فهرست مطالب jalil morshedian

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.

This study introduces a novel polyvinyl chloride (PVC)/tungsten composites with characterization of their shielding properties by employing different techniques. The PVC/tungsten composites were produced by employing various weight fractions of tungsten micro-particles including 0, 20, and 40 % wt via melt blending method. In the next step, the linear attenuation coefficients of prepared composite samples were experimentally measured at 662 keV γ-ray, and then were compared to the data estimated using MCNP simulation code and XCOM software. Also the shielding properties of samples were evaluated experimentally with an X-ray tube at 40 kVp. Recorded results showed that by increasing the weight percentage of the tungsten micro-particles, the coefficient of linear attenuation and also the absorbed dose values were increased dramatically. Samples containing 20, and 40% wt of tungsten micro-particles reached to 89.60 and 92.26 %of dose absorption, respectively. Interestingly the proposed composition were approximately 2.3 lighter than the commercial shields. The linear attenuation coefficient of the composite shields has been calculated to be 0.20 cm-1, which was comparable with commercial Pb-based shields. Tungsten micro-particles addition to PVC matrix can increase the absorbed dose value. Plasticized PVC has suitable flexibility and low stiffness value, therefore it can be a good alternative for commercial aprons and other Pb-based shields in low energy voltages.

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.

Membranes are thin layers that act as selective barriers to separate the components of materials and control the mass transfer between different phases. Therefore, their two main functions include: component selectivity and the permeability characteristics. Membranes according to their material sources are classified into four categories referred as polymeric, ceramic, metal and liquid types. Among these, polymeric membranes are the most favorable materials because of their availability in various chemical structures, their optimum physical properties and lower prices. Polymeric membranes are produced by four main methods known as solution casting, stretching, template leaching and track etching. Among them, stretching technique is inexpensive and because no solvent is used in this process, stretching method has lower environmental impacts. Among different polymers, polyolefines such as polyethylene (PE) and polypropylene (PP), due to their lower price, semi-crystallinity, good mechanical properties, chemical stability and easy process ability, are more appropriate for manufacturing of polymeric membranes by stretching method. Porous membranes are used in applications such as battery separators and drug delivery devices for controlling the permeation rate of chemical components. In this paper, we present some useful information on the above subject by reviewing the related published works in this area.

Hypothesis: Polymer nanocomposites have found enormous applications owing to superior physical and mechanical properties such as modulus, strength and barrier behaviour, etc. Contrary to polymer microcomposites, polymer nanocomposites benefit from lower density and being less problematic in processing. In this study, nanocomposites of polyolefin elastomer (POE)/nanosilicon carbide (SiC) and polyolefin elastomer/nanoclay with different percentages of nanoparticles were prepared using melt mixing method in the presence of vinyltriethoxy silane as interfacial modifier.
Nanocomposite samples were prepared in a Brabender internal mixer using a roller mixing equipment. The fill factor was selected as 0.75. The mixing was carried out at a speed of 60 rpm at 120°C. The resulting nanocomposites were then subjected to various tests to investigate their physical, mechanical and rheological properties.
Findings: Sheet-like nanoclay particles have higher aspect ratio compared to spherical nanoSiC particles. Nevertheless, the results indicated that POE/SiC nanocomposites had higher tensile strength and elongation-at-break compared to nanoclay-reinforced composites. This was attributed to higher interactive efficiency between SiC nanoparticles and POE matrix. The moduli of nanocomposites at similar content of nanoparticles showed the same values regardless of the type of nanoparticles. Higher rheological properties were observed for nanoclay nanocomposites, though; the amount of increase was lower than those reported in literature. Morphology investigations of SiC and clay nanocomposites exhibited a comparable degree of dispersion of nanoparticles for both types of nanocomposites at similar compositions. Thermal properties of nanocomposites were studied by thermogravimetric analysis and differential scanning calorimetry. The results showed that the melting temperature and degree of crystallinity of both types of nanocomposites decreased with increasing nanoparticles content; however, the observed decrement was higher for POE/SiC nanocomposites. Thermal stability of POE/clay nanocomposites was higher, which could be attributed to the nanoparticle geometry.

