جستجوی مقالات مرتبط با کلیدواژه « نانولوله های کربن » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

Hypothesis: Electrospinning of nanoparticles/polymer solutions offers the potential to achieve novel composite nanofibers in a variety of high performance applications. In this respect, the aspect ratio and purity of multi-walled carbon nanotubes (MWCNTs) were examined to study the morphological and electrical properties of the electrospun composite nanofibers. In the first step, MWCNTs samples were characterized using scanning electron microscopy (SEM) and Raman spectroscopy. Next, nanocomposite solutions containing MWCNTs were prepared by physical dispersion method in presence of a non-ionic surfactant. Finally, the prepared composite solutions were loaded to a glass syringe and connected to a DC power supply device. The electrospinning was performed by applying a high voltage of 15kV between the needle and the rotating collector. Findings: It is generally accepted that a combination of G-band intensity and G/D ratio is useful to evaluate the purity and crystallinity of MWCNTs. The morphological properties of the electrospun composite nanofibers showed their high dependency on carbon nanotubes dimensions, so that at higher aspect ratios the morphological properties generally improved. The morphological analysis of the composite nanofibers revealed that the deformation of the nanofibers increased with increasing MWCNTs diameter. Very smooth surfaces of the composite electrospun nanofibers even with 1 wt% MWCNT concentration were successfully achieved because of the high stability of MWCNT dispersions. The composite nanofibers with higher purity and aspect ratio presented better electrical conductivity. The electrical conductivity of electrospun composite nanofibers could be adjusted from ~10–8 S/cm (insulator) to ~10–3 S/cm (conductor) by different aspect ratios and purities of MWCNTs. MWCNTs with high aspect ratio and high purity offer a promising way to develop electrospun composite nanofibers with improved morphological and electrical properties.

In order to achieve better mechanical properties of the nanocomposites containing carbon nanotubes, the carbon nanotubes should be oriented in a specific direction in the polymer matrix. This produces nanocomposites with anisotropic properties. Experimental study on the effect of injection direction and carbon nanotubes orientation on the mechanical properties of a multi-walled carbon nanotube (MWCNT)/polymethyl methacrylate (PMMA) anisotropic nanocomposite is the main aim of this article. Therefore, variable input factors including MWCNT concentration (0, 0.5, 1 and 1.5 wt%) and its in-flow and perpendicular directions were studied. First, nanocomposites were produced by co-rotating twin-screw extrusion. After that the nanocomposite sheets were fabricated by injection molding and test samples were cut into standard dimensions by laser cutting. The parameters including elastic module, yield strength, elongation, impact strength and hardness were studied. In addition, the effect of MWCNT on the melt flow index and optical properties was studied. Morphology of nanocomposites was carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Increasing the elastic modulus by about 51%, tensile strength by 19% and elongation by 27% with addition of 1.5 %wt MWCNTs were also found. The results also illustrated that the elastic modulus improved by 10% and tensile strength by 13 % in the direction perpendicular to the flow direction. Yet more elongation was observed in in-flow direction. A little drop in hardness, a slight increase in impact strength and a decrease in luster and transparency by increases in MWCNTs loading were other noticeable results. A reduction in melt flow impact from 11 to 6.3 g/10min was another remarkable finding.

Poly(vinylidene fluoride) (PVDF) has received great popularity because of their excellent mechanical properties, chemical stability and ferroelectricity. It has a simple chemical structure and is crystallized in five different phases including α, β, γ, δ and ε. Since β-phase has a greater dipole moment, its pyro and piezoelectric activity is very high. To date, various techniques including mechanical stretching, applying high pressure, cooling, use of polar solvents, injection molding, polarization under high strain and electrical field, its copolymers derivatives, addition of nano fillers and electrospinning have been discovered and provided in order to increase the β-phase proportion in poly(vinylidene fluoride). The purpose of this review article is to collect and study numerous research reports performed to prepare and characterize of PVDF/multi-walled carbon nanotubes, PVDF/nanoclay and PVDF/other nanofiller polymeric nanocomposites. For updating and helping the readers in order to understand the importance of nanotechnology, it has been tried to study and gather data from authentic journals in the field of PVDF nanocomposites. Moreover, the focus of the present review article is how it is possible to increase the amount of β-phase of PVDF and consequently its piezoelectric property.

