Electrical and thermal conductivity and tensile and flexural properties of carbon nanotube/polycarbonate resins

Adding conductive carbon fillers to insulating thermoplastic polymers increases the resulting composite's electrical conductivity. Carbon nanotubes (CNTs) are very effective at increasing composite electrical conductivity at low loading levels without compromising composite tensile and flexural properties. In this study, varying amounts (2–8 wt %) of CNTs were added to polycarbonate (PC) by melt compounding, and the resulting composites were tested for electrical conductivity (1/electrical resistivity), thermal conductivity, and tensile and flexural properties. The percolation threshold was less than 1.4 vol % CNT, likely because of CNTs high aspect ratio (1000). The addition of CNT to PC increased the composite electrical and thermal conductivity and tensile and flexural modulus. The 6 wt % (4.2 vol %) CNT in PC resin had a good combination of properties for electrical conductivity applications. The electrical resistivity and thermal conductivity were 18 Ω‐cm and 0.28 W/m · K, respectively. The tensile modulus, ultimate tensile strength (UTS), and strain at UTS were 2.7 GPa, 56 MPa, and 2.8%, respectively. The flexural modulus, ultimate flexural strength, and strain at ultimate flexural strength were 3.6 GPa, 125 MPa, and 5.5%, respectively. Ductile tensile behavior is noted in pure PC and in samples containing up to 6 wt % CNT. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of epoxy composites with high carbon nanotube loading and effects of tubular and wavy morphology on composite strength and modulus

Single-walled carbon nanotube (SWCNT)/epoxy composites with a high nanotube loading up to ∼39.1 wt% are fabricated by combining the mixed-curing-agent assisted layer-by-layer method and the hot press process. This combined method is an efficient and effective approach for making composite sheets in practical applications since the hot press process makes it possible and easy to readily prepare thick and large composites. The tensile and dynamic properties are greatly improved by the incorporation of SWCNTs. At ∼39.1 wt% SWCNTs, compared with those of the neat epoxy, the tensile strength and Young’s modulus are increased by 183% and 408%, respectively. The storage modulus is also significantly increased by 406% at room temperature due to this high loading of SWCNTs. Moreover, the loss factor in the temperature range −100-200 °C shows dramatic improvements by the introduction of high loading SWCNTs. Finally, analytical modeling is proposed to predict the strength and modulus of the CNT/epoxy composites by considering the effects of the tubular and wavy morphology of the CNTs. Both composite strength and composite modulus are found to decrease substantially with increasing waviness ratio. The predicted results show reasonable agreement with experimental data.     

Improvement in mechanical,electrical, and shape memory properties of the polystyrene-based carbon fiber-reinforced polymer composites containing carbon nanotubes

Carbon fiber-reinforced polymers based on polystyrene matrix containing elastomer and carbon nanotubes (CNTs) were produced by compression molding. The effects of carbon fabric (CF) concentration and silane treatment on the morphology, mechanical, electrical, and shape memory properties of the multilayer composites were investigated. The SEM analyses showed that fibers of the silane-treated CFs were more homogeneously covered with the polymer layers than the untreated CFs. The tensile strength and modulus of the composites increased by 521% and 125%, respectively, with an increasing number of CF plies from one to five. Upon silane treatment, the tensile strength of the multilayer composite improved by 26%, and the tensile modulus decreased by 18.4%. Electrical conductivities of the composites were in the semiconductor region due to the presence of both CNTs and CFs. 100% shape recovery less than a minute recovery time was obtained for all the composites with electrically triggered bending test.     

