In-situ preparation of multi-walled carbon nanotube (MWNT)/cellulose nanocomposites and their physical properties

The multi-walled carbon nanotube (MWNT)/cellulose nanocomposites were prepared by using monohydrated Nmethylmorpholine-N-oxide (NMMO) as a solvent for dispersing the acid-treated MWNTs (A-MWNTs) as well as for dissolving the cellulose. The A-MWNTs were well dispersed in both monohydrated NMMO and the nanocomposite films. The nanocomposite films were prepared by a film-casting method onto a glass plate. The tensile strain at break, Young’s modulus, and toughness of nanocomposite films increased by ～5, ～2 and ～12 times, respectively at ? (A-MWNT content in the nanocomposite)=0.8 wt%, as compared to those of the pure cellulose film. The thermal degradation temperature of the nanocomposite films also increased from 329 to 339 oC by incorporation of 1 wt% A-MENTs. The electric conductivities of the A-MWNT/cellulose nanocomposites at ? =1 and 10 wt% were 2.09×10^?5 and 3.68×10^?3 S/cm, respectively. The transmittances were 86, 69 and 55 % at 550 nm for 0.4, 0.8 and 1 wt% nanocomposite films, respectively. Thus, these nanocomposites are promising materials in terms of all the properties studied in this paper and can be used for many applications, such as toughened cellulose fibers, transparent electrodes, etc.     

The addition of carbon fiber on the tribological properties of poly(vinylidene fluoride) composites

The current study examines the tribological performance of poly(vinylidene fluoride) (PVDF) and carbon fiber reinforced PVDF (CF/PVDF) under dry sliding condition. Different contents of carbon fibers were employed as reinforcement. All filled and unfilled polyimide composites were tested against CGr15 ball and representative testing was performed. The effects of carbon fiber content on tribological properties of the composites were investigated. The worn surface morphologies of neat PVDF and its composites were examined by scanning electron microscopy (SEM) and the wear mechanisms were discussed. Moreover, all filled PVDFs have superior tribological characteristics to unfilled PVDFs. The optimum wear reduction was obtained when the content of carbon fiber is 20 vol %.     

Characterization and electrochemical properties of poly(aniline-co-o-methoxyaniline)/multi-walled carbon nanotubes composites synthesized by solid-state method

The composites of copolymers of aniline (An) and o-methoxyaniline (OMA) with multi-walled carbon nanotubes, named as copolymers/MWNT, (poly(An-co-OMA)/MWNT) were prepared by solid-state synthesis method at room temperature. The homopolymers/MWNT composites were synthesized for comparison. The structure and morphology of these composites were characterized by FT-IR spectroscopy, UV-Vis absorption spectroscopy, X-ray diffraction (XRD) and TEM. The electrochemical performances of the composites were investigated by galvanostatic charge-discharge, cyclic voltammetry (CV) and cycle life measurements. The results from FT-IR and UV-Vis spectra showed that different molar ratio of [An]/[OMA] in reaction system has great influence on the oxidation degree, conjugation length and doping level of the copolymers in these composites. The presence of MWNT in the composites was confirmed from the characteristic peaks of MWNT in XRD patterns and the enwrapped MWNT in TEM images. The TEM images further indicates that the MWNT uniformly distributed and enwrapped with polymer in the case of composite from molar ratio of [An]/[OMA]=1:1. The results also showed that the morphology, crystallinity and solubility of composites were highly affected by the incorporation of OMA unit copolymer chain. The results from electrochemical performances suggested that the molar ratio of [An]/[OMA]=3:1 in reaction system can make the obtained composites displayed a higher specific capacitance, good rate ability and cycling stability.     

Enhanced thermal transport performance for poly(vinylidene fluoride) composites with superfullerene

High thermal conductive polymer composites have recently attracted much attention, along with the quick development to the electronic devices toward higher speed. The addition of high thermal conductive fillers is an efficient method to solve this problem. Here, we introduced superfullerene (SF), a novel zero-dimensional carbon-based filler, and incorporated into PVDF by a solution method. The effects of SF filler on the thermal conductivity of PVDF composites were systematically investigated. It was found that PVDF composites exhibited an improvement in thermal conductivity at a low SF loading. PVDF composites with only 5 wt% SF filler present the thermal conductivity value of 0.365 Wm^-1K^-1, which is as much as 121 % enhancement in comparison with that of neat PVDF. In view of the excellent thermal transport performance, the composites may enable some applications in thermal management in the future.     

