Interfacially reinforced methylphenylsilicone resin composites by chemically grafting multiwall carbon nanotubes onto carbon fibers

Both silane and multiwall carbon nanotubes (CNTs) were grafted successfully onto carbon fibers (CFs) to enhance the interfacial strength of CFs reinforced methylphenylsilicone resin (MPSR) composites. The microstructure, interfacial properties, impact toughness and heat resistance of CFs before and after modification were investigated. Experimental results revealed that CNTs were grafted uniformly onto CFs using 3-aminopropyltriethoxysilane (APS) as the bridging agent. The wettability and surface energy of the obtained hybrid fiber (CF-APS-CNT) were increased obviously in comparison with those of the untreated-CF. The CF-APS-CNT composites showed simultaneously remarkable enhancement in interlaminar shear strength (ILSS) and impact toughness. Moreover, the interfacial reinforcing and toughening mechanisms were also discussed. In addition, Thermogravimetric analysis and thermal oxygen aging experiments indicated a remarkable improvement in the thermal stability and heat oxidation resistance of composites by the introduction of APS and CNTs. We believe the facile and effective method may provide a novel interface design strategy for developing multifunctional fibers.     

Thermal and mechanical properties of phenolic-based composites reinforced by carbon fibres and multiwall carbon nanotubes

The thermal, mechanical and ablation properties of carbon fibre/phenolic composites filled with multiwall carbon nanotubes (MWCNTs) were investigated. Carbon fibre/phenolic/MWCNTs were prepared using different weight percentage of MWCNTs by compression moulding. The samples were characterized by scanning electron microscopy (SEM), flexural tests, thermal gravimetric analysis and oxyacetylene torch tests. The thermal stability and flexural properties of the nanocomposites increased by increasing MWCNTs content (wt% ⩽1), but they decreased when the content of MWCNTs was 2 wt%. The linear and mass ablation rates of the nanocomposites after modified with 1 wt% MWCNTs decreased by about 80% and 52%, respectively. To investigate the material post-test microstructure, a morphological characterization was carried out using SEM. It was shown that the presence of MWCNTs in the composite led to the formation of a strong network char layer without any cracks or opening.     

Fabrication and mechanical properties of well-dispersed multiwalled carbon nanotubes/epoxy composites

Multiwalled carbon nanotubes (MWCNTs)/epoxy nanocomposites were fabricated by using ultrasonication and the cast molding method. In this process, MWCNTs modified by mixed acids were well dispersed and highly loaded in an epoxy matrix. The effects of MWCNTs addition and surface modification on the mechanical performances and fracture morphologies of composites were investigated. It was found that the tensile strength improved with the increase of MWCNTs addition, and when the content of MWCNTs loading reached 8 wt.%, the tensile strength reached the highest value of 69.7 MPa. In addition, the fracture strain also enhanced distinctly, implying that MWCNTs loading not only elevated the tensile strength of the epoxy matrix, but also increased the fracture toughness. Nevertheless, the elastic modulus reduced with the increase of MWCNTs loading. The reasons for the mechanical property changes are discussed.     

Free-volume correlation with mechanical and dielectric properties of natural rubber/multi walled carbon nanotubes composites

The microstructure, mechanical strength, dielectric properties, Doppler broadening measurements and positron life time studies of the composites containing multi walled carbon nanotubes (MWCNTs) and natural rubber (NR) are investigated. The uniform distribution of MWCNTs in the elastomer medium is studied by Raman spectroscopy and the electron microscopy images show the composite’s internal microstructure. Free volume sizes and interstitial mesopore sizes of the nanocomposites are determined by positron annihilation lifetime spectroscopy (PALS). PALS investigates the influence of the nanotubes in regulating the interphase nanoscale character. Strong interfacial interaction causes an apparent reduction of the free-volume fraction of NR probably by depressing the formation of free-volume holes in the interfacial region. The mechanical percolation and percolation observed from the dielectric measurements are correlated with the life time values. It is established that the sub-nano level free volumes and nano level structure of the composites have significant roles in regulating the mechanical properties.     

