Preparation,processing and analysis of physical properties of calcium ferrite-CNTs/PET nano-composite

The present work is focused on the preparation of composites based on Poly(ethylene terephthalate) (PET) and novel nano-hybrid filler composed of Calcium Ferrite (CF)-Carbon Nanotubes (CNTs), obtained by direct growth of CNTs on CF based iron catalysts. The carbon content in the hybrid filler was 76 wt%. Composites loaded with 1.0, 1.5, 2.0, 3.0 wt% of filler were obtained by melt compounding and processed by thin-wall injection molding. Unfilled Poly(ethylene terephthalate) was processed using the same techniques. Structural characterization and physical properties (thermal, mechanical and electrical) were analyzed and correlated to the hybrid filler loading, and to the percentage of carbon nanotubes.     

A comparative study of EMI shielding properties of carbon nanofiber and multi-walled carbon nanotube filled polymer composites

Electromagnetic interference shielding properties of carbon nanofiber- and multi-walled carbon nanotube-filled polystyrene composites were investigated in the frequency range of 8.2-12.4 GHz (X-band). It was observed that the shielding effectiveness of composites was frequency independent, and increased with the increase of carbon nanofiber or nanotube loading. At the same filler loading, multi-walled carbon nanotube-filled polystyrene composites exhibited higher shielding effectiveness compared to those filled with carbon nanofibers. In particular, carbon nanotubes were more effective than nanofibers in providing high EMI shielding at low filler loadings. The experimental data showed that the shielding effectiveness of the composite containing 7 wt% carbon nanotubes could reach more than 26 dB, implying that such a composite can be used as a potential electromagnetic interference shielding material. The dominant shielding mechanism of carbon nanotube-filled polystyrene composites was also discussed.     

Morphological and mechanical properties of bile salt modified multi-walled carbon nanotube/poly(vinyl alcohol) nanocomposites

Non-covalently functionalized carbon nanotubes are more attractive for multifunction composites because they preserve nearly all the nanotubes’ intrinsic properties and enhance the electroconductivity of polymer composites. However, It is seldom reported that they make dramatic improvement in mechanical properties. In this paper we have successfully prepared a poly(vinyl alcohol) (PVA) nanocomposite with a non-covalently functionalized carbon nanotube (DOC-MWNTs) using a simple method, which achieve a significant enhancement in mechanical properties. The tensile modulus and tensile yield strength of the PVA composite film containing 5 wt% DOC-MWNTs increased by 140% and 65%, respectively, comparing to the pure PVA film. FT-IR, TEM, SEM, and DSC were used to investigate the MWNTs and PVA/MWNTs nanocomposites. The results show that the separately dispersed DOC-MWNTs filler throughout the PVA matrix and the strong adhesion between the DOC-MWNTs filler and the PVA matrix are responsible for the significant reinforcement of the mechanical properties of the composite prepared.     

Facile preparation of graphene nanoribbon filled silicone rubber nanocomposite with improved thermal and mechanical properties

In the present study, graphene nanoribbon was prepared through unzipping the multi walled carbon nanotubes, and its reinforcing effect as a filler to the silicone rubber was further investigated. The results showed that carbon nanotubes could be unzipped to graphene nanoribbon using strong oxidants like potassium permanganate and sulfuric acid. The prepared graphene nanoribbon could homogeneously disperse within silicone rubber matrix using a simple solution mixing approach. It was also found from the thermogravimetric analysis curves that the thermal stability of the graphene nanoribbon filled silicone rubber nanocomposites improved compared to the pristine silicone rubber. Besides, with the incorporation of the nanofiller, the mechanical properties of the resulting nanocomposites were significantly enhanced, in which both the tensile stress and Young’s modulus increased by 67% and 93% respectively when the mass content of the graphene nanoribbon was 2.0 wt%. Thus it could be expected that graphene nanoribbon had large potentials to be applied as the reinforcing filler to fabricate polymers with increased the thermal and mechanical properties.     

