فهرست مطالب ismail ghasemi

The paper aims to study differential, dynamic-mechanical and biodegradability analysis of polylactic acid/wood fiber (PLA) composites using three levels of nano-graphene (0.75, 1.5 and 3%). In order to mix the materials together and to make standard specimens, an internal mixer and pressure press were used. In the analysis of differential polishing calorimeter, the addition of fibers as well as nano-graphene had a positive effect on the glass transition temperature and the degree of crystallinity, which indicates a change from softness and flexibility to hardness and hardness. Dynamic-mechanical analysis has shown that the addition of wood fibers to pure polylactic acid can case an increase in the storage modulus of the composite and with the addition of nano-graphene to increasing composition, while the highest amount of storage modulus was related to polylactic acid composites / 30% of fibers and 30% of fibers. Results of tan δ peak showed that with the presence of wood fibers and nano-graphene, the temperature was transferred to a higher temperature and the limited movement of molecules due to the improvement of the fiber reaction in the PLA polymer. The results of biodegradability test also showed that the addition of fibers to pure PLA caused a significant increase in the weight loss of the composite. Additionally, nano-graphene to PLA composites decreases with the less weight in composites.

In this study, nanocomposites based on epoxy, nano-silica and short glass fibers were prepared with hand molding method. The resin material consisted of epoxy resin and polyamine. Nano-silica and glass fibers, with average length of 6 mm, were added to epoxy polymer matrix in three levels 0, 0.75 and 1.5 wt.% for nano-silica and 5, 10 and 15 wt.% for glass fibers, respectively. After sample preparation, tensile tests are performed to study tensile properties of composites and results were compared and analyzed. Results showed that by adding 0.75 wt.% nano-silica, tensile strength, elastic modulus and elongation increased and by addition 1.5 wt.% of nano-silica the mentioned properties decreased. On the other hand, adding just glass fibers enhanced elastic modulus continuously and declined tensile strength of the nanocomposite. Furthermore, simultaneous presence of glass fibers and nano-silica caused an enhancement in elastic modulus and a reduction in tensile strength and elongation at break.

Every year, large quantities of date palm seeds are produced as byproducts in date processing and packaging industries, which is discarded or used as low-value materials for animal feeds and composts. However, these bioresources may include potentials to produce high-value added products in food industries. The major aim of the current study was to assess phenolic profiles and contents and antioxidant and antibacterial activities of four Iranian date palm seed extracts, namely Zahedi, Kabkab, Mazafati and Rabbi. Total phenolic contents, phenolic compounds profile and antioxidant and antibacterial activities of extracts from four Iranian date palm seeds were assessed using Folin-Ciocalteu, reversed-phase high-performance liquid chromatography, 2, 2-diphenyl-1picrylhydrazyl radical scavenging, agar disc diffusion and broth microdilution methods, respectively.Results and Total phenolic contents varied 1480-3380 mg GAE 100 g-1 dw. cinnamic, chlorogenic, caffeic and 3, 5-dihydroxybenzoic acid included the primary phenolic compounds, respectively. Of the varieties, Kabkab and Mazafati seed extracts with IC50 values of 16.56 and 22.6 µg ml-1 demonstrated the highest and lowest radical scavenging activity, respectively. Results obtained from disc diffusion method revealed that all extracts included inhibitory effects against Staphylococcus aureus, but not against Escherichia coli. Minimum inhibitory concentration and minimum bactericidal concentration of the extracts ranged 1.563.125 and 3.125-12.5 mg ml-1 for Staphylococcus aureus, respectively. Based on the findings, Iranian date seeds are good sources of extractable phenolic compounds with notable antioxidant activities, which can be used as natural additives in formulations of various products such as functional foods and dietary supplements. Furthermore, these seeds can be converted to value added products through biotechnological processes.Conflict of interest: The authors declare no conflict of interest.

In this study, mechanical properties of nano-composites based on epoxy reinforced with graphene nano-platelets and XNBR is investigated. Fillers were added to the epoxy matrix in 0, 0.75 and 1.5 wt. % levels for graphene nano-platelets and 0, 5 and 10 wt. % levels for XNBR. Samples were prepared by hand method and mechanical tests were performed in room temperature to determine tensile strength, tensile modulus, elongation at break and impact strength. FESEM images were used to determine the state of graphene nano-platelets dispersion. It was observed that graphene nano-platelets had well dispersion in 0.75 wt.% but in high loading of them, aggregation was observed. Graphene nano-platelets decreased tensile strength and elongation. On the other hand, enhanced tensile modulus and impact strength by 20% and 23%, respectively. Adding XNBR declined tensile strength and modulus by ~18% and increased impact strength and elongation by considerable amount of 130% and 46%, respectively. Simultaneous presence of graphene nano-platelets and XNBR in epoxy matrix decreased tensile strength by ~10%. On the other hand, tensile modulus, elongation and impact strength increased by 6%, 29% and 143% compared to neat epoxy.