Enhanced thermal conductivity and retained electrical insulation for polyimide composites with SiC nanowires grown on graphene hybrid fillers

Polyimide (PI) composites containing one-dimensional SiC nanowires grown on two-dimensional graphene sheets (1D–2D SiC_NWs-GSs) hybrid fillers were successfully prepared. The PI/SiC_NWs-GSs composites synchronously exhibited high thermal conductivity and retained electrical insulation. Moreover, the heat conducting properties of PI/SiC_NWs-GSs films present well reproducibility within the temperature range from 25 to 175 °C. The maximum value of thermal conductivity of PI composite is 0.577 W/mK with 7 wt% fillers loading, increased by 138% in comparison with that of the neat PI. The 1D SiC nanowires grown on the GSs surface prevent the GSs contacting with each other in the PI matrix to retain electrical insulation of PI composites. In addition, the storage modulus and Young’s modulus of PI composites are remarkably improved in comparison with that of the neat PI.     

Preparation and properties of sisal microfibril/gelatin biomass composites

In this work, the natural sisal fibers were fibrillated by enzyme hydrolysis or mechanical disintegration into microfibrils with a width of 5-10 μm and different aspect ratios. The sisal microfibrils or microfibril mats were added into the gelatin to prepare biomass composites, by solvent-casting or solution impregnation techniques, respectively. The morphology, mechanical properties, biodegradation property, and water adsorption behaviors of the composites were investigated. It was found that the tensile strength of the composites was dramatically increased with the addition of sisal microfibrils. The degradation ratio of the composites decreased continuously with increasing the sisal fibril content. The addition of sisal microfibrils decreased the water uptake at equilibrium and the water diffusion coefficient. Scanning electron microscopy characterization showed that the sisal microfibrils were very well embedded in the gelatin matrix, showing a good interfacial adhesion.     

Preparation and properties of hollow glass microsphere-filled epoxy-matrix composites

Hollow glass microsphere (HGM)–filled epoxy composites, with filler content ranging from 0 to 51.3 vol.%, were prepared in order to modify the dielectric properties of the epoxy. The results showed that the dielectric constant (D_k) and dielectric loss (D_f) of the composites decreased simultaneously with increasing HGM content, which was critical for the provision of superior high-frequency device performance. Other properties of the composite, such as the coefficient of thermal expansion (CTE) and the glass transition temperature (T_g), were also improved. The improvement in these properties was related to strong interaction between the HGM and epoxy, which was indicated by the formation of an interphase between the HGM and epoxy-matrix. It was unsatisfactory in this study that the thermal conductivity of the composites also decreased with HGM content. In order to obtain relatively high thermal conductivity and a low dielectric constant simultaneously, this paper suggests further adding other filler.     

Mechanical and electrical properties of carbon nanotube/poly(phenylene sulphide) composites incorporating polyetherimide and inorganic fullerene-like nanoparticles

The mechanical and electrical properties of single-walled carbon nanotube (SWCNT) reinforced poly(phenylene sulphide) (PPS) composites prepared by melt-extrusion have been evaluated. The wrapping of SWCNTs in polyetherimide (PEI) and the addition of inorganic fullerene-like tungsten disulfide (IF-WS₂) nanoparticles provided an effective method for dispersing the SWCNTs, leading to enhanced properties of the resulting hybrid composites. Mechanical tests demonstrated significant enhancements in stiffness, strength and toughness by the addition of both nanofillers, and the Young’s modulus of the hybrid composites was fairly well predicted by two-phase modelling. The electrical conductivity of PPS improved dramatically at low SWCNT content (0.1-0.5 wt%). At higher concentrations, the replacement of part of the SWCNTs with IF-WS₂ maintained the level of conductivity of the composites. Overall, the hybrids possess superior performance than composites reinforced solely with wrapped or non-wrapped SWCNTs, and their properties can be tailored by modifying the SWCNT/IF-WS₂ ratio.     

