Structure,electrical and mechanical properties of polyamide 66/acid-treated MWCNT composite films prepared by solution mixing in the presence of nonionic surfactant

Two different sets of polyamide 66(PA66)-based composite films containing 2.0-10.0 wt% acid-treated multiwalled carbon nanotubes (MWCNT) were manufactured by solution mixing and casting method in the presence or absence of a nonionic surfactant. For the improved dispersion and interfacial interaction of MWCNTs in the PA66 matrix, carboxylic acid-functionalized MWCNTs were prepared by the acid-treatment of pristine MWCNTs. The uniform dispersion of the acidtreated MWCNTs in the PA66 matrix was confirmed from FE-SEM images of the fractured composite film surfaces. DSC thermograms supported that the acid-treated MWCNTs served as nucleating agents for the melt-crystallization of PA66 in both composite films prepared with/without the addition of the surfactant. The electrical and tensile mechanical properties of the composite films prepared with the surfactant were ~20 % higher than those of the composite films manufactured without the surfactant. For both composite films, sheet resistivity and tensile mechanical properties were found to be highly decreased and increased, respectively, with the increment of the acid-treated MWCNT content.     

Electrospun nanostructures based on polyurethane/MWCNTs for strain sensing applications

Electrically conductive nanofibers were fabricated from elastic polyurethane (PU) and PU/multiwalled carbon nanotubes (MWCNTs) nanocomposite by electrospinning method. The nanocomposites were electrospun at various MWCNTs loading. Electron microscopy was used to investigate nanofibers morphology and dispersion of MWCNTs in the electrospun nanofibers. The results showed that the presence of the MWCNTs promoted the creation of fibrous structures in comparison with the PU without MWCNTs. On the other hand, increasing the MWCNTs content resulted in a slight increase in the average fiber diameter. TEM micrographs and mechanical properties of the electrospun mats indicated that the homogeneous dispersion of MWCNTs throughout PU matrix is responsible for the considerable enhancement of mechanical properties of the nanofiber mats. Electrical behavior of the conductive mats was also studied, in view of possible sensor applications. Cyclic experiments were conducted to establish whether the electrical properties were reversible, which is an important requirement for sensor materials.     

Effects of Chemical Functionalization of MWCNTs on the Structural and Physical Properties of Elastomeric Copolyetherester-based Composite Fibers

Elastomeric copolyetherester (CPEE)-based composite fibers incorporating various neat and functionalized multiwalled carbon nanotubes (MWCNTs) were prepared through a conventional wet-spinning and coagulation process. The influence of functionalized MWCNTs on the morphological features, and the thermal, mechanical properties and electrical conductivity of CPEE/MWCNT (80/20, w/w) composite fibers were investigated. FE-SEM images show that a composite fiber containing poly(ethylene glycol)-functionalized MWCNTs (MWCNT-PEG) has a relatively smooth surface owing to the good dispersion of MWCNT-PEGs within the fiber, whereas composite fibers including pristine MWCNTs (p-MWCNT), acid-functionalized MWCNTs (a-MWCNT), and ethylene glycol-modified MWCNTs (MWCNT-EG) have quite a rough surface morphology owing to the presence of MWCNT aggregates. As a result, the CPEE/MWCNT-PEG composite fiber exhibits noticeably increased thermal and tensile mechanical properties as well as a faster crystallization behavior, which stems from an enhanced interfacial interaction between the CPEE matrix and MWCNT-PEGs.     

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.     

Enhanced mechanical and dielectric properties of poly(vinylidene fluoride)/polyurethane/multi-walled carbon nanotube nanocomposites

Multi-walled carbon nanotubes (MWNTs) nanocomposites with the polymer matrix composed of blends of poly(vinylidene fluoride) (PVDF) and polyurethane (PU) were prepared via functionalization of 3,4,5-triflouroaniline (TFA) on MWNTs. The MWNTs/polymer nanocomposites showed a dominantly enhanced elongation due to incorporation of PU molecules in PVDF matrix and the improved MWNTs dispersion in the polymer matrix resulting from functionalization of MWNTs with TFA. The functionalization of TFA on MWNTs was confirmed by the measurements of Raman, FT-IR spectra, SEM, and TEM images. In addition, the dielectric constant of nanocomposites increased with an increase of TFA-functionalized MWNTs in PVDF/PU/MWNTs nanocomposites. The polymer blend nanocomposites incorporating MWNTs may be available as an alternative potential route for the actuator materials.     