This research has been conducted with the view of the effect of various polymeric processing aids (PPA) on the stick-slip phenomenon in polyethylene compounds. In the extrusion process of thermoplastic polymers, such as polyethylene, for proper and efficient products like wire coatings, pipes, bottles, and films, it is desirable that the final products, gain a smooth surfaces and be polished. In the industry, it is also necessary that the rate of extrusion process is as high as possible, dislike the pressure of this process is as low as possible, so that it can be used for the most part from process machines and thus reduce process costs so much as practical. In this study, MBM and MBR masterbatches (containing 35-40% carbon black) were added to high density polyethylene powder (PE100) and the effect of these masterbatches on the reduction of viscoelastic phenomenon was confirmed. In the next step, three types of PPA with commercial names of Viton, Fx and Daikin with concentrations of 50, 100 and 150 ppm were added to the PE100MBR and PE100MBM compounds to reduce the melt fracture of the samples. The capillary rheometry test determined the quantity changes in the stick-slip phenomenon. The microscopy test also showed qualitatively the changes that occurred in the extrudates. The torque meter test also determined the effect of the PPA on the ampere and the energy consumed by the extruder. Finally, samples were produced with these features due to the importance of reducing energy in the process as well as improving the quality of the extrudates. Depending on the structure of the fluoroelastomer and hyper branch polymers, it has been found that adding these kind of materials has improved processability, and finally the appearance of the product is smoother and polished.

In this study, mechanical and thermal properties of a two-phase polymeric matrix composite including polypropylene and EPDM, reinforced with glass fibers and graphene nanoplates is investigated. Compounds were containing 0, 1 and 2 wt.% of graphene nanoplates and 10, 20 and 30 wt.% of glass fibers and 10 and 15 wt.%EPDM, which were prepared by an internal mixer. Samples for mechanical testing were obtained by a hot press machine. Mechanical and thermal tests were performed to determine the impact strength, tensile strength, modulus of elasticity and melting and crystallization temperature of compounds. It was observed that by using of glass fibers, impact strength was increased 46% and tensile strength and elastic modulus were increased slightly compared to the basic ingredients PP / EPDM. By using of up to 1 wt% of graphene nanoplates, impact strength was increased 16%. The more graphene nanoplates used resulted in a decrease in intensile strength. Adding geraghene nanoplates generally increased elastic modulus up to 13%. Also by adding of EPDM, impact strength of the samples was increased 18% but theirother mechanical peorperties were decreased. Graphene nanoplates also slightly increased the crystallization temperature of samples but their melting temperature have not been affected

In this study, mechanical properties, including elastic modulus and impact strength of nanocomposites based on polypropylene and polyethylene, linear low-density blends, in the presence of titanium oxide nanoparticles have been studied. 0, 2 and 4 wt% titanium dioxide nanoparticles were added to the basic ingredients polypropylene / polyethylene linear low density with a fixed ratio of 60/40 wt. % to reach the final composition that was prepared using an extruder. Tensile and impact tests were carried out in order to determine the elastic modulus and impact strength of compounds. It was observed that the presence of titanium dioxide nanoparticles at 2 wt. %, elastic modulus and impact strength compared to the basic polypropylene/polyethylene linear low-density increase and the presence of higher level of titanium dioxide nanoparticles up to 4 wt. % decrease mechanical properties of compounds. It was also seen that usilng low weight percent of nano particles, increase impact strength of the samples up to 7 percenrt.