Fluorinated graphene reinforced polyimide films with the improved thermal and mechanical properties

In order to explore the addition effect of fluorinated graphene (FG) on the mechanical and thermal performances of polyimide (PI) matrix, FG sheets are first prepared and employed as the nanofillers to construct PI/FG nanocomposite films. The prepared film is optically transparent at low content of FG and experimental results demonstrate that the addition of FG can effectively enhance the properties of PI matrix. Especially, compared with pure PI matrix, the addition of 0.5 wt% FG in PI can endow 30.4% increase in tensile stress and 115.2% increase in elongation at break. Experimental analyses considering the morphology and microstructure are also conducted, and the results indicate that the improved mechanical properties of the PI/FG nanocomposite films are mainly attributed to the good dispersibility of FG sheets in PI host, and the effective stress transfer between the polymer and the FG.     

Structure and properties of highly oriented polyoxymethylene/multi-walled carbon nanotube composites produced by hot stretching

Highly-oriented polyoxymethylene (POM)/multi-walled carbon nanotube (MWCNT) composites were fabricated through solid hot stretching technology. With the draw ratio as high as 900%, the oriented composites exhibited much improved thermal conductivity and mechanical properties along the stretching direction compared with that of the isotropic samples before drawing. The thermal conductivity of the composite with 11.6 vol.% MWCNTs can reach as high as 1.2 W/m K after drawing. Microstructure observation demonstrated that the POM matrix had an ordered fibrillar bundle structure and MWCNTs in the composite tended to align parallel to the stretching direction. Wide-angle X-ray diffraction results showed that the crystal axis of the POM matrix was preferentially oriented perpendicular to the draw direction, while MWCNTs were preferentially oriented parallel to the draw direction. The strong interaction between the POM matrix and the MWCNTs hindered the orientation movement of molecules of POM, but induced the orientation movement of MWCNTs.     

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.     

Hybrid network structure and thermal conductive properties in poly(vinylidene fluoride) composites based on carbon nanotubes and graphene nanoplatelets

A small quantity of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) were introduced into the poly(vinylidene fluoride) (PVDF)/GNP and PVDF/CNT composites, respectively, to prepare the corresponding ternary PVDF/CNT/GNP and PVDF/GNP/CNT composites. The results demonstrated that adding CNTs into the PVDF/GNP composites greatly promoted the formation of the hybrid network structure of fillers. This was much different from the scenario that adding GNPs into the PVDF/CNT composites. GNPs and CNTs exhibited excellent nucleation effects for the crystallization of PVDF matrix; however, the variation of the PVDF crystallinity was small. Adding CNTs into the PVDF/GNP composites greatly enhanced the electrical conductivity of the PVDF/CNT/GNP composites. This was also different from the scenario of the PVDF/GNP/CNT composites. Furthermore, the PVDF/CNT/GNP composites exhibit higher thermal conductivity and higher synergistic efficiency compared with the PVDF/GNP/CNT composites. The conductive mechanisms and the synergistic effects of the ternary composites were then analyzed.     

Effects of poly(oxyethylene)-block structure in polyetheramines on the modified carbon nanotube/poly(lactic acid) composites

The hybrids of multi-walled carbon nanotube and poly(lactic acid) (MWCNT/PLA) were prepared by a melt-blending method. In order to enhance the compatibility between the PLA and MWCNTs, the surface of the MWCNTs was covalently modified by Jeffamine® polyetheramines by functionalizing MWCNTs with carboxylic groups. Different molecular weights and hydrophilicity of the polyethermaines were grafted onto MWCNTs with the assistance of a dehydrating agent. The results showed that low-molecular-weight Jeffamine® polyetheramine modified MWCNTs can effectively improve the thermal properties of PLA composites. On the other hand, high-molecular-weight and poly(oxyethylene)-segmented polyetheramine could render the modified MWCNTs of well dispersion in PLA, and consequently affecting the improvements of mechanical properties and conductivity of composite materials. With the addition of 3.0 wt% MWCNTs, the increment of E′ of the composite at 40 °C was 79%. For conductivity, the surface resistivity decreased from 1.27 × 10¹² Ω/sq for neat PLA to 8.30 × 10⁻³ Ω/sq for the composites.     

