Thermotropic LCP/CNF nanocomposites prepared with aid of ultrasonic waves

Ultrasound assisted twin screw extrusion process was developed to disperse carbon nanofibers (CNFs) in a polymer matrix. CNFs were separately added into the melt stage to reduce the breakage of CNFs and to avoid intense stresses in the feed zone. The effect of ultrasound and CNFs loading on die pressure, rheological, mechanical, electrical and morphological properties of liquid crystalline polymer (LCP) filled with 0-20 wt% CNFs was studied. Ultrasonic treatment caused a reduction in die pressure and a decrease in electrical percolation threshold value of treated samples. It was also found that mechanical properties of ultrasonically treated LCP/CNF nanocomposite moldings were preserved, improved or slightly decreased in comparison with those of LCP. This is in contrast to available literature typically showing a deterioration of mechanical properties with addition of CNFs. SEM studies have indicated an improved dispersion of CNFs and a reduction of LCP rich area in nanocomposites upon ultrasonic treatment.     

Effects of crystallization on dispersion of carbon nanofibers and electrical properties of polymer nanocomposites

Polymer nanocomposites filled with low volume fractions of carbon nanofibers (CNFs) were prepared by melt‐compounding. Three types of polymers with different crystallization behavior, i.e., weakly‐crystallized low density polyethylene (LDPE), strongly crystallized high density polyethylene (HDPE) and amorphous polystyrene (PS), were selected as matrices for the nanocomposites. The effects of polymer crystallization on the dispersion of CNFs were examined. Optical and electron microscopic examinations revealed that the dispersion of CNFs in the nanocomposite matrices was strongly depended on the crystallization behavior of polymer matrices. The CNFs were found to disperse uniformly in weakly crystallized LDPE and amorphous PS matrices, but agglomerated in HDPE due to its strong crystallization tendency. Such a distinct dispersion behavior of CNFs in polymers had a profound effect on the electrical properties of the nanocomposites investigated. The PS/CNF nanocomposites exhibited the lowest percolation threshold. The HDPE/CNF nanocomposites showed the largest percolation threshold due to the CNF agglomeration within the amorphous phase of HDPE. POLYM. ENG. SCI., 48:177–183, 2008. © 2007 Society of Plastics Engineers     

Preparation and characterization of carbon nanofiber reinforced thermoplastic polyurethane nanocomposites

The effect of CNFs on hard and soft segments of TPU matrix was evaluated using Fourier transform infrared (FTIR) spectroscope. The dispersion and distribution of the CNFs in the TPU matrix were investigated through wide angle X‐ray diffraction (WAXD), field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM), polarizing optical microscope (POM), and atomic force microscope (AFM). The thermogravimetric analysis (TGA) showed that the inclusion of CNF improved the thermal stability of virgin TPU. The glass transition temperature (T_g), crystallization, and melting behaviors of the TPU matrix in the presence of dispersed CNF were observed by differential scanning calorimetry (DSC). The dynamic viscoelastic behavior of the nanocomposites was studied by dynamical mechanical thermal analysis (DMTA) and substantial improvement in storage modulus (E') was achieved with the addition of CNF to TPU matrix. The rheological behavior of TPU nanocomposites were tested by rubber processing analyzer (RPA) in dynamic frequency sweep and the storage modulus (G') of the nanocomposites was enhanced with increase in CNF loading. The dielectric properties of the nanocomposites exhibited significant improvement with incorporation of CNF. The TPU matrix exhibits remarkable improvement of mechanical properties with addition of CNF. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Temperature dependence of electrical resistivity in carbon nanofiber/unsaturated polyester nanocomposites

