Facile preparation and characterization of free-standing stiff carbon-based composite films with excellent performance

Novel free-standing stiff all carbon films based on multi-walled carbon nanotube (MWNT)/glassy carbon (GC) with excellent performance were fabricated. MWNTs, as excellent reinforcing materials, were successfully dispersed in polyimide (PI) matrix by in situ polymerization. The resultant MWNT/PI nanocomoposite films were used as precursors and underwent carbonization process. As a result, all carbon constituted MWNT/GC composite films were obtained. Mechanical results showed the maximum 3-point bending strength and modulus reached 575.5 MPa and 7.7 GPa respectively, improved by 54% and 78% compared to those of neat GC films. This method is simple, and the free-standing composite films can be prepared in large scales, which hold great potential in many applications.     

Electrical and mechanical characterization of stretchable multi-walled carbon nanotubes/polydimethylsiloxane elastomeric composite conductors

Stretchable, elastomeric composite conductor made of multi-walled carbon nanotubes (MWNTs) and polydimethylsiloxane (PDMS) has been fabricated by simple mixing. Electrical percolation threshold, amount of filler at which a sharp decrease of resistance occurs, has been determined to be ∼0.6 wt.% of MWNTs. The percolation threshold composition has also been confirmed from swelling experiments of the composite; the equilibrium swelling ratio slightly increases up to ∼0.6 wt.%, then decreases at higher amount of filler MWNTs. Upon cyclic stretching/release of the composite, a fully reversible electrical behavior has been observed for composites having filler content below the percolation threshold value. On the other hand, hysteretic behavior was observed for higher filler amount than the threshold value, due to rearrangement of percolative paths upon the first cycle of stretching/release. Finally, mechanical moduli of the composites have been measured and compared by buckling and microtensile test. The buckling-based measurement has led to systematically higher (∼20%) value of moduli than those from microtensile measurement, due to the internal microstructure of the composite. The elastic conductor may help the implementation of various stretchable electronic devices.     

Electromechanical response of semiconducting carbon–polyimide nanocomposite thin films

Electromechanically responsive polymer nanocomposite thin films can provide embedded microscale sensing elements for unobtrusive monitoring of strain, torque and pressure particularly for composite structures. Thin nanocomposite carbon–polyimide films with thicknesses up to 90 μm were produced with carbon contents that yield semiconducting behaviour attributable to distance dependent electron hopping between isolated nanoparticles. The tensile modulus and the strain at break indicated minimum interaction between polymer and nanoparticle surfaces. A decreasing storage modulus with increasing temperature indicated increasing free volume inducing polymer chain motions.     

Preparation and characterization of transparent Al doped ZnO/epoxy composite as thermal-insulating coating

In this article, transparent Al doped ZnO (AZO)/epoxy composite, as glass thermal insulation coating, was prepared by incorporating AZO nanoparticles into a transparent epoxy matrix. First, the as-synthesized AZO nanoparticles by the polymer pyrolysis method were characterized and the effect of Al doping content on the electrical conductivity of AZO nanoparticles was investigated. The results reveal that the AZO nanoparticles doped with 6 mol% Al obtained from calcination at 600 °C show the optimal electrical conductivity. The effects of AZO content on the optical and thermal insulation property of AZO/epoxy coating were also studied. It is shown that the AZO/epoxy composite coating with 0.5 wt% AZO possesses excellent optical properties, i.e. visible light transmittance above 50% and shading coefficient of 0.45 are simultaneously achieved. In addition, the large temperature difference between the chambers coated respectively with the AZO/epoxy coated glasses and the common glass indicates that the prepared AZO/epoxy coating has an excellent thermal insulation property.     

