Direct dye removal by using UV/hydrogen peroxide/multiwalled carbon nanotubes

In this study, decoloration of Direct Blue 71 (DB71) and Direct Red 23 (DR23) has been discussed by using Multiwalled Carbon Nanotubes (MWCNTs) and Hydrogen peroxide under UV radiation. The purpose of this study is removal of organic compounds by using carbon nanotubes that are effective adsorbents for different types of pollutants, due to their porous nature and large surface area. It also causes catalytic decomposition of hydrogen peroxide. Adsorption rate was investigated under various parameters (initial dye concentration, salt, temperature and pH). The main objective of this study is to appraise the synergic effect between H₂O₂ and MWCNTs under UV radiation. The dye adsorption results of spectrophotometer, showed that by decreasing the dye concentration from 0.2 g/l to 0.05 g/l with the optimal value of MWCNTs 0.2 g/l and hydrogen peroxide 2 g/l at pH=4 and 6 cm distance from the UV lamp, the dye removal increased.     

Influences of organic-modified Fe-montmorillonite on structure, morphology and properties of polyacrylonitrile nanocomposite fibers

The Fe-montmorillonite (Fe-MMT) combined catalysis effects of Fe ion with barrier effects of silicate clays, was firstly synthesized by hydrothermal method, and then was modified by cetyltrimethyl ammonium bromide (CTAB). The organic-modified Fe-montmorillonite (Fe-OMT) was dispersed in the N, N-dimethyl formamide (DMF) and then compounded with polyacrylonitrile (PAN) solution which was dissolved in DMF. The composite solutions were electrospun to form PAN/Fe-OMT nanocomposite fibers. The influences of the Fe-OMT on the structure, morphology, thermal, flammability and mechanical properties of PAN nanocomposite fibers were respectively characterized by X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM), Scanning electron microscopy (SEM), Thermogravimetric analyses (TGA), Micro Combustion Calorimeter (MCC) and Electronic Single Yarn Strength Tester. It was found from XRD curves that there was not observable diffraction peak of silicate clay, indicating that the silicate clay layers were well dispersed within the PAN nanofibers. The HRTEM image indicated that the multilayer stacks of nanoclays could be found within the nanofibers and were aligned almost along the axis of the nanofibers. The SEM images showed that the diameters of nanocomposite fibers were decreased with the loading of the Fe-OMT. The TGA analyses revealed that the onset temperature of thermal degradation and charred residue at 700°C of PAN nanocomposite fibers were notably increased compared with the pure PAN nanofibers, contributing to the improved thermal stability properties. It was also observed from MCC analyses that the decreased peak of heat release rate (PHRR) of the PAN nanocomposite fibers reduced the flammability properties. The loadings of Fe-OMT increased the tensile strength of PAN nanocomposite fibers, but the elongation at break of PAN nanocomposite fibers was lower than that of the PAN nanofibers.     

The demonstration of a dense and stable circumferential layer in the subsurface of polyacrylonitrile fibers for carbon fibers

The radial structure of polyacrylonitrile (PAN) copolymer fibers was investigated quantitatively by etching layer by layer in an improved permanganic etchant; meanwhile the effect of the etchant on the fiber surface was taken into consideration. The aggregated structure (crystal size, crystallinity, orientation and density) and thermal stability of each circumferential layer of PAN fibers were determined in detail according to a model proposed in the study. A denser layer with a thickness of about 1 µm was observed in the subsurface (2 µm from the PAN fiber surface), possessing a greater crystal size and crystallinity as well as a relatively higher thermal stability than other layers. This layer was considered to be a barrier for the diffusion of oxygen into PAN fibers during the stabilization and accelerated the formation of a core-shell structure in the resulting carbon fibers.     

Thermal and mechanical properties of polypropylene filaments reinforced with multiwalled carbon nanotubes via melt compounding

This study examined the thermal and mechanical properties of polypropylene filaments reinforced with multi-walled carbon nanotubes (MWNTs). The MWNTs were functionalized with maleic anhydride polypropylene to increase the interfacial interactions between the CNTs and polypropylene. PP/MWNT composites with different concentrations of MWNTs were prepared by melt compounding using a twin screw extruder. The composites of the filament were then post drawn and heat treated. Tensile tests showed increased strength with the addition of only 0.1 wt% while there were only slight changes in elongation. The thermal properties were also slightly enhanced by the MWNTs.     