Postgrowth processing of carbon nanotube arrays-enabling new functionalities and applications

Highly ordered carbon nanotube arrays were fabricated by pyrolysis of acetylene using anodic-aluminum-oxide templates. To avoid the natural tendency of the nanotubes sticking together and forming haystack-like bundles when exposing the nanotubes from the growth template, a new postgrowth treatment process using a mixture of 6 wt% phosphoric acid and 1.8 wt% chronium oxide as the etchant, and 0.1 wt% Gum Arabic or 5 wt% polymethacrylic acid as the dispersant, was developed yielding for the first time well aligned and spatially free-standing carbon nanotube arrays. The dispersants can be adsorbed on both the surface of carbon nanotubes and that of the alumina film resulting in the elimination of aggregation of exposed carbon nanotubes, a more uniform dissolution of alumina, and a lower, thereby, more controllable etching rate. The as-prepared carbon nanotube arrays, which are vertically aligned and well separated could be used for many applications such as mechanical oscillators, field emission, and sensors, and the exposed nanotubes offer a good platform for study on collective behavior of electrical and magnetic nano arrays.     

Alignment of carbon nanotubes and reinforcing effects in nylon-6 polymer composite fibers

Alignment of pristine carbon nanotubes (P-CNTs) and fluorinated carbon nanotubes (F-CNTs) in nylon-6 polymer composite fibers (PCFs) has been achieved using a single-screw extrusion method. CNTs have been used as filler reinforcements to enhance the mechanical and thermal properties of nylon-6 composite fibers. The composites were fabricated by dry mixing nylon-6 polymer powder with the CNTs as the first step, then followed by the melt extrusion process of fiber materials in a single-screw extruder. The extruded fibers were stretched to their maxima and stabilized using a godet set-up. Finally, fibers were wound on a Wayne filament winder machine and tested for their tensile and thermal properties. The tests have shown a remarkable change in mechanical and thermal properties of nylon-6 polymer fibers with the addition of 0.5?wt% F-CNTs and 1.0?wt% of P-CNTs. To draw a comparison between the improvements achieved, the same process has been repeated with neat nylon-6 polymer. As a result, tensile strength has been increased by 230% for PCFs made with 0.5% F-CNTs and 1% P-CNTs as additives. These fibers have been further characterized by DSC, Raman spectroscopy and SEM which confirm the alignment of CNTs and interfacial bonding to nylon-6 polymer matrix.     

Multi-Wall Carbon Nanotubes/Styrene Butadiene Rubber (SBR) Nanocomposite

A floating catalyst chemical vapor deposition (FC-CVD) method was designed and fabricated to produce high-quality and -quantity carbon nanotubes. The design parameters like the hydrogen flow rate; reaction time and reaction temperature were optimized to produce high yield and purity of Multi-Wall Carbon Nanotubes (MWCNTs). Multi-Walled Carbon Nanotubes (MWNTs) were used to prepare natural rubber (NR) nanocomposites. Our first efforts to achieve nanostructures in MWNTs/styrene butadiene rubber (SBR) nanocomposites were formed by incorporating carbon nanotubes in a polymer solution and subsequently evaporating the solvent. Using this technique, nanotubes can be dispersed homogeneously in the NR matrix in an attempt to increase the mechanical properties of these nanocomposites. The properties of the nanocomposites such as tensile strength, tensile modulus, elongation at break and hardness were studied. Using different percentages of carbon nanotubes from 1 wt% to 10 wt%, several nanocomposites samples were fabricated. Significant improvements in the mechanical properties of the resulting nanocomposites showed almost 10% increase in the Young's modulus for 1 wt% of CNTs and up to around 200% increase for 10 wt% of CNTs.     

The effect of the aspect ratio of carbon nanotubes on their effective reinforcement modulus in an epoxy matrix

The potentiality of carbon nanotubes as reinforcement material is not only due to their exceptional high modulus, but also to their high aspect ratio. Indeed, the nanotubes contribution to the mechanical reinforcement in a polymer is strongly dependent on their distribution within the hosting matrix. In fact, the clustering of carbon nanotubes does limit the theoretical enhancement of the composite mechanical properties by a reduction of their effective aspect ratio.In this work, the reinforcement efficiency of carbon nanotubes having different aspect ratios has been experimentally investigated at low filler contents in an epoxy system. From a theoretical point of view, the classical theory (Cox, 1952 [25]) concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube Random Contact Model (Philipse, 1996 [33]) which explicitly accounts for the progressive reduction of the tubes effective aspect ratio as the filler content increases. The validity of the proposed model was assessed by a comparison with available literature data, providing a good agreement.     