Adhesives are one of materials which mankind have been used from many years ago. Adhesive used in many cases and different situations, one of these uses is joints. Joints play an important role in structural uses, so the adhesive which use in joints, must meet the requirement of a structural adhesive and can be use in different service conditions and environmental situation. These days with changes in industrial needs, appearing new technologies, increased commercial availability and reduce prices, reinforcement of adhesives with nano reinforcements widely researched and reported. Nanoreinforcements due to their high ratio aspect and specific area, can improve polymer properties when add to polymer matrix as a reinforcement. In this paper, adhesive and mechanisms of adhesion explained, nanoreinforcements as an appropriate alternative to other kind of fillers and reinforcements are introduced, also those kind of adhesive properties which addition of nanoreinforcements made changes on them are explained. Nano reinforcements in 3 categories (inorganic, Carbon Nanotube and carbon Nanofiber) are introduced and their effects on adhesive polymer are discussed.

Novel hydrogel nanocomposites, based on κ-carrageenan polysaccharide, were prepared by graft copolymerization of acrylamide (AAM) and maleic anhydride (MAH) as comonomers in the presence of multiwall carbon nanotubes (MWCNT), using methylene bisacrylamide (MBA) and ammonium persulfate (APS),former as a crosslinking agent and the latter as an initiator. The hydrogel nanocomposites structure was characterized by FTIR spectroscopy, scanning electron microscopy (SEM) and XRD patterns, and their thermal stability was investigated by TGA thermal analysis. The hydrogel nanocomposites were evaluated using gel content measurements and swelling rate in distilled water and in saline solutions. The carbon nanotube content was examined in relation to its effect on the properties of nanocomposites. The results showed that with increasing carbon nanotube content, the rate of water absorbency and equilibrium swelling in distilled water decreased whereas the water absorbency in the saline solutions increased. Water retention capacity was also studied and the results indicated that the inclusion of carbon nanotube increased water retention under heating condition. Furthermore, the experimental conditions of adsorption kinetics and dynamics for the removal of cationic dye, Brilliant Green (BG), were studied in the range of 6-8 for pH, 10-60 min for time (t), and 10-300 mg/L for initial concentration (C0) of the dye. The optimum conditions obtained for adsorption of Brilliant Green dye were pH 7, t= 50 min and C0= 10 mg/L. Also, the results indicated that more than 98% of the maximum adsorption capacity toward Brilliant Green dye was achieved within the initial 10 min. The experimental tests showed that the hydrogels could be used as fast–responsive and high capacity sorbents in Brilliant Green removal processes from industrial waste water.

The nanofiller reinforced polymer matrixes are a class of composites material، which have received significant attention both in academia and industry due to having higher mechanical، physical and thermal properties. The carbon nanotubes (CNTs) are the most important nanofillers which can be used as ideal reinforcing agents for high performance polymer matrixes because of their excellent mechanical، thermal and electrical properties and multi-functionality. CNTs are rolled-up graphene sheets which are made long coaxial cylinders. The properties of carbon nanotubes depend on atomic arrangement، the diameters and length of the tubes and morphology or nanostructure. Since CNTs usually agglomerate due to Van de Waals interactions، they are extremely difficult to disperse and align in a polymer matrix. The critical challenge is the development of methods to improve the dispersion of CNTs in the polymer matrix because their enhanced dispersion in polymer matrices greatly improves the mechanical، electrical and optical properties of composites. The functionalization of CNT is an effective way to prevent nanotube aggregation which can maximize interfacial adhesion between CNTs and the polymer matrix. CNTs can be prepared using various methods. In this review، the methods for the dispersion of nanotubes in the polymer matrix، funtionalization and effect of dispersion and funtionalization on properties of composites are described.

Today, hydrogen storage as a clean and renewable energy source has main rule in the energy saving studies. Adsorption of hydrogen molecules on the adsorbent surface is an effective method in this point. In this paper, application of nanostructure carbon metrials such as carbon nanotubes, nanohorns and fullerene molecules in the hydrogen adsorption are investigated. Generally Nanotube carbons have low specific surface area and therefore have low affinity in hydrogen adsorption, but this affinity can improve. Some examples of these improvements are impregnation with metals such as Li, chemical treatment with KOH and heat treatment in temperature 400-500 oC. Nanohorns have higher specific surface area than nanotubes and their surface area can improve to 1900 m2/gr by means of heat treatment. In this condition, hydrogen storage capacity are around 4 wt% at T=77 K. Hydrogen storage of fullerenes improve with both mechanisms of adsorption within molecular structure and hydride formation. In addition, activated carbons produced from fullerene have high adsorption capacity to storage of hydrogen.