Iranian Journal of Polymer Science and Technology
Year:2007 | Volume:20 | Issue:2 (ISSUE NO. 88)|Papers Count:11

PP/PEP blends, because of different solubility factors, are incompatible. The aim of this research was to use PP-g-MA compatibilizer in a two-component blend. After preparing this compatibilizer in internal mixer and investigating different parameters on producing process, optimum compatibilization was obtained. PP/PET (60/40) Blend fibers with different percentages of this compatibilizer in two groups, including recycled and. virgin PET were prepared. The results show that PP-g-MA causes smaller PET phase in fibers including vir- gin PET but in fibers with recycled PET, up to 5 wt% of compatibilizer, the cross-section uniformity is reduced. In addition, by increasing compatibilizer, the mechanical properties of two groups including recycled and virgin PET, at first increase and then decrease. Cold drawing causes increase in crystallinity and therefore enhancement of tensile strength. It is obvious that fibers with recycled PET and compatibilized fibers demonstrate better mechanical properties by cold drawing.

As we know oxygen is one of the main inhibitors of polymerization of vinyl acetate. Therefore, nitrogen is used in order to make sure of system's high purity. To maintain purity it is necessary to find out the rate of the oxy-gen solution in polymerization system under different conditions of polymerization. It is concluded that incoming nitrogen to the system would remove the oxygen from the system and on the other hand the increase in temperatures a great help. The time length for this process is evaluated in polymerization system at the same time.

In this research, the effect of temperature on the physical and chemical behavior of nylon 66 tire cords in the range of 50-200°C and 16 h testing was studied. The results showed that heat treatment considerably reduced the breaking strength of cords. The intensity of reduction of breaking strength below 100°C and above 120°C was more pronounced than intermediate temperatures. The changes in properties above 120°C were attributed to broadening of molecular weight distribution as ascertained by GPC studies. The increase of irregularity in the polymeric chains was ascertained by shrinkage and birefringence studies. It is found that by raising the temperature, both chain folding and thermal degradation occur, because there is decomposition of the amorphous region occurring as evident by FTIR spectroscopy and elastic modulus and birefringence studies. The changes in properties below 100°C were attributed mainly to decomposition of the amorphous region. On the other hand the percentage of crystallinity increased and tire cord became more brittle and its tensile strength below 100°C was decreased. The lower reduction of tensile properties in the intermediate temperatures of 100-120°C was due to no change in polydispersity and irregularity of the polymeric chains compared to higher temperatures as well as smaller increase in percentage-of, crystallinity compared to lower temperature treatments.

In many processes polymeric foams can be produced by using chemical or physical blowing agents. In this work for polyethylene foam production, the chemical blowing agents and compression molding process were employed. At first, by using DSC diagram of two polyethylene grades, a suitable polyethylene grade was selected for foam production and then we discuss about blowing agent critical percent in foam production. Usually it was assumed that foam density decreases by increasing the chemical blowing agent concentration, but it is discovered in this work that there is a critical percent for each chemical blowing agent, for beyond critical percentage foam density increases by increasing blowing agent percent. The level of critical quantity is related to the amount of released gas of each chemical blowing agent. In this study, we have used three types of chemical blowing agents. Because of relationship between foam properties and foam density, a formulation is presented which is applicable for a special end use.

In this research, shape memory effect of polycaprolactone based polyurethane/poly (vinylchloride) blends in which the PVC weight percentage are 10,20, 30, 40, 60 and 80 were studied using DMA apparatus. The compatibility, tension and dynamic-mechanical properties of these blends have been studied by the authors and this paper specifically deals with the tests results of shape memory effect. The results of tension tests in about 20 percent showed that with increasing PVC content in the blends, recovery rate of temporary shape to permanent shape, the degree of recovery, and the fixity in quantity of temporary shape are improved. Therefore, the supplementary shape memory tests were performed on the blend with the highest PVC weight percent (80 percent). In this blend, with increasing tension in thermomechanical cycle, the amount of recovery to earlier shape is decreased due to higher plastic strain. The shape memory tests in consecutive cycles were done on this blend and the behavior of the first cycle was compared with the second and the third cycles. One small tensile handy apparatus was used in order to accomplish shape memory tests in higher tension values and the DMA results were registered. In this research the blend with 80 weight percent of PVC as the best shape memory effect was selected.