Preparation, characterisation and processing of carbon fibre/polyamide-12 composites for selective laser sintering

Aiming at developing carbon fibre/polyamide-12 (CF/PA) composite powders for manufacturing high-performance components by selective laser sintering (SLS), the preparation, characteristics and sintering process of the composite powders and mechanical properties of sintered components were studied. Surfaces of the carbon fibres were treated by the oxidation modification and coated with polyamide-12 through the dissolution-precipitation process to provide good interfacial adhesion and homogenous dispersion within the polyamide-12 matrix. The particle size and micro-morphology analyses show that the CF/PA composite powders with 30 wt%, 40 wt% and 50 wt% carbon fibres present the suitable powder sizes and format for SLS. The incorporation of carbon fibres into the polyamide-12 matrix decreases the initial melting temperature and consequently lowers the SLS part bed temperatures, implying lower energy requirement and less thermal degradation in the sintering process. The CF/PA composites also represent higher thermal stability than the pure polyamide-12. The CF/PA sintered components with 30 wt%, 40 wt% and 50 wt% carbon fibres exhibit the greatly enhanced flexural strengths by 44.5%, 83.3%, 114%, and the flexural modulus by 93.4%, 129.4%, 243.4%, respectively, as compared with the pure polyamide-12 sintered parts. Fractured surface analysis shows that the carbon fibres are encapsulated and bonded well with the polyamide matrix. The complex SLS parts with the thinnest wall of 0.6 mm, the density of 1.09 ± 0.02 g/cm³ and the relatively density of 94.13 ± 1.72% were manufactured using the CF/PA composite powder with 30 wt% carbon fibres. This study demonstrates that the CF/PA composite powders prepared by the surface treatment and dissolution-precipitation method represent suitable interfacial adhesion, filler dispersion, particle sizes and sintering behaviours for SLS and enable the manufacture of complex components with high performance.     

Thermal conductivity of polymer composites based on the length of multi-walled carbon nanotubes

The anisotropic development of thermal conductivity in polymer composites was evaluated by measuring the isotropic, in-plane and through-plane thermal conductivities of composites containing length-adjusted short and long multi-walled CNTs (MWCNTs). The thermal conductivities of the composites were relatively low irrespective of the MWCNT length due to their high contact resistance and high interfacial resistance to polymer resins, considering the high thermal conductivity of MWCNTs. The isotropic and in-plane thermal conductivities of long-MWCNT-based composites were higher than those of short-MWCNT-based ones and the trend can accurately be calculated using the modified Mori-Tanaka theory. The in-plane thermal conductivity of composites with 2 wt% long MWCNTs was increased to 1.27 W/m·K. The length of MWCNTs in polymer composites is an important physical factor in determining the anisotropic thermal conductivity and must be considered for theoretical simulations. The thermal conductivity of MWCNT polymer composites can be effectively controlled in the processing direction by adjusting the length of the MWCNT filler.     

Electrical and thermal properties of polyamide 12 composites with hybrid fillers systems of multiwalled carbon nanotubes and carbon black

Hybrid filler systems of multiwalled carbon nanotubes (MWCNTs) and carbon black (CB) were incorporated into two types of polyamide 12 (PA12) using small-scale melt mixing in order to identify potential synergistic effects on the interaction of these two electrical conductive fillers. Although no synergistic effects were observed regarding the electrical percolation threshold, at loadings well above the percolation threshold higher volume conductivities were obtained for samples containing both, MWCNT and CB, as compared to single fillers. This effect was more pronounced when using a higher viscous PA12 matrix. The formation of a co-supporting network can be assumed. The combined use of CB and MWCNTs improved the macrodispersion of MWCNT agglomerates, which can be assigned as a synergistic effect. DSC measurements indicated an effect of the nanofiller on crystallisation temperatures of PA12; however this was independent of the kind or amount of the carbon nanofiller.     