This article described the temperature dependence of electrical resistivity for carbon nanofiber (CNF)/unsaturated polyester resin (UPR) nanocomposites prepared by a solvent evaporation method. It was found that the CNF/UPR nanocomposites had quite low electrical percolation threshold due to CNFs having a large aspect ratio and being well dispersed into the UPR matrix. A sharp decrease in the electrical resistivity was observed at about 1 wt% CNF content. The influence of CNF content on the electrical resistivity was investigated as a function of temperature in detail. The nanocomposites showed a positive temperature coefficient effect for the resistivity, and had a strong temperature dependence near the percolation threshold. When the number of thermal cycles was increased, the electrical resistivity decreased and had a weak temperature dependence, especially in the case of melting temperature. Moreover, the size influences of CNFs on the electrical properties of nanocomposites were analyzed and discussed. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Influence of carbon nanofibers reinforcement on thermal and electrical behavior of polysulfone nanocomposites

Carbon nanofiber (CNF) based polysulfone (PSU) nanocomposites have been developed successfully by a innovative solution mixing technique to explore the effect of state of dispersion and wt% loading of CNFs on different properties of PSU. In order to enhance the interfacial adhesion between CNFs and PSU, CNFs were functionalized by air oxidation. Thermal properties were characterized by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) and it was seen that thermal stability of PSU was increased with increase in CNFs loading. The state of dispersion of CNFs throughout the PSU matrix and PSU–CNFs interaction were confirmed using field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) study. The electrical properties of nanocomposites were studied from direct current (DC) and alternating current (AC) resistivity measurement. DC resistivity registered a very low percolation threshold in‐between 0.5–1 wt% of CNFs loading. DC resistivity of PSU was decreased by nine orders of magnitude with the addition of 1 wt% CNFs loading. Dielectric constant and dissipation factor of nanocomposites were significantly increased with increase in CNFs content in nanocomposites. The enhancement in these properties suggests a great potential application of the resulting nanocomposites as multifunctional materials in various electronics industries. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Effect of carbon nanofiber (CNF) silanization on the properties of CNF/epoxy nanocomposites

Carbon nanofibers (CNFs) were functionalized by a multistage process including oxidation, reduction and silanization. The chemical modifications were examined by Fourier transform infrared spectroscopy, X‐ray photoelectron spectrometry, Raman spectroscopy and thermogravimetric analysis. The silanized CNFs were then added into an epoxy resin (EPON 828) to study the effect of the surface modification of CNFs on the properties of nanocomposites. For comparison, nanocomposites containing original unmodified CNFs were also investigated. Scanning electron microscopy indicates better dispersion of modified fibers in the epoxy polymer matrix; the mechanical and thermal properties of composites are also improved; the electrical conductivity of the composites is reduced. Copyright © 2011 Society of Chemical Industry     

Thermally stable electromagnetic interference shielding material from polysulfone nanocomposites: Comparison on carbon nanotube and nanofiber reinforcement

The present investigation aims to develop thermally stable electromagnetic interference shielding materials from polysulfone (PSU) nanocomposites filled with multiwall carbon nanotubes (MWCNT) or carbon nanofibers (CNF). The effect of filler type and their structural features such as aspect ratio (length/diameter) and wall integrity on the different properties of nanocomposites has been investigated. Nanocomposite filled with MWCNT/CNF exhibits higher thermal stability compared with the neat PSU matrix. The onset degradation temperature of PSU at 532°C enhances to 537 and 538°C at 3 wt% MWCNT and 3 wt% CNF loading, respectively. CNFs filled nanocomposite shows higher electromagnetic interference shielding effectiveness (EMISE) compared with MWCNT filled one at the same filler loading. Compared with MWCNT, CNF imparts lower electrical percolation threshold. Nanocomposite filled with MWCNTs possesses percolation threshold at 1.5 wt%, whereas nanocomposite filled with CNFs possesses the same at 0.9 wt%. The EMISE of 20–45 dB are obtained from only 1 mm thick CNF filled nanocomposites from the filler loading 3 to 10 wt%. This value of EMISE above 40 dB suggests that the prepared nanocomposite can be used as an effective lightweight EMI shielding material for high frequency (8.2–12.4 GHz) applications, where high thermal stability is required. POLYM. COMPOS. 36:566–575, 2015. © 2014 Society of Plastics Engineers     

