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Designing a material from the chain architecture to achieve a tailored crystalline morphology in a molding condition is a grand challenge. Here, the crystalline morphology of high-density polyethylene is tuned by tailoring its molecular weight distribution for coupling with the secondary flow field under gas-assisted injection molding (GAIM). The selected N-PE and the tailored B-PE have similar weight-average molecular weights (Mw), but the latter possesses a broader molecular weight distribution (MWD). Although a weaker flow field is triggered due to the slightly slower melt advance rate in the cavity, B-PE is capable of better coupling with secondary flow field in comparison with N-PE, which causes much more oriented crystals in molded parts, such as shish kebab, and shows higher orientation behaviors in the corresponding zones. These significant results provide an important step to explore the coupling of chain architectures and secondary flow field for designing desired crystalline morphology.

A mass of stretched molecular chains in the entire thickness direction of gas-assisted injection molding (GAIM) composites is induced due to the redistribution and amplifi cation of the shear fl ow caused by the introduction of polycarbonate (PC) microfi bril under intense shear stress. In the vicinity of the PC microfi brils, stretched chains are either absorbed by PC microfi brils with a large diameter to form a transcrystallinity, or captured by ultrafi ne PC microfi brils to fi rstly form shish nuclei and fi nally form hybrid shishkebab structures. Typical shish-kebab superstructures are formed in the zone with the absence of PC microfi brils. In summary, multiform crystalline superstructures across the thickness direction are successfully obtained by the GAIM. Thus, this work can open a new way for the preparation of high-performance polymer composites in industrial processing.

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.

Polypropylene (PP) was blended with ethylene–propylene–diene terpolymer (EPDM) and calcium carbonate nanoparticles (nano-CaCO3), where all the components were in different initial mixing states, i.e., all in solid (solid blending composite), nano-CaCO3 and EPDM first forming solid master batch, then being mixed with solid PP (master batch blend composite) and all in melt (melt blending composite). The phase morphology, especially the distribution of nano-CaCO3, and mechanical properties of the resultant composites and their dependence on the initial mixing states of the components were studied systematically. Morphological observation revealed that essentially different from the respectively dispersed morphology of nano-CaCO3 particles and EPDM phase in the PP matrix in the solid blending composite, abundant well-dispersed nano-CaCO3 particles concentrating around EPDM phase in the melt blending composite. Due to the cavitation initiated by the debonding and the fibrillation present at interface as a result of well-dispersed nano-CaCO3 particles, its impact strength was pronouncedly enhanced, increasing 280 % compared to PP/EPDM composite. Our work paves the way to obtain high-performance PP composites.

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.

The effect of vinyl acetate (VA) content on the Properties of Intumescent flame retardant ethylene-vinyl acetate copolymer (IFR EVA) material was studied. Ammonium polyphosphate and pentaerythritol (APP/PER) was used to prepare the IFR EVA materials. The burning behavior, thermal stabilization, and mechanical properties of the IFR EVAs composites were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 test, and tensile measurements. The content of VA had a large influence on the flame retardancy. The curves of V 1max (the first maximal weight loss rate) and LOI values with respect to the VA values had the same trends. The larger the V 1max value was, the more significant the thermal degradation of the acetate functions. The IFR EVA composites (with 10 wt% VA content) had the highest LOI value with the lowest residual weight. This indicated that the decomposition rate, char-forming rate of the IFR materials had an influence on the flame retardancy of these materials. A goo...

Polypropylene (PP) sheets obtained through a two-step process (masterbatch method) were crosslinked by electron beam irradiation. The crosslinked PP sheets were foamed in an oven under different processing conditions. The effects of foaming temperature and time on the mechanical properties and cell structure of PP foams were studied. With the foaming temperature increasing and foaming time lengthening, both the compression modulus and compression strength dropped. Scanning electron microscope (SEM) was employed to study the morphology and cell structure of different samples and the related morphology parameters were acquired. The results showed there was an optimum temperature and time that produced the maximum expansion ratio or the minimum foam density. As foaming temperature or time increased, the cell size increased and the cell density decreased regularly. Excessively high foaming temperature and overly long foaming time caused the coalescence and even the collapse of the cells.