In the present study the sol-gel method is used for synthesis of amorphous nanostructure silica polymer using tetraethoxysilane (TEOS) as silicon source. This polymer can be used in manufacturing of nanoporous asymmetric membranes. The effect of catalyst on silica particle size has been studied under acidic and basic conditions. Acid-catalyzed reaction leads to the formation of fine particles while the base-catalyzed reaction produces larger particles. The presence of cationic template surfactant namely cetyl pyridinium bromide (CPB) directs the structural formation of the polymer by preventing the highly branched polymeric clusters. This will increase the effective area of the produced silica membrane. Nitrogen physisorption tests by Brunaver- Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods revealed that the surface area of the membrane increases significantly around 5-folds when acid-catalyzed reaction is used. 29Si-NMR test is also used to study the aging time effect on the level of silica polymer branching. The results show that in acidic condition, aging time up to three weeks can still affect branching. The calcinations process, in which the organic materials and CPB (surfactant) are burned and released from the silica particles, is studied on template free silica materials as well as templated silica materials using TGA and DTA techniques.

Low temperature plasma technology is well established in surface modification of polymer materials on industrial scale. This method modifies surface properties of polymers without chemicals, manual work and reducing chemicals and energy consumption. In this study, low pressure plasma treatment was used to develop hydrophilic properties of polyethylene terephthalate (PET) fabrics. It was found that, plasma treatment had a significant effect on the hydrophilicity properties of PET fibers. Plasma treatment increases wetting, wicking and electric conduction of fibers but the recovery of fibers was not affected by the plasma treatment. Also, scanning electron microscopy (SEM) micrograph show some surface fibers etching that created some voids.

Among various reported membrane-based gas separation processes, the best explanation is generally achieved by the solution-diffusion model. The main factors in this model are the solubility and diffusivity of permeation components through the membrane. The prediction of permeability and diffusivity in multicomponent gas permeation as well as the separation evaluation equilibrium and kinetic interactions requires a proper explanation of sorption and diffusive phenomena in the polymer matrix. Investigation made by various researchers in this area shows that the equilibrium interaction (sorption step) plays the key role in determining diffusion and permeation in multi component system. Therefore, the proper description of sorption behavior of gas mixture in the polymer is an essential task. The dual-mode sorption (Langmuir-Henry) is usually used for the description of equilibrium isotherm of gases in glassy polymers based on this model; the diffusive behavior of the system is subsequently analyzed by the partial immobilization model. In this study, the equilibrium sorption of CO2/CH4 mixture in various polymers was modelled using the experimental data available in the literature. The differences in the mechanism of adsorption for CO2 and CH4 were analyzed by considering variations in mode of sorption for each adsorbed component at different pressures. By introducing a new adsorption parameter, P50/50, (the pressure at which the portion of two modes in sorption are equal the contribution of each adsorbed component in occupying Longmuir sites was evaluated. The results indicate that the relative significance of sorption mode for each component is a function of pressure and it is different for various polymers.

In some special cases, rubber compounds with high amounts of unsaturated elastomer are recommended with organic sulfur donors instead of mineral sulfurs. In this condition, activated sulfur is produced in situ and curing process is facilitated without accelerators. Organic sulfur donor compounds have low thermal stability and in the vulcanization temperature produce free and activated sulfurs. The advantages of these compounds are:1. High effectiveness of curing agent in low quantities in rubber compounds manufacturing.2. Producing activated sulfurs in controlled condition and avoiding the over curing of rubber compounds.In this report the novel synthesis of some derivatives of diamino-disulfides which can be applied as sulfur donors in vulcanization of special rubber compounds is introduced. The key process is reaction of sulfur mono chloride with amines in petroleum ether as solvent in low temperature. Dithio-dimorpholine (DTDM), dithio-dipipyridyl (DTDP), dithio-bis dibutylamine (DTBDB) and dithio-bisdiisopropyl amine (DTBDI) were prepared according to this method. All products thus obtained were characterized by 1H and 13C-NMR spectroscopes. The effects of accelerating and sulfur donoring of all prepared agents were detected in rubber compounds with natural and synthetic rubber bases. All physical, chemical, reo logical and mechanical properties of rubber compounds based on prepared sulfur donors were characterized.

Nanocomposite materials have recently attracted increasing interests in the field of modeling. Finite element modelling can be used for computation of bulk properties of polymer/clay nanocomposites. In this study, by considering the structure of a nano-composite material, a quasi real model is proposed. The model has been used to predict the elastic constants by selection of suitable elements and boundary conditions. The effects of nano-structural parameters on the mechanical properties of a polymer/clay nano-composite are studied. The geometrical overlap of particles, horizontal distance between particles, length of particles and nano-clay volume fraction are defined as functions of the nano-structural parameters and their effects on mechanical properties of nano-composites are studied by a finite element modelling technique.