Fabrication and Properties of Ethylene Vinyl Acetate-Carbon Nanofiber Nanocomposites

Carbon nanofiber (CNF) is one of the stiffest materials produced commercially, having excellent mechanical, electrical, and thermal properties. The reinforcement of rubbery matrices by CNFs was studied in the case of ethylene vinyl acetate (EVA). The tensile strength was greatly (61%) increased, even for very low fiber content (i.e., 1.0 wt.%). The surface modification of the fiber by high energy electron beam and gamma irradiation led to better dispersion in the rubber matrix. This in turn gave rise to further improvements in mechanical and dynamic mechanical properties of EVA. The thermal conductivity also exhibited improvements from that of the neat elastomer, although thermal stability of the nanocomposites was not significantly altered by the functionalization of CNFs. Various results were well supported by the morphological analysis of the nanocomposites.     

Novel in situ carbon nanofiber/polydimethylsiloxane nanocomposites: Synthesis,morphology, and physico‐mechanical properties

A series of carbon nanofiber (CNF)/polydimethylsiloxane (PDMS)‐based nanocomposites was prepared by anionic ring opening polymerization of octamethylcyclotetrasiloxane (D₄) in presence of pristine CNF and amine‐modified CNF. A detailed study of morphology–property relationship of the nanocomposites was carried out in order to understand the effect of chemical modification and loading of filler on property enhancement of the nanocomposites. An elaborate comparison of structure and properties was carried out for the nanocomposites prepared by in situ and conventional ex situ methods. Pronounced improvement in degree of dispersion of the fillers in the matrix on amine modification of CNFs was reflected in mechanical properties of the modified nanocomposites. Maximum upliftment in mechanical properties was observed for in situ prepared amine modified CNF/hydroxyl PDMS nanocomposites. For 8 phr filler loading, tensile strength increased by 370%, while tensile modulus showed an increase of 515% compared with the virgin elastomer. Furthermore, in situ prepared unmodified CNF/hydroxyl PDMS nanocomposites showed an increase of 141°C in temperature of maximum degradation (T_max) for 8 phr CNF loading. These results were correlated with the morphological analysis through transmission electron microscopic studies. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Nano-engineering of high-performance PA6.6 nanocomposites by the integration of CVD-grown carbon fiber on graphene as a bicomponent reinforcement by melt-compounding

In this study, long carbon nanofibers (CNFs) were grown on graphene nanoplatelets (GNPs) by chemical vapor deposition (CVD) technique to develop three-dimensional (3D) bicomponent nanostructures. The structure and properties of graphene before and after CVD process were investigated in details. X-ray photoelectron analysis depicted the formation of Fe-C bonds by the deposition of carbon atoms on the catalyst surface of Fe₂O₃. This hybrid additive was firstly used as a reinforcing agent in melt compounding to fabricate PA6.6-based nanocomposites with enhanced mechanical and thermal properties. Both GNP and CNF-GNP have enough surface oxygen functional groups to improve the interfacial interactions with polyamide matrix and thus provide good wettability. Also, both neat GNP and its bicomponent additive with CNF also acted as a nucleating agent and allowed the crystal growth in nanocomposite structure. Homogeneous dispersion of nanoparticles was achieved by using thermokinetic mixer during compounding by applying high shear rates. Mechanical results showed that 23 and 34% improvement in flexural and tensile modulus values, respectively, was attained by the addition of 0.5 wt % CNF-GNP hybrid additive. The heat distortion temperature and Vicat softening temperature of the resulting PA6.6 nanocomposites were improved compared to neat PA6.6 material indicating performance enhancement at higher service temperature conditions. CNF was successfully grown on Fe-loaded GNP by CVD method and this hybrid additive was compounded with PA6.6 by melt-mixing process. Mechanical results showed that 34% improvement in tensile modulus value was attained by the addition of 0.5 wt % CNF-GNP hybrid additive because it acted as a nucleating agent and allowed the crystal growth in the nanocomposite structure. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48347.     