Morphology and properties of polyacrylonitrile/single wall carbon nanotube composite films

Composite films were prepared by casting the solution of polyacrylonitrile (PAN) and single wall nanotube (SWNT) in DMF subsequent to sonication. The SWNTs in the films are well dispersed as ropes with 20–30 nm thickness. Moreover, AFM surface image of the composite film displays an interwoven fibrous structure of nanotubes which may give rise to conductive passways and lead to high conductivity. The polarized Raman spectroscopy is an ideal characterization technique for identification and the orientation study of SWNT. The well-defined G-peak intensity at 1580 cm⁻¹ shows a dependency on the draw ratio under cross-Nicol. The degree of nanotube orientation in the drawn film was measurable from the sine curve obtained by rotating the drawn film on the plane of cross-Nicol of polarized Raman microscope. The threshold loading of SWNT for electrical conductivity in PAN is found to be lower than 1 wt% in the composite film. The electrical conductivity of the SWNT/PAN composite film decreased with increasing of draw ratio due to the collapse of the interwoven fibrous network of the nanotubes with uniaxial orientation.     

Interfacial localization of multiwalled carbon nanotubes in immiscible blend of poly(ethylene terephthalate)/polyamide 6

In this study, multiwalled carbon nanotubes (MWCNTs) were confined or localized in an immiscible blend of poly(ethylene terephthalate)/polyamide 6 (PET/PA6). A co-rotating twin-screw extruder and melt-compounding were used to prepare nanocomposites of PET/PA6 (60/40, w/w) and MWCNTs with various MWCNT contents in the range 0.001–2 phr. The raw, unfunctionalized MWCNTs were used as fillers. A remarkable change in the morphology of the blend happened on the basis of the amount of MWCNTs added to the blend: the PET phase converted into the PA6 phase at a certain MWCNT content. Although the PA6 phase was formed as a domain phase in the PET matrix in blends containing less than 0.01 phr of MWCNTs, the PET phase suddenly became discontinuous because of phase conversion in the PA6 matrix in blends containing 0.01 and 0.05 phr of MWCNTs. In the blends containing more than 0.1 phr of MWCNTs, the initial morphology was recovered, that is, the PET phase became the matrix phase again. Moreover, in the recovered state, the of the PA6 domain was much larger in the blends containing more than 0.1 phr of MWCNTs than it was in the composites that did not contain any MWCNTs and in those that contained 0.001 phr of MWCNTs. The MWCNTs, on the other hand, selectively located at the interface of the PET and PA6 phases. The rheological, electrical, and crystallization behaviors of the blends were also investigated to study the effects of the concentration of MWCNTs on the structure of the prepared composites.     

Chemically grafting carbon nanotubes onto carbon fibers by poly(acryloyl chloride) for enhancing interfacial strength in carbon fiber/unsaturated polyester composites

We propose a novel method to uniformly graft high density carbon nanotubes (CNTs) onto carbon fiber (CF) using poly (acryloyl chloride) (PACl) as coupling agents. Compared to micromolecule couping agent previously reported in literature [2,3], PACl can supply much more active groups, which is beneficial for grafting high density CNTs onto CF surface. Moreover, in order to further increase the grafting density of CNTs, the solvothermal strategy was used for improving the reactive activity between CF and CNTs. After CNTs grafting treatment, there are still substantial amounts of reactive groups which can further react with various types of molecules to meet different requirements. In order to create chemical bonding between CF and unsaturated polyester (UP), CF-CNT was further grafted with undecylenic alcohol (UA) to get CF-CNT-UA hierarchical reinforcement. The interfacial adhesion of the resulting composites showed a dramatic improvement.     