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.

The focus of this work is to investigate the effect of different manufacturing methods on nanoparticles dispersion and rheological properties of polycarbonate (PC) filled nano-calcium carbonate (CaCO3) nanocomposites. Two methods were used to prepare the PC/CaCO3 nanocomposites through twin-screw extruder: one was compounding PC with CaCO3 nano-powder, named PC-CP; another was compounding PC with CaCO3 aqueous suspension, named PC-CAS. The relationship between the processing method and the particle dispersion, matrix molecular weight and rheological properties of the nanocomposite was discussed. Morphological observation showed that nanoparticles were dispersed more homogeneously in PC-CAS. Gel permeation chromatography (GPC) test showed that molecular weight drop of PC-CAS was smaller than PC-CP when CaCO3 content under 2.2 wt%. Melt flow rate (MFR) and capillary rheological behavior indicated the change of rheological property of PC-CP was larger than PC-CAS while CaCO3 content under 2.6 wt%. In general...

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.

Transient heat transfer problems with phase-changes, also known as the “Stefan problems” or “moving-boundary problems,” are practically significant in many engineering and technological fields. Injection molding, one of the most widely used plastics processing techniques, mainly consists of filling, packing, and cooling, and the cooling stage is crucial since it considerably affects the productivity and quality of the molded parts. Thus, solutions for transient phase-change heat conduction problems during injection molding will be instructive. In this article, the enthalpy transforming scheme proposed by Cao and Faghri, which could handle the Stefan problems for generalized multidimensional phase-change structures, is applied coupled with the control-volume/finite-difference techniques. Considering the polydispersity and hierarchical structures, the polymer extended phase change temperature range or mushy zone was included in the two-dimensional enthalpy formulation to forecast the transient phase-change heat conduction during the cooling stage for injection-molded high density polyethylene (HDPE) parts. Experiments were performed and good agreement has been achieved, which reveals that the enthalpy transforming model gives good prediction, especially for the cooling analysis for the injection molding of thick-walled parts of crystalline polymers. The understanding of the phase-change heat conduction characteristics may facilitate the optimal designs of polymer injection molding process for industrial applications. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

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.

An novel compounding process using nano-CaCO3 aqueous suspension for preparing polymer/nano-CaCO3 composites with nanoparticles dispersed at the nanoscale is reported. The process is called the mild mixing method. In this method, the pre-dispersed nano-particle suspensions are blended with melting polymers in a weak shearing field using an extruder, followed by removing the water from the vent. The four typical polymeric nanocomposites were prepared by mild mixing method. The dispersion of nano-CaCO3 in the matrix of the polymer at the nanoscale was confirmed by scanning electron microscopy (SEM). The molecular weights of polycarbonate (PC) and its nanocomposite showed that the degradation had not occurred during the mild mixing processing. The mechanical properties of the composite with 1.5 wt-% nano-CaCO3 improve slightly. It proved that this approach is suitable for the preparation of nano-composites based on both polar and non-polar polymers.

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.

Melamine–formaldehyde (MF) resin microcapsules containing decabromodiphenyl ether (DBDPO) with better thermal stability were successfully prepared by in situ polymerization, DBDPO being the core material and MF resins being the wall materials. Chemical structure of the prepared microcapsules was characterized by Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Morphologies and thermal properties were also investigated by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA), respectively. The results indicated that MF microcapsules with DBDPO particles prepared in this study showed better thermal stability, and could be used as effective flame retardant even for the resins which should be processed at temperatures higher than 350 °C.

