Iranian Journal of Polymer Science and Technology
Year:2007 | Volume:20 | Issue:1 (ISSUE NO. 87)|Papers Count:11

Production of polymeric foams by extrusion method has found a special important place in plastics processing in recent years. Today the most important polymeric foams which are made by this method are polystyrene and polyethylene foams. Polyethylene because of its low water absorption, easy processability, electrical and weather resistance and ability to produce foams with different densities is specifically important. In this paper, low-density polyethylene (LDPE) foam extrusion process by chemical blowing agent with a die and calibrator design is discussed. The effect of die angle and foam formulation on the expansion ratio and foam morphology is studied. The results show that LDPE foams can be produced in normal polyolefin extruders by changing the die design.

Cure kinetics of the SBR compound were studied using rheometer, direct temperature determination by a multi-recorder and RPA machine. The compound was first prepared in an internal mixer and a two-roll mill. Then rheometry technique was carried out at different temperatures to calculate the degree and rate of cure.By a non-linear fitting procedure, different parameters and errors mean for every kinetics model were determined. By using kinetic parameters and direct determination temperature by a multi-recorder machine from the compound in the center of mould and introduction of time-temperature profile in RPA programme, the deviations of degree of curing in non-isothermal conditions were calculated. By numerical diffractions and integration methods, we know that autocatalytic model results showed good agreement compared to RPA machine data. Therefore, autocatalytic model can provide an acceptable explanation of curing behavior of compound in isothermal and non-isothermal conditions.

In the present work, some membranes were prepared under thermal phase inversion from ethylene/vinyl acetate (EVA) with 18 and 28 percentage vinyl acetate content. Polymers were dissolved in hot tetrahydrofurane (THF) and were cast on glass plate. The permeability and morphology of the prepared films were investigated. The oxygen passage was determined at various operating pressures from 2 to 11 bars. The morphological studies were carried out by using scanning electron microscopy (SEM). The results showed that the carbon dioxide permeation is higher than nitrogen and oxygen and while, oxygen and nitrogen permeation through both EVA do not change with pressure, but carbon dioxide permeation increased from 18 to 23 barrer for EVA-28 and 15 to 20 barrer for EVA-18 by pressure variations. Increasing of vinyl acetate groups led to selectivity of CO2 permeability of polymer. The variations of O2/N2 selectivity changes against CO2/N2 were not considerable. The SEM photographs showed an asymmetric integrally skinned structure with porous substrate in all samples.

Slurry polymerization of HDPE using THT catalyst at 7 bar pressure and 700C was carried out in a 5 L semibatch reactor in absence of hydrogen as chain transfer agent. In this study, the effect of different co-catalysts including tri-ethyl aluminium (TEAl), tri-isobutyl aluminium (TiBAl) and tri-n-octyl aluminium (TnOAl), on the polymerization kinetics has been investigated. Furthermore, the effect of temperature and pressure on the polymerization of HDPE has been studied, using TEAl co-catalyst. The rate of polymerization increases with increasing the ratio of co-catalyst concentration to Ti, into a certain level, and decreases after reaching an optimum level. The polymerization rate and yield with TEAl cocatalyst is greater in comparison to TiBAl and TnOAl. The effect of co-catalyst concentration on polymerization rate is similar to results derived from Longmuir-Hineshelwood equation. The activity of catalyst reaches a maximum at 70oC. Polymerization rate is proportional with monomer pressure powered by 1.69.

Blends of poly (caprolactone) based polyurethane with poly (vinyl chloride) are produced to study the shape memory effect of the systems. The said polyurethane is composed of very fine soft and hard phases which the soft phase or diol being poly (caprolactone) and the hard phase is the corporation of methylene-bisphenyl diisocyanate and butane diol as the chain extender. Blends of polyurethane/poly (vinyl chloride) with weight percentages of 0, 10, 20, 30, 40, 60 and 80 for polyurethane were made using solution procedure with dimethyl acetamide as a solvent. Then the compatibility, tensile properties and the extent of dispersion of one phase in to another were analyzed. The existence of one transition temperature in dynamic-mechanical tests curves and the displacement of peaks with changing composition in FTIR spectra show the compatibility of two polymers. The pictures of optical and electron microscopes indicate a suitable dispersion of two polymers. FTIR Spectra show that with increasing PVC percentage, the intensity of phase separation between the hard and soft phases improves. The results give storage indication of these blends having shape memory effect.

