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     

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     

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.     

Maleic anhydride polypropylene modified cellulose nanofibril polypropylene nanocomposites with enhanced impact strength

Development of cellulose nanofibrils (CNFs) reinforced polypropylene (PP) nanocomposites using melt compounding processes has received considerable attention. The main challenges are to obtain well‐dispersed CNFs in the polymer matrix and to establish compatible linkages between the CNFs and PP. Manufacturing of CNF reinforced PP nanocomposites was conducted using a twin‐screw co‐rotating extruder with the masterbatch concept. Modifications of CNFs using maleic anhydride polypropylene were performed. The best mechanical properties of the nanocomposites are 1.94 GPa (tensile modulus), 32.8 MPa (tensile strength), 1.63 GPa (flexural modulus), 50.1 MPa (flexural strength), and 3.8 kJ m⁻² (impact strength), which represents about 36, 11, 21, 7, and 23% improvement, respectively, compared to those of pure PP (1.43 GPa, 29.5 MPa, 1.35 GPa, 46.9 MPa, and 3.1 kJ m⁻²). Fracture morphology examination indicated good dispersion of CNFs in the PP matrix was achieved through this specific manufacturing process. MAPP treatments enhanced the interfacial adhesion between the CNFs and PP. POLYM. COMPOS., 37:782–793, 2016. © 2014 Society of Plastics Engineers     

Fabrication and characteristics of graphene oxide/nanocellulose fiber/poly(vinyl alcohol) film

Poly(vinyl alcohol) (PVA), PVA/nanocellulose fiber (CNF), and PVA/CNF/graphene oxide (GO) films were prepared simply by casting stable aqueous mixed solutions. FTIR investigation indicated that hydrogen bonding existed between the interface of GO and PVA‐CNF. Scanning electron microscopy and X‐ray diffraction analysis showed that GO was uniformly dispersed in PVA‐CNF matrix. Introducing CNF into PVA caused a significant improvement in tensile strength, and further incorporating GO into PVA/CNF matrix led to a further increase. The tensile strength of the neat PVA film, PVA/CNF composite, and PVA/CNF/GO film (0.6 wt % GO) was 43, 69, and 80 MPa, respectively. Moreover, when incorporating 8 wt % CNF into PVA matrix, O₂ permeability and water absorption decreased from 13.36 to 11.66 cm³/m²/day and from 164.2% to 98.8%, respectively. Further adding 0.6 wt % GO into PVA/CNF matrix resulted in a further decrease of permeability and water absorption to 3.19 cm³/m²/day and 91.2%, respectively. Furthermore, for all composite samples, the transmittance of visible light was higher than 67% at 800 nm. CNF and GO‐reinforced PVA with high mechanical and barrier properties are potential candidates for packaging industry. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45345.     

Preparation of polyester resin/graphene oxide nanocomposite with improved mechanical strength

Graphene oxide (GO) has attracted huge scientific interest due to its unique physical and chemical properties as well as its wide‐scale applicability including facile synthesis and high yield. Here, we report preparation of nanocomposites based on GO and unsaturated polyester resin (PE). The synthesized samples were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, thermogravimetric analysis, and tensile strength measurements. A good dispersion of the GO sheets within the resin matrix was observed from the morphological analysis. A significant enhancement in mechanical properties of the PE/GO composites is obtained at low graphene loading. Around 76% improvement of tensile strength and 41% increase of Young's modulus of the composites are achieved at 3 wt % loading of GO. Thermal analysis of the composite showed a noticeable improvement in thermal stability in comparison to neat PE. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of surface modification of carbon nanofibers on the mechanical properties of polyamide 1212 composites

