Structures and physical properties of graphene/PVDF nanocomposite films prepared by solution-mixing and melt-compression

We have manufactured poly(vinylidene fluoride) (PVDF)-based nanocomposite films with different graphene contents of 0.1～10.0 wt% by ultrasonicated solution-mixing and melt-compression. As a reinforcing nanofiller, graphene sheets are prepared by rapid thermal expansion of graphite oxide, which are from the oxidation of natural graphite flakes. Graphene sheets are characterized to be well exfoliated and dispersed in the nanocomposite films. X-ray diffraction data confirm that the α-phase crystals of PVDF are dominantly developed in the nanocomposite films during the meltcrystallization. DSC cooling thermograms show that the graphene sheets serve as nucleating agents for the PVDF α-form crystals. Thermal stability of the nanocomposite films under oxygen gas atmosphere is noticeably improved, specifically for the nanocomposite with 1.0 wt% graphene. Electrical volume resistivity of the nanocomposite films is substantially decreased from ～10¹⁴ to ～10⁶ W cm, especially at a critical graphene content between 1.0 and 3.0 wt%. In addition, mechanical storage modulus is highly improved with increasing the graphene content in the nanocomposite films. The increment of the storage modulus for the nanocomposite film at 30 °C with increasing the graphene content is analyzed by adopting the theoretical model proposed by Halpin and Tsai.     

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.     

Electrospinning and microwave absorption of polyaniline/polyacrylonitrile/multiwalled carbon nanotubes nanocomposite fibers

Electrical conductive nanocomposite fibers were prepared with polyaniline (PANI), polyacrylonitrile (PAN) and multi-walled carbon nanotubes (MWCNTs) via electrospinning. The morphology and electrical conductivity of the PANI/PAN/MWCNTs nanocomposite fibers were characterized by scanning electron microscope (SEM) and Van De Pauw method. Electrical conductivity of nanocomposite fibers increased from 1.79 S·m^?1 to 7.97 S·m^?1 with increasing the MWCNTs content from 3.0 wt% to 7.0 wt%. Compared with PANI/PAN membranes, the mechanical property of PANI/PAN/MWCNTs nanocomposites fiber membranes decreased. The microwave absorption performance of composite films was analyzed using waveguide tube, which indicated that with the thickness increasing the value of R_L reduced from ?4.6 to ?5.9 dB.     

Hybrid organic-inorganic POSS (polyhedral oligomeric silsesquioxane)/polypropylene nanocomposite filaments

Octamethyl-POSS and Octaphenyl-POSS reinforced polypropylene nanocomposite monofilaments were prepared by melt blending route. It was observed that incorporation of Octamethyl-POSS and Octaphenyl-POSS in polypropylene show improvement in mechanical as well as thermal properties. Octaphenyl POSS/PP nanocomposites show significant increase in thermal stability even at very low concentration as compared to neat polymer matrix. An increase of 100 and 140 °C was observed in thermal degradation temperature at 5 wt% loss and maximum degradation over neat PP filaments respectively at low OP-POSS loadings (<5 wt%). Both Octamethyl-POSS and Octaphenyl-POSS act as lubricating agents facilitating drawing which results in improvement in orientation as well as mechanical properties.     

POSS/polypropylene hybrid nanocomposite monofilaments by reactive extrusion

The Allyl-heptaisobutyl-polyhedral oligomeric silsesquioxane (AHO-POSS) grafted polypropylene (PP) was prepared by reactive extrusion and by physical blending routes. The structure and properties of physically blended and reactively blended POSS/PP nanocomposites were investigated by FTIR, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetric analysis, SEM, spherutlic growth and mechanical properties studies. Chemical bonding of POSS with PP in reactive extrusion was confirmed by FT-IR spectroscopy. DSC and TGA studies showed that the thermal stability of AHO-POSS/PP nanocomposite prepared by reactive extrusion improved significantly as compared to only physically blended nanocomposites. WAXD studies showed decrease in crystallinity of the AHO-POSS/PP nanocomposites prepared by reactive extrusion. SEM studies showed aggregation tendency in case of physically blended AHO-POSS/PP nanocomposites. Spherulite growth studies show reactive blending retards spherulite growth in PP polymer.     

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.     