The effects of the draw temperature and the strain rate on the tensile deformation of polyamide 6 (PA6) were investigated using three PA6 samples with different initial shapes and physical dimensions. It is observed that the special double yielding phenomenon is indeed present in PA6, provided that certain temperature and strain rate are given, as well as the appropriate initial structure. The results also show that the dependence of the first yield stress on temperature is nearly linear while on strain-rate is logarithmic. The temperature and strain-rate sensitivity change at the draw temperature in the vicinity of the glass transition temperature of PA6. The double yielding of PA6 is not only the combination of two thermally activated rate processes depending on temperature and strain rate, but also associated with the initial structure of samples. The yielding manner for PA6 seems to be determined by the synergetic effect of both the deformation of amorphous and crystalline phases. Thus some special structure involving the crystalline and amorphous phases should come into being in PA6 exhibiting double yielding. Especially the important role of inter- and intra-link should be taken into account. The theory of partial melting–recrystallization cannot account fully for the double yielding of PA6.

Poly (vinyl chloride) (PVC)/ethylene-vinyl acetate copolymer (EVA) blends were prepared to investigate the effect of EVA content on the phase morphology and fracture behaviour, evaluated by means of the essential work of fracture method (EWF). The results clearly showed the prominent influence of phase transformation on fracture toughness of the blends. At low EVA content (

The rheological properties of PC/EVA blends had been investigated by a Haake torque rheometer. The effects of blending temperature, a polycarbonate and a catalyst on the rheological properties of PC/EVA blends were discussed. The transesterification between PC and EVA, catalyzed by dibutyl tin oxide (DBTO), were investigated by differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). The results indicate that the chain break of PC or EVA can be accelerated by DBTO, which induces the equilibrium torque of PC or EVA to decrease as the DBTO content increases. But for the PC/EVA blend, as the blending temperature of increases, the increase of viscosity induced by the generation of the PC-EVA copolymer exceeds the decrease of viscosity induced by the chain break of PC and EVA. Therefore, the equilibrium torque of the PC/EVA blend with varying DBTO content is higher than that of uncatalyzed PC/EVA blend at the higher temperature, 250°C, compared with the lower temperature, 210°C. The con...

A complex double yielding behavior is observed in the engineering stress–strain curves of injection molded specimens of polyamide 6 (PA6) under tensile loading, and a simple method is put forward to judge the apparentness of the double yielding process. By thermal treatment, the effect of the crystallinity level on the double yielding behavior is studied in some detail. The results show that the second yield stress becomes larger than the first after the thermal treatment, which is contrary to the case without thermal treatment. With the annealing time decreasing and the annealing temperature increasing, the percentage crystallinity becomes higher, and the second yield point is much more apparent with a decrease of crystallinity of the specimens. A possible crystallinity window may exist in double yielding behavior of PA6 material. These results indirectly show that the second yield point is not only associated with the deformation of the crystalline region.

The tensile and impact properties of glass bead (GB)-filled linear low-density polyethylene (LLDPE) were studied in this article. The tensile stress–strain behaviors of GB-filled LLDPE composites do not show any obvious difference from that of pure LLDPE, but the overall mechanical properties of GB-filled LLDPE composites are improved quite a lot, which demonstrates that in a relatively small bead size range, the inorganic spherical particle can effectively increase the mechanical properties of LLDPE. The elastic modulus and the elongation to break are almost constant for various filler contents, while the yield strength greatly increases when the filler content is very low, and then remains at about that level up to a 20% filler concentration. After a sharp increase when the filler concentration is 5% by weight, the impact strength gradually increases with increasing filler content, and obtains a 40% improvement above the resin, showing significant toughening effect. Combining the effects of bead size and filler concentration studied on the mechanical properties of GB-filled LLDPE composites, it is found that for glass beads with relatively small particle size, the bead size plays a significant role, which seems to be inconsistent with some results from the literature. From investigation of the morphology of the filled specimen, it is found that though the glass beads are not surface treated, the glass beads used present quite good interfacial adhesion with the matrix LLDPE, and the distribution of the bead in the matrix is the main influencing factor on the mechanical properties of the LLDPE composites.