Structural characterization, thermal and mechanical properties of polyurethane/CoAl layered double hydroxide nanocomposites prepared via in situ polymerization

Dodecyl sulfate (DS), one kind of sulfate anion, was intercalated in the interlayer space between CoAl layered double hydroxide (CoAl-LDH) layers, and then polyurethane (PU) based nanocomposites were prepared by in situ intercalation polymerization with different amounts of the organo-modified CoAl-LDH. An exfoliated dispersion of CoAl-LDH layers in PU matrix was verified by the disappearance of the (0 0 3) reflection of the XRD results when the LDH loading was less than 2.0 wt%. Tensile testing indicated that excellent mechanical properties of PU/LDH nanocomposites were achieved. The weak alkaline catalysis of DS to polyurethane chains, combined with the dehydration and structural degradation of the LDH below 300 °C, accounted for the process of proceeded degradation as shown in TGA results. The real-time FTIR revealed that the as-prepared nanocomposites had a slower thermo-oxidative rate than neat PU from 160 °C to 340 °C, probably due to the barrier effect of LDH layers. These results suggested potential applications of CoAl-LDH as a promising flame retardant in PUs.     

Highly conductive graphene oxide/polyaniline hybrid polymer nanocomposites with simultaneously improved mechanical properties

Graphene oxide (GO) was added to a polymer composites system consisting of surfactant-wrapped/doped polyaniline (PANI) and divinylbenzene (DVB). The nanocomposites were fabricated by a simple blending, ultrasonic dispersion and curing process. The new composites show higher conductivity (0.02–9.8 S/cm) than the other reported polymer system filled with PANI (10⁻⁹–10⁻¹ S/cm). With only 0.45 wt% loading of GO, at least 29% enhancement in electric conductivity and 29.8% increase in bending modulus of the composites were gained. Besides, thermal stability of the composites was also improved. UV–Vis spectroscopy, X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) revealed that addition of GO improves the dispersion of PANI in the polymer composite, which is the key to realize high conductivity.     

Preparation,characterization and properties of polycaprolactone diol-functionalized multi-walled carbon nanotube/thermoplastic polyurethane composite

Multi-walled carbon nanotubes (MWCNTs) were chemically functionalized to prepare thermoplastic polyurethane (PU) composites with enhanced properties. In order to achieve a high compatibility of functionalized MWCNTs with the PU matrix, polycaprolactone diol (PCL), as one of PU’s monomers, was selectively grafted on the surface of MWCNTs (MWCNT–PCL), while carboxylic acid groups functionalized MWCNTs (MWCNT–COOH) and raw MWCNTs served as control. Both MWCNT–COOH and MWCNT–PCL improved the dispersion of MWCNTs in the PU matrix and interfacial bonding between them at 1 wt% loading fraction. The MWCNT–PCL/PU composite showed the greatest extent of improvement, where the tensile strength and modulus were 51.2% and 33.5% higher than those of pure PU respectively, without sacrificing the elongation at break. The considerable improvement in both mechanical properties and thermal stability of MWCNT–PCL/PU composite should result from the homogeneous dispersion of MWCNT–PCL in the PU matrix and strong interfacial bonding between them.     

Interfacial polymerization to high-quality polyacrylamide/polyaniline composite hydrogels

Conducting polymer hydrogels composed of polyacrylamide (PAAm) and polyaniline (PAn) have been successfully synthesized through the interfacial polymerization. Compared to the conventional preparation methods, the interfacial polymerization is much more economical and effective because the PAn formed at the water/organic-solvent interface assembles spontaneously and exclusively into the PAAm hydrogel. In contrast to conventional materials, the resulting PAAm/PAn composite hydrogel exhibits high qualities including homogeneous structure, enhanced mechanical toughness, high electrical conductivity and the ability to reversibly interconvert between the doped and dedoped states. As-described interfacial polymerization for the fabrication of conducting polymer hydrogels does not depend on specific kinds of organic solvents or acid dopants.     