Fabrication and Characterization of Graphene Enriched Polysulfon Amide Nanocomposites by Electrospinning System

In this paper, we report on the fabrication and characterization of poly(sulfone amide)/graphene (PSA/G) nonwoven based nanocomposite mat assembled via electrospinning technique. Different types of nanocomposite mats were electrospun by varying the weight percentage of graphene in the polymer solution. The surface morphologies, chemical structural, thermal, and electrical properties of the nanocomposites were evaluated systematically. The morphology of the PSA/G nanocomposites exhibited that mesh-like ultrafine nanofibers were densely aligned. Thermal stability and electrical properties of the PSA/G composites could be improved obviously with the addition of graphene. And the thickness uniformity of the nanocomposite mat was improved by using an electrospinning system. Our experimental results suggested that the PSA/G nanocomposites have potential to serve in many different applications, especially in the area of electronic components.     

Preparation and crystallization behavior of polylactide nanocomposites reinforced with POSS-modified montmorillonite

We herein report the preparation and crystallization behavior of polylactide (PLA) nanocomposites reinforced with polyhedral oligomeric silsesquioxane-modified montmorillonite (POSS-MMT), which is prepared by exchanging sodium cations of pristine sodium montmorillonite (Na-MMT) with protonated aminopropylisobutyl polyhedral oligomeric silsesquioxane (POSS-NH₃ ⁺). PLA nanocomposites with 1–10 wt% POSS-MMT contents are manufactured via melt-compounding, and their structures and melt-crystallization behavior are investigated. It is characterized that POSS-MMT nanoparticles in the nanocomposites have an exfoliated structure of MMT silicates with POSS-NH₃ ⁺ and partial POSS-NH₂ crystals. DSC cooling thermograms suggest that the overall melt-crystallization rates of the nanocomposite with only 3 wt% POSS-MMT are remarkably enhanced in comparison with the neat PLA. From the isothermal crystallization analysis based on the Avrami model, the overall melt-crystallization of PLA/POSS-MMT nanocomposites is found to be dominated by the heterogeneous nucleation and three-dimensional spherulite growth. Isothermal melt-crystallization experiments using a polarized optical microscope show that the spherulite nucleation density of PLA/POSS-MMT nanocomposites is much higher than that of the neat PLA, whereas the spherulite growth rates of all the nanocomposites are almost identical with the rate of the neat PLA. It is concluded that the highly enhanced melt-crystallization rates of PLA/POSS-MMT nanocomposites stem from the dominant nucleation effect of POSS-MMT nanoparticles for PLA crystals.     

Electrical properties of graphene/waterborne polyurethane composite films

Graphene is classified as a carbon-based material. Structurally, graphene is made up of carbon-based two-dimensional atomic crystals and a one atom thick planar sheet of sp²-bonded carbon atoms. This sort of arrangement in graphene makes it a unique material with exceptional mechanical, physicochemical, thermal, electrical, optical, and biomedical properties. Methods for graphene-based fabric production mainly use graphene-based materials such as graphene (G), graphene oxide (GO), and reduced graphene oxide (rGO) coated on fabric or yarn. Waterborne polyurethane (WPU) is one of the most rapidly developing and active branches of polyurethane chemistry. More and more attention is being paid to graphene-coated fabrics owing to their low temperature flexibility, the presence of zero or very few VOCs (volatile organic compounds), water resistance, pH stability, superior solvent resistance, excellent weathering resistance, and desirable chemical and mechanical properties. It is used as a coating agent or adhesive for fibers, textiles, and leather. Also, graphene-containing materials have been used to enhance the properties of WPU. In this study, graphene/WPU composite solution and film was prepared to conduct basic research for developing electrical heating textiles which is not harmful to the human body, flexible and excellent in electrical properties. Graphene/WPU composite solutions were prepared with a graphene content of 0, 2, 4, 8, and 16 wt%, and graphene/WPU film was prepared with solution casting method. The graphene contents were analyzed for their surface morphology, electrical properties, and electrical heating properties.     

Polystyrene nanocomposites viaIn-situ intercalated free radical polymerization

Organically modified montmorillonite (C₈PPh-MMT) was obtained using the ion exchange reaction between Na⁺-montmorillonite (Na⁺-MMT) and 1-octenyltriphenyl phosphonium chloride (C₈PPh-Cl⁻). Polystyrene nanocomposites were then prepared by in-situ free-radical polymerization of the styrene containing intercalated C₈PPh-MMT. The resulting polystyrene hybrids with various organoclay contents were investigated with FT-IR, which confirmed that PS hybrids were successfully prepared via the reaction of styrene monomer in the interlayers of the clays. The variations of the thermal behaviors of the hybrids with increases in the organoclay content from 0 to 8 wt% were determined. The glass transition temperatures (T_g) and initial thermal degradation temperatures (T_D ⁱ) of the PS hybrids were found to increase linearly with increases in the organoclay loading. Regardless of the organoclay content of the hybrids, the clay was found to be dispersed homogeneously in the matrix polymer. This is direct evidence that the PS hybrids formed nanocomposites. This result was confirmed with XRD and TEM.     

