Electrical conductivity and mechanical properties of multiwalled carbon nanotube-reinforced polypropylene nanocomposites

In this paper, the electrical conductivity and mechanical properties such as elastic modulus of multiwalled carbon nanotubes (MWCNTs) reinforced polypropylene (PP) nanocomposites were investigated both experimentally and theoretically. MWCNT-PP nanocomposites samples were produced using injection mold at different injection velocities. The range of the CNT fillers is from 0 up to 12?wt%. The influence of the injection velocity and the volume fraction of CNTs on both electrical conductivity and mechanical properties of the nanocomposites were studied. The injection speed showed some effect on the electrical conductivity, but no significant influence on the mechanical properties such as elastic modulus and stress-strain relations of the composites under tensile loading. Parallel to the experimental investigation, for electrical conductivity, a percolation theory was applied to study the electrical conductivity of the nanocomposite system in terms of content of nanotubes. Both Kirkpatrick (Rev Mod Phys 45:574?C588, 1973) and McLachlan et?al. (J Polym Sci B 43:3273?C3287, 2005) models were used to determine the transition from low conductivity to high conductivity in which designates as percolation threshold. It was found that the percolation threshold of CNT/PP composites is close to 3.8?wt%. For mechanical properties of the system, several micromechanical models were applied to elucidate the elastic properties of the nanocomposites. The results indicate that the interphase between the CNT and the polymers plays an important role in determining the elastic modulus of the system.     

Dramatic mechanical and thermal increments of thermoplastic composites by multi-scale synergetic reinforcement: Carbon fiber and graphene nanoplatelet

We report an easy and efficient approach to the development of advanced thermoplastic composites based on multi-scale carbon fiber (CF) and graphene nanoplatelet (GN) reinforcement. Poly (arylene ether nitrile) (PEN)/CF/GN composites, prepared by the twin-screw extrusion, exhibited excellent mechanical properties. For example, the flexural modulus of PEN/CF/GN composites was 18.6 GPa, which is 1.7, 4.5 and 6.4 times larger than those of PEN/CF composites, PEN/GN composites and PEN host, respectively. Based on the SEM image observation, such mechanical enhancements can be attributed to the synergetic effect of micro-scale CF and nano-scale GN in the PEN matrix (decreased matrix-rich and free-volume regions and enhanced interfacial interactions). For 5 wt.% GN-filled PEN/CF/GN composites, the T_d30% of PEN/CF/GN composites was 145 °C and 62.8 °C compared with those of PEN host and PEN/CF composites, respectively. This study has demonstrated that multi-scale CF and GN have an obvious synergetic reinforcing effect on the mechanical properties and thermal stabilities of thermoplastic composites, which provides an easy and effective way to design and improve the properties of composite materials.     

A surfactant dispersed SWCNT-polystyrene composite characterized for electrical and mechanical properties

Single wall carbon nanotubes (SWCNTs) were dispersed in polystyrene (PS) at 0.1, 0.2, 0.3 and 1.0 wt.% (weight percent) concentrations using a surfactant assisted method. The resulting nanocomposites were characterized for their electrical conductivity, mechanical strength and fracture toughness properties. Results show a significant improvement in electrical conductivity with electrical percolation occurring by 0.2 wt.% SWCNT loading and the SWCNT-PS nanocomposite fully conductive at 1.0 wt.%. Three-point bend tests showed a decline in flexural strength and break strain with the addition of 0.1 wt.% SWCNTs. Improvements in the flexural modulus, strength and break strain with increasing SWCNT wt.% content followed The fracture toughness of the SWCNT-PS nanocomposites, in terms of the critical stress-intensity factor K_IC, was reduced relative to the neat material. From optical and high resolution scanning electron microscopy the presence of the carbon nanotubes is shown to have an adverse effect on the crazing mechanism in this PS material, resulting in a deterioration of the mechanical properties that depend on this mechanism.     