A novel multi-wall carbon nanotubes/poly(n-butylacrylate-co-butyl methacrylate) hybrid resin: synthesis and oil/organic solvents absorption

A novel multi-wall carbon nanotubes/poly(n-butylacrylate-co-butyl methacrylate) hybrid resin (MWCNTs- PBABMA), which was further applied to absorb oils and organic solvents, was synthesized by using a combination of surface modification and suspension polymerization. Firstly, the surfaces of MWCNTs-COOH were modified and functionalized by silane coupling agent (KH 570) to enhance the surface reactivity. Then, the MWCNTs-PBABMA hybrid resin was synthesized by suspension polymerization. The oil absorption properties of the hybrid resin are investigated by varying the amount of surface modified carbon nanotubes, and the results indicated that the oil absorption properties of prepared MWCNTs-PBABMA hybrid resin could be improved by the addition of MWCNTs. Besides, the absorption properties of the MWCNTs-PBABMA hybrid resin for oils and organic solvents are 2.01-37.87 g/g, partly depending on the density and viscosity of the absorbate. The MWCNTs-PBABMA hybrid resins could be reused for oils absorption, at least four times, with a slight decline in their absorption properties. These results indicate that hybrid resins may potentially serve as oils absorbents for treatment of oily wastewater.     

Spinnability in pre-gelled gel spinning of polyacrylonitrile precursor fibers

The spinnability in pre-gelled gel spinning of polyacrylonitrile (PAN) precursor fibers was investigated. The spinning solutions were aged at 25 °C for different times prior to fiber spinning. The pre-gelled spinning solution aged for 2.5 h was much more strain hardening than the ungelled one, which can increase the spinnability of the solution. The maximum take-up velocity of the first winding roller V _1m, which reflects the spinnability of the spinning solutions, was found to be largest when the aging time was 1.5 h. The spinnability increased with the increase of the air gap length and the lengthdiameter ratio L/D of the spinnerette. Once the L/D increased beyond 15, the spinnability hardly changed. The fibers spun from the spinning solution aged for 1.5 h had the best mechanical properties and favorable structure, showing that good spinnability favors the performance increase of resultant PAN precursor fibers.     

Effect of boric acid on oxidative stabilization of polyacrylonitrile fibers

The coating modification of polyacrylonitrile (PAN) fibers with boric acid to enhance the controllability of thermally oxidative stabilization process. The stabilization process, cross-section morphologies of oxidized and carbonized products were investigated by means of optical microscopy, SEM, XPS and in-situ thermal shrinkage indicator. The results indicated that the coating with boric acid on fiber surface was effective to avoid skin-core heterogeneity on the cross section and, in the stabilization process, that boric acid as a crosslinking agent to tie together the adjacent oxidative molecular chains was confirmed. It was suggested that the crosslinked structures should play an essential role in controlling the formation of uniform oxidized structures, which is favorable for tensile properties of carbon fibers.     

The characterization of polyacrylonitrile fibers stabilized by electron beam irradiation

This study investigates polyacrylonitile(PAN) fibers stabilized with various doses of electron beam irradiation (EBI) ability to produce carbon fibers. Feasibility was verified by FT-IR, the percent of gel fraction, density, DSC, XRD, and mechanical measurements. FT-IR spectra showed that the intensities of the stretching C??N bonds decreased at 2,244 cm^?1 with increasing EBI dose. This de crease was related to cyclization of nitrile groups during EBI-stabilization. The degree of cyclization was determined from the gel fraction and density tests. The gel content and density of PAN fibers stabilized by EBI increased with an increase in the EBI dose. Thermal properties were characterized by differential scanning calorimetry (DSC) and thermally activated reactions. DSC curves showed that EBI treatment influenced the quantity of released heat and the exothermic position at low temperature over a wide temperature range. The strongest diffraction peak from the PAN precursor fiber arose from the (100) plane; its stabilization index (SI) was evaluated by X-ray diffraction. The X-ray results showed that the peak intensity decreases gradually with increasing EBI dose. In addition, tensile strength decreased the EBI stabilization level.     

Fabrication of homogeneous multi-walled carbon nanotube/poly (vinyl alcohol) composite films using for microwave absorption application

Poly (vinyl alcohol) (PVA)/multi walled carbon nanotubes (MWNT) nanocomposite films were fabricated and their microwave absorption behavior were evaluated using vector network analyzer in the frequency range of 8–12 GHz (Xband). The uniform, stable dispersion and well oriented MWNT within the PVA matrix were achieved through using sodium dodecyl sulfate (SDS) as dispersing agent. The surface morphology of the PVA/SDS/MWNT films was examined by scanning electron microscope (SEM). The SEM analysis of the film samples revealed the uniform appearance in the whole surfaces of the fabricated composite films. However, some roughness on the surface was observed due to the presence of MWNT in the film structure. The PVA/SDS/MWNT films show significant increase in microwave absorption which is improved by increasing the MWNT content. The PVA/SDS/MWNT nanocomposite film sample with MWNT loading of 10 wt% showed the maximum and the relatively high microwave absorption of 28.00 dB at the frequency of 8.6 GHz.     

