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The relationship between morphology and temperature-resistivity effect of injection-molded isotactic polypropylene/high density polyethylene/carbon black (iPP/HDPE/CB) composites with special orientation structure is investigated in detail. The morphological variation induced by melting, disorientation, crystallization and movement of CB particles is responsible for the change of electrical conductivity of the iPP/HDPE/CB composites during the heating and cooling. The room temperature volume resistivity of the composites reduces markedly after a round of heating and cooling because the network is improved through morphological changes and movement of particles during annealing. The continuity of HDPE/CB phase and the effective concentration of the CB particles in HDPE simultaneously determine the temperature-resistivity effects of the composites. Samples with iPP/HDPE mass ratio of 50/50 achieve a better balance of the two factors, which results in more stable conductive properties varying with temperature.

In this work, PP/EPDM/HDPE ternary blends were applied. Morphologies and melt crystallization behavior, rheological property and mechanical properties of these blends were studied by scanning electron microscopy (SEM), differential scanning calorimeter (DSC), dynamic rheology analysis and mechanical properties tests. It was found that the viscosity of EPDM had greatly effect on the morphology of PP/EPDM/HDPE blends. The more perfect encapsulation structure (core of HDPE and shell of EPDM) can be formed in the PP/EPDM/HDPE 70/20/10 blend with lower viscosity EPDM2 and the Notched Izod impact strength of blend was greatly improved. The melting points of PP and HDPE in PP/EPDM1/HDPE blend decrease with the content of phenolic resin varying from 0.5 wt% to 1.5 wt% in two processing methods (the direct extrusion and lateral injection method). The ternary blends of PP/EPDM/HDPE prepared by two methods with different content of phenolic resin showed different rheological behavior: The storage (G’) and loss modul...

Graphene has unique two-dimensional nanostructure with high specific surface areas, superior mechanical properties which has promising applications for the development of high performance nanocomposite materials. Most of previous work on graphene nanocomposites addresses on polymer matrix. In the present work, we have fabricated zirconia and graphene nanocomposites (ZrO2/GNS) by simple mechanical mixing and pressureless sintering process. Microstructural observations of the composite show the homogeneous and random distributions of graphene nanosheet in the zirconia matrix. Scanning electronic microscopy observes partially pulled out graphene nanosheets with well combined interface with the matrix in fractural surface, showing promising reinforcement effects.

Ultrafine full-vulcanized powdered rubber (UFPR) was added into intumescent fire retardant polypropylene (IFR-PP) composites, and fire retardance, morphology, and properties of the composite were analyzed. Ammonium polyphosphate and pentaerythritol were used as the intumescent fire retardants (IFR). The mechanical properties (elongation at break increased from 70% to 110%) and the melt flowability of IFR-PP improved by adding a small quantity of UFPR (less than 0.5 phr) but decreased when the UFPR was more than 0.5 phr. At the same time, the fire retardance, as measured by the limiting oxygen index and the UL94 vertical test rating, and other mechanical properties decreased appreciably with adding UFPR. The reasons were analyzed by using SEM micrographs, and a model was proposed to explain the reasons.

In this work, isotactic polypropylene (iPP) composites filled with multiwalled carbon nanotubes (MWCNTs) were prepared by compounding iPP melt with MWCNT aqueous suspension using a corotating twin-screw extruder, and the morphology and crystallization behavior of the composites were investigated. Scanning electron microscopy micrographs showed that MWCNTs dispersed individually at nanoscale in the iPP matrix when the MWCNTs concentration was low, though MWCNTs aggregates were detected when the filler concentration increased. The results of differential scanning calorimetry, wide-angle X-ray diffraction, and polarized light microscopy indicated that the β-form crystal of iPP was induced by MWCNTs at the concentration of 0.1 wt.% which was dispersed individually in the iPP matrix. At higher content, however, MWCNTs acted as α-nucleating agent, and the crystals in the iPP/MWCNT composites showed higher degree of perfection than that of pure iPP though smaller in dimension. Crystallization rate of iPP increased significantly with increasing MWCNT content.