Novel nanocomposites based on hydroxyethyl cellulose and graphene oxide

In the present study, nanocomposites films formed by hydroxyethyl cellulose (HEC) and graphene oxide (GO) were synthesized and characterized. Compared with pure hydroxyethyl cellulose film, the thermal stability and mechanical properties of the composite materials were significantly improved. When the graphene loading was only 1.0 wt%, the maximum weight loss temperature increased 11.14 °C. The tensile strength and Young’s modulus of HEC/GO nanocomposites films were increased by 30.28 and 75.63 % compared to the pure HEC films, with only 1.0 wt% GO. The X-ray diffraction and Fouriertransform infrared spectroscop showed that GO sheets were completely exfoliated in the HEC matrix and suggested the presence of the weak interaction between HEC and GO sheets because of large number of oxygen-containing hydrophilic functional groups on the surface and edge of GO sheets. Furthermore, the well-dispersed GO nanosheets in the films can be inferred from the SEM and Halpin-Tsai model analysis. On the other hand, the composite films showed improved barrier properties against oxygen. This simple process for preparation of HEC/GO films is attractive for potential development of high-performance films for packing applications.     

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.     

Preparation and characterization of porous carbon based nanocomposite for supercapacitor

Porous nanocomposites are prepared by electrospinning blended polyacrylonitrile, copper acetate and mutiwalled carbon nanotube in N, N-dimethylformamide. The electrospun nanofiber webs are oxidatively stabilized and then carbonized resulting in composite carbon nanofibers. The study reveals that composite nanofibers with relatively smooth surface morphology are successfully prepared. X-ray diffraction is used to confirm the presence of Cu in carbon nanofibers. The carbon nanofibers with CNTs have better thermal stability and higher electrical conductivity. The Brunauer-Emmett-Teller analysis reveals that C/Cu/CNTs nanocomposites with mesopores possess larger specific surface area and narrower pore size distribution than that of C/Cu nanofibers. The electrochemical properties are investigated by cyclic voltammetry and galvanostatic charge-discharge tests. The nanocomposite with 0.5 wt.% CNT loading exhibits an energy density of 2 Whkg^?1, power density of 1916 Wkg^?1, a specific capacitance of about 225 Fg^?1 at a current density of 2 Ag^?1 and its capacitance decreased to 78 % of its initial value after 3,000 cycles.     

Effect of nanoclay incorporation method on mechanical and water vapor barrier properties of starch-based films

The objective of this study was to investigate the influence of nanoclay incorporation procedure on the mechanical and water vapor barrier properties of starch/nanoclay composite films. Cassava starch films were prepared with (nanocomposite) and without nanoclay (control) in two steps: firstly the production of extruded pellets and secondly thermo-pressing. The nanocomposite films were prepared via two different methods: in D samples the nanoclay was dispersed in glycerol and subsequently incorporated into the starch; and in ND samples all ingredients were added in a single step before the extrusion. All the composite-films were prepared with cassava starch using 0.25 g of glycerol/g of starch and 0.03 g of nanoclay/g of starch. Control samples showed V_A-type crystallinity induced by the manufacturing process and the nanocomposites presented a semicrystalline and intercalated structure. The nanoclay improved the water vapor barrier properties of the starch film and this effect was more pronounced in D samples, where the water vapor permeability (K^w) was 60% lower than that of the control samples. The K^w reduction was associated with decreases in the effective diffusion coefficient (approximately 61%) and in the coefficient of solubility (approximately 22-32%). On the other hand, the incorporation of nanoclay increased the tensile strength and the rigidity of the films and this effect was more significant when the nanoclay was dispersed in glycerol. Thus, the incorporation of nanoclay into starch-based films is a promising way to manufacture films with better mechanical and water vapor barrier properties.     

