Polymer processing
Milad Moradian; Taher Azdast; Ali Doniavi
Abstract
Polyolefins have been widely used in the electrical insulation and cable industry in recent years. One of the main usages of these materials is dielectric insulation in coaxial cables. Low attenuation and high signal transmission speed are among the desired features in coaxial cables. The role of polyethylene ...
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Polyolefins have been widely used in the electrical insulation and cable industry in recent years. One of the main usages of these materials is dielectric insulation in coaxial cables. Low attenuation and high signal transmission speed are among the desired features in coaxial cables. The role of polyethylene foam on signal transmission speed in the coaxial cables is the main focus of this study. In the present study, the velocity factor of coaxial samples with different dielectric structures is investigated in both theoretical and experimental approaches. In theoretical formulation, only the void fraction of foam is taken into consideration and other foam properties such as cell density, cell size, and foam structure are neglected. This is the reason for the difference observed between theoretical and experimental results. In theoretical results, a linear increase in the velocity factor is witnessed with the increase of the void fraction while in experimental results there are some exceptions. The foaming degree of the samples was reached 63% causing a 37.7% decrease in theoretical relative permittivity and consequently a 26.8% increase in theoretical velocity factor. On the other hand, up to 36% increase is observed in the experimentally measured velocity factor of foamed dielectric samples compared to the samples with solid polyethylene dielectric.
Polymer processing
Moammadreza Nakhaei; Ali Ahmadi; Ghasem Naderi
Abstract
Polyamide 6 / nitrile butadiene rubber / nanoclay (PA6/NBR/clay) nanocomposite has gathered wide acceptance in industry. Laser welding, as a fabrication method, is applied to welding of polymer nanocomposites. In this study, the input parameters (clay (Closite 30B) content, laser power, scan velocity ...
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Polyamide 6 / nitrile butadiene rubber / nanoclay (PA6/NBR/clay) nanocomposite has gathered wide acceptance in industry. Laser welding, as a fabrication method, is applied to welding of polymer nanocomposites. In this study, the input parameters (clay (Closite 30B) content, laser power, scan velocity and stand-off-distance) are varied to achieve the best responses (tensile strength of welds). Response surface methodology (RSM) is utilized to investigate the effect of input parameters on mechanical properties. Morphology and tensile properties of nanocomposites were observed with scan electron microscopy (SEM), transmission electron microscopy (TEM) and tensile test. The results demonstrated that increasing the clay content from 1 to 5%wt and stand-off-distance from 4 to 8 mm decreased tensile strength of welds about 15% and 5%, respectively. The tensile strength of PA6/NBR composite is 25.6, whereas the prediction models showed that under optimal conditions of laser power of 105 W, scan velocity of 300 mm/min and stand-off-distance of 4 mm, the maximum tensile strength of PA6/NBR nanocomposite with 1, 3 and 5 % nanoclay are 27.2 MPa, 27.6 MPa and 24.7 MPa, respectively. These tensile strengths are about 99, 89 and 73% of the strength of these nanocomposites before welding.
Polymer processing
Ali Mahmoudi Yayshahri; Seyed Jamaleddin Peighambardoust; Abolfazl Shenavar
Abstract
High impact polystyrene (HIPS)/corn starch blends were prepared in presence of glycerol as a plasticizer via melt extrusion process by a twin-screw extruder. The novelty of this work is first, because of the use of pre-gelatinized corn starch as modified one and second, the procedure of making blends ...
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High impact polystyrene (HIPS)/corn starch blends were prepared in presence of glycerol as a plasticizer via melt extrusion process by a twin-screw extruder. The novelty of this work is first, because of the use of pre-gelatinized corn starch as modified one and second, the procedure of making blends by extruder which makes it ease of access and also industrially possible. The blends were then characterized by scanning electron microscopy (SEM) to visualize morphology of blends and dispersion of starch in HIPS matrix, soil burial test (SBT) to investigate of blend biodegradability by measuring weight loss of samples, Izod impact strength test to evaluate of impact properties, melt flow index (MFI), thermo-gravimetric analysis (TGA) and Vicat softening point (VSP) tests to evaluate their thermal properties of prepared blend samples. Results indicated that these properties were affected by the amount of starch and glycerol used for preparation of blends in a way that addition of starch and glycerol led to a faster degradation rate especially in first two weeks, more decomposition stages through TGA, decrease in values of Izod impact strength and VSP. Measurements also showed that higher amount of starch led to decrease in the value of melt flow rate (MFR), although it was increased by addition of glycerol.
Polymer processing
Fatemeh Hassan; Mehdi Entezam
Abstract
Irradiation of polymers is one of the most effective and economical methods for modifying their properties and for changing their applications. In this study, an extrusion grade polypropylene (PP) was treated by electron beam irradiation to produce a PP suitable for injection molding. Irradiation was ...
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Irradiation of polymers is one of the most effective and economical methods for modifying their properties and for changing their applications. In this study, an extrusion grade polypropylene (PP) was treated by electron beam irradiation to produce a PP suitable for injection molding. Irradiation was carried out at different doses (0-80 kGy) under atmosphere air and at ambient temperature. Melt flow index (MFI) measurements showed PP samples irradiated in the range of 10 to 40 kGy are suitable to use in injection molding. Electron beam irradiation decreased the viscosity and the shear thinning rheological behavior of PP. The differential scanning calorimetry (DSC) analysis revealed that electron beam irradiation increased the crystallinity percentage and temperature of PP, but decreased the melting temperature. Among all treated samples, the PP20, irradiated at the dose of 20 kGy, showed the highest impact resistance. It had higher Young’s modulus and tensile strength, but lower elongation-at-break in comparison with untreated PP.