Through the lower‐melting temperature component processing (LTCP) of the blends (where the processing temperature of the lower‐melting temperature component in a blend is used), high interfacial contact (pseudo‐adhesion) in poly(ethylene terephthalate) (PET)/polyethylene (PE) and polycarbonate (PC)/PE blends is obtained from the difference in the contraction of the dispersed particles and the matrix during cooling from the processing temperature to room temperature. As a result of the pseudo‐adhesion, the tensile strength and modulus of the PET/PE and PC/PE blends with high interfacial contact are superior to those of their corresponding classical blends and, additionally, the PC reinforcement on the matrix is more noticeable than the PET. Morphological observation indicates that during uniaxial deformation at a tensile rate of 50 mm/min, numerous PC microfibers are in situ formed in the PC/PE blend, whereas in the PET/PE blend, ellipsoidal particles appear, resulting from slippage taking place b...

A novel in situ microfiber reinforced blend (MRB) based on poly(ethylene terephthalate) (PET) and polyethylene (PE) was prepared by extrusion-hot stretching-quenching process, and was compatibilized with ethylene vinyl acetate copolymer (EVA) in the presence of the transesterification reaction catalyst, dibutyltin oxide (DBTO). The effects of compatibilization on the essential work of fracture parameters in PET/PE MRB were examined. It is found that the specific essential work of fracture (we) and the specific non-essential work of fracture (wp) were significantly increased, when adding 1 and 2.5 phr of EVA to PET/PE MRB and it was further increased with the addition of 0.5 phr of DBTO as the catalyst of the transesterification reaction. The fracture surfaces study by scanning electron microscope (SEM) further proved that EVA is a successful compatibilizer for PET/PP blend. The morphology study of the blends shows that the well-defined fibers with the diameter of several microns were generated in situ during melt extrusion-hot stretch-quenching processing.

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

An in-situ microfiber-reinforced composite (MRC) based on polyethylene (terephthalate) (PET) and polyethylene (PE) was prepared by slit die extrusion followed by hot stretching. Test specimens were prepared by injection molding at the processing temperature of the PE matrix. At this temperature, far below the melting temperature of PET, the PET phase is solid and able to keep its shape during processing. The morphological characteristics of the dispersed PET phase in the blend, at a fixed weight composition (15:85) of PET and HDPE, were dependent upon the hot stretching ratio. When the hot stretching ratio was increased from 1 (no stretching) to 47.62, the PET particles changed from spheres and ellipsoids to rodlike particles and finally to microfibers. The maximum and average diameters of the PET particles decreased steadily, while the minimum fiber diameter remained constant. The tensile modulus and strength of PET/PE blends were significantly enhanced with increasing hot stretching ratio, indicating that the microfibers have good reinforcement. Ultimate elongation decreased with increasing hot stretching ratio and there was a critical hot stretching ratio above which a ductile-brittle transition occurred.

Infrared spectra of polyamide-6 (PA6) with and without epoxidized natural rubber (ENR) are presented. The influence of ENR used as a compatibilizer on the morphologies, crystallizability, mechanical properties, and thermal behavior of the polyamide-6/polyolefins (PO) blends are studied. The infrared spectra suggest that under normal processing conditions, the carboxyl end groups of PA6 could chemically react in situ with the epoxy groups of ENR, and ester groups are created. This means that the PA6-ENR grafting copolymer could be obtained during processing. All the morphological characterizations and thermal analyses show that the compatibility of PA6/PO blends is obviously improved by ENR because the copolymer increases the interaction between PA6 and PO. It is also found that the toughness of PA6/PO blends increase significantly after using ENR, while the tensile strength and the softening temperature of PA6/PO blends have almost no change. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 398–403, 2003

This article dealt with the tensile properties of in-situ microfiber-reinforced composite (MRC) based on poly(ethylene terephthalate) (PET) and polyethylene (PE). The MRC was prepared through slit die extrusion and hot-stretching, followed by injection molding at the processing temperature of PE matrix, far below the melting temperature of PET in order to maintain the formed microfibers. As expected, the tensile modulus and strength of PET/PE MRC can be significantly elevated at some composition. On the other hand, the reinforcement is heavily dominated by PET concentration; neither low nor high PET content was desirable for reinforcement. Results from elongation tests showed that the ultimate elongation between the samples with mincrofiers and spherical particles at some PET concentrations was extremely different, which was illustrated by the model proposed in which great slippage between the particles and the matrix occurred for the system with spherical particles, whereas there was no slippage between the microfibers and the matrix for MRC.