Unsaturated polyester nanocomposites filled with nano alumina

Alumina nanoparticles (60–70 nm) were prepared by the sol–gel technique using citric acid and aluminum nitrate. Casting technique was used to make nanocomposites of unsaturated polyester (UPR) and nano alumina. Transmission Electron Microscopy (TEM) study demonstrated that nano alumina particles were dispersed uniformly in the UPR matrix and agglomeration of particles was found at higher filler loading (>5 wt%). The nanocomposites show higher tensile, flexural and impact strength than pristine UPR. Scanning Electron Microscopy (SEM) of the fractured surface of tensile test samples show that the ductile fracture of UPR was converted to brittle fracture with the addition of nano alumina. Dynamic Mechanical Analysis (DMA) studies showed the storage modulus increased up to 5 wt% loading of nano alumina. The impact strength and storage modulus results agree well. The thermogravimetric studies revealed that the nanocomposites were having higher thermal stability than the pure UPR. As the concentration of the nano alumina in the UP resin increased, the char yield was also increased.     

Mechanical performance of epoxy matrix hybrid nanocomposites containing carbon nanotubes and nanodiamonds

A novel class of epoxy matrix hybrid nanocomposites has been developed containing multiwalled carbon nanotubes (MWCNTs) and nanodiamonds (NDs) to explore the combined effect of nanoreinforcements on the mechanical performance of nanocomposites. Both the nanofillers were functionalized before incorporating into epoxy matrix to promote interfacial interactions. The concentrations of both MWCNTs and NDs in the nanocomposites were increased systematically, i.e. 0.05 wt.%, 0.1 wt.% and 0.2 wt.% while composites containing individual nanoreinforcements were also manufactured for comparison. The developed nanocomposites were characterized microstructurally by scanning electron microscopy (SEM) and mechanically by tensile, flexural, impact and hardness tests. Homogeneous dispersion of MWCNTs and NDs was observed under SEM, which resulted in the enhancement of mechanical properties of nanocomposites. The composites containing 0.2 wt.% MWCNTs and 0.2 wt.% NDs showed 50% increase in hardness while tensile strength and modulus enhanced to 70% and 84%, respectively. Flexural strength and modulus also showed a rise of 104% and 56%, respectively. Interestingly, fracture strain also increased in both the tensile and flexural testing. The impact resistance increased to 161% showing a significant improvement in the toughness of hybrid nanocomposites.     

Facile preparation,characterization and performance of noncovalently functionalized graphene/epoxy nanocomposites with poly(sodium 4-styrenesulfonate)

Graphene was noncovalently functionalized with poly(sodium 4-styrenesulfonate) (PSS) and then successfully incorporated into the epoxy resin via in situ polymerization to form functional and structural nanocomposites. The morphology and structure of PSS modified graphene (PSS-g) were characterized with transmission electron microscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The effects of PSS-g additions on tensile, electrical and thermal properties of the epoxy/graphene nanocomposites were studied. Noncovalent functionalization improved interfacial bonding between the epoxy matrix and graphene, leading to enhanced tensile strength and modulus of resultant nanocomposites. The PSS-g additions also enhanced electrical properties of the epoxy/PSS-g nanocomposites, resulting in a lower percolation threshold of 1.2 wt%. Thermogravimetric and differential scanning calorimetric results showed the occurrence of a two-step decomposition process for the epoxy/PSS-g nanocomposites.     

Polyacrylonitrile/vapor grown carbon nanofiber composite films

Polyacrylonitrile (PAN)/vapor grown carbon nanofiber (VGCNF) composite films were processed from N, N-dimethylformamide (DMF) at various nanofiber loadings: 5, 10, 20, 40, 60, 80, and 90 wt%. Tensile, dynamic mechanical, electrical, structural, and morphological properties of these composite films were studied. Enhancement in tensile properties was observed in composites with nanofiber loading up to 40 wt%. The storage modulus of PAN increased upon incorporation of nanofiber particularly above the glass transition temperature. The tan δ peak broadens and shifts to higher temperatures with the addition of VGCNF. The activation energy for PAN molecular motion was higher than that in the control PAN film. The electrical conductivity of composite films increased with increasing nanofiber loading and exhibited a percolation at 3.1 vol%. Scanning electron microscopy (SEM) indicated PAN coated nanofibers in the composite film.     