Core-sheath polyurethane-carbon nanotube nanofibers prepared by electrospinning

The core-sheath nanofibers consisting of polyurethane (PU) core and PU composites sheath with multi-walled carbon nanotubes (MWNTs) were prepared by electrospinning. At low MWNT concentration, MWNTs appeared highly aligned along the fiber axis with some curving in nanotubes, whereas in case of high concentration, some aggregation of MWNTs appeared due to difficulty in full dispersion of nanotubes. In comparison of the single component nanofiber webs, the core-sheath nanofiber webs showed much better mechanical properties of modulus and breaking stress, including an exceptional elongation-at-break. It indicates that the CNT-incorporated core-sheath structure is very effective for enhancing the mechanical properties of nanofiber webs. In addition, the core-sheath nanofibers demonstrated the fast shape recovery, compared with one component fibers of pure shape memory PU and PU/MWNTs, which provides the possibility of fabricating more sensitive intelligent materials.     

Improvement of high-velocity impact properties of anisogrid stiffened composites by multi-walled carbon nanotubes

The present study represents the influence of adding different weight fractions (0, 0.1, 0.25 and 0.4 wt.%) of multi-walled carbon nanotubes (MWCNT) on the high velocity impact behavior of anisogrid stiffened composite (AGSC) plates. AGSC plates were fabricated through hand lay-up method where E-glass woven fabrics and unidirectional carbon fiber rovings were used as fibrous reinforcement of ribs and skin, respectively. High velocity impact test was performed on these plates by cylindrical projectile with conical nose. Obtained results revealed that the maximum improvement of the high velocity impact properties of AGSC plates were obtained through addition of 0.4 wt.% of MWCNTs. Field emission scanning electron microscopy (FESEM) examinations of the fracture surfaces clearly indicated the improvement in the interfacial adhesion between the fibers and epoxy matrix in the case of the nanocomposite specimens. Also, it was observed that the addition of MWCNTs to the AGSC specimens led to reduce the damage area and increased the damage tolerance, considerably.     

Influence of the draw ratio on the mechanical properties and electrical conductivity of nanofilled thermoplastic polyurethane fibers

Electrically conducting textile fibers were produced by wet-spinning under various volume fractions using thermoplastic polyurethane (TPU) as a polymer and carbon black (CB), Ag-powder, multi-walled carbon nanotubes (MWCNTs), which are widely used as electrically conducting nanofillers. After applying the fiber to the heat drawing process at different draw ratios, the filler volume fraction, linear density, breaking to strength, and electrical conductivity according to each draw ratio and volume fraction. In addition, scanning electron microscopy (SEM) images were taken. The breaking to strength of the TPU fiber containing the nanofillers increased with increasing draw ratio. At a draw ratio of 2.5, the breaking to strength of the TPU fiber increased by 105 % for neat-TPU, 88 % for CB, 86 % for Ag-powder, and 127 % for MWCNT compared to the undrawn fiber. The breaking to strength of the TPU fiber containing CB decreased gradually with increasing volume fraction, and in case of Ag-powder, it decreased sharply owing to its specific gravity. The electrical conductivity of the TPU fiber containing CB and Ag-powder decreased with increasing draw ratio, but the electrical conductivity of the TPU fiber containing MWCNT increased rapidly after the addition of 1.34 vol. % or over. The moment when the aggregation of MWCNT occurred and its breaking to strength started to decrease was determined to be the percolation threshold of the electrical conductivity. The heat drawing process of the fiber-form material containing the anisotropic electrical conductivity nanofillers make the percolation threshold of the electrical conductivity and the maximum breaking to strength appear at a lower volume fraction. This is effective in the development of a breaking to strength and electrical conductivity.     

Effects of wet-spinning conditions on structures,mechanical and electrical properties of multi-walled carbon nanotube composite fibers

A series of composite fibers composed of multi-walled carbon nanotube (MWCNT) and poly(vinyl alcohol) (PVA) are prepared by varying co-flowing wet-spinning conditions such as spinning geometry and PVA concentration, which affect aligning shear stress for MWCNTs during the wet-spinning. Then, structural features, mechanical and electrical performances of MWCNT/PVA composite fibers are investigated as a function of the aligning shear stress of the wet-spinning process. SEM images of the composite fibers exhibit that MWCNTs are wetted effectively with PVA chains. Polarized Raman spectra confirm that the alignment of MWCNTs is enhanced along the composite fiber axis with increasing the aligning shear stress of the spinning process. Accordingly, initial moduli and tensile strengths of the composite fibers are significantly increased with the increment of the aligning shear stress. In addition, it is found that electrical conductivities of MWCNT/PVA composite fibers increase slightly with the aligning shear stress, which is associated with the formation of efficient electrical conduction paths caused by well-aligned MWCNTs along the composite fiber axis.     