In this study, shape memory polymers (SMPs) based on thermoplastic polyurethane/ poly(vinylchloride)/ graphen nanoplatelet (TPU/PVC/GNP) were produced via solution method using tetrahydrofuran(THF) solvent. Blend ratio of the all samples was 60/40 (w/w) and GNP concentration were 0.5, 1 and 2 W.t% from neat and functionalized GNP. In order to get better dispersion of GNP and inhibit from their agglomeration, functionalization with polycaprolactam was accomplished. At first, nanoparticles were treated with nitric acid and in the next step acylation was done using tionylcholride and finally polycaprolactam was grafted on the surface of nano platelet graphen. The functionaliztion reactions were tracked using fourier transfer infra red (FTIR), thermal gravimetric analysis (TGA) and ultraviolet chromatography.The results of these tests showed the successful reaction has been occurred and polycaprolactam was grafted on the surface of GNP. The presence of new peaks in FTIR spectra at 1165 and cm-1 and the loss weight in TGA by 10 and 30wt. % for modified nanoparticles in comparison to pristine one revealed the successful occurrence of modifications reaction reactions.Morphology of the samples was studied using scanning electron microscopy (SEM) and the results depicted that a fine dispersion of graphen nanoplatelet was obtained in comparison to samples including unfunctionalized nanoparticles. Shape memory induction and the measurement of shape fixity and shape recovery were done using thermal-mechanical analyzer (TMA). The results showed that the shape fixity was increased from 76.8 to 83% and shape recovery was increased from 81.5 to 86.7% for the sample containing modified GNp due to better dispersion of the nanoparticles.

The method by which a polymer structure develops during polymer processing has important effects on the quality of final product. Among the structural development methods, crystallization process is of the highest interest. In this study, isothermal crystallization behavior of poly(lactic acid) (PLA) and its nanocomposites with graphene was investigated under quiescent and shear conditions. Neat PLA and its noncomposites containing 0.5, 1, 2 and 3 wt% graphene were prepared via melt mixing method in an internal mixer. Structural analysis and crystallization behavior of the nanocomposites before and after applying shear stress were investigated by differential scanning calorimetric (DSC) analyses. The effect of shear rate, shear time and concentration of nano-graphene on the progress of crystallization process was studied at 135°C using rheometic method. The preshear rates of 0.1, 0.3, 0.5, 1.1 and 1.8 s-1 were applied at temperature of 200°C for 60 s. The increase of storage modulus indicated to the formation of crystalline structure. Results showed that by increasing nano-graphene content the storage modulus was rapidly reached its ultimate value and the induction time of crystallization was decreased. The crystallization process was enhanced by applying preshear stress, particularly in high concentration of nano-graphene platelets. Increasing the shear time to 300 and 600 s, the induction time was decreased. DSC analysis results showed that degree of crystallization increased after applying preshear stress.

The effect of modified starch on the properties of poly(styrene-ethylenepropylene- styrene) tri-block copolymer was studied. Chemical treatment of starch with maleic anhydride was accomplished in an internal mixer in the presence of glycerol. The reaction was confirmed using Fourier infrared spectroscopy (FTIR) and titration. The blend samples containing 10, 20, 30 and 50 wt% were obtained by melt blending and their mechanical, morphological and dynamic-mechanical properties were studied. Scanning electron microscopy (SEM) images displayed droplet-matrix morphology and with increases in modified starch up to 50 wt% some partial co-continuous morphology was also observed. With increase of modified starch in the compound, the size of dispersed phase increased. DMTA results revealed that the partial compatibility was obtained because of slight difference between glass transition temperatures of two phases in the presence of modified starch. The peak of modified starch shifted to higher values and the differences between the two peaks decreased, indicating partial compatibility. Mechanical properties including tensile, elongation-at-break and modulus were also determined and the results showed that the mechanical properties of the sample were higher than those of neat TPS because of the higher compatibility. Tensile strength was decreased with increase in modified starch content due to the absence of strong interfacial adhesion. Moduli of the samples were increased with increase in modified starch content due to higher stiffness of starch. Biodegradability of the samples was evaluated by weight loss percentage using compost test. A rapid degradation was observed in the first 45 days and with increase of the modified starch content the degree of degradation was increased.

In this study, using design of experiments, the effect of the total weight percentage of graphene nanosheets and nano clay and their weight ratio and weight percentage of compatibilizer (PPg-MA) on the tensile properties of polypropylene/ graphene/ nano clay/ PP-g-MA nanocomposites were investigated. Design of experiments and analysis of experimental data with Minitab 16 software and response surface methodology were carried out. Making nanocomposites, based on the melt mixing was performed. All combinations and pure states materials were mixed together in a co-rotating twin-screw extruder and then injection molded into standard tensile test samples. The tensile properties of all samples including tensile strength, Young's modulus and elongation at break was studied experimentally. Statistical models provided by response surface methodology had good agreement with experimental findings. Statistical analysis showed that with increasing the percentage of nanoparticles, tensile strength and elongation at break of nanocomposites reduced. Also increasing the percentage of nanoparticles increase the stiffness of nanocomposites without compatibilizer, however, with the increasing amount of compatibilizer, reduced modulus. Compounds morphology by Scanning Electron Microscopy (SEM) was performed. Micrographes showed better dispersion of the particles in lower percentages.