Vertically oriented bamboo-like nitrogen-containing carbon nanotube (CNT) arrays were grown on an alumina (Al 2 O 3 ) substrate by the injection chemical vapor deposition (CVD) process using ethanol as a carbon source and ethylenediamine as a nitrogen source. The substrate is a sintered Al 2 O 3 plate with a rough surface consisting of polycrystalline Al 2 O 3 micro-grains. The concentration of ferrocene in ethanol played a major role in the growth of CNT arrays. Aligned multi-walled CNT arrays were obtained under optimized catalyst concentrations (0.015 g/ml) and growth temperature (900 °C) with the height of the arrays attaining 160 μm after the growth for 1 h. The growth of CNT occurred predominately between 30 and 40 min and ceased growth beyond 60 min. X-ray photoelectronic spectrum detects the incorporation of nitrogen atoms in the CNTs with an atomic ratio of 1.2%. The present study indicates that it is possible to grow high quality carbon nanotube arrays over a cheap alumina substrate of a rough surface.

A large-size circular-disc (CD) assembly of carbon nanotubes (CNTs) was formed from injection catalytic chemical vapor deposition (CVD) reactions. The CNT-CD assembly, which has an outer diameter of 830 nm, consists of closely packed rings of double-walled carbon nanotubes (DWNTs), in twenty-eight circles, and stacked in five layers. A structural interpretation suggests that the CNT-CD assembly is coiled from a “tape-like” bundle of DWNTs, whose coiling to form the CNT-CD resembles the rolling up of tape to form a disc. The large CD assembly was formed within milliseconds in the transient gas flow reactions, and the coiling of nanotubes or “nucleation” of the circular assembly was associated with shears generated by gas disturbances in the vapor phase.

The molecular weight of ethylene- block - co -polypropylene (co-PP) was adjusted by reactive extrusion with the incorporation of dicumyl peroxide (DCP), and the effect of molecular weight on the crystallization behavior, crystal morphology, and fracture behavior was investigated. It was found that, with increasing DCP content, the molecular weight (MW) decreased and the polydispersity ( M w / M n ) slightly decreased. After modification, the number of spherulites with obscure boundaries increased, and the size of the spherulites was more even due to increasing amount of grafting and micro-cross-linking structures, generated in co-PP degradation, which were acting as nucleating agents. Evaluated by essential work of fracture method, the specific essential work of fracture, w e , was found to be strongly dependent on the molecular weight, especially, on the number average molecular weight ( M n ) linearly, while the specific non-essential work of fracture, βw p , was enhanced with decreasing z-average molecular weight ( M z ), probably owing to the reduction of ultra-high molecular weight component in degraded co-PP.

Large area of vertically aligned bamboo-structured carbon nanotubes (CNTs) films was grown on quartz substrates by the injection CVD reactions using a double injection regime involving separate injection of a hydrocarbon liquid and a promoter. Excellent arrays of all bamboo carbon nanotubes were obtained using ethanol as the carbon source by this reaction design. Arrays of the bamboo nanotubes were obtained also using toluene and pyridine in replace of ethanol as the carbon source. A high growth rate of the film which is double of that reported earlier, was obtained by controlling the ratio of ethanol and ethylenediamine, with the film thickness attained 160 μm after the growth for 20 min. We found that ethylenediamine played a key role in the formation of the bamboo structures. When a single injection was used in absence of ethylenediamine, the reaction could still yield the arrays of nanotubes which, however, of the normal tubule structures rather than the bamboos structures. The fine structures of the bamboo nanotubes changed with the sort of the carbon source, the carrying gases and the synthesis temperatures. The present double injection CVD reactions allow the use of mutually insoluble hydrocarbons and promoters, avoiding the possible reactions among the reactants, and, more importantly, provides the feasible control over the nanotube arrays from the tubule to the bamboo structures.