Masterbatch-based multi-walled carbon nanotube filled polypropylene nanocomposites: Assessment of rheological and mechanical properties

Polypropylene (PP)/multi-wall carbon nanotubes (MWNTs) nanocomposites were prepared by diluting a PP/MWNT masterbatch by melt compounding with a twin screw extruder and prepared nanocomposites were characterized for their rheological, mechanical and morphological properties in terms of MWNT loading. The rheological results showed that the materials experience a fluid–solid transition at the composition of 2 wt.%, beyond which a continuous MWNT network forms throughout the matrix and in turn promotes the reinforcement. The tensile modulus and yield stress of the nanocomposites are substantially increased relative to the neat polypropylene. Nanotube reinforcement thus enhanced the yield stress, while reducing the ductility. The same behavior is observed in flexural tests. Charpy impact resistance of the notched samples increases slightly by the addition of MWNT, while impact resistance for the un-notched samples decreases with the addition of MWNTs. Finally, optimum in mechanical properties was observed at 2 wt.% MWNTs, which is near the rheological percolation threshold. From transmission electron microscopic (TEM) and scanning electron microscopy (SEM) images, it was observed that nanotubes are distributed reasonably uniformly indicating a good dispersion of nanotubes in the PP matrix. These results reveal that, preparation of nanocomposites from masterbatch dilution is an excellent method to obtain well-dispersed CNTs, while limiting the handling difficulties in plastics processing industrial workshops.     

Effect of nanoclays on physico-mechanical properties and adhesion of polyester-based polyurethane nanocomposites: structure–property correlations

Polyester–polyurethane nanocomposites based on unmodified and modified montmorillonite clays were compared in terms of their morphology, mechanical, thermal, and adhesive properties. Excellent dispersion of the modified nanoclay in polymer with 3 wt% loading was confirmed from X-ray diffraction, and low-, and high-magnification transmission electron micrographs. The properties of the clay-reinforced polyurethane nanocomposites were a function of nature and the content of clay in the matrix. The nanocomposite containing 3 wt% modified clay exhibits excellent improvement in tensile strength (by ~100%), thermal stability (20 °C higher), storage modulus at 25 °C (by ~135%), and adhesive properties (by ~300%) over the pristine polyurethane.     

Click coupled stitched graphene sheets and their polymer nanocomposites with enhanced photothermal and mechanical properties

The chemically stitched graphene oxide (GO) sheets were obtained using a click chemistry reaction between azide-functionalized GO and alkyne-functionalized GO. The click coupled GO (GO-click-GO) sheets showed the largely increased electrical conductivity and near infrared laser-induced photothermal properties compared to the GO sheets, which result from formation of triazole ring as a bridging linker between the GO sheets. The polyurethane (PU) nanocomposites incorporating the GO-click-GO sheets exhibited enhanced mechanical properties of breaking stress and modulus than the GO/PU nanocomposites. The modulus of GO-click-GO/PU nanocomposites was higher than that of the GO/PU nanocomposites at the same filler loading of 0.1 and 0.5 wt%. The GO-click-GO/PU nanocomposites also showed a significantly improved photothermal properties compared to the GO/PU nanocomposites at the same filler loading. The click coupled stitched GO sheets in this study can be used as the superior reinforcing fillers for mechanically and photothermally high performance polymer nanocomposites.     

Mode I interlaminar fracture behavior and mechanical properties of CFRPs with nanoclay-filled epoxy matrix

The mechanical properties and fracture behavior of nanocomposites and carbon fiber composites (CFRPs) containing organoclay in the epoxy matrix have been investigated. Morphological studies using TEM and XRD revealed that the clay particles within the epoxy resin were intercalated or orderly exfoliated. The organoclay brought about a significant improvement in flexural modulus, especially in the first few wt% of loading, and the improvement of flexural modulus was at the expense of a reduction in flexural strength. The quasi-static fracture toughness increased, whereas the impact fracture toughness dropped sharply with increasing the clay content.Flexural properties of CFRPs containing organoclay modified epoxy matrix generally followed the trend similar to the epoxy nanocomposite although the variation was much smaller for the CFRPs. Both the initiation and propagation values of mode I interlaminar fracture toughness of CFRP composites increased with increasing clay concentration. In particular, the propagation fracture toughness almost doubled with 7 wt% clay loading. A strong correlation was established between the fracture toughness of organoclay-modified epoxy matrix and the CFRP composite interlaminar fracture toughness.     