Enhanced thermal conductivity for PVDF composites with a hybrid functionalized graphene sheet-nanodiamond filler

A new thermal conductive poly(vinylidene fluoride) (PVDF) composite has been developed via a hybrid functionalized graphene sheets (FGS)-nanodiamonds (NDs) filler by a simple solution method. The PVDF composite showed different thermal conductivities at different proportion of hybrid filler. The thermal conductivity of the composite was up to 0.66 W/m·K for a mixture containing 45 wt% hybrid filler, which is about 2-fold increment in comparison to the PVDF martrix. The PVDF composites consisting of 20 wt% hybrid FGS/ND filler at the weight ratio of 1:3 shows the best thermal stability. The electrical conductivity of composites was increased from 5.1×10^?15 S cm^?1 (neat PVDF) to 7.1×10^?7 S cm^?1 of the PVDF composite with 10 wt% hybrid filler.     

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.     

Characteristics of Electrical Heating Elements Coated with Graphene Nanocomposite on Polyester Fabric: Effect of Different Graphene Contents and Annealing Temperatures

This paper reports the fabrication of electrical heating elements based on the graphene/waterborne polyurethane (WPU) composite coated on polyester fabric with toughness like that of artificial leather. Samples were prepared with 0, 4, 8, and 16 wt% of graphene by using the knife edge method, and then, the samples were annealed from 100 oC to 160 °C. The graphene content had a large effect on the electrical and electrical heating properties. The surface resistivity was decreased by approximately 6 orders of magnitude with an increase from 0 wt% to 16 wt% graphene/WPU composite fabric. The electric heating properties were also improved, as indicated by the percolation threshold. Samples with various graphene contents were annealed, and it was found that the electrical and electrical heating properties were improved, and the most enhanced properties were obtained when the samples were annealed at 120 °C. The initial modulus and tensile strength were increased in comparison with those of 0 wt% and 16 wt% graphene/WPU composite coated on fabrics, but the elongation at break value was slightly decreased with an increasing graphene content. When the samples were annealed, initial modulus and tensile strength of samples were improved at 120 °C and 140 °C, and they were slightly decreased at 160 °C. However, the elongation at break showed an opposite tendency to the tensile strength. With the increase in content of graphene and annealing at 120 °C and 140 °C, the samples were more stiff and tough, and at 160 °C, the samples were softer. Therefore, graphene/WPU composite coated on polyester fabric by use of the annealing process may have applications in electrical heating elements due to its excellent heating performance and toughness like that of artificial leather.     

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.     

Preparation of starch-based polyurethane films and their mechanical properties

In this study, polyurethane films were prepared using starch as the main polyol component, and the mechanical properties of these films were investigated. The starch content of the polyols was 30–50 wt%. To confirm the formation of a urethane linkage between the −OH of starch and −NCO of toluene 2,4-diisocyanate, Fourier transform infrared (FT-IR) spectroscopic analysis was performed. Differential scanning calorimetry (DSC) thermograms of the polyurethanes resulted in two endothermic peaks, which shifted to higher temperatures with increasing starch content and −NCO/−OH molar ratio. Due to the melting behavior of polyurethane, films could be prepared by hot pressing at an appropriate temperature. Polyurethane films were prepared with various polyol starch content and −NCO/−OH molar ratios. Tensile testing indicated that the breaking stress and elastic modulus increased significantly with starch content and −NCO/−OH molar ratio. In addition, bending tests indicated an increase in breaking stress and bending modulus with starch content and −NCO/−OH molar ratio and decreased breaking strain. The strain rate in both tensile and bending tests had a significant effect on the mechanical properties.     

Processing and characterization of liquid crystalline copoly-(ethylene terephthalate-co-2(3)-chloro-1,4-phenylene terephthalate)/polycarbonate blends

Liquid crystalline (LC) poly(ethylene terephthalate-co-2(3)-chloro-1,4-phenylene terephthalate) (50/50, mole/mole) [PECPT] was synthesized and blended with polycarbonate (PC). LC properties of PECPT and thermal, morphological, and rheological behaviors of the PECPT/PC blend were studied. PECPT showed the nematic LC phase and much longer relaxation time than poly(ethylene terephthalate) (PET). The apparent melt viscosity of PECPT was one third of that of PET. An abrupt torque change was observed during the blending process due to the orientation of LC domains. For the blends containing 10∼30 wt% of PECPT, the complex viscosities were higher than that of PC. As PECPT content increases above 40 wt%, shear thinning was observed. The lowest complex viscosity was obtained at 40∼50 wt%. Transesterification of PECPT and PC was confirmed by the selective chemical degradation of carbonate groups in PC.