In this study, the effects of carbon nanofiber (CNF) surface modification on mechanical properties of polyamide 1212 (PA1212)/CNFs composites were investigated. CNFs grafted with ethylenediamine (CNF‐g‐EDA), and CNFs grafted with polyethyleneimine (CNF‐g‐PEI) were prepared and characterized. The mechanical properties of the PA1212/CNFs composites were reinforced efficiently with addition of 0.3 wt % modified CNFs after drawing. The reinforcing effect of the drawn composites was investigated in terms of interfacial interaction, crystal orientation, crystallization properties and so on. After the surface modification of CNFs, the interfacial adhesion and dispersion of CNFs in PA1212 matrix were improved, especially for CNF‐g‐PEI. The improved interfacial adhesion and dispersion of CNFs in PA1212 matrix was beneficial to reinforcement of the composites. Compared with pure PA1212, improved degree of crystal orientation in the PA1212/CNF‐g‐PEI (CNF‐g‐EDA) composites was responsible for reinforcement of mechanical properties after drawing. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41424.     

Surface modification of carbon nanofibers via deposition of an ultrathin coating of plasma‐polymerized poly(acrylic acid) and its effect on the properties of polyamide 6/CNF nanocomposites

Carbon nanofibers (CNFs) were coated with an ultrathin layer of poly(acrylic acid) (PAA) via plasma polymerization. The effect of the plasma reactor parameters on the extent of the CNF modification was studied. SEM micrographs showed that surface roughness increased with the plasma treatment. The thickness of the ultrathin PAA layer deposited on the CNF was determined by STEM to be ca. 8 nm. Untreated and treated CNF were melt‐mixed with polyamide 6 (PA6) in a Brabender mixing chamber to obtain PA6/CNF nanocomposites. The effect of the plasma treatment on the dispersion and compatibility was examined and found to improve markedly. Fractured tensile specimens showed that the CNF seemed to be completely embedded in the polymer matrix, indicating high compatibility between the PA6 and the PAA‐coated CNF. Tensile stress and tensile modulus of PA6 nanocomposites with treated CNF were found to increase by 30 and 48%, respectively, when compared with those with untreated CNF. However, the increase in tensile stress and modulus with respect to pure PA6 was 52 and 88%, respectively. Finally, XRD showed that the CNF induce the formation of the α (alpha)‐crystalline phase in PA6. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Processing and properties of polymer composites containing aligned functionalized carbon nanofibers

AC electric field was used to align functionalized carbon nanofibers (CNFs), carboxylic acid-functionalized CNFs (O-CNFs) and amine-functionalized CNFs (A-CNFs), in an epoxy resin. The resulting composites were characterized for dispersion and alignment structure as well as for their mechanical and electrical properties in the CNF alignment direction. Optical images of the composites revealed uniform distribution and alignment of the CNFs in the direction of the electric field. Due to the similarity in the alignment structure, it was observed that alignment of the functionalized CNFs was independent of the functional groups attached to the CNFs. Compression tests (parallel to the direction of the aligned A-CNFs) of A-CNF/epoxy composites showed an increase of 19% in compressive modulus and 9% in compressive strength at a CNF concentration of 4.5 wt.%, with respect to the neat composite. Electrical resistivity of composites measured parallel to the direction of aligned CNFs (containing up to 4.5 wt.% O-CNFs and A-CNFs) were found to be approximately three orders of magnitude lower than composites with non-aligned CNFs. The electrical resistivity percolation threshold for composites with aligned O-CNFs and A-CNFs occurred at approximately 0.75 wt.%. Discussion regarding the contribution of CNF type towards the mechanical and electrical properties is also presented.     

Preparation and characterization of polychloroprene nanocomposites with cellulose nanofibers from oil palm empty fruit bunches as a nanofiller

Cellulose nanofibers (CNFs) from oil palm empty fruit bunches were chemically modified by acetylation with acetic anhydride and pyridine (as the solvent and catalyst). The acetylated CNFs showed good dispersion in a polychloroprene (PCR) matrix. The tensile strength and modulus of neat PCR were improved, whereas its elongation at break decreased with increasing nanofiber content. Above the glass‐transition temperature (T_g), the dynamic mechanical analysis profiles showed that the storage modulus of the PCR–cellulose nanocomposites was higher than that of neat PCR. Meanwhile, the thermal stability was still maintained, and the T_g was close to the neat PCR at the 5 wt % addition level of CNFs. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40159.     