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.     

Influence of functionalization on properties of MWCNT-epoxy nanocomposites

The effects of various functionalized multi-walled carbon nanotubes (MWCNTs) on morphological, thermal, and mechanical properties of an epoxy based nanocomposite system were investigated. Chemical functionalization of MWCNT by oxidation (MWCNT-COOH) and direct-fluorination (MWCNT-F) were confirmed by FTIR, Raman spectroscopy, and TGA. Utilizing in situ polymerization, 1 wt% loading of MWCNT was used to prepare epoxy-based nanocomposites. Compared to the neat epoxy system, nanocomposites prepared with MWCNT-COOH showed 25.5% increase in ultimate flexural strength and 54.8% increase in flexural modulus. A decrease in strength was observed for the MWCNT-F nanocomposites. The premature degradation was attributed to a presumable catalyzation by hydrofluoric acid, HF, which evolved from the MWCNT-F during the curing process. However, only the MWCNT-F nanocomposites showed 22% increase in thermal properties (T_g). All nanophased systems showed increase in storage modulus.     

Cost-efficient high performance polyetheretherketone/expanded graphite nanocomposites with high conductivity for EMI shielding application

The cost efficient expanded graphite (EG) filled polyetheretherketone (PEEK) nanocomposites were prepared by hot pressing, which exhibited an electrical conductivity percolation threshold of 1.5 wt%. The electrical conductivity of the 1.5 wt% nanocomposite increased approximately eleven orders of magnitude than that of pure PEEK. The conductivities of 5 wt% and 10 wt% nanocomposites were increased to about 3.24 S cm⁻¹ and 12.3 S cm⁻¹, respectively. Scanning electron microscope showed 3-dimensional conductive network of EG across the PEEK matrix. The significant increase in electrical conductivity of the nanocomposites leads to the tremendous increase in electromagnetic interference shielding effectiveness.     

The physical properties of polyurethane/graphite nanosheets/carbon black foaming conducting nanocomposites

Using polyester polyol and diphenylmethane diisocyanate (MDI) as basic component, and using graphite nanosheets (GN) and carbon black (CB) as conductive filler, polyurethane/graphite nanosheets/carbon black foaming conducting nanocomposites have been prepared by filling mold curing reaction. The morphology, electrical properties and mechanical properties of the prepared PU/GN foams have been investigated. It showed that the percolation threshold effect of PU/GN composite occurred at the content around 12 wt.% of the GN, which was lower than that of carbon black (CB) composite. Besides, PU/GN foams showed much better conductive properties and mechanical properties than that of CB system.     

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

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

Preparation and properties of polyarylene ether nitrites/multi-walled carbon nanotubes composites

Polyarylene ether nitriles (PEN)/multi-walled carbon nanotube (MWNT) composites have been successfully fabricated via PEN solution mixing MWNT and then solution-casting. The cast nanocomposite films were characterized by SEM, thermal properties and mechanical properties. The Young's modulus of PEN/MWNT composites was greatly increased with the increase of MWNT concentration. The crystalline behaviors of nanocomposites increased with the increase of MWNT concentration. Thermogravimetric analysis (TGA) measurement showed that MWNT could stabilize PEN when its weight content was greater than 2.0%, and a high char yield in N₂ could be obtained for PEN/MWNT composite at 600 °C.     