Tribological properties of fluorinated graphene reinforced polyimide composite coatings under different lubricated conditions

The tribological properties of polyimide (PI) and PI/fluorinated graphene (FG) nanocomposites, as a new class of graphene reinforced polymer, are investigated using a ball-on-disk configuration under different lubricated conditions of dry sliding, water lubrication and oil lubrication. Experimental results reveal that single incorporation of FG can effectively improve the tribological performance of PI under all the three conditions. In addition, compared to the results under dry sliding, the phenomenon that the friction coefficient decreases while the wear rate increases under water lubrication condition is observed and researched in detail. The worst anti-wear performance under water-lubricated condition can be ascribed to the fact that the water can be adsorbed by the polar imide radicals of the PI and PI/FG nanocomposite, therefore leading to the property deterioration of the PI and PI/FG nanocomposite coatings.     

Graphite-like carbon nitride and functionalized layered double hydroxide filled polypropylene-grafted maleic anhydride nanocomposites: Comparison in flame retardancy,and thermal,mechanical and UV-shielding properties

Graphite-like carbon nitride (g-C₃N₄) and borate modified layered double hydroxides (LDH-B) were successfully fabricated by thermal pyrolysis and modified aqueous miscible organic solvent treatment methods, respectively. Then these nano-additives were introduced to prepare polypropylene-grafted maleic anhydride (PP-g-MA)/g-C₃N₄ and PP-g-MA/LDH-B nanocomposites using a modified solvent mixing strategy. Several important parameters of the nanocomposites including thermal, mechanical and UV-blocking properties were investigated. Results indicated that pure g-C₃N₄ exhibited 347.6 and 427.2 °C increase in onset decomposition temperature under air and nitrogen conditions, respectively, compared with LDH-B. In case of PP-g-MA nanocomposites, both T_-10 and T_-50 (the temperature at 10% and 50% weight loss, respectively) were improved by 14.6 and 27.7 °C, respectively, by the addition of g-C₃N₄ while those only increased by 2.3 and 17.8 °C upon introducing LDH-B. Furthermore, PP-g-MA/g-C₃N₄ system showed a remarkable increment (9.8 °C) in crystallization temperature while an increase of 4.2 °C for PP-g-MA/LDH-B nanocomposite. Introducing g-C₃N₄ and LDH-B into PP-g-MA led to a reduction of 28% and 19% in pHRR, respectively. It was noted that the incorporation of g-C₃N₄ caused significant improvement in storage modulus from 2445.0 MPa for neat PP-g-MA to 2783.5 MPa for PP-g-MA/g-C₃N₄ while that of PP-g-MA/LDH-B was dramatically decreased by 27.3%. Optical results indicated that PP-g-MA/g-C₃N₄ was rendered fascinating UV adsorption ability relative to PP-g-MA/LDH-B. It is expected that the novel two-dimensional nanomaterial could bring new creativity into polymer composites.     

Review of the mechanical properties of carbon nanofiber/polymer composites

In this paper, the mechanical properties of vapor grown carbon nanofiber (VGCNF)/polymer composites are reviewed. The paper starts with the structural and intrinsic mechanical properties of VGCNFs. Then the major factors (filler dispersion and distribution, filler aspect ratio, adhesion and interface between filler and polymer matrix) affecting the mechanical properties of VGCNF/polymer composites are presented. After that, VGCNF/polymer composite mechanical properties are discussed in terms of nanofibers dispersion and alignment, adhesion between the nanofiber and polymer matrix, and other factors. The influence of processing methods and processing conditions on the properties of VGCNF/polymer composite is also considered. At the end, the possible future challenges for VGCNF and VGCNF/polymer composites are highlighted.