Increasing growth of using PET bottles has effected made some impacts on different methods of improving their recycling processes. One of the most important feasible methods for this purpose is mechanical recycling. In this research, PP/PET blend fibers with different percentages of PET, in two groups including recycled and virgin PET, were prepared by melt spinning method and their properties have been compared. Testing in this study has been included tensile test, optical microscopy (OM) and scanning electron microscopy (SEM). On the basis of tensile test, tensile strength of fibers with recycled PET is lower than fibers including virgin PET but their elongation-at-break shows higher values. According to OM and SEM micrographs, in both of these groups including virgin and recycled PET, a lack of continuity is observed in moderate percentage. In general the results show that samples with recycled PET have comparable properties with ones including virgin PET.

In this investigation, the influence of nanoclay on mechanical performance of an epoxy resin was evaluated. XRD and transmission electron microscopy show intercalation of clay in the epoxy matrix. The results of mechanical tests indicate that the addition of nanoclay increases compressive yield strength, tensile modulus and fracture toughness of epoxy. Based on the electron microscopy studies, crack deflection, formation of new surfaces and breakage of the clay stacks are the most dominant toughening mechanisms in the intercalated nanocomposite.

Physical and mechanical properties of rigid polyurethane (PU) foams are extensively depending on their preparation procedure and foaming behavior. Compression strength of the PU foams and morphological behavior of their cellular structure parallel to foaming rise direction is completely different to vertical direction. The rigid polyurethane foams were prepared from 4,4' -diphenylmethane isocyanate and ester type polyol. The prepared foams were moulded using a steel mould, an open and a closed paper moulds. The density of PU foams varied between 75 and 200 kg/m3. The scanning electron microscopy (SEM) micrographs show that in short and closed mould, the morphological behavior of cellular structure is almost similar in parallel and vertical directions of foaming rise. But, the results obtained from samples prepared by long and open mould illustrated that cellular morphology in parallel and vertical directions to foaming rise is clearly different from each other. Furthermore, the results of compression strength tests in parallel and vertical to foaming rise direction show a significant increase in modulus and compression strength in parallel direction and the resulted foam has anisotropic properties.

Two frequently used polystyrene grades used for preparing polystyrene disposable containers including general purpose polystyrene (GPPS) and high impact polystyrene (HIPS) were heat decomposed. Decomposition reactions were carried out in the presence of hydrated and anhydrous metal sulfates and metal oxides catalysts at temperatures 280-3500C and crude styrene monomer was obtained. In order to obtain an optimum condition of reaction, the effect of different parameters on decomposition reaction efficiency such as catalyst type and percent, temperature, polystyrene type and vacuum application were examined. The best efficiency obtained was 0.87. The results showed considerable increase in reaction efficiency by carring out decomposition reaction under vacuum.

One of the methods used to overcome the corrosion problem associated with steel rebars in reinforced concrete is the application of composite rebars. In this study, composite rebars having four different surface configurations were constructed and examined. These include an externally wound FRP deformation on a pultruded rod (RT), pultruded rod with sand sprayed on the surface (RS) and a combination of the latest two methods (RTS). For comparison, a pultruded rod with a smooth surface (RO) was used in these experiments. To assess the bonding strength to concrete, rebars were embedded in concrete columns in embedment lengths of 10 and 15 times of rebar root diameter, 12 and 18 cm, and the pull out force as well as force-displacement behavior were evaluated. The results showed that an increase in surface roughness of composite rebars by whatever means, has a positive effect on increasing the adhesion of rebar to concrete. The RO composite rebar showed, however, the lowest bonding strength to concrete followed by RT, RS and RTS rebars. Bonding strength to concrete in rebars with FRP wounded surface was entirely controlled by bonding strength of the externally wound FRP to pultruded rods. Also, RTS rebars with embedment length of 12cm showed greater adhesion to concrete, whereas, in samples with embedment length of 18 cm, RTS and RS rebars showed close results. In all pull-out tests, sand sprayed and FRP wounded rebars, delamination of the surface configuration was the major mode of failure. In addition, RTS rebars showed the best performance in adhesion to concrete among the others.