Effects of mechanical strain on the electric conductivity of multiwalled carbon nanotube (MWCNT)/polyurethane (PU) composites

Conducting polymers have been under development for more than thirty years as replacements for metals in various applications, such as fuel cells, solar cells, actuators, etc. In this study, we investigate conducting polymer composites and attempt to fabricate composite polyurethane/multiwalled carbon nanotubes. The multiwalled carbon nanotubes (MWCNTs) were acid-treated to add functional groups such as -OH or -COOH so they could then be chemically bonded to diisocyanate to form a urethane linkage. Because they have fewer impurities and reduced surface roughness (as confirmed by TEM micrographs), acid-treated MWCNTs can be better dispersed in a polyurethane (PU) matrix than untreated MWCNTs, and acid-treated MWCNTs exhibit better adhesion with the PU matrix, as well. In addition, the conductance test of MWCNT/PU films as a function of elongation showed that the conductance of the acid-treated MWCNT/PU increased up to a certain % elongation, while that of the untreated MWCNT/PU decreased monotonically with % elongation.     

Unique crystallization behavior of multi-walled carbon nanotube filled poly(lactic acid)

Although poly(lactic acid) (PLA) possesses many desirable properties such as miscible, reproducible, nontoxic, and biodegradable properties, extremely slow crystallization rate is a weak point in comparison with other commercial thermoplastics. Addition of nucleating agents can be a good method to increase the overall crystallization rate and multi-walled carbon nanotube (MWCNT) is generally known as a good nucleating agent as well as reinforcement. MWCNT reinforced PLA nanocomposites were prepared by melt blending and the unique nucleation and crystallization behaviors of pure PLA and MWCNT/PLA nanocomposites were investigated. Slow homogeneous nucleation and crystallization behavior of the pure PLA and fast heterogeneous crystallization behavior of MWCNT/PLA nanocomposites were observed. Crystallization behavior of MWCNT/PLA nanocomposites was irrespective of cooling rate and the peculiar behavior was due to fast heterogeneous crystallization caused by the nucleating effect of MWCNT and fast PLA chain mobility.     

Enhanced mechanical and thermal properties of hybrid graphene nanoplatelets/multiwall carbon nanotubes reinforced polyethylene terephthalate nanocomposites

The effects of graphene nanoplatelets (GNP) and multiwall carbon nanotube (MWCNT) hybrid nanofillers on the mechanical and thermal properties of reinforced polyethylene terephthalate (PET) have been investigated. The nanocomposites were melt blended using the counter rotating twin screw extruder followed by injection molding. Their morphology, mechanical and thermal properties were characterized. Combination of the two nanofillers in composites formulation supplemented each other which resulted in the overall improvement in adhesion between fillers and matrix. The mechanical properties and thermal stability of the hybrid nanocomposites (PET/GNP1.5/MWCNT1.5) were significantly improved compared to PET/GNP3 and PET/MWCNT3 single filer nanocomposites. However, it was observed that GNP was better in improving the mechanical properties but MWCNT resulted in higher thermal stability of Nanocomposite. The transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) revealed uniform dispersion of the hybrid fillers in PET/GNP1.5/MWCNT1.5 nanocomposites while agglomeration was observed at higher filler content. The MWCNT prevented the phenomenal stacking of the GNPs by forming a bridge between adjacent GNP planes resulting in higher dispersion of fillers. This complimentary geometrical structure is responsible for the significant improvement in the thermal stability and mechanical properties of the hybrid nanocomposites.     

Enhanced dielectric properties of electrospun titanium dioxide/polyvinylidene fluoride nanofibrous composites

Titanium dioxide/polyvinylidene fluoride (TiO₂/PVDF) composite was prepared by electrospinning process to enhance the dielectric properties for application as a gate insulator in organic thin-film transistors (OTFTs). Scanning electron microscopy, thermogravimetric analysis, and X-ray diffraction were employed to characterize the as-prepared samples, and then their dielectric constants were investigated by impedance analysis. The impedance results show that the dielectric constant of the electrospun TiO₂/PVDF nanofibers is higher than those of other samples, demonstrating that electrospun TiO₂/PVDF composite can be a proper candidate for gate insulators in OTFTs.     

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.     