In this study, effect of adding graphene and poly olefin elastomer (POE) in polypropylene matrix, in various mix time were studied. Method of fabrication samples were melt-blending samples with 0, 2, and 4 %wt of graphene, 0, 15, and 30 %wt of POE and 8,12, and 16 minute mixing time were used. For a better analysis of mechanical properties, tensile and impact tests and DSC, SEM analyses were employed. Results of tensile tests indicated that adding of POE caused reduction of elastic modulus, reduction of tensile strength, good improvement of impact strength and poor improvement of elongation. While presence of graphene caused a good improvement of modulus, without meaningful effect on tensile strength, reduction of elongation and poor improvement of impact strength. DSC analysis of samples showed that graphene and POE has no visible effect on degree of crystallinity but graphen cause temperature of crystallinity increased. SEM observations showed that byincreasing of mixing time an improvehappens on dispersion of grapheme.A reduction in size of POE particles in blending of course agglomerations of grapheme in all samples were showed that for the method of fabrication, surface area of graphene and percents of graphene in samples was not unexpected.

In this study, the mechanical properties of PP/Graphene and PP/Talc/Graphene hybrid nanocomposites compared. All samples were prepared by melt mixing technique using an internal mixer. The coupling agent between filler and matrix was Maleic anhydride grafted polypropylene. For PP/Graphene binary nanocomposites, by adding 0.75wt. % Graphene, elastic modulus, tensile and impact strength were increased. In higher amounts of Graphene, modulus was increased while tensile and impact strength were decreased. For PP/Talc/Graphene hybrid nanocomposites, adding 15% wt. Talc to PP caused an increase in elastic modulus and a decrease in tensile and impact strength. Furthermore, after adding Graphene to PP/Talc, elastic modulus, tensile and impact strength were increased. In higher amounts of Graphene (0.75 to 1.5% wt.), tensile and impact strength were decreased. The morphology of the samples was characterized by using Scanning Electron Microscopy (SEM) technique and crystallinity behavior was characterized by Differential Scanning Calorimetry (DSC). The SEM micrographs shows that there is no good adhesion between talc and PP matrix. Also from SEM, in higher amounts of Graphene, its plates stack together. The DSC result shows that talc has no considerable effect and Graphene has negative effect on the crystallinity. The results showed that hybrid nanocomposites containing 15% wt. Talc and 1.5% wt. Graphene had highest elastic modulus while PP/Graphene nanocomposites containing 0.75% wt. Graphene had highest tensile and impact strength.

In this study، mechanical and thermal properties of nanocomposites based on polypropylene/ linear low density polyethylene/ nano titanium dioxide (PP/LLDPE/Tio2) were studied. The samples were produced using a co-rotating twin screw extruder including 0،2،4 Wt. % of nano particles، 20،40،60 Wt. % of LLDPE and styrene-ethylene-butylene-styrene (SEBS) as comptabilizer. Tensile properties (modulus، tensile strength and elongation at break)، impact resistance and thermal properties (meltingand crystallization temperatures) were evaluated. The results showed that modulus was increased by 9% with addition of nano particles in comparison to PP/LLDPE. In addition، impact resistance was increased and tensile strength and elongation at break were decreased. Melting and crystallization temperatures of PP were increased less or more while، these temperatures for LLDPE did not show meaningful differences.

Recently، using nanoparticles in polymeric blend have been considered by many researchers a new epoch for generation of materials to meet different requirements in various industries such as car، sport، military، structure and electronic. The transesterification reaction in polyester blends during melt mixing plays an important role in the components compatibility، and the ultimate properties of the blend affected by this reaction. In this study the transesterification reaction in the blend of poly (butylene terephthalate) (PBT) /polycarbonate (PC) was studied at the presence of three commercial organic modified montmorillonite namely Cloisite 30B، Cloisite 20A and Cloisite 15A. The main difference among these nanoparticles is their surface chemical structures and initial gallery heights. Fourier transform infrared spectroscopy (FTIR) and small angel X-ray scattering (SAXS) analysis showed that tranesterification reaction was improved at the presence of Cloisite 20A and Cloisite 15A and an intercalation morphology was obtained. While in the samples containing Cloisite 30B a thermal degradation occurred and initial gallery of the nanoparticles was increased. Dynamical mechanical thermal analysis results revealed that by addition of nanoclay to polymer blend، the glass transition of polymers draw on to each other which means more compatibility has been obtained and transestrification reaction has been improved at presence of the nanoparticles. Scanning electron microscope (SEM) micrographs showed droplet-matrix morphology for PC/PBT: 70/30 ratio and co-continuous for PC/PBT: 50/50. By incorporation of nanoparticles the finer morphology was obtained in PC/PBT: 70/30 and co- continuous morphology changed to micro co-continuous in PC/PBT: 50/50.