Preparation and properties of alkaline functionalized carbon nanotubes reinforced polyurethane composites

Composites consisting of polyurethane (PU)/carbon nanotubes (CNTs) have been successfully prepared by solution mixing method. CNTs were modified through mechano-chemical reaction to increase the compatibility with PU via hydrogen bondings. SEM microphotographs proved that modified CNTs (M-CNTs) became shorter and FTIR spectra showed that hydroxyl groups had been introduced to the surface of M-CNTs. SEM images of PU/M-CNTs composites also proved that M-CNTs were effectively dispersed in PU matrix. Mechanical property tests showed that addition of M-CNTs could significantly improve the tensile properties of PU/M-CNTs composite (breaking strength enhancement ratio for composite with 5.0 wt% M-CNTs was 103.81 %). The thermal stability of composites with M-CNTs was also improved. The initial degradation temperature enhancement was 19.9 oC for the composite with 0.5 wt% M-CNTs. Electrical property tests showed that the electrical properties were improved by adding M-CNTs. The volume conductivities increased 3 and 5 orders of magnitude for the composites with 5.0 wt% and 10 wt% M-CNTs, respectively. The addition of M-CNTs had little effect on the elastic properties of the composites.     

Facile fabrication of carbon nanotubes/polystyrene composite nanofibers for high-performance electromagnetic interference shielding

Polystyrene (PS) composites with nanofibrous structure consisting of multi-walled carbon nanotubes (MWCNTs) with 0-10 wt.% of nanofiller have been fabricated via electrospinning technique. The surface morphology and thermal properties of the composites were evaluated by scanning electron microscopy (SEM) and thermo-gravimetric analysis (TGA). The SEM analysis of the composite nanofibers samples revealed that the average diameter of the nanofibers increases with increasing MWCNTs content. The resultant MWCNTs/PS composite nanofibers diameters were in the range of 391±63 to 586±132 nm. The thermal stability of composites was increased after addition of MWCNTs to PS matrix. The electrical conductivity of the composites with different weight percentage of MWCNTs was investigated at room temperature. Electrical conductivity of MWCNTs/PS composite nanofiber followed percolation theory having a percolation threshold V _c= 0.45 vol% (~0.75 wt. %) and critical exponent q=1.21. The electrical conductivity and thermal properties confirmed the presence of good dispersion and alignment MWCNTs encapsulated within the electrospun nanofibers. The electromagnetic interference (EMI) shielding effectiveness of the MWCNTs/PS composites was examined in the measurement frequency range of 8.2-12.4 GHz (X-band). The total EMI shielding efficiency of MWCNTs/PS composite nanofibers increased up to 32 dB. The EMI shielding results for MWCNTs/PS composite nanofibers showed that absorption loss was the major shielding mechanism and reflection was the secondary mechanism. The present study has shown the possibility of utilizing MWCNTs/PS composite nanofibers as EMI shielding/absorption materials.     

Highly conductive cellulosic nanofibers for efficient water desalination

Electrically conducting nanofibers based on cellulosic materials offer cheap and safe class of materials that can be used for water desalination. In the present work, high conducting cellulose triacetate (CTA) nanofibers containing multiwall carbon nanotubes (MWCNTs) with very low percolation threshold concentration (0.014 wt%) were produced by electrospinning. Unprecedentedly, a hydrophilic ionic liquid consists of 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) was used to dissolve CTA producing a solution of 10 wt%. This CTA solution was used to engineer both bare CTA nanofibers and CTA nanofibers impregnated with MWCNT. The fabricated nanofibers were characterized by the field emission-scanning electron microscopy (FE-SEM) and the high-resolution transmission electron microscopy (HR-TEM). Both FE-SEM and HR-TEM images showed that the MWCNTs were inserted and uniformly distributed inside electrospun nanofibers. Furthermore, mechanical properties such as tensile strength of MWCNTs loaded-CTA electrospun nanofibers was significantly improved by up to 280 % and 270 % for the Young modulus, when compared with the bare CTA fibers. In addition, the surface properties as the hydrophilicity of electrospun nanofibers membrane was enhanced due to the presence of MWCNTs. Moreover, the electrical conductivity of MWCNT loaded-CTA electrospun nanofibers was greatly enhanced after the implementation of the MWCNTs inside the CTA fiber. The performance of composite nanofiber for water desalination was examined in a lab-scale classic capacitive deionization (CDI) unit, at different concentrations of salt. The obtained data revealed that the electro-adsorption of anions and cations on the surface of MWCNTs loaded-CTA electrospun nanofibers electrodes were monitored with time and their concentration were decreased progressively with time and reaches equilibrium.     