The hot stretching of thick, extruded sheets at high temperatures is a very important process in the production of finished biaxially oriented polypropylene (BOPP) films with special inner structures. Through a simulation of hot stretching in the machine direction (MD) of the processing of BOPP films, it was found that at high temperatures, the stretching ratio greatly influenced the obtained crystalline structure, as observed by differential scanning calorimetry (DSC). Also, in MD hot stretching, the crystallinity increased by an average of 20%. Wide-angle X-ray diffraction patterns of extruded sheet samples with and without stretching confirmed the structural changes shown by DSC, and the results proved that β-crystal modification did not occur during the MD hot-stretching process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 686–690, 2003

In this study, an increase in the cooling rate of high-density polyethylene parts was carried out via a change in the fluid flow pattern to introduce gas cooling under a gas-assisted injection-molding process; this was conducive to the retention of orientation chains shaped during the injection stage and further developed into much more oriented crystals. Morphological observation showed that the parts without gas cooling (WOGC) were composed of oriented crystals except the gas channel zone, whereas the parts with gas cooling (WGC) were full of oriented crystals, especially much more interlocking shish-kebab structures in the subskin zone. The WGC parts had a higher degree of orientation than the corresponding zone of the WOGC parts. Although the lower crystallinity, the wider orientation regions, and much more interlocking shish-kebab structures led to considerable increases from 32 and 990 MPa in the WOGC parts to 36 and 1150 MPa in the WGC parts for the yield strength and elastic modulus, respectively. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40349.

Combining carbon nanotubes (CNTs) with graphene has been proved to be a feasible method for improving the performance of graphene for some practical applications. This paper reports a water-assisted route to grow graphene on CNTs from ferrocene and thiophene dissolved in ethanol by the chemical vapor deposition method in an argon flow. A double injection technique was used to separately inject ethanol solution and water for the preparation of graphene/CNTs. First, CNTs were prepared from ethanol solution and water. The injection of ethanol solution was suspended and water alone was injected into the reactor to etch the CNTs. Thereafter, ethanol solution was injected along with water, which is the key factor in obtaining graphene/CNTs. Transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and Raman scattering analyses confirmed that the products were the hybrid materials of graphene/CNTs. X-ray photo-electron spectroscopy analysis showed the presence of oxygen rich functional groups on the surface of the graphene/CNTs. Given the activity of the graphene/CNT surface, CdS quantum dots adhered onto it uniformly through simple mechanical mixing.

The performance of carbon nanotube fibers (CNTFs) significantly depends on the packing styles of carbon nanotube (CNT) bundles. Revealing the structures and characterizations of CNT bundles is contributive to understanding the structures, properties and even the formation of CNTFs during chemical vapor deposition (CVD) processing. In this paper, bundles consisting of collapsed double-walled carbon nanotubes (CDWNT) in continuous CNTFs fabricated from CVD processing were characterized and analyzed by transmission electronic microscopy (TEM) and x-ray diffraction (XRD). TEM observations show that the continuous CNTFs are composed of CDWNT-bundle units. CDWNT-bundle units of 10-20 nm in thickness contain near numbers of collapsed tubes. The degree of collapse of the CDWNTs varies with their location in the bundle and their own diameter. CDWNT-bundle units pack side by side or face to face, assembling into super-bundles with diameters of 200-300 nm. XRD patterns show that three novel and strong peaks appear at 10°-15°, 21.3° and 23.7°, respectively, corresponding to CDWNT two side pores (10°-15°) and CDWNT layers (21.3° and 23.7°), which indicates the collapsed tube structures in CNTFs are common characterizations. Finally, a collapse mechanism is discussed from the observation and analysis.