Injection molding of foam articles has always attracted much interest because of elimination of sink mark, good dimensional stability and reduced production cost. In this study, the nanocomposite samples based on low-density polyethylene/ethylene vinyl acetate/organo montmorillonite were processed into foams by injection molding method. Nanocomposites were prepared by co-rotating a twin-screw extruder. The experimental design was based on Box–Behnken method and parameters such as injection rate, mold temperature and nanolayered silica content were examined in relation to physico-mechanical properties of foams using response surface methodology. Three levels of injection rate (30, 60 and 90 mm/s), nanoclay content (0, 3 and 6 phr) and mold temperature (160, 175 and 190 °C) were chosen. The mathematical model and response surface graphs were employed to illustrate the relationship between the variable parameters and foam properties. The results revealed that the cell size and cell density as the main characteristics of the foams were affected by all parameters. Cell density of samples was affected by mold temperature, injection rate and nanoclay content. At high level of nanocontent the increase of injection rate was accompanied by decreases in density. Tensile strength and specific compression modulus of samples passed through a maximum versus mold temperature due to competition between cross-linking reaction and cell growth. At high mold temperature and injection rate, the cell rupture occurred because of low viscosity of the compounds at these conditions.

Application of supramolecular polymer blending in preparation of materials with adjustable mechanical properties is addressed. It is anticipated that the microstructure and properties of polymer blends are drastically controlled by the inter-molecular interactions. On this basis, the effect of strongly dimerising ureidopyrimidinone end groups (UPy) with the capability of quadruple hydrogen bonding array formation on the material properties of polycaprolactone/ polyhydrofuran supramolecular polymer blends has been studied. The mechanical test results revealed that the supramolecular strategy resulted in up to 110% and 500% increase in tensile strength and Young's modulus, respectively. Observation of a single glass transition temperature in DSC traces of the blends shows that phase compatibility improved significantly upon blending.

Interfacial strength between polymeric matrix and lignocellulosic reinforcement hasdirect effects on the properties of wood plastic composites (WPCs). There are twoapproaches to improve the interfacial adhesion between two phases in WPC:modification of the polymeric matrix or modification of the lignocellulosic fibres. Thiswork focuses on the chemical modifications of natural fibres such as lignocellulosic,enhanced by silane, alkali, benzoyl chloride and acid acrylic. The chemically treatedfibres were then compounded with polypropylene at 190°C and 40 wt%, in an internalmixer equipped with cam rotor, for all samples. Changes in the chemical structure ofchemically treated fibres were tracked by Fourier transform infra red (FTIR)spectroscopy. The intensity of O-H bond at 3400 cm-1 and formation of ester bond at1740 cm-1 were indications of changes in the chemical structure of the fibres. Theinterfacial adhesion was evaluated using adhesion factor which was obtained fromdynamic mechanical thermal analysis data. The results showed that the minimumadhesion factor is related to silane treatment which provides the best interactionbetween polymer and fibres. The tan δ peak was shifted to higher temperature for filledsamples in comparison to neat polypropylene and the amount of shift was related to themethod of chemical treatment. Different morphologies were observed in samples dueto different chemical modifications of fibres and among them, silane treatment methodof the fibres provides the best wetting action by polymeric matrix. Tensile properties andimpact resistance of the samples were determined to evaluate the effect of interfacialadhesion on the performance of the composites.

RNA molecules are employed by diverse mechanisms in the cell. In recent years, researches have demonstrated that RNAs are important as regulators of gene expression. These include antisense RNAs, micro RNAs, siRNAs, ribozymes and riboswitches. Riboswitches are segments of the 5’-untranslated region of some RNAs. These elements act as sensors of signals through mechanisms of molecular recognition. The plasticity of RNA in molecular recognition show high potential of this molecule to act as suitable regulator. According to this ability, researchers attempt to engine riboregulator systems and in last years several riboregulator systems have been engineered. Engineered RNAs could be employed as sensors of intracellular and environmental stimuli to explore the behavior of biological networks and engineered cellular control systems, as antibacterial and as biosensor to detect pathogens. In this review we will focus on some engineered riboregulators and riboswitches as RNA sensors.

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.

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.