In vitro assesment of antimicrobial activity and characteristics of polyamide 6/silver nanocomposite fibers

In this study, the preparation method and characteristics of silver (Ag) nanoparticle (NP) loaded polyamide 6 (PA6) nanocomposite and its antimicrobial activity against Klebsiella pneumonia and Staphylococcus aureus were investigated. The melt intercalation method was used to prepare a series of PA 6 nanocomposite fibers containing, 0; 1; 3; 5 % (wt.) Ag. PA6/Ag nanocomposite fibers exhibit increased antimicrobial efficiency with the increase of nanoparticle contents. On the other hand, thermal characterization tests show that the increased concentration of Ag nanoparticles reduces the mechanical properties due to their partial agglomeration leading to flaw generation. The crystallinity of the fibers was found to decrease about 10 % with increase of Ag to 5 %. This was attributed to faster cooling rate experienced in the presence of high thermal conductivity Ag particles.     

Electrospinning and mechanical properties of polymeric fibers using a novel gap-spinning collector

Tissue engineering is an interdisciplinary field which combines the basic principles of life sciences and engineering. One promising idea is the combination of scaffolds and living cells in order to produce new functional tissue. The scaffolds play the role of a microenvironment that guides the cells towards tissue formation and regeneration. One of the most frequently used techniques to produce scaffolds is electrospinning. Tissue engineered constructs have to exhibit physiological and mechanical properties comparable to the native tissue they are intended to replace. To create polymeric fibers with controlled orientation, a cylindrical collector that rotates at a certain speed could be used, creating fibers that run longitudinally. The process of gap-spinning enables the production of specifically aligned fibers. Aim of this study was to develop a novel setup capable of producing multilayered structures with controlled fiber angle. The structural, morphological and mechanical characteristics of the fibers were accessed using scanning electron microscopy and uniaxial tensile tests. Longer pre-stretching led to thinner (in the sub-micron scale), more brittle and less elastic fibers. In a nutshell, the results indicated that fiber mats of desired orientation, fiber diameter and mechanical properties could be produced by controlled gap-spinning with a translational collector.     

Properties of polyacrylonitrile/single wall carbon nanotube composite films prepared in nitric acid

Nanocomposite films were prepared by casting the solution of polyacrylonitrile (PAN) and single wall nanotube (SWNT) in nitric acid subsequent to sonication. Even though SWNT shows good dispersion visually, the reinforcing effect was not satisfactory. The G-band Raman spectra of the drawn film clearly demonstrated that SWNTs in the film are well-oriented along the drawing axis of the film. The electrical resistivity of the film prepared using nitric acid was lower than that of the film using DMF. Thus, nitric acid is presumably more effective in dispersing nanotubes than DMF.     

Dyeing behavior of polyacrylonitrile nanofibers: Physicochemical parameters of dyeing with basic dye in comparison with regular polyacrylonitrile fibers

Polyacrylonitrile nanofibers were produced using the electrospinning method and dyed with a basic dye alongside regular polyacrylonitrile fibers. In order to investigate the effect of high surface area to volume ratio of nanofibers on their adsorption behavior in comparison with regular fibers, the dyeing conditions for both types of fibers were kept just the same. Physiochemical parameters of dyeing such as adsorption isotherm, standard affinity, enthalpy change, rate of dyeing constant, diffusion coefficient, and activation energy of diffusion were investigated for both types of fibers. The results showed that the adsorption process can be well described with the Langmuir adsorption isotherm for both types of fibers whereas the standard affinity of dye to nanofibers was higher than regular fibers and the higher negative values of enthalpy changes were obtained for regular fibers. The nanofibers rate of dyeing was faster than regular fibers with higher amounts of diffusion coefficients and lower amounts of activation energy of diffusion. This study also revealed that in spite of the approximately same amount of dye exhaustion for both types of fibers, the color strength of regular fibers was noticeably higher than nanofibers.     