Synergistic effects in network formation and electrical properties of hybrid epoxy nanocomposites containing multi-wall carbon nanotubes and carbon black

Epoxy nanocomposites including multi-wall carbon nanotubes (MWCNT) and carbon black (CB) were produced and investigated by means of electrical conductivity measurements and microscopical analysis. Varying the weight fraction of the nanoparticles, electrical percolation behaviour was studied. Due to synergistic effects in network formation and in charge transport the inclusion of both MWCNT and CB in the epoxy matrix leads to an identical electrical behaviour of this ternary nanocomposite system compared to the binary MWCNT-epoxy system. For both types of nanocomposites an electrical percolation threshold of around 0.025 wt% and 0.03 wt% was observed. Conversely, the binary CB nanocomposites exhibit a three-times higher percolation threshold of about 0.085 wt%. The difference between the binary MWCNT-epoxy and the ternary CB/MWCNT-epoxy in electrical conductivity at high filler concentrations (e.g. 0.5 wt%) turns out to be less than expected. Thus, a considerable amount of MWCNTs can be replaced by CB without changing the electrical properties.     

The effect of boron nitride on electrical conductivity of nanocarbon-polymer composites

The electrical conductivity concentration and temperature dependences of polymer composite materials (CMs) with nanocarbon fillers [graphite nanoplatelets and multi-walled carbon nanotubes (MWCNTs)] were investigated. Epoxy resin modified with organosilicon compound was used as polymer matrix. The content of nanocarbon filler in varied from 1 to 10 wt%. To study of the synergetic properties the additional dispersed dielectric filler—boron nitride (BN) was added to given systems in content of 27 wt%. The electrical resistivity of CMs was investigated in the temperature range of 77–300 K. In the studied CMs the percolation transition at sufficient low filler content (0.01–0.022 vol. fr.) was observed. The values of critical index varied from 3.0 to 5.2. The electrical conductivity of investigated CMs was analyzed in the framework of proposed model that takes into consideration the morphology of filler particles. It was shown that the increase of electrical conductivity of GNP-polymer CM in the presence of BN is attributed to the decrease of contact resistance between filler particles, while for MWCNT-polymer CM is due to the increase of the number of conductive chains in this particular system.     

Process optimization and microstructural analysis of aluminum based composite reinforced by multi‐walled carbon nanotubes with various aspect ratios

The dispersion of carbon nanostructures in metallic matrix with strong bonding is a very important challenge to achieve a composite with high mechanical properties. In this work, the effect of aspect ratio of reinforcement phase, weight percent and using improved mechanical alloying process and sonication on the well dispersion of multiwalled carbon nanostructures (MWCNTs) were investigated. Moreover, the hot pressing conditions were optimized by factorial design technique to achieve the highest relative density. Field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM) and X‐ray diffraction were used to analyse the microstructure. Also, the particle size of the grain structure of composite containing multi‐walled carbon nanotubes determined for evaluating the influence of aspect ratio on grain growth. The results verified that by using conventional method of alloying, grinding process and agglomeration of 2 wt% multi‐walled carbon nanotubes with long length can be occurred. By decreasing the weight percent of multi‐walled carbon nanotubes to 1 wt%, dispersion process progressed slightly. Short length multi‐walled carbon nanotubes showed more clustering and minor damage in both 1 and 2 wt%. By using modified design of alloying (using magnet), both types of multi‐walled carbon nanotubes dispersed better than conventional design in the matrix with good bonding at initial times.     

Synthesis and properties of poly(hexamethylene terephthalate)/multiwall carbon nanotubes nanocomposites

Poly(hexamethylene terephthalate) (PHT)/carbon nanotubes (CNT) nanocomposites containing 1% and 3% (w/w) of filler were prepared by two procedures: in situ ring-opening polymerization of hexamethylene terephthalate cyclic oligomers in the presence of CNT and melt blending of PHT/CNT mixtures. Arc discharge multiwalled carbon nanotubes, both pristine (MWCNT) and hydroxyl functionalized (MWCNT-OH), were used. The objective was to evaluate the effect of preparation procedure, nanotube side-wall functionalization and amount of nanotube loaded on properties of PHT. All nanocomposites showed an efficient distribution of the carbon nanotubes within the PHT matrix but interfacial adhesion and reinforcement effect was dependent on both functionalization and nanotubes loading. Significant differences in thermal stability and mechanical properties ascribable to functionalization and processing were observed among the prepared nanocomposites. All the prepared nanocomposites showed enhanced crystallizability due to CNT nucleating effects although changes in melting and glass transition temperatures were not significant.     