Mechanical and thermal transmission properties of carbon nanofiber‐dispersed carbon/phenolic multiscale composites

The present article reports the development and characterization of carbon nanofiber (CNF)‐incorporated carbon/phenolic multiscale composites. Vapor‐grown CNFs were dispersed homogeneously in to phenolic resin using an effective dispersion route, and carbon fabrics were subsequently impregnated with the CNF‐dispersed resin to develop carbon fiber/CNF/phenolic resin multiscale composites. Mechanical and thermal transmission properties of multiscale composites were characterized. Elastic modulus and thermal conductivity of neat carbon/phenolic and multiscale composites were predicted and compared with the experimental results. It was observed that incorporation of only 1.5 wt % CNF resulted in 10% improvement in Young's modulus, 12% increase in tensile strength, and 36% increase in thermal conductivity of carbon/phenolic composites. Fracture surface of composite samples revealed the formation of stronger fiber/matrix interface in case of multiscale composites than neat carbon/phenolic composites. Enhancement of above properties through CNF addition has been explained, and the difference between the predicted values and experimental results has been discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Carbon nanofiber type and content dependence of the physical properties of carbon nanofiber reinforced polypropylene composites

The variation of the physical properties of four different carbon nanofibers (CNFs), based‐polymer nanocomposites incorporated in the same polypropylene (PP) matrix by twin‐screw extrusion process was investigated. Nanocomposites fabricated with CNFs with highly graphitic outer layer revealed electrical isolation‐to‐conducting behaviors as function of CNF's content. Nanocomposites fabricated with CNFs with an outer layer consisting on a disordered pyrolitically stripped layer, in contrast, revealed better mechanical performance and enhanced thermal stability. Further, CNF's incorporation into the polymer increased the thermal stability and the degree of crystallinity of the polymer, independently on the filler content and type. In addition, dispersion of the CNFs' clusters in PP was analyzed by transmitted light optical microscopy, and grayscale analysis (GSA). The results showed a correlation between the filler concentration and the variance, a parameter which measures quantitatively the dispersion, for all composites. This method indicated a value of 1.4 vol% above which large clusters of CNFs cannot be dispersed effectively and as a consequence only slight changes in mechanical performance are observed. Finally, this study establishes that for tailoring the physical properties of CNF based‐polymer nanocomposites, both adequate CNFs structure and content have to be chosen. POLYM. ENG. SCI., 54:117–128, 2014. © 2013 Society of Plastics Engineers     

Effect of amine functionalization of CNF on electrical, thermal, and mechanical properties of epoxy/CNF composites

This paper presents experimental results of the effect of amine functionalization of carbon nanofibers (CNF) on the electrical, thermal, and mechanical properties of CNF/epoxy composites. The functionalized and non-functionalized CNFs (up to 3 wt%) were dispersed into epoxy using twin screw extruder. The specimens were characterized for electrical resistivities, thermal conductivity (K), UTS, and Vicker’s microhardness. The properties of the nanocomposites were compared with that of neat epoxy. The volume conductivity of the specimens increased by E12 S/cm and E09 S/cm in f-CNF/epoxy and CNF/epoxy, respectively, at 3 wt% filler loading. The increase in K for former was 106% at 150 °C, while for the latter it was only 64%. Similarly, UTS increased by 61% vs. 45% and hardness 65% vs. 43%. T _g increased with increase in filler content. SEM examinations showed that functionalization resulted in better dispersion of the nanofibers and hence greater improvement in the studied properties of the nanocomposites.     