Review of functionalization,structure and properties of graphene/polymer composite fibers

Fibrous materials usually have good mechanical, heat-resistant, acid-resistant, alkali-resistant and moisture regained properties which originate from its composition, condensed structure and crosslinking styles. However, these materials often lack of good electrical conductivity, flame retardance, anti-static and anti-radiation properties which are desired for varied specific applications. Graphene, as a new emerging nanocarbon material, has some unique properties including superb thermal and electrical conductivity, strong mechanical and anti-corrosive property, extremely high surface area etc. Therefore, graphene has attracted extensive interests in recent years. Upon modification with graphene, fibers exhibit a number of enhanced or new properties such as adsorption performance, anti-bacteria, hydrophobicity and conductivity which are beneficial for broader applications. In this review, the strategies to modify the fibers with graphene and the corresponding effects on the fibers as well as the relevant applications in varied areas were discussed.     

Effect of multi-walled carbon nanotubes on mechanical,thermal and electrical properties of phenolic foam via in-situ polymerization

In this study, phenolic foam (PF)/multi-walled carbon nanotubes (MWCNTs) composites were fabricated by in-situ polymerization, and carbonized foams based on these PF foams were prepared and the electrical property was investigated. TEM results indicated excellent dispersion of MWCNTs in the phenolic resin matrix. Scanning electron microscope results indicated that PF composites exhibited smaller cell size, thicker cell wall thickness, and higher cell density, compared with pure PF. The incorporating of MWCNTs significantly improved the mechanical properties of PF. All PF composites showed a lower thermal conductivity versus pure PF. Moreover, the carbonized pure and composites PF exhibited open-cell three-dimensional skeleton carbon structure and the MWCNTs were well-dispersed on the surface of the skeletons. It is noteworthy that the introduction of MWCNTs significantly improved the electrical performances of foams and carbonized foams by construction of conductive MWCNTs network.     

Preparation and characteristics of a vapor-grown carbon fiber/ceramic composite using a methylsilicone precursor

Vapor-grown carbon fiber (VGCF)/silicon oxycarbide ceramic composites have been prepared by pyrolysis of a VGCF/methylsilicone precursor (MSR) composite produced through polymer melt-mixing. The electrical resistivity of the composite before and after pyrolysis was drastically reduced by VGCF (above 5 wt% in MSR), and reached the order of 10⁰ Ω cm. However, the ceramic composite could not always maintain its shape because of shrinkage from the weight loss of MSR during pyrolysis. To overcome this difficulty, polymethyl methacrylate (PMMA) microbeads were added as a sacrificial processing aid during melt-mixing to enable the material to maintain its shape through the microporous structure generated. The microcellular VGCF/ceramics obtained from VGCF/MSR/PMMA were characterized in terms of their shrinkage, mechanical, structural and electrical properties, and their composition was optimized. It was found that microcellular VGCF/ceramics derived from an optimal VGCF/MSR/PMMA composition of 5/45/45 (by weight) gave a low electrical volume resistivity (around 1.0 Ω cm), comparable to that of VGCF/ceramics from 10/90 (by weight) VGCF/MSR.     

Fluorographene/polyimide composite films: Mechanical,electrical, hydrophobic,thermal and low dielectric properties

Nowadays, dielectric materials with excellent mechanical and hydrophobic properties are desired for use in the integrated circuits (ICs). For this reason, low dielectric constant fluorographene/polyimide (FG/PI) composite films were prepared by a facile solution blending method, suggesting that the mechanical, electrical, hydrophobic and thermal properties were significantly enhanced in the presence of FG. With addition of 1 wt% FG, the tensile strength, Young’s modulus and elongation at break were dramatically increased by 139%, 33% and 18% respectively when compared with pure PI film. Furthermore, composite films exhibit superior hydrophobic and thermal stability performance. Especially, the FG/PI film with 0.5 wt% of FG possessing a low dielectric constant of 2.48 and a good electrical insulativity that is lower than 10⁻¹⁴ S m⁻¹. Therefore, by their excellent performance, FG/PI hybrid films represent suitable candidate solutions with applications in the microelectronics and aerospace industries.     