Poly(vinylidene fluoride)/poly(ethylene-co-vinyl acetate) (20/80) blend. I. Miscibility and crystallization behavior

The miscibility and crystallization behavior of the blends of poly(vinylidene fluoride) (PVDF) and ethylene/vinyl acetate(20/80) copolymer (EVAc80) have been studied using a differential scanning calorimeter and a polarizing microscope equipped with a heating stage. From the melting point depression, the values of interaction energy densityB were calculated to be −1.3004 (cal/cm³) and the Flory-Huggins interaction parameterχ ₁₂ was found to be −0.0818 at 445.6 K. With increasing concentration of EVAc80, the radial growth rate of spherulite was reduced drastically. The FT-IR analysis of samples quenched from the melt to various temperatures showed increasing content ofβ-phase with increasing amount of blended EVA80 along with lower quenching temperature.     

Poly(vinylidene fluoride)/poly(ethylene-co-vinyl acetate) (20/80) blend. II. Crystalline structure and morphology

We investigated the effect of ethylene and vinyl acetate (20/80 mole ratio) copolymer (EVAc80) content in poly(vinylidene fluoride) (PVDF/EVAc80) blends and also varying isothermal crystallization temperatures on the crystalline structure and morphology, and surface topography using different spectroscopic and microscopic techniques. As crystallization temperature increases for the same blend composition, the lamellar splay type spherulite is changed to the concentric ring-banded spherulite, and then to the spiral-ringed spherulite with further increasing temperature. With increasing EVAc80 content in the PVDF/EVAc80 blends, the temperature range, where spiral-ringed spherulites and lamellar splay typeγ-spherulites are present predominantly, becomes much broader. Furthermore, the non-textured spherulite was observed more at highest crystallization temperature with increasing EVAc80 content. The band spacing between bright and dark zone and periodicity between ridge and valley increase with increasing amorphous EVAc80 content.     

Enhanced mechanical and thermal properties of carbon fiber composites with polyamide and thermoplastic polyurethane blends

In this article, we demonstrated the preparation of carbon-fiber-reinforced composites using a polyamide 6 (PA6)/thermoplastic polyurethane (TPU) blend, in which the addition of TPU resulted in superior mechanical performances and increased thermal stability. According to various characterization techniques, these results are attributed to an enhanced adhesion and a homogeneous dispersion of long-carbon-fibers (LCFs) with TPU sizing in blended polymer matrix. Above all, dynamic-mechanical thermal analysis (DMTA) measurements clearly show that the dynamic storage modulus (E') of the blend composites is increased by threefold with temperature ranges below and above the glass transition temperature. The presence of LCFs in TPU systems induces effective fiber orientation, exhibiting simultaneous improvements in the tensile strength, flexural strength, and thermal stability.     

Effect of surfactant functionalization of multi-walled carbon nanotubes on mechanical,electrical and thermal properties of epoxy nanocomposites

The present paper compares the mechanical, electrical and thermal properties of epoxy nanocomposites (prepared by solution blending method) by adding four different multi-walled carbon nanotubes (MWCNTs), which are pristine, cationic, anionic and non-ionic surfactant functionalized MWCNTs, respectively. This investigation focused on the effects of dispersion of MWCNTs on the physical properties. Systematical characterization on the dispersion of MWCNTs in different solvents were did via UV-Vis spectrophotometer. The Hansen solubility parameters (HSPs) and dispersion of MWCNTs in solvent and epoxy were both changed after surfactants introduced especially for the non-ionic surfactant. Finally, mechanical, fracture toughness, electrical and thermal properties of epoxy composites were found can be improved because of good dispersion of MWCNTs (especially non-ionic surfactant).     

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.     

SiO2-kaolinite affecting the surface properties of ternary poly(vinyl chloride)/silica/kaolinite nanocomposites

The products from the dispersion of nanoscale particulates such as the layered clays or the spherical inorganic minerals within the polymeric matrices are called polymeric nanocomposites. In this paper, we prepared poly(vinyl chloride) (PVC) based nanocomposites containing SiO₂-kaolinite by melt compounding. The influence of SiO₂-kaolinite on the surface properties of PVC was investigated by the use of various surface analysis techniques including a ttenuated total reflectance spectroscopy (ATR), wide angle X-ray diffractometry (WAXD), atomic force microscopy (AFM), scanning electron microscopy (SEM), electron dispersive X-ray spectrometer (EDX), contact angle measurement (CAM), and reflectance spectroscopy (RS). ATR spectroscopy showed possible interaction between layered kaolinite and PVC at surface. Microscopic methods illustrated an increased surface roughness compared to the pure PVC. Contact angle measurements of the resultant PVC nanocomposites demonstrated that the wettability of substrates depends on the surface interactions between kaolinite layers and PVC matrix. Optical properties of nanocomposite films were finally measured by the aid of reflectance spectrophotometer. It can be seen from optical studies that reflectance values were increased after incorporation of SiO₂-kaolinite in nanocomposite.     