Controlled placement of carbon nanotubes is important for carbon-based nanodevice assembly. However, it is difficult to manipulate individual nanotubes because of their extremely small dimensions. Ultra-fine tubes are often in the form of bundles and are hard to efficiently move on a surface due to the strong adhesion among themselves and between the tubes and the substrate. This paper presents a novel manipulation approach of individual double-walled carbon nanotubes encased in a thick amorphous carbon shell. With an atomic force microscope, we are able to freely displace the nanotubes within a casing shell, and unpack it from the shell on a silicon surface. The theoretical analysis demonstrates that the unpacking process is determined by the difference of the static friction between the shell and the substrate and the resistance force between the shell and the embedded nanotube.

A continuous cotton-like carbon nanotube fiber yarn, consisting of multiple threads of high purity double walled carbon nanotubes, was fabricated in a horizontal CVD gas flow reactor with water vapor densification by the direct chemical vapor deposition spinning process. The water vapor interaction leads to homogeneous shrinking of the CNT sock-like assembly in the gas flow. This allows well controlled continuous winding of the dense thread inside the reactor. The CNT yarn is quite thick (1-3 mm), has a highly porous structure (99%) while being mechanically strong and electrically conductive. The water vapor interaction leads to homogeneous oxidation of the CNTs, offering the yarn oxygen-functionalized surfaces. The unique structure and surface of the CNT yarn provide it multiple processing advantages and properties. It can be mechanically engineered into a dense yarn, infiltrated with polymers to form a composite and mixed with other yarns to form a blend, as demonstrated in this research. Therefore, this CNT yarn can be used as a "basic yarn" for various CNT based structural and functional applications.

Masses of highly uniform silica-shelled carbon nanotube (CNT) coaxial fibers are synthesized in a single step by the catalytic gas-flow reaction method. This method involves the generation of CNTs in the gas flow from the injection catalytic gas flow reactions and the in situ deposition of silica over the gas dispersed CNTs via the decomposition of a polysiloxane downstream of the CNT flow. Silicone grease consisting of polydimethylsiloxane (PDMS) was used as the precursor for silica. The coaxial fibers produced by this process are highly uniform, with each fiber containing a CNT core enclosed in a uniform silica shell. The growth of silica from PDMS over CNTs is efficient, with ∼50 wt% of PDMS converted into silica. The key controlling factor of the growth of the coaxial fibers is the hydrogen flow, which is required for both the growth of CNTs and the formation of silica from the polysiloxanes. The highly localized deposition of silica over the CNTs with the composition of Si/O in silica close to that of PDMS is likely associated to the condensation from Si–O chains decomposed from PDMS. The silica phase of the coaxial fiber resulting from this process is highly oxygen deficient and, as the result, the coaxial fibers emit strong photoluminescence under ultraviolet excitation. Meanwhile, the silica shell phase is highly hydrogenated, which permits the uniform bonding of nanocrystallines on the fibers. The present process provides an effective means to fabricate high quality silica-CNT coaxial fibers for potential functional applications.

A nanocomposite anode material for lithium batteries is designed and fabricated by the insertion of graphite nanosheets (GNS) into the ceramic network of silicon oxycarbide (SiOC) ceramics for the development of structurally and electrochemically stable lithium batteries. The GNS forms a layered phase in the SiOC ceramic network from the self-assembly of graphite oxides (GO) introduced in a polysiloxane precursor through thermal transformations after pyrolysis. The composite anode (GNS/SiOC) exhibits an initial discharge capacity attaining 1141 mAh g−1. The discharging capacity decreases in the first eight cycles and stays at 364 mAh g−1 in the following cycles. This reversible discharging capacity is higher than that of a graphite reference (328 mAh g−1) and a SiOC monolithic. Correlating the discharge capacities to the material compositions and structures suggest that the interface between SiOC and GNS contributes to the enhanced capacity of the composite anode, in addition to those from GNS and SiOC. Further increasing the electrochemical performance is possible by the increase of the amount of GNS in the composite.