Shielding radiation from both x-rays and gamma-rays is important for personnel in medical fields e.g. interventional radiology, nuclear power stations, and other inspection facilities where radiation is involved. Lead is known for its effective shielding property against these high energy radiations, however heaviness and toxicity are its main drawback. In this study effectiveness of non-lead polymeric composite materials, which include high-atomic-number / or known barrier elements to absorb photons from the radiations was evaluated. High density polyethylene as matrix and powders of spherical W and lamellar MoS2 and B4C as particulate fillers with different loadings were melt mixed in an internal mixer, followed by compression molding in to sheet form. The goodness of dispersion was manifested via SEM and EDX images. Radiation attenuation capability of these compounds was examined with direct diagnostic x-ray exposure and compared with that of Pb. Dynamic rheology measurements were carried out to evaluate viscoelastic properties of the molten composite materials, necessary in shaping process operations. The mechanical and thermal properties were further investigated from the product performance point of view. Results demonstrated that the flexible composite sheet made with 45% (wt) tungsten provided comparable x-ray absorption to non-flexible lead sheet but much lighter in weight. Significant difference was observed between flow characteristics and yield strength of composite materials of highly loaded spherical metallic particles and lamellar particles of metallic compounds. The melt viscoelastic behavior of former was similar to that of neat matrix melt.

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.

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.

In order to increasing of hydroxy functionality of HTPB, an in-situ nitroxide mediated polymerization (NMP) of 1,3-butadiene was carried out in presence of TEPA as a polyfunctional nitroxide precursor. The effects of this new hydroxyl-terminated polybutadiene on thermal and dynamic-mechanical properties of its corresponding polyurethane elastomer were studied by DSC and DMTA tests. A significant enhancement in crosslink density of the elastomeric product with small increase in glass transition temperature was achieved using PFHTPB. Also the absence of any endothermic peak in DSC thermogram was an indication of no crystalline domain existing in these samples.

In this research the influence of using waste Poly Ethylene Terephthalate on the mechanical and rheological properties of wood flour filled PP composites has been studied. PET contents varied from 10-33 wt%. Mechanical properties were characterized by tensile testing، while their fracture resistance was determined by impact measurements. The melt rheological behavior of the composites was also studied by a rheometer in the oscillatory mode and dynamic rheological properties such as complex viscosity، storage modulus، loss modulus and damping factor were evaluated at190°C. The results showed that stiffness increases by adding waste Poly Ethylene Terephthalate. PET when added in low concentrations، caused tensile strength to be lower than that of PP composites filled with pure wood flour. Increasing the concentration of waste PET، led to composites with higher amount of tensile strength. The samples containing waste PET had higher complex viscosity and storage modulus than composite without PET. Likewise، it was observed that the damping factor in the PP/Wood composite decreased by incorporating waste PET to the compositions.

Anionic ring-opening polymerization of ε-caprolactam leads to the formation ofpolyamide 6 (PA6). This reaction takes place at a significantly faster reaction rateand gives a narrower molecular weight distribution than the other techniques.Due to this advantage, anionic polymerization of ε-caprolactam towards PA6 in meltblending was investigated in this work. PA6 was prepared in an internal mixer via meltpolymerization of ε-caprolactam as a monomer with sodium caprolactam as its catalystand hexamethylene diisocyanate as an activator. The effects of various concentrationsof catalyst and activator on the initiation time of the reaction and on the residualmonomer were determined. The residual monomer was collected using a solventextraction method and determined by GC-mass technique. The physical andmechanical properties of the PA6 prepared via melt blending and of a commercial PA6prepared were determined by differential scanning calorimetry (DSC), thermalgravimetric analysis (TGA), tensile and impact tests. The experimental results showedthat addition of 3% catalyst and 3% activator to the formulation gave the bestproperties. These conditions led to the lowest residual monomer and bettermechanical properties as well. The other novel aspect of this investigation was theformation of nanofibril during melt polymerization of ε-caprolactam. Mechanicalproperties showed that the PA6 prepared by using this technique and theabove formulation were similar to the PA6 commercial grade.