Preparation and characterization of sulfonated poly(1,3,4-oxadiazole)/multi-walled carbon nanotube composite films with high performance in electric heating and thermal stability

For manufacturing thermally stable electric heating composite films, a sulfonated poly(1,3,4-oxadiazole) (sPOD) was synthesized and it was composited with pristine MWCNT of 0.1–10.0 wt% by an ultrasonicated solution mixing and casting. SEM images revealed that the pristine MWCNTs were dispersed well in the composite matrix via π–π interaction between the MWCNTs and the aromatic rings of sPOD backbone. The electrical resistivity of the composite films decreased considerably from ∼10⁹ Ω cm to ∼10⁰ Ω cm with the increment of the MWCNT content by forming a percolation threshold at ∼0.026 wt%. The composite films with 5.0–10.0 wt% MWCNT contents, which had sufficiently low electrical resistivity of ∼10³–10⁰ Ω cm, exhibited excellent electric heating performance by attaining high maximum temperatures as well as electric energy efficiency. Since the dominant thermal decomposition of the composite films took place at ∼500 °C, sPOD/MWCNT composite films with low electrical resistivity could be used for high performance electric heating materials for advanced applications.     

Mechanical characterization of hierarchical carbon fiber/nanofiber composite laminates

Susceptibility to matrix driven failure is one of the major weaknesses of continuous-fiber composites. In this study, helical-ribbon carbon nanofibers (CNF) were dispersed in the matrix phase of a continuous carbon fiber-reinforced composite. Along with an unreinforced control, the resulting hierarchical composites were tested to failure in several modes of quasi-static testing designed to assess matrix-dominated mechanical properties and fracture characteristics. Results indicated CNF addition offered simultaneous increases in tensile stiffness, strength and toughness while also enhancing both compressive and flexural strengths. Short-beam strength testing resulted in no apparent improvement while the fracture energy required for the onset of mode I interlaminar delamination was enhanced by 35%. Extrinsic toughening mechanisms, e.g., intralaminar fiber bridging and trans-ply cracking, significantly affected steady-state crack propagation values. Scanning electron microscopy of delaminated fracture surfaces revealed improved primary fiber–matrix adhesion and indications of CNF-induced matrix toughening.     

The preparation of high performance and conductive poly (vinyl alcohol)/graphene nanocomposite via reducing graphite oxide with sodium hydrosulfite

Sodium hydrosulfite is used to reduce graphite oxide in current study. The preparation of poly (vinyl alcohol) (PVA)/graphene nanocomposites is realized using two simple steps: the synthesis of PVA/graphite oxide (GO) nanocomposites film and immersion of such a film in the reducing agent aqueous solution. This method prohibits the agglomeration of GO during direct reduction in PVA/GO aqueous solution, and opens a new way to scale up the production of graphene nanocomposites using a simple reducing agent. A 40% increase in tensile strength and 70% improvement in elongation at break have been obtained with only the addition of 0.7 wt.% of reduced graphite oxide. Furthermore, a good level of conductivity and a variation in the surface property of the prepared films have been observed for the composites containing graphene.     

Self-assemblies of linearly aligned diamond fillers in polysiloxane/diamond composite films with enhanced thermal conductivity

The relocation of diamond fillers was performed in polysiloxane-based composite films under different electric fields. The microscale diamond filler particles were dispersed by sonication in a prepolymer mixture of polysiloxane, followed by high-speed mixing. The homogeneous suspension was cast onto a polyamide spacer of microscale thickness and subjected to three different electric fields: AC, DC, and switched DC, before the mixture became cross-linked. Analysis revealed that self-assemblies of linearly aligned diamond fillers (LADFs) were fabricated in the composite film, connecting the film planes as bridges with different thicknesses depending on the applied electric field. Composites with assemblies of LADFs exhibited enhanced thermal conductivity and electrical insulation, and are attractive for application as thermal interface materials in the semiconductor industry.     

Synthesis and characterization of novel hyperbranched polyimides/attapulgite nanocomposites

Novel hyperbranched polyimides/attapulgite (HBPI/AT) nanocomposites were successfully synthesized by in situ polymerization. HBPI derived from novel 2,4,6-tri[3-(4-aminophenoxy)phenyl]pyridine (TAPP) and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA). 4,4′-diphenylmethane diisocyanate (MDI) modified AT copolymerized with HBPI and the nanocomposites formed multilinked network. Chemical structure, morphology, thermal behavior, and mechanical properties of nanocomposites were investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), thermal gravimetric analysis (TGA), dynamic mechanical analysis (DMA), and tensile testing et.al. Results indicated that modified AT was homogeneously dispersed in matrix and resulted in an improvement of thermal stability, mechanical properties and water resistance of HBPI/AT nanocomposites.     