Scavenging phenomenon and improved electrical and mechanical properties of polyaniline–divinylbenzene composite in presence of MWCNT

A semi-doped polyaniline (PANI)–dodecylbenzenesulfonic acid (DBSA) complex is added with a suspension of multiwall carbon nanotubes (MWCNT)–divinylbenzene (DVB) to prepare PANI–MWCNT based thermosetting conductive resin system. Firstly, unreinforced nanocomposites with various loading of MWCNT are prepared. Continuous improvement in the electrical conductivity is observed with increasing MWCNT loading in the composite, while improvement in the mechanical properties is observed only up to 0.2 wt% MWCNT loading. On further MWCNT loading, the decrease in mechanical properties is observed. Flexural strength increased by 18% with 0.2 wt% of MWCNT in the unreinforced nanocomposite while electrical conductivity increased continuously to 0.68 S/cm (at 0.5 wt% of MWCNT loading) from 0.25 S/cm (neat sample). DSC and TGA analysis show that MWCNT effectively contributed to enhance the scavenging effect of PANI, affecting degree of DVB polymerization at higher loading of MWCNT. Samples were characterized by FTIR analysis. DMA analysis is also performed to understand the mechanical behavior of the cured unreinforced nanocomposite under dynamic loading. SEM observation has been employed to understand the dispersion behavior of MWCNT into the matrix. PANI-wrapping behavior on MWCNT is observed from the SEM images. Wrapping of PANI on MWCNT increased doping state and surface area of PANI which subsequently contribute to the increased scavenging behavior of PANI at higher MWCNT loading. A structural thermosetting nanocomposite with electrical conductivity of 0.68 S/cm, flexural modulus of 1.87 GPa and flexural strength up to 35 MPa is prepared. In addition, PANI–DBSA/DVB matrix with MWCNT is also used to impregnate carbon fabrics to prepare highly conductive CFRPs. A CFRP with 1.67 S/cm electrical conductivity in through-thickness direction and 328 MPa flexural strength is obtained with the addition of 0.2 wt% MWCNT into the resin system.     

Morphological,thermal, rheological,and mechanical properties of polypropylene-nanoclay composites prepared from masterbatch in a twin screw extruder

A commercial homopolymer polypropylene was melt blended with commercial nanoclay masterbatch at different concentrations of nanoclay using twin screw extruder (TSE). The influence of three different concentrations (5, 10, and 15 wt%) of the nanoclay on the morphological, thermal, rheological, and mechanical properties was investigated. The morphology of the nanocomposites was characterized using Scanning Electron Microscope (SEM), whereas, the thermal behavior (e.g., melting and crystallization) was characterized using Differential Scanning Calorimetry (DSC). The melt rheology and dynamic mechanical properties were analyzed using a torsional rheometer. Additionally, the tensile properties were characterized as well. The morphological analysis showed that the nanoclay was well distributed in the PP matrix as indicated by the SEM micrographs. The DSC results showed that the presence of nanoclay in the PP matrix increased the degree of crystallinity of PP-nanoclay composites, which reached a maximum at 5 wt% of nanoclay concentration. However, the melting temperature of the PP-nanoclay composites was not affected by the presence of nanoclay particles. In addition, rheological analysis showed that the melt response gradually changed from pseudo-liquid like to pseudo-solid like as the nanoclay concentration increased. Moreover, the storage modulus (G′) increased by increasing nanoclay content. Furthermore, tensile test results showed that the addition of nanoclay leads to a significant enhancement in the mechanical properties of the PP nanocomposites.     

Effect of chemical functionalization of multi-walled carbon nanotubes with 3-aminopropyltriethoxysilane on mechanical and morphological properties of epoxy nanocomposites

Nanocomposites based on epoxy resin and different weight percentages of unmodified, oxidized, and silanized multi-walled carbon nanotubes (MWCNTs) were prepared by cast molding method. Effects of MWCNTs content on the flexural properties were examined. The results showed that as the loading of the MWCNTs increased, improved flexural strength and flexural modulus were observed. The mechanical properties decreased when the MWCNTs content exceeded 0.2 wt.% due to agglomeration of MWCNTs. These results prove the effect of functionalization on the interfacial adhesion between epoxy and MWCNTs. This was further confirmed by morphology study of fractured surfaces of nanocomposites by SEM and TEM.