Perspectives on Polyvinyl Chloride and Carbon Nanofiller Composite: A Review

This review mainly concentrates on polyvinyl chloride/carbon nanofiller-based composites. The present study focused upon synthetic strategies and relevance of polyvinyl chloride/graphite, polyvinyl chloride/graphene, polyvinyl chloride/graphene oxide, and polyvinyl chloride/carbon nanotube nanocomposite. Among carbon-based reinforcement, graphene oxide nanofiller depicted better dispersion in polyvinyl chloride matrix. The electrical, mechanical, thermal, and morphological properties of these nanocomposites are also discussed. Moreover, future potential of these materials are elucidated. There is relatively little literature available regarding polyvinyl chloride-based nanocomposite. The main aim of this article is to therefore particularize the polyvinyl chloride-based nanocomposites and expose their concealed properties to enable better use of these new materials in different technical fields.     

Surface modification of CNFs via plasma polymerization of styrene monomer and its effect on the properties of PS/CNF nanocomposites

Carbon nanofibers (CNF) were modified via plasma assisted polymerization in a specially designed reactor. The effect of the plasma reactor conditions, such as power and time, on the extent of the CNFs modification was examined. Polystyrene (PS) coated nanofibers plus PS polymer were then processed in a Brabender torque rheometer mixing chamber to obtain PS/CNF nanocomposites, with 0.5, 1.0, 3.0, and 5.0 wt % of CNF. The effect of the plasma treatment on the dispersion of the nanofibers and on the compatibility between the nanofibers and the polymer matrix was also examined. Modification of the CNFs was assessed by measuring the contact angle of water in a “bed” of nanofibers and by examining its dispersion in several solvents. The morphology of PS/CNF nanocomposites was studied through scanning electron microscopy (SEM). Contact angles decreased in all cases, indicating a change in hydrophobicity of the modified CNFs. This change was confirmed in the CNF dispersion tests in several solvents. SEM micrographs show the difference between the original and the PS coated CNF. In addition, fractured samples show the effect of this treatment, in the sense that the CNF seem to be completely embedded in the polymer matrix, which clearly indicates the high compatibility between the PS and the modified (PS coated) CNF. As a consequence, a much better dispersion of the treated CNF was observed. Finally, the tensile modulus of PS/CNF composites increased slightly with respect to PS when using untreated CNFs, but more than doubled when using plasma treated CNFs. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Functional nanocomposites with graphene-DNA hybrid fillers: Synthesis and surface properties under UV irradiation

In this work, nanocomposites containing assemblies of graphene nanoplatelets (GNP) and double-stranded DNA are investigated as UV-sensitive materials, as they show good electrical properties combined with the chemical sensitivity of DNA to UV radiation, particularly to the more energetic UV-C band. Nanocomposite films were prepared by drop-casting technique after embedding the graphene-DNA fillers in a flexible polydimethylsiloxane (PDMS) matrix using a suitable solvent. The synthesis was optimized in order to improve the dispersion of the graphene-DNA elements in the polymer matrix, as the sensing properties of the nanocomposite materials are highly affected by the amount and homogeneity of the filler dispersion. The electrical and thermal properties of the GNP-DNA/PDMS films, as well as their surface morphology and wettability, were investigated before and after exposure to UV-C radiation using complementary techniques. Results give information on the potential applications of these novel functional nanocomposites for radiation monitoring in environments that are characterized by high levels of biologically-damaging UV radiation.     

Hyperbranched polyol/carbon nanofiber composites

Carbon nanofiber (CNF) and carbon nanotube (CNT) composites have enhanced mechanical and electrical properties that make these composites desirable for antistatic and electronic dissipation technology. These applications require a homogenous dispersion of CNFs within a polymer matrix. To improve the compatibility/dispersability of CNFs within a polymer matrix, a hyperbranched polyol CNF composite was synthesized by the chemical modification of oxidized CNFs with glycidol and boron trifluoride diethyl etherate. The resulting polyol CNFs were characterized by TGA, FTIR, TEM/SEM and XPS. The hydroxyl groups were reacted with heptafluorobutyryl chloride to determine the amount of oxidized groups in the sample. The resulting composite was characterized by FTIR and elemental analysis. The amount of hydroxyl groups increased by 550% for the polyol CNFs as compared to the oxidized CNFs and an improvement in dispersion ability was observed.     