Production and characterization of polymer nanocomposites with highly aligned single-walled carbon nanotubes

We report the production and characterization of polymer nanocomposites with single-walled carbon nanotubes having improved mechanical properties and exceptional nanotube alignment. High-pressure carbon monoxide nanotubes (HiPco) were efficiently distributed in polystyrene (PS) and polyethylene (PE) with a twin-screw compounder. Nanotube concentrations were 1, 5, 10, and 20 wt% in PE composites and 0.7 wt% in PS composites. PE composites were melt-spun into fibers to achieve highly aligned nanotubes. Polarized Raman spectroscopy shows that the degree of alignment increases with decreasing fiber diameter and decreases with increasing nanotube loading. The orientation distribution function of a 1 wt% HiPco/PE composite had a full width at half-maximum of approximately 5 degrees. The elastic modulus increases up to 450% relative to PE fibers for 20 wt% nanotube loading at an intermediate fiber diameter of 100 microns.     

Monitoring the mechanical behaviour of electrically conductive polymer nanocomposites under ramp and creep conditions

Various amounts of carbon black (CB) and carbon nanofibres (CNF) were dispersed in an epoxy resin to prepare nanocomposites whose mechanical behaviour, under ramp and creep conditions, was monitored by electrical measurements. The electrical resistivity of the epoxy resin was dramatically reduced by both nanofillers after the percolation threshold (1 wt% for CB and 0.5 wt% for CNF), reaching values in the range of 10(3)-10(4) omega . cm for filler loadings higher than 2 wt%. Due to the synergistic effects between the nanofillers, an epoxy system containing a total nanofiller amount of 2 wt%, with a relative CB/CNF ratio of 90/10 was selected for the specific applications. A direct correlation between the tensile strain and the increase of the electrical resistance was observed over the whole experimental range, and also the final failure of the samples was clearly detected. Creep tests confirmed the possibility to monitor the various deformational stages under constant loads, with a strong dependency from the temperature and the applied stress. The obtained results are encouraging for a possible application of nanomodified epoxy resin as a matrix for the preparation of structural composites with sensing (i.e., damage-monitoring) capabilities.     

Rubber composites based on graphene nanoplatelets,expanded graphite,carbon nanotubes and their combination: A comparative study

Solution styrene butadiene rubber (S-SBR) composites reinforced with graphene nanoplatelets (GnPs), expanded graphite (EG), and multiwalled carbon nanotubes (MWCNTs) were prepared and the electrical and various mechanical properties were compared to understand the specific dispersion and reinforcement behaviours of these nanostructured fillers. The electrical resistivity of the rubber composite gradually decreased with the increase of filler amount in the composite. The electrical percolation behaviour was found to be started at 15 phr (parts per hundred rubber) for GnP and 20 phr for EG filled systems, whereas a sharp drop was found at 5 phr for MWCNT based composites. At a particular filler loading, dynamic mechanical analysis and tensile test showed a significant improvement of the mechanical properties of the composites comprised of MWCNT followed by GnP and then EG. The high aspect ratio of MWCNT enabled to form a network at low filler loading and, consequently, a good reinforcement effect was observed. To investigate the effect of hybrid fillers, MWCNT (up to 5 phr) were added in a selected composition of EG based compounds. The formation of a mixed filler network showed a synergistic effect on the improvement of electrical as well as various mechanical properties.     

Spark Plasma Sintered Hydroxyapatite/Graphite Nanosheet and Hydroxyapatite/Multiwalled Carbon Nanotube Composites: Mechanical and in Vitro Cellular Properties

Hyroxyapatite (HA) and its nanocomposites reinforced with 0.5, 1, 1.5, and 2 wt% graphite nanosheets (GNs) and multi‐walled carbon nanotubes (MWNTs) are fabricated by means of spark plasma sintering (SPS) process. The effects of MWNT and GN additions on the morphology, mechanical behavior, cell adhesion, and biocompatibility of HA were studied. Three‐point‐bending test shows that the bending strength of MWNT/HA nanocomposites increases with increasing MWNT content. However, the bending strength of GN/HA nanocomposites initially increases by adding 0.5 wt% GN, and then decreases markedly as the filler content increases. Cell culture and viability test results demonstrate that the GNs with diameters of several micrometers retard osteoblast cell adhesion and proliferation on the GN/HA nanocomposite. In contrast, the addition of 2 wt% MWNT to HA is beneficial to promote osteoblast adhesion and proliferation, thereby enhancing the biocompatibility of MWNT/HA nanocomposite.     