Hybrid multi-scale basalt fiber-epoxy composite laminate reinforced with Electrospun polyurethane nanofibers containing carbon nanotubes

In this study, we report the fabrication and evaluation of a hybrid multi-scale basalt fiber/epoxy composite laminate reinforced with layers of electrospun carbon nanotube/polyurethane (CNT/PU) nanofibers. Electrospun polyurethane mats containing 1, 3 and 5 wt% carbon nanotubes (CNTs) were interleaved between layers of basalt fibers laminated with epoxy through vacuum-assisted resin transfer molding (VARTM) process. The strength and stiffness of composites for each configuration were tested by tensile and flexural tests, and SEM analysis was conducted to observe the morphology of the composites. The results showed increase in tensile strength (4–13 %) and tensile modulus (6–20 %), and also increase in flexural strength (6.5–17.3 %) and stiffness of the hybrid composites with the increase of CNT content in PU nanofibers. The use of surfactant to disperse CNTs in the electrospun PU reinforcement resulted to the highest increase in both tensile and flexural properties, which is attributed to the homogeneous dispersion of CNTs in the PU nanofibers and the high surface area of the nanofibers themselves. Here, the use of multi-scale reinforcement fillers with good and homogeneous dispersion for epoxy-based laminates showed increased mechanical performance of the hybrid composite laminates.     

Functionalized multi-walled carbon nanotubes with hyperbranched aromatic polyamide for poly(methyl methacrylate) composites

Multi-walled carbon nanotubes (MWCNTs) were functionalized with hyperbranched aromatic polyamide (HAP) by in situ polymerization and by the AB ₂ approach to enhance the mechanical properties of poly(methylmethacrylate) (PMMA) composites. Various concentrations of HAP-functionalized MWCNTs (HAP-f-MWCNTs) were used to prepare HAP-f-MWCNT-reinforced PMMA composite films. The covalent attachment of HAP to the MWCNTs, as achieved by in situ functionalization, resulted in effective dispersion of the MWCNTs in the PMMA matrix, thus enhancing the mechanical and thermal properties of the composite films. The breaking stress of the composites increased largely with the HAP-f-MWCNT loading.     

Synthesis and properties of shape memory polyurethane nanocomposites reinforced with poly(ɛ-caprolactone)-grafted carbon nanotubes

Nanocomposites of polyurethane (PU) and multi-walled carbon nanotubes (MWNTs) were prepared via in-situ polymerization of poly(ɛ-caprolactone)diol (PCL)-grafted-MWNTs, 4,4′-methylene bis(phenyl isocyanate), and 1,4-butanediol. The grafting of PCL onto MWNTs was confirmed by Fourier transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM). The nanocomposites showed more improved mechanical properties compared to conventional nanocomposites with the same MWNT loading. The thermo-responsive shape recovery as measured in a cyclic tensile test was observed to be approximately 80 % for in-situ nanocomposites, though it showed a reduced trend as the wt% of MWNTs increased. X-ray diffraction investigation also showed that the addition of MWNTs into the polyurethane increased the crystallinity. Scanning electron microscopy and TEM measurements showed better dispersion of MWNTs in the nanocomposites synthesized using in-situ method. Consequently, the presence of PCL-g-MWNTs made an important contribution to the enhancement of the mechanical and shape memory properties of polyurethane.     

Dependence of montmorillonite dispersion in nanocomposites on polymer matrix and compatibilizer content, and the impact on mechanical properties

A series of polyurethane (PU)/monmorillonite (MMT) or nylon 66/MMT nanocomposite were prepared by melt-compounding method to take a close look at the MMT dispersion in the nanocomposite depending on the polymer matrix and the compatibilizer content. Cloisite 30B, the brand name, was selected as MMT, because surface was covered with methyl tallow bis-2-hydroxyethyl ammonium group and the reduced surface hydrophilicityity rendered MMT dispersed better in polymer matrix compared to bare MMT. MMT dispersion, due to the difference in hydrophilicity and the fondness of similar hydrophilicity, was better in nylon than PU. Maximum stress and tensile modulus could be increased by the control of MMT content for both nylon and PU, and the compatibilizer, when added at the same MMT content, also could increase the tensile properties of both nylon and PU. It was found from this investigation that the good dispersion of MMT in polymer matrix can improve the mechanical properties of nanocomposite.     