Nanocomposites of poly(ether ether ketone) with carbon nanofibers: Effects of dispersion and thermo-oxidative degradation on development of linear viscoelasticity and crystallinity

Poly(ether ether ketone), PEEK, is a widely used engineering plastic that is especially suitable for high temperature applications. Compounding of PEEK with carbon nanofibers, CNF, has the potential of enhancing its mechanical and thermal properties further, even at relatively low CNF concentrations. However, such enhancements can be compromised by myriad factors, some of which are elucidated in this study. Considering that the dispersion of the CNF into any high molecular weight polymer is a challenge, two different processing methods, i.e., melt and solution processing were used to prepare PEEK nanocomposites with low aspect ratio carbon nanofibers. The linear viscoelastic material functions of PEEK nanocomposites in the solid and molten states were characterized as indirect indicators of the dispersion state of the nanofibers and suggested that the dispersion of nanofibers into PEEK becomes difficult at increasing CNF concentrations for both solution and melt processing methods. Furthermore, the time-dependence of the linear viscoelastic material functions of the PEEK/CNF nanocomposites at 360-400 °C indicated that PEEK undergoes thermo-oxidative cross-linking under typical melt processing conditions, thus preventing better dispersion by progressive increases of the mixing time and specific energy input during melt processing. The crystallization behavior of PEEK is also affected by the presence of CNF and degree of cross-linking, with the rate of crystallization decreasing with increasing degree of cross-linking and upon the incorporation of CNFs both for the solution and melt processed PEEK nanocomposites.     

Comparative study of the rheological behavior of multiwalled carbon nanotubes and nanofiber composites prepared by the dilution of a masterbatch of polypropylene

In this investigation, the characteristics and the rheological properties of two different nanocomposite systems were investigated. These systems consisted of a dispersion of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) in a polypropylene (PP) matrix. The mixing process was carried out by melt compounding with a twin‐screw corotating extruder with different reinforcement amounts (0.2–20 wt %) from concentrated masterbatches (20 wt %) of PP/CNT and PP/CNF. The results show a remarkable increase in the viscosity for both blends as the reinforcement amount was increased. It was important to evaluate the rheological behavior to understand the effect of the nanocarbon particles on the internal structures and their processing properties of the obtained composites. CNFs were a more viable reinforcement from a processability point of view because the obtained viscosities of the PP/CNF blends were more manageable. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization of novel addition cured polydimethylsiloxane nanocomposites using nano‐silica sol as reinforcing filler

A series of novel addition cured polydimethylsiloxane (PDMS) nanocomposites with various amounts of nano‐silica sol were prepared via hydrosilylation for the first time. The influence of various amounts of nano‐silica sol on the morphology, thermal behavior, mechanical and optical properties of these PDMS nanocomposites was studied in detail. It was found that with an increment in the amount of nano‐silica sol the reinforcing effect of the nano‐silica sol on the thermal and mechanical properties of the PDMS nanocomposites was very noticeable compared with the reference material. The prominent improvements in resistance to thermal degradation and mechanical properties can probably be attributed to the strong interaction of PDMS chains and uniformly dispersed particles resulting from the nano‐silica sol. However, the transparency of the PDMS nanocomposites slightly decreased with an increment in weight fraction of nano‐silica, compared with that of PDMS composite without nano‐silica (Sol‐0), which can probably be ascribed to an increasing size of the aggregated particles in the PDMS nanocomposites. The optimum amount of nano‐silica sol for preparing novel addition curing PDMS nanocomposites was about 15 wt%. © 2015 Society of Chemical Industry