Fabrication of high strength PVA/SWCNT composite fibers by gel spinning

High-strength composite fibers were prepared from polyvinyl alcohol (PVA) (Degree of polymerization: 1500) reinforced by single-walled carbon nanotubes (SWCNTs) containing few defects. The SWCNTs were dispersed in a 10 wt.% PVA/dimethylsulfoxide solution using a mechanical homogenizer that reduced the size of SWCNT aggregations to smaller bundles. The macroscopically homogeneous dispersion was extruded into cold methanol to form fibers by gel spinning followed by a hot-drawing. The tensile strength of the well-oriented composite fibers with 0.3 wt.% SWCNTs was 2.2 GPa which is extremely high value among PVA composite fibers ever reported using a commercial grade PVA. The strength of neat PVA fibers prepared by the same procedure was 1.7 GPa. Structural analysis showed that the PVA component in the composite fibers possessed almost the same structure as that of neat PVA fibers. Hence a small amount of SWCNTs straightforward enhanced by 0.5 GPa the tensile strength of PVA fibers. The results of mechanical properties and Raman spectra for the SWCNT composites suggest the relatively good interfacial adhesion of the nanotubes and PVA that improves the load transfer from the polymer matrix to the reinforcing phase.     

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     

Thermal,morphological, and mechanical characterization of novel carbon nanofiber‐filled bismaleimide composites

Novel carbon nanofiber (CNF) ‐filled bismalemide composites were fabricated by a thermokinetic mixing method. The thermal and mechanical properties of composites containing 1 wt % and 2 wt % CNFs were investigated. Thermogravimetric analysis demonstrated that minimal improvement in thermal stability of the nanocomposites was obtained by the addition of CNFs. Dynamic mechanical analysis showed an increase in storage modulus (E′) and glass transition temperature (T_g) upon incorporation of nanofibers. Limiting oxygen index (LOI) has also been found to increase with incorporation of CNFs. Morphological studies of fractured surfaces of the composites has been carried out by scanning electron microscopy to determine the effect of fiber content and dispersion on the failure mechanism. In general, good dispersion was observed, along with agglomeration at some points and some fiber matrix interfacial debonding. A decrease in mechanical strength has been observed and debonding was found as the main failure mechanism. Further research outlook is also presented. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Poly(trimethylene terephthalate‐block‐tetramethylene oxide) elastomer/single‐walled carbon nanotubes nanocomposites: Synthesis,structure, and properties

Nanocomposites based on poly(trimethylene terephthalate)‐block‐poly(tetramethylene oxide) (PTT‐PTMO)‐segmented copolymer and COOH‐functionalized single‐walled carbon nanotubes (SWCNTs) were prepared by in situ polymerization method. The obtained nanocomposites were characterized by thermogravimetric analysis, scanning electron microscopy, differential scanning calorimetry (DSC), DMTA, wide‐angle x‐ray scattering (WAXS), small‐angle X‐ray scattering, and tensile testing. The nanocomposites with low SWCNTs loading (<0.5 wt %) shows uniform dispersion of CNT in polymer matrix. As the SWCNTs loading in the nanocomposites increase, the significant improvement of thermo‐oxidative stability was observed. It was found that the nanocomposites have slightly higher degree of crystallinity (determined by DSC and WAXS) of poly(trimethylene terephthalate) (PTT) hard phase than neat PTT‐PTMO copolymer. The melting point of PTT hard phase and glass transition temperature of poly(tetramethylene oxide)‐rich phase were not affected by the presence of CNTs in polymer matrix. The SWCNTs played a role as nucleating agent in PTT‐PTMO matrix, which led to increase in the crystallization rate. Tensile tests showed that the tensile strength of the nanocomposites with 0.05–0.3 wt % loading of SWCNTs have improved tensile strength in comparison to the neat PTT‐PTMO copolymer without reduction elongation at break. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Water‐based amorphous carbon nanotubes filled polymer nanocomposites