Preparation and properties of poly (p-phenylene sulfide)/multiwall carbon nanotube composites obtained by melt compounding

In this paper, electrical and mechanical properties of Poly (p-phenylene sulfide) (PPS)/multi-wall carbon nanotubes (MWNTs) nanocomposites were reported. The composites were obtained just by simply melt mixing PPS with raw MWNTs without any pre-treatment. The dispersion of MWNTs and interfacial interaction were investigated through SEM &TEM and Raman spectra. The rheological test and crystallization behavior were also investigated to study the effects of MWNTs concentration on the structure and chain mobility of the prepared composites. Though raw MWNTs without any pre-treatment were used, a good dispersion and interaction between PPS and MWNTs have been evidenced, resulting in a great improvement of electrical properties and mechanical properties of the composites. Raman spectra showed a remarkable decrease of G band intensity and a shift of D bond, demonstrating a strong filler–matrix interaction, which was considered as due to π–π stacking between PPS and MWNTs. The storage modulus (G′) versus frequency curve presented a plateau above the percolation threshold of about 2–3 wt% with the formation of an interconnected nanotube structure, indicative of ‘pseudo-solid-like’ behavior. Meanwhile, a conductive percolation threshold of 5 wt% was achieved and the conductivity of nanocomposites increased sharply by several orders of magnitude. The difference between electrical and rheological percolation threshold, and the effect of critical percolation on the chain mobility, especially on crystallization behavior of PPS, were discussed. In summary, our work provides a simple and fast way to prepare PPS/MWNTs nanocomposites with good dispersion and improved properties.     

High performance polyimide composite films prepared by homogeneity reinforcement of electrospun nanofibers

Highly aligned polyimide (PI) and PI nanocomposite fibers containing carbon nanotubes (CNTs) were produced by electrospinning. Scanning electron microscopy showed the electrospun nanofibers were uniform and almost free of defects. Transmission electron microscopy indicated that the CNTs were finely dispersed and highly oriented along the CNT/PI nanofiber axis at a relatively low concentration. The as-prepared well-aligned electrospun nanofibers were then directly used as homogeneity reinforcement to enhance the tensile strength and toughness of PI films. The neat PI nanofiber reinforced PI films showed good transparency, decreased bulk density and significantly improved mechanical properties. Compared with neat PI film prepared by solution casting, the tensile strength and elongation at break for the PI film reinforced with 2 wt.% CNT/PI nanofibers were remarkably increased by 138% and 104%, respectively. The significant increases in the overall mechanical properties of the nanofibers reinforced polyimide films can be ascribed to good compatibility between the electrospun nanofibers and the matrix as well as high nanofiber orientation in the matrix. Our study demonstrates a good example for fabricating high performance and high toughness polyimide nanocomposites by using this facile homogeneity self-reinforcement method.     

A novel process to improve yield and mechanical performance of bamboo fiber reinforced composite via mechanical treatments

The aims of the present study are to produce bamboo fiber reinforced composite (BFRC) with high yield and to investigate the mechanical properties of BFRC comparing with those of commercial bamboo scrimber (BS) and laminated bamboo lumber (LBL). A novel process was developed for production of BFRC using oriented bamboo fiber mat (OBFM) made by a pilot machine. The yield and the mechanical properties of BFRC were investigated and analyzed in comparing with those of raw bamboo and other bamboo-based composites. The results show that the novel process produces 92.54% yield of OBFM due to without any chemical and special removing of inner and outer layer of bamboo during processing. In addition, all the mechanical properties and the variability of BFRC were significantly enhanced comparing with those of raw bamboo and other bamboo-based composites.