碳纳米管-ZrB2-SiC陶瓷基复合材料的制备与性能研究

研究了用热压烧结方法制备的不同碳纳米管(CNTs)含量的ZrB₂-SiC- xwt% CNTs (x=0、1.0、2.5、4.0) 复合材料的工艺条件、力学性能和微观结构. 用TEM观察了试样的微观结构, 用SEM观察了试样断口形貌和裂纹扩展情况, 并对其强韧化机制进行了分析. 研究表明, 碳纳米管主要分布沉积在ZrB2颗粒内部, 形成内晶型结构, 在CNTs含量为2.5%时, 相对密度、维氏硬度和弯曲强度分别为99.6%、21.7GPa和542MPa, 断裂韧性达到6.10MPa·m^1/2. 碳纳米管加入后材料致密性提高、晶粒细化,所形成的内晶型结构是材料强度和韧性得以提高的原因.     

Carbon nanotube reinforced aluminum nanocomposite via plasma and high velocity oxy-fuel spray forming

Free standing structures of hypereutectic aluminum-23 wt% silicon nanocomposite with multiwalled carbon nanotubes (MWCNT) reinforcement have been successfully fabricated by two different thermal spraying technique viz Plasma Spray Forming (PSF) and High Velocity Oxy-Fuel (HVOF) Spray Forming. Comparative microstructural and mechanical property evaluation of the two thermally spray formed nanocomposites has been carried out. Presence of nanosized grains in the Al-Si alloy matrix and physically intact and undamaged carbon nanotubes were observed in both the nanocomposites. Excellent interfacial bonding between Al alloy matrix and MWCNT was observed. The elastic modulus and hardness of HVOF sprayed nanocomposite is found to be higher than PSF sprayed composites.     

Single-walled carbon nanotube incorporated novel three phase carbon/epoxy composite with enhanced properties

In the present work, single-walled carbon nanotubes were dispersed within the matrix of carbon fabric reinforced epoxy composites in order to develop novel three phase carbon/epoxy/single-walled carbon nanotube composites. A combination of ultrasonication and high speed mechanical stirring at 2000 rpm was used to uniformly disperse carbon nanotubes in the epoxy resin. The state of carbon nanotube dispersion in the epoxy resin and within the nanocomposites was characterized with the help of optical microscopy and atomic force microscopy. Pure carbon/epoxy and three phase composites were characterized for mechanical properties (tensile and compressive) as well as for thermal and electrical conductivity. Fracture surfaces of composites after tensile test were also studied in order to investigate the effect of dispersed carbon nanotubes on the failure behavior of composites. Dispersion of only 0.1 wt% nanotubes in the matrix led to improvements of 95% in Young's modulus, 31% in tensile strength, 76% in compressive modulus and 41% in compressive strength of carbon/epoxy composites. In addition to that, electrical and thermal conductivity also improved significantly with addition of carbon nanotubes.     

Mechanical and thermal behaviour of biodegradable composites based on polycaprolactone with pine cone particle

Polycaprolactone (PCL) was reinforced with natural fibres as they not only permit a substantial reduction of the material costs, but also play a role as reinforcement in mechanical properties. This work was focused on the estimation of mechanical and thermal behaviour based on PCL and Pine Cone particles (PCP) filler at different weight percentages (0, 5, 10, 15, 30 and 45 wt%). Tests results indicated considerable improvement in mechanical properties, corresponding to a gain in impact strength and % elongation of 6 and 9.2% at 15 wt% particle loading, respectively. Some decrease in thermal stability was observed for composites with increasing filler content where as composite at 15% PCP was not significantly affected. Lower melting and crystallization enthalpies and higher crystallinity values were obtained for bio-composites compared with neat PCL. Some decrease in thermal stability and increase in oxygen and water vapour barrier properties were also observed for composites with increasing filler content.