. In the experiments carried out to investigate the effect of these absorbents on normal method of yoghurt concentration (use of permeable membrane), type of bed (wide and vertical) and time are also studied. The percentage of total soluble solids and dry solids of dewatered samples were measured in different time intervals up to 180 min. The results showed that superabsorbent on a wide bed would reduce the concentration time to one third. In other words, in a certain time interval, more than 70% increase in yoghurt dry solids was observed compared to normal method. These results show that acrylic superabsorbent hydrogel can be applied as highly hydrophilic material in non-thermal food dewatering methods.

Photooxidation as an important process, which significantly affects the service life of the polypropylene products, has been the subject of much theoretical and experimental study. Pigments used often change the light stabilities of polypropylene. Out-door applications of pigmented polypropylene are now increasingly developed in products such as artificial grass. The aim of this work is to examine the effect of photo-oxidation on the structure of isotactic polypropylene (iPP) in film and filament forms, where phthalocyanine pigment is used. For production of films and filaments, iPP granules with MFI 25 g/10min were used, with and without phthalocyanine pigment. Samples were exposed to xenon lamp for various time lengths. The extent of the changes in chemical and structural parameters was examined by differential scanning calorimetry, Fourier transform infrared spectroscopy and wide angle x-ray diffraction. The results show that carbonyl and hydroperoxide indices increase during the exposure to the radiation. The changes in melting points of the samples were not significant after irradiation process. The effects of phthalocyanine pigment in the photooxidation of film and filament were different. Crystalline fractions of the non-pigmented filament samples decreased during the irradiation time while increased in film samples. Build up of hydroperoxide and carbonyl group in filament was higher than in film samples; that could be due to the differences in structural parameters. Crystallinity variations during photooxidation are related to the nucleation effect of the pigment, chemical crystallization and phase transformation.

The separation of olefin/paraffin mixtures is an important process in petrochemical industries, which is traditionally performed by low temperature distillation with a high-energy consumption, or complex extractive distillation and adsorption techniques. Membrane separation process is emerging as an alternative for traditional separation processes with respect to low energy and simple operation. Investigations made by various researchers on polymeric membranes it is found that special glassy polymers render them as suitable materials for olefin/paraffin mixture separation. In this regard, having some knowledge on the possible transport mechanism of these processes would play a significant role in their design and applications. In this study, separation behavior of olefin/paraffin mixtures through glassy polymers was modeled by three different approaches: the so-called dual transport model, the basic adsorption-diffusion theory and the general Maxwell-Stefan formulation. The systems chosen to validate the developed transport models are separation of ethane-ethylene mixture by 6FDA-6FpDA polyimide membrane and propane-propylene mixture by 6FDA-TrMPD polyimide membrane for which the individual sorption and permeation data are available in the literature. A critical examination of dual transport model shows that this model fails clearly to predict even the proper trend for selectivities. The adjustment of pemeabilities by accounting for the contribution of non-selective bulk flow in the transport model introduced no improvement in the predictability of the model. The modeling results based on the basic adsorption-diffusion theory revealed that in this approach only using mixed permeability data, an acceptable result is attainable which fades out the advantages of predictability of multi component separation performance from pure component data. Finally, the results obtained from the model developed based on Maxwell-Stefan formulation approach show a close agreement between the predicted values and experimental data in terms of permeabilities and selectivities. The results also indicate that kinetic coupling plays no role in transport across the membrane for the systems under study and can be ignored safely. However, the equilibrium coupling shown makes a major contribution to the transport via membrane and should be considered in the transport model using a proper equilibrium sorption isotherm.

This research work is devoted to the footprint analysis of a steel-belted radial tyre (185/65R14) under vertical static load using finite element method. Two models have been developed in which in the first model the tread patterns were replaced by simple ribs while the second model was consisted of details of the tread blocks. Linear elastic and hyper elastic (Arruda-Boyce) material models were selected to describe the mechanical behavior of the reinforcing and rubbery parts, respectively. The above two finite element models of the tyre were analyzed under inflation pressure and vertical static loads. The second model (with detailed tread patterns) was analyzed with and without friction effect between tread and contact surfaces. In every stage of the analysis, the results were compared with the experimental data to confirm the accuracy and applicability of the model. Results showed that neglecting the tread pattern design not only reduces the computational cost and effort but also the differences between computed deformations do not show significant changes. However, more complicated variables such as shape and area of the footprint zone and contact pressure are affected considerably by the finite element model selected for the tread blocks. In addition, inclusion of friction even in static state changes these variables significantly.