This article introduced the morphologies of in situ microfiber reinforced composite (MRC) based on poly(ethylene terephthalate) (PET) and polyethylene (PE). The PET/PE MRC was prepared through slit-die extrusion and hot-stretching, followed injection molding at the processing temperature of PE matrix, far below the melting temperature of PET in order to maintain the microfibers. Morphological observation indicated that the PET microfibers could be achieved by the way used in this study, and the microfiber characteristics, such as diameter, diameter distribution, were mainly dominated by PET content at a fixed hot-stretching ratio (HSR) of 19.17. Increasing the PET content the fiber diameter became bigger and the diameter distribution wider, but the minimum fiber diameter always remained constant.

O,O′-diallyl bisphenol A (DBA) and N,N′-diallyl p-phenyl diamine (DPD) were used for the reactive diluents of 4,4′-bismaleimidodiphenol methane (BDM). The objective was to obtain a modified BDM resin system suitable for resin transfer molding (RTM) process to prepare the advanced composites. The processing behavior was determined by time–temperature–viscosity curves, gel characteristics, and differential scanning calorimetry (DSC). The injection temperature of the resin system in RTM could be 80°C, at which its apparent viscosity was only 0.31 Pa/s, and the apparent viscosity was still less than 1.00 Pa/s after the resin was held at 80°C for 16 h. The gel time test result indicated that at low temperatures, the reactivity of the resin system is low, whereas at high temperatures, the resin could cure very fast, which was beneficial to RTM. The postcure of the cured resin at a given temperature was necessary because the resin had a wide and flat cure exothermic peak, observed by DSC curve. The cured resin displayed both high heat and hot/wet resistance and high mechanical properties, especially tensile strength, tensile modulus, and flexural strength at room temperature, which reached 96.2 MPa, 4.8 GPa, and 121.4 MPa, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2245–2250, 2001

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.

Porous cobalt oxide (Co3O4) has been a promising anode material for lithium ion batteries because of its excellent redox activity, high specific capacity, and relatively low cost. In this study, porous nanowired Co3O4 was successfully synthesized on the 3D porous nickel foam substrate using a facile hydrothermal approach. The porous nanowired structure of Co3O4 was demonstrated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the anode phase structure was confirmed by X-ray diffraction (XRD). During charge/discharge processes, cyclic voltammetry (CV) was performed to investigate electrochemical reaction of Co3O4 with lithium. As expected, the proposed porous nanowired anode obtained good cyclic performance and rate capability under galvanostatic charge/discharge test. Our results demonstrated that this anode design could effectively improve Co3O4 anode performance resulting from the special porous nanostructure and the high contact area of the anode with electrolyte.

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In this study, lead-free piezoelectric ceramics ( Na0.52K0.44Li0.04 )( Nb0.88Sb0.08Ta0.04 ) O3 -doped 0.52 Ba ( Zr 0.2 Ti 0.8) O 3-0.48( Ba 0.7 Ca 0.3) TiO 3( BCZT -x KNNLST ) are investigated. The effects of the KNNLST addition on the microstructures and the electrical properties of the ceramics sintered at the temperature as low as 1350°C are studied. The X-ray diffraction data show that the addition of KNNLST could diffuse into BCZT lattice and a pure perovskite phase is formed. With the increase of KNNLST addition, the average grain size is first increased and afterwards decreased. The ceramics with x = 0.005 exhibit a good piezoelectric behavior of d 33 ~ 464 pC/N and k p ~ 0.44 after three month's aging, which indicates the BCZT -x KNNLST ceramics could be promising for lead-free practical applications.

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.