Effect of multi walled carbon nanotube on the crystalline structure of polypropylene fibers

Polypropylene fibers containing varying amounts of multi walled carbon nanotube (MWCNT) have been spun using a conventional melt spinning and drawing apparatus. Changes in morphology and crystalline structure of composite fibers induced by addition of MWCNT were studied by small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS), Fourier transform infrared spectroscopy (FTIR) and birefringence measurements. The results of SAXS experiments showed an increase in lamellar thickness, long period and crystallinity of the composite fibers in comparison to pure polypropylene fibers. Molecular orientation and helical content of the fibers were increased due to the addition of MWCNT to the polypropylene matrix. WAXS results, being in agreement with the SAXS results, also showed an increase in crystallinity of the composite fibers due to the increase in MWCNT content. This is probably because of nucleating effect of nanotubes in the fiber matrix, causing more crystallization and orientation of molecules to take place around them.     

Fabrication and Characterization of Poly(L-lactic Acid) Fiber Mats Using Centrifugal Spinning

Polylactic acid (PLA) fine fibers and multi walled carbon nanotube (MWCNT) reinforced PLA fine fiber composites were developed utilizing a centrifugal spinning process. Chloroform and chloroform combined with dimethylformamide (DMF) were used to prepare solutions with varying concentrations of PLA and MWCNTs. The optimum spinning conditions to produce PLA fibers and its composites were determined. The morphology of the fibers was analyzed using scanning electron microscopy. In addition, X-ray diffraction analysis and thermo-physical characterization was conducted using thermogravimetric analysis and differential scanning calorimetry. PLA fibers with an average diameter of 481 nanometers and PLA/MWCNT fibers with an average diameter of 358 nanometers were obtained. A decrease in the crystallinity of the fibers was observed when compared to bulk PLA values.     

Microstructures and electrical properties of composite films based on carbon nanotube and para-aramid containing cyano side group

We report the microstructures and electrical properties of poly(2-cyano-1,4-phenylene terephthalamide) (cyPPTA)-based composite films including pristine multi-walled carbon nanotube (MWCNT) of 0.3-10.0 wt%, which were manufactured by ultrasonication-based solution mixing and casting techniques. FT-IR spectra of the composite films revealed the existence of specific interaction between cyPPTA and MWCNT. Accordingly, the pristine MWCNTs were found to be dispersed uniformly in the cyPPTA matrix, as confirmed by TEM images. The electrical resistivity of the composite films decreased considerably from ~10¹⁰ Ω cm to ~10⁰ Ω cm with the increase of the MWCNT content by forming a conductive percolation threshold at ~0.525 wt%. The composite films with 3.0-10.0 wt% MWCNT contents, which have sufficiently low electrical resistivity of ~10²-10⁰ Ω cm, exhibited excellent electric heating performance by attaining high maximum temperatures and electric power efficiency under given applied voltages of 10-100 V. Since the thermal decomposition of the composite films took place at 520-600 °C under air atmosphere, cyPPTA/MWCNT composite films could be used for high performance electric heating, antistatic, and EMI shielding materials.     

Microstructure and mechanical properties of polyurethane/nylon/montmorillonite nanocomposite

Nanocomposite of polyurethane (PU), Nylon66 (nylon), and montmorillonite (MMT) was prepared by a twin screw extruder, and the dispersion of MMT and the mechanical properties of the nanocomposite were analyzed. Dimethyl hydrogenated tallow 2-ethylhexyl ammonium modified Cloisite 25A (C25A) and methyl tallow bis-2-hydroxyethyl ammonium modified Cloisite 30B (C30B) were used as MMT. XRD and TEM analysis indicated that the continuous melt mixing by a twin screw extruder was effective in MMT dispersion. C30B having hydroxyl group on its surface has better dispersion than C25A in the PU/nylon matrix. Maximum stress and strain at break were the maximum at 1 wt% MMT regardless of matrix composition, and decreased at higher MMT content. Best MMT dispersion was also observed at 1 wt% MMT for the entire matrix composition. Aggregation of MMT occurred at MMT content higher than 1 wt%. Nylon addition also induced the aggregation of MMT because of the high polarity of nylon surface. Dispersion of MMT was very important in improving the mechanical properties of PU/nylon nanocomposite.