Thermal and mechanical properties of modified CaCO3 filled poly (ethylene terephthalate) nanocomposites

Poly(ethylene terephthalate) (PET)/CaCO₃ and PET/modified-CaCO₃ (m-CaCO₃) nanocomposites were prepared by melt blending. The morphology indicated that m-CaCO₃ produced by reacting sodium oxalate and calcium chloride, was well dispersed in PET matrix and showed good interfacial interaction with PET compared to CaCO₃. No significant differences in the thermal properties such as, glass transition, melting and degradation temperatures, of the nanocomposites were observed. The thermal shrinkage of PET at 120 °C was 10.8 %, while those of PET/CaCO₃ and PET/m-CaCO₃ nanocomposites were 2.9–5.2 % and 1.2–2.8 %, respectively depending on filler content. The tensile strength of PET/CaCO₃ nanocomposite decreased with CaCO₃ loading, whereas that of PET/m-CaCO₃ nanocomposites at 0.5 wt% loading showed a 17 % improvement as compared to neat PET. The storage modulus at 120 °C increased from 1660 MPa for PET to 2350 MPa for PET/CaCO₃ nanocomposite at 3 wt% loading, and 3230 MPa for PET/m-CaCO₃ nanocomposite at 1 wt% loading.     

Crystallization behavior,rheology, mechanical properties,and enzymatic degradation of poly(L-lactide)/poly(D-lactide)/glycidyl methacrylate grafted poly(ethylene octane) blends

Poly(L-lactide) (PLLA)/poly(D-lactide) (PDLA)/poly(ethylene octene) grafted with glycidyl methacrylate (GPOE) were prepared by simple melt blending method at PDLA loadings from 1 to 5 wt%. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) demonstrated the formation of the stereocomplex in the blends. The addition of PDLA led to the increase of nucleation density from polarized microscope (POM) observations. Rheological measurements indicated that the blends exhibited a rheological fluid-solid transition and an enhanced elastic behavior in that ternary system as the PDLA loadings reached up to 5 wt%. By adding 1-2 wt% PDLA, the ternary system has better tensile and impact properties. Dynamic Mechanical Analysis (DMA) results showed that SC crystal formation and its effect on the enhancement of thermal stability at higher temperature. It is interesting that the enzymatic degradation rates have been enhanced clearly in the PLLA/PDLA/GPOE blends than in the PLLA/GPOE blend, which may be of great use and significance for the wider practical application of PLLA/GPOE blends.     

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.     

Crystal structure and thermal properties of poly(vinylidene fluoride)-carbon fiber composite films with various drawing temperatures and speeds

PVDF-CF composite films were prepared using a melt pressing method. The PVDF-CF composite films were cut into rectangular shapes with a gauge length and width of 10 and 5 mm, respectively. The films were drawn using a universal testing machine equipped with a hot chamber. The drawing temperatures and speeds were 50∼150 °C and 100∼000 %/min, respectively. The crystal structure and physical properties of the resulting PVDF-CF films were investigated by wide angle X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis and scanning electron microscopy. The crystal form of the initial films was the 〈alpha〉 phase (non polarity, lamellar structure) of PVDF. The maximum draw ratio was 4.2. The drawn PVDF-CF films prepared at 100 °C were mainly the 〈beta〉 phase (polarity, fibrillar structure) of PVDF. With increasing drawing speeds, the 〈alpha〉 phase became the dominant phase of PVDF in the PVDF-CF films. The thermal properties of the PVDF-CF films improved with increasing drawing temperature, and the dynamic mechanical properties improved with increasing drawing speed.     

Preparation and characterization of poly(L-lactic acid)/hollow silica nanospheres nanocomposites

This paper-reports the development of a unique nanocomposite material based on poly(L-lactic acid) and hollow silica nanospheres. The composites were produced by melt blending in a twin-screw extruder and then spun into fibers. In order to improve the compatibility between the polymer and the inorganic additive, the surface of the hollow silica nanospheres was modified by a silane coupling agent, acetoxypropyltrimethoxysilane. It was demonstrated by electron microscopy that the modified silica nanospheres were well-dispersed in the polymer matrix. The resulting nanocomposites exhibited slightly improved thermal stability, crystallinity and softness. Remarkably, the hollow spheres, which could encapsulate any active substances, remain intact after the melt processing, allowing promising applications in biomedical fields.