Preparation of bacterial cellulose/carbon nanotube nanocomposite for biological fuel cell

In this study, electrically conducting composite membranes were prepared by incorporating carboxylic multi-walled carbon nanotubes (c-MWCNTs) into Bacterial Cellulose (BC) pellicles. The biocathode and bioanode were prepared by a simple method of adsorption. An enzyme biological fuel cell (EBFC) composed of a biocathode and an enzymatic bioanode were developed and tested. The materials was characterised by field emission scanning electron microscope (FESEM), Fourier Transform Infrared (FTIR) Spectroscopy and Thermogravimetric analysis (TGA). The results showed that the presence of c-MWCNTs on BC was certified, on which c-MWCNTs loading was calculated as 30.02/100 g. The BC/c-MWCNTs/Lac composite membranes was characterized by cyclic voltammetry (CV). An EBFC was characterized by linear sweep voltammetry (LSV). The results showed EBFC exhibited excellent performance with the largest open circuit voltage (0.76 V) and a maximum power density value (55 uW/cm³). Additionally, the cell also exhibited acceptable stability over the recording of 30 days. BC was considered to be suitable for advanced applications such as an enzymatic carrier of biological fuel cells.     

Mechanical property optimization of wet-spun lignin/polyacrylonitrile carbon fiber precursor by response surface methodology

Lignin, nature’s abundant polymer with a remarkably high carbon content, is an ideal bio-renewable precursor for carbon fiber production. However, the poor mechanical property of lignin-derived fibers has hindered their industrial application as carbon fiber precursor. In this work, process engineering through the application of computational modeling was performed to optimize wet-spinning conditions for the production of lignin precursor fibers with enhanced mechanical properties. Continuous lignin-derived precursor fibers with the maximum possible lignin content were successfully produced in a blend with polyacrylonitrile, as a wet-spinning process facilitator. Response surface methodology was employed to systematically investigate the simultaneous influence of material and process variables on mechanical properties of the precursor fibers. This allowed generating a mathematical model that best predicted the tensile strength of the precursor fibers as a function of the processing variables. The optimal wet-spinning conditions were obtained by maximizing the tensile strength within the domain of the developed mathematical model.     

The role of thermal stabilization on the structure and mechanical properties of polyacrylonitrile precursor fibers

The thermal stabilization stage of polyacrylonitrile (PAN) fibers is characterized by a steady and continuous reduction in fiber diameter and linear density values together with color changes from reddish brown to shiny black with increasing stabilization time. Thermally stabilized PAN fibers acquire infusible and nonburning characteristics prior to the carbonization stage. Structural characterization of thermally stabilized polyacrylonitrile fibers was carried out using an indepth analysis of equatorial X-ray diffraction traces. Curve fitting of X-ray diffraction traces provided accurate peak parameters which were subsequently used for the evaluation of apparent crystallinity, apparent crystallite size and X-ray stabilization index. The results showed the loss of crystallinity due to the amorphization processes together with a steady and continuous decrease in lateral crystallite size with increasing stabilization time. With the progress of thermal stabilization, a new amorphous phase with a crosslinked and aromatized structure is formed which is expected to withstand high carbonization temperatures. Mechanical properties of the thermally stabilized PAN precursor fibers were found to be adversely affected with the progress of stabilization time. Due to the influence of thermal degradation mechanisms heavily involving chain scission along the fiber axis direction, tensile strength and tensile modulus values were found to decrease by significant proportions with the prolonged stabilization times.     

Evaluation of mechanical properties of jute/glass/carbon fibers reinforced hybrid composites

A study on the tensile and flexural properties of jute-glass-carbon fibers reinforced epoxy hybrid composites in inter-ply configuration is presented in this paper. Test specimens were manufactured by hand lay-up process and their tensile and flexural properties were obtained. The effects of the hybridization, different fibers content and plies stacking sequence on the mechanical properties of the tested hybrid composites were investigated. Two-parameter Weibull distribution function was used to statistically analyze the experimental results. The failure probability graphs for the tested composites were drawn. These graphs are important tools for helping the designers to understand and choose the suitable material for the required design and development. Results showed that the hybridization process can potentially improve the tensile and flexural properties of jute reinforced composite. The flexural strength decreases when partial laminas from a carbon/epoxy laminate are replaced by glass/epoxy or jute/epoxy laminas. Also, it is realized that incorporating high strength fibers to the outer layers of the composite leads to higher flexural resistance, whilst the order of the layers doesn’t affect the tensile properties.