Cross-linking of polyethylene is a subject of interest, having been emerged as a result of the need to meet application requirements which were not satisfied by the neat polyethylene itself. Although this review is aimed at silane method of cross-linking, the other cross-linking methods, namely: radiation, peroxide and azo methods have been presented briefly for a better understanding of the merits of perspectives of the more recent methods, especially the two-step silane method. Freeradical grafting of unsaturated hydrolyzable alkoxy-silanes onto polyethylene chains by a peroxide initiator followed by moisture cross-linking is the most versatile crosslinking method and may be successfully used for other thermoplastics as well. Different techniques of silane cross-linking, i.e., the “one step” Monosil® process and the “two-step” Sioplas® process have been discussed with more emphases on Sioplas® process, as it is less expensive and readily achievable. The grafting step which is performed by reactive processing is the major and key process in Sioplas® technique. The state-of-the-art of a two-step silane grafting and cross-linking has been presented. In this regard, the effects of various parameters, such as the type and quantity of silane, peroxide, stabilizing agent, catalyst, micro and macromolecular structures and physical form of polyethylene, additives, and reaction temperature and time have been described in relation to efficiency of grafting and cross-linking. These data were evaluated in turn by torque, MFI, FTIR, and gel content studies.

Dynamic rheological behaviour and mechanical properties of neat and reactive LDPE/PDMS immiscible blends were investigated, focusing on low frequency data analysis as an approach for microstructural characterization. It was observed that by analyzing low frequency data, some microstructural features such as development of continuity in the minor phase and occurrence of interfacial slip phenomenon of neat blends could be revealed. Development of continuity in the minor phase, as proved by SEM micrographs, resulted in a significant increase in low frequency values of η′ and η″ while interfacial slip phenomenon was inferred by comparing the rheological data with predictions of log-additivity and inverse mixing rules. To induce reactive blending, different amounts of DCP as curing agent was added to PDMS phase. By studying the influence of reactive blending on thermal behaviour and viscoelastic properties in low frequency region it is revealed that curing reaction during melt mixing could lead to formation of an interphase layer which acts as an efficient compatibilizer between the phases. Thus, reactively compatibilized blends exhibit desirable tensile properties.

Most polymer blends are immiscible and need to be compatibilized. Compatibilization can be accomplished either by addition of a compatibilizer or by reactive processing. Grafting has been the most common method for compatibilizing two immiscible polymers during reactive processing. In this work, the reactive blending of EPDM (ethylene- propylene-diene monomer) rubber and SAN (styrene-acrylonitrile) copolymer was studied. The blends were prepared in an internal mixer with three types of organic peroxides as initiator. The effects of initiator type and concentration, EPDM content, and mixing sequences of components were investigated. Blends were separated to their structural components (i.e., SAN, EDPEM, SAN-g-EPDM, and gelled EPDM) which were then characterized by FTIR spectroscopy and SEM microscopy techniques. Mechanical properties including tensile and impact strength as well as elongation-atbreak were measured. From the three initiators used, the blends which have 2,5- dimethyl-2,5-di-(t-butyl peroxy) hexane as initiator show better mechanical properties. Also, SEM studies reveal a good compatibility for SAN/EPDM blends using this initiator. The blend using 40 wt% of EPDM of the mentioned initiator contains 16.24 wt% SANg- EPDM. Impact strength of the blends was affected by mixing sequences of the components. The Blends prepared by mixing sequences of SAN/initiator/EPDM show the highest impact strength of the order of 45 J/m.

