Composites and nanocomposites
Tohid Abdolahzadeh; Jalil Morshedian; Shervin Ahmadi
Abstract
Researchers have studied the possibility of various polymer composites for radiation shielding applications. Lightness and non-toxicity of these materials are their significant advantages compared to Pb base traditional and common shields. In this research, polyethylene (HDPE)-based composites for shielding ...
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Researchers have studied the possibility of various polymer composites for radiation shielding applications. Lightness and non-toxicity of these materials are their significant advantages compared to Pb base traditional and common shields. In this research, polyethylene (HDPE)-based composites for shielding against X-ray radiations were prepared by utilizing several weight fractions of the nano tungsten oxide, bismuth oxide, and barium sulfate, which were decorated on nanographene oxide (10, 15, 20, and 25 wt%). The linear and mass attenuation coefficient values of samples were investigated experimentally with an X-ray tube at radiology energy ranges and estimated theoretically by using MCNP code (Mont Carlo Nanoparticle program). Results illustrate that by increasing the nanoparticles content, the linear attenuation coefficient parameter and the absorbed dose values increased dramatically. The shielding efficiency of the prepared samples has been shown by measuring the HVL values. Furthermore, the effect of sample thicknesses on the attenuation properties of nanocomposites was studied in this research. The morphological properties of the samples were evaluated with SEM. The collected results showed that the particle size of the nanoparticles used has a uniform dispersion in the polymer matrix. The mechanical properties of nanocomposite samples were characterized by DMTA and tensile test. Nanocomposites containing 20% and 25% of tungsten oxide and bismuth oxide particles reached to 88% and 90% dose absorption, respectively.
Structure and property relationship
Majid Habibollahi; Morteza Ehsani; Jalil Morshedian
Abstract
In this study, poly carbonate (PC) and poly (ethylene terephthalate) (PET) were reactive melt-blended under two different conditions to produce PC/PET copolymers. For each condition, samples were taken at specified mixing times representative a specific structure of copolymers and each one employed to ...
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In this study, poly carbonate (PC) and poly (ethylene terephthalate) (PET) were reactive melt-blended under two different conditions to produce PC/PET copolymers. For each condition, samples were taken at specified mixing times representative a specific structure of copolymers and each one employed to physically compatibilize a PC/PET blend with a fixed composition. Reactive blending and copolymer structure are described by solubility analysis results. Continues declining and going through a minimum are two trends of solubility versus mixing time depending on reactive blending condition. Decreasing and increasing patterns of solubility curves were attributed to the formation of copolymers with longer and shorter block lengths, respectively, and the level of solubility was related to the amount of produced copolymers. Differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) techniques were employed to investigate blend compatibility. The content and structure of copolymers showed favorable correlation of Tg differences of blend components and PET crystallinity. As expected, Tg of blend components approached to each other by the addition of copolymers, and the copolymers with longer block length caused less Tg differences. The melting point and crystallinity of PET were affected by introducing the copolymers too. In addition to the main melting endotherm, melting endotherm peaks of compatibilized blends had a shoulder that its corresponding melting point and crystallinity are related to the copolymer structure so that the longer length of block copolymer or higher its amount leads to the higher melting points. The SEM micrographs showed that, after the addition of the copolymer, smaller PET particles formed and uniformly dispersed in the PC matrix. A strong correlation between the blend morphology and the level of blend compatibility was demonstrated. The more compatibilized PC/PET blend, the better dispersion of PET particles in the PC matrix was obtained. The results of this study could be a basis for designing and production of compatibilizers suitable to achieve a desired level of compatibility in PC and polyester blends, specially in PC/PET blend.
Structure and property relationship
Ali Yadegari; Jalil Morshedian; Hossein-Ali Khonakdar; Udo Wagenknecht
Abstract
High density polyethylene (HDPE) films were produced using cast film extrusion process with different draw ratios, ranging from 16.9 to 148.8. Morphology, crystallinty and orientation state of crystalline and amorphous phases of the cast films were investigated using scanning electron microscopy (SEM), ...
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High density polyethylene (HDPE) films were produced using cast film extrusion process with different draw ratios, ranging from 16.9 to 148.8. Morphology, crystallinty and orientation state of crystalline and amorphous phases of the cast films were investigated using scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and polarized Fourier transform infrared spectroscopy (FTIR) analyses, respectively. The anisotropic crystalline structures of row-nucleated lamellar morphology were observed for the films produced with high draw ratios. The crystalline phase axes orientation functions were found to be significantly dependent on the applied draw ratios. As expected, annealing increased the crystallinity and melting point temperature (Tm) of the cast films and on the other hand, it also enhanced the crystalline phase orientation. However, the results revealed that annealing also promoted non-twisted lamellar structures, since it increased fc values (c-axis orientation function) and decreased fa values (a-axis orientation function) simultaneously. Additionally, it was found that the annealing induced enhancement in c-axis orientation function was more significant for the cast films with lower draw ratios, therefore, it was dependent on the draw ratio.
Structure and property relationship
Jalil Morshedian; Yousef Jahani; Farshad Sharbafian; Foroogh Sadat Zarei
Abstract
HDPE monofilaments were obtained using different extruders and drawn by post-extruder equipments. After solidification, drawn and undrawn monofilaments (draw ratio 7:1) were irradiated with 10 MeV electron beams in air at room temperature at 25, 50, 75, 100 and 125 kGy dose ranges to induce a network ...
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HDPE monofilaments were obtained using different extruders and drawn by post-extruder equipments. After solidification, drawn and undrawn monofilaments (draw ratio 7:1) were irradiated with 10 MeV electron beams in air at room temperature at 25, 50, 75, 100 and 125 kGy dose ranges to induce a network structure. HDPE crosslinking was studied on the basis of gel content measurements. The fibers were examined by differential scanning calorimetry (DSC) and measurements of mechanical properties.It was noted that gel fraction increased with irradiation dose up to 75 kGy and showed a significant increase with draw ratio, but at higher doses remained without considerable change. Melting temperature of drawn fiber increased with raising irradiation dose but decreased in undrawn sample. Also a bimodal endotherm peak was observed for drawn polyethylene irradiated in air.The changes in melting temperature and appearance of bimodal endotherm were related to the radiation chemistry of polyethylene in the presence of oxygen and interlamellar interactions. Heat of fusion and degree of crystallinity slightly increased for undrawn and drawn samples but, heat of crystallization was reduced by increasing irradiation dose due to increase the degree of crosslinking. Results of mechanical properties reveal that no significant changes seen in Young’s modulus by increasing irradiation dose. As a result of oxidative degradation happened by presence the oxygen molecules during the irradiation process, tensile properties of irradiated fibers decreased but elongation at yield for undrawn and elongation at break for drawn fibers boosted by increasing irradiation dose up to 125 kGy.