A novel method of making water‐based amorphous carbon nanotubes (ACNTs) for advanced polymer nanocomposites is presented. In this approach, sodium dodecyl sulfate (SDS) is introduced onto the amorphous carbon nanotubes to improve the solubility in water and the dispersion in polyvinyl alcohol [PVA] matrix. As a result, the addition of 0.6 wt % ACNTs in the polymer resulted in the significant improvement (167.5 and 175.8%) in the tensile strength and modulus of the polymer, respectively. The improved mechanical property could be ascribed to the load transfer to the nanotubes in the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

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     

Thermoplastic composites of polyamide‐12 reinforced by cellulose nanofibers with cationic surface modification

Cellulose nanofibers (CNFs) have many useful properties, including high strength and low thermal expansion, and are also environmentally friendly, readily renewable, safe, and biodegradable. The focus of this study was the development of lightweight thermoplastic polymer composites with good mechanical properties based on the incorporation of CNFs that have undergone surface pretreatment with a cationic reagent. The polyamide (PA12) was mixed with surface‐treated CNFs using a twin screw extruder and the resulting pellets were injection molded. The Izod impact strength without notch of CNF‐based composites exceeded that of composites incorporating organophilic montmorillonite (OMMT), a representative nanocomposite material. When the Izod impact test without notch, the impact hammer was stopped by the specimen with incorporation of surface treated CNF. Furthermore, the bending modulus and strength were equal to or greater than that of OMMT composites. The heat distortion temperature was improved as 33°C from neat PA12, and moreover improved as 29°C from OMMT composites. Cationic pretreatment of the CNF surfaces was found to increase the dispersion of the fibers and also to greatly improve the mechanical and thermal properties of the composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40920.     

Preparation and crystallization behavior of multiwalled carbon nanotubes/poly(vinyl alcohol) nanocomposites

The poly(vinyl alcohol) (PVA)‐based nanocomposites embedded with modified multiwalled carbon nanotubes (MWCNTs) were prepared. To enhance the interfacial interaction between MWCNTs and PVA, acid‐treated MWCNTs were grafted with PVA chains, compatibilizing MWCNTs and the matrix. The better dispersion of MWCNTs in PVA matrix was obtained by the introduction of MDI reaction bridges and then PVA molecules onto the surface of MWCNTs. Moreover, strong interaction between MWCNTs and PVA matrix was evidenced through the measurement results of the melting behavior, polarized Raman measurement, and nonisothermal crystallization behavior of the nanocomposites. Owing to the reinforcement of MWCNTs, the tensile strength and modulus of PVA nanocomposite containing 0.9 wt% MWCNTs were increased by 160.7 and 109.2%, respectively, compared to neat PVA. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

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.     

Synthesis and characterization of polyurethane/Mg‐Al layered double hydroxide nanocomposites

Layered double hydroxide (LDH) is a new type of nanofiller, which improves the physicochemical properties of the polymer matrix. In this study, 1, 3, 5, and 8 wt % of dodecyl sulfate‐intercalated LDH (DS‐LDH) has been used as nanofiller to prepare a series of thermoplastic polyurethane (PU) nanocomposites by solution intercalation method. PU/DS‐LDH composites so formed have been characterized by X‐ray diffraction and transmission electron microscopy analysis which show that the DS‐LDH layers are exfoliated at lower filler (1 and 3 wt %) loading followed by intercalation at higher filler (8 wt %) loading. Mechanical properties of the nanocomposite with 3 wt % of DS‐LDH content shows 67% improvement in tensile strength compared to pristine PU, which has been correlated in terms of fracture behavior of the nanocomposites using scanning electron microscope analysis. Thermogravimetric analysis shows that the thermal stability of the nanocomposite with 3 wt % DS‐LDH content is ≈ 29°C higher than neat PU. Limiting oxygen index of the nanocomposites is also improved from 19 to 23% in neat PU and PU/8 wt% DS‐LDH nanocomposites, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009