Film blowing is the most important method in producing polyethylene films. For years, low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) blends have been used in blown film manufacture. In this paper basic mathematical models and response surface graphs have been used to illustrate the relationship between blown film fabrication variables and mechanical and optical properties of 50μm films made from LLDPE and LDPE blends. These films are currently used in various non-barrier packaging applications. Using a Box-Behnken statistical design experiment methodology, the effects of LLDPE/LDPE ratios (25-75%), blow up ratio (1.5-2.5), melt temperature (215-235oC) and frost line height (1-3D) were evaluated on the mechanical properties, e.g., tensile and tear properties in both machine direction (MD) and transverse direction (TD) and impact strength as well as optical property such as haze. The R2 values of all the responses of mathematical models are obtained to be more than 0.85 which is an indication of very good fiting of the model with the experimental data of response surface method used. Although this study is confined to the equipment and resin types used, it can offer some curves and equations for predicting the properties of produced films. The processors can use these data to find the first approximation of the most important blown film parameters to achieve their favorite product properties.

Mixing and injection processes of polycarbonate and ABS (acrylonitrile-butadienestyrene) blend were studied in order to optimize the impact strength. Mixing time (rotation speed) and temperature were selected as the main mixing process factors. In the course of injection step, temperature and pressure of injection, and mould temperature were chosen as process factors and blend composition was selected as material factor. The Taguchi orthogonal array was applied to determine the significance level of each factor. An experimental model was developed to predict and optimize the impact strength. Based on the analysis of variance (ANOVA), blend composition, mixing time, and temperature, and mould and injection temperatures, had more effect on impact strength of the blend, respectively. However, injection pressure has no significat effect. Then, the level of each factor for maximum impact strength was determined. The validation test approves the result. Hence, the model is suitable for PC/ABS part design with desired impact strength.

One of the most important post-reactor modifications of polyethylene is cross-linking. It improves some properties of polyethylene such as environmental stress cracking resistance, chemical and abrasion resistance, and service temperature. In this study, the effect of peroxide cross-linking on the rheological behaviour of low density polyethylene was investigated by using a combination of creep test and differential scanning calorimeter (DSC) in isotherm condition. The used peroxide was di-cumyl peroxide and its concentration was 2 wt%. The experiments were carried out at 150,160, and 170oC and the change of bulk viscosity due to network developing was determined. For delivering of local derivatives smoothing techniques were applied on creep data. The rate of increment of viscosity increased with increasing the temperature, and the major of this increment took place in the first stages of reaction.

Epoxy resins are considered as one of the most important classes of thermosetting polymers for many industrial applications, but unfortunately they are characterized by a relatively low toughness. In this respect, many efforts have been made to improve the toughness of cured epoxy resins by the introduction of rigid particles, reactive rubbers, interpenetrating polymer networks and thermoplastics within the matrix. In this work, hydroxyl-terminated polybutadiene (HTPB) as a modifier, firstly, was crosslinked by variable content of divinylbenzene (DVB) in the presence of epoxy resin (ER) and then the modified matrix was cured with 1-methylimidazole as a curing agent. Infrared spectra showed the existence of a chemical reaction between modified HTPB (MHTPB) and the ER. Most of the tensile properties attained a peak at an approximately 20 phr (part per hundred rubber) DVB content, where the toughening reached its maximum. For both notched and un-notched specimens, a two-fold increase in izod impact strength was obtained by the addition of just 20 phr DVB compared to the neat resin. On the addition of DVB, the Izod impact strength varied from 0.54 to 0.71 kJ/m2 for notched specimens and from 1.43 to 6.66 kJ/m2 for un-notched specimens. Whereas, KIC varied from 1.35 to 2.59 MPa.m1/2 with increasing DVB content. By SEM analysis the average diameter was found to be about 5 μm (corresponding to maximum of toughness) for modified rubber particles. The overall results have shown that it is possible to obtain an excellent impact strength and good mechanical properties with the use of MHTPB as a tougheningagent for the epoxy resins.

The electron beam radiation technique has been explored as the latest and most effective means of forming chemically active sites on LDPE surface. In this novel work a solventless grafting of 2-hydroxyethyl methacrylate (HEMA) on to LDPE surface was conducted. Thus prepared active sites were exploited to subsequently solventless graft copolymerization of HEMA onto LDPE by high energy electron beam radiation (10 MeV) at dose range of 10 up to 200 kGy at atmospheric pressure in air. As HEMA could not wet LDPE surface, its synthesized tacky polymer was used for coating and then grafting purposes. LDPE film and sheet surfaces were impregnated with the prepared adhesive and were irradiated. FTIR Spectra showed that the concentration of characteristic bonds of poly(HEMA-g-LDPE) (C=O in ester groups, in hydroxyl groups as C-OH, and ether carbon bonds as C-O) increased with increasing irradiation dose, also, the percentage of grafting significantly increased up to 60%. The hydrophilicity of the grafted surface considerably increased compared to that of the ungrafted ones as contact angle measurements showed a 72% decrease. Furthermore, the yields of gel content measurement were investigated and the topology of the surface and cross-section of poly(HEMAg- LDPE) films and sheets was studied by means of SEM. Moreover, the mechanism of achieving up to 70% cross-linked network in solid semi-crystalline LDPE is discussed.

Brominated flame-retardants are one of the common and efficient groups in producing flame retardant plastics, such as high impact polystyrene. Antimony trioxide is often used as a synergistic agent for halogenated flame-retardants. Aluminium trihydrate (ATH), also is a primitive additive for making flame retardant plastics but no report exists on synergistic effect of this compound in presence of brominated flame-retardant. In this research, the synergistic effect of Sb2O3 and ATH, in presence of tetrabromobisphenol- A as a flame-retardant agent has been compared. Limited oxygen indexes (LOI) of the compounded samples were measured by flammability tests. Also thermal gravimetry analysis (TGA) and scanning electron microscopy (SEM) were applied in order to study the thermal behaviour and morphology of the samples, respectively.

The properties of polyurethanes strongly depend on the microstructure, functionality, and molecular weight of their initial polyol used. Therefore, in this work, microstructure of polybutadiene-ol, a pre-polymer used for producing special purpose polyurethanes was determined by two analytical methods, namely, FTIR and 1H NMR spectroscopy. In the FTIR method, after obtaining εi (molar absorption in each wavelength) of a specified polyol, the microstructure (trans, vinyl and cis content) of prepolymer was measured by analyzing IR absorption bands in 966 cm-1, 912 cm-1, and 725 cm-1 due to trans,1,2-vinyl and cis configurations, respectively. In the 1H NMR spectra of polyols, microstructure was determined using the ratio of peak areas of various protons (alkylic, olefinic and methylenic) as well as signals at 2.5-4.5 ppm which indicate the position of hydroxyl groups in the back-bone of the polyol. Determination by NMR spectroscopy is an easier method and the information obtained on microstructure of the polyol is more precise than the FTIR method. Finally we established an equation to convert values obtained by FTIR to NMR.

Peroxide cross-linking of polyethylene is one of the most important methods for the production of cross-linked polyethylene (PEX). The kinetic study of the crosslinking reaction of low density polyethylene (LDPE) in the presence of 2,4- diphenyl-4-methyl-1-pentene (MSD), pentaerythritol triacrylate (PETA) and divinylbenzene (DVB) as the co-agent and dicumyl peroxide(DCP) as the cross-linking agent was carried out by differential scanning calorimeter (DSC, non-isothermal condition), rheometer and internal mixer (isothermal condition). The reaction was first order and independent of DCP and the co-agent concentration. The activation energy and ln ko (ln ko defined as the intercept of ΔH vs.1/T) did not change with DCP concentration but energy of activation decreased with co-agent and the highest decrement was observed with respect to MSD. The overall reaction rate constant (with constant value of DCP) increased with temperature due to the faster decomposition rate of peroxide at higher temperatures. By comparison of the three methods used, it was found that the different results obtained were in good agreement with each other. However, because of the higher shear rate and mechanical stress experienced in the internal mixer, the measured overall reaction rate constants were of higher values with respect to those obtained from other methods.