Evaluation of mechanical properties of untwisted carbon nanotube yarn for application to composite materials

Carbon nanotubes (CNTs) with superior mechanical properties have been of interest as reinforcement for polymer composites. However, the length of individual CNTs is limited. As a solution, yarns spun by twisting together multi-walled carbon nanotubes (MWCNTs) have been reported. In this study, untwisted CNT yarns were prepared by a non-conventional method drawing CNTs through a die. The MWCNTs in these yarns are held together by strong van der Waals forces that arise due to the interactions on the long and smooth surfaces of the MWCNTs. Here, mechanical properties of untwisted CNT yarn were studied by tensile tests. The strength of the CNT yarn was increased by increasing the apparent density of the yarn. The CNT yarns showed high tensile strength of 1 GPa and elastic modulus of 79 GPa at a yarn diameter of 35 μm. The interfacial shear strength between the CNT yarn and epoxy resin was studied by the microdroplet method, and it was very low. The wettability of the CNT yarn was affected by a type of curing agent. A unidirectional composite of epoxy resin and CNT yarn was prepared by the pultrusion molding method. Mechanical properties of the unidirectional composite were affected by the type of curing agent.     

Effect of CNT-coated carbon fibres in HDPE composites

The mechanical properties of thermoplastic HDPE composites filled with CF and CNT were studied. Coupling agent surface-treated CF-filled HDPE composites increased their tensile strength and impact strength, which is further increased with the addition of CNT. Coupling agent was proved to play an important role in the improvement of the interfacial adhesion of the CF/HDPE composite. SEM showed that CNT coating-treated CF/HDPE composites show better dispersion of the ?ller into the matrix.     

Raman microscopy of residual strains in carbon nanotube/epoxy composites

Carbon nanotube (CNT) strain variations with temperature, as measured with Raman microscopy, are reported for pristine and functionalized CNT/epoxy composites. The CNT strain is derived from the difference in frequencies of the CNT vibrational G⁺-mode in the composite and that of a relaxed CNT, and shown to serve as a measure of the local residual strains in the composites. The magnitudes of these strains vary with both CNT functionalization and CNT concentration. At room temperature and with the same local concentration of CNTs in the composite, the strains of oxidized and polyamidoamine-functionalized CNTs are found to be 2.5 times higher than that of the composite containing pristine CNTs. The higher residual strain of the composites loaded with functionalized CNTs reflects their better adhesion and integration in the polymer matrix. These findings are in accordance with the improved tensile properties measured for the functionalized CNT composites.     

Carbon nanotube/epoxy composites fabricated by resin transfer molding

Carbon nanotube (CNT)/epoxy composites with controllable alignment of CNTs were fabricated by a resin transfer molding process. CNTs with loading up to 16.5 wt.% were homogenously dispersed and highly aligned in the epoxy matrix. Both mechanical and electrical properties of the CNT/epoxy composites were dramatically improved with the addition of the CNTs. The Young’s modulus and tensile strength of the composites reach 20.4 GPa and 231.5 MPa, corresponding to 716% and 160% improvement compared to pure epoxy. The electrical conductivity of the composites along the direction of the CNT alignment reaches over 1 × 10⁴ S/m.     

Improved fracture toughness of carbon fiber composite functionalized with multi walled carbon nanotubes

Woven carbon fiber (CF) laminae are functionalized in situ with carbon nanotubes (CNTs) to test the hypothesis that growing CNTs on CF (i.e., carbon fiber bundles or tow) would enhance the properties of polymeric carbon composites, specifically epoxy–carbon composites that are used in aerospace applications. The CNT as-grown on the woven CF were shown to substantially improve the fracture toughness of the cured composite on the order of 50%. This was accompanied by no loss in structural stiffness of the final composite structure. In fact, the flexural modulus increased approximately 5%. The significant increase in the fracture toughness as tested under the ASTM D 5528 standard indicates that the damage tolerance of a composite structure would benefit from the CNT material applied in this way. Our approach has allowed for significantly larger samples to be uniformly functionalized with CNTs than is reported elsewhere in the open literature. In addition, this work demonstrated CNT functionalization on flexible substrates that remains flexible after functionalization, whereas most CNT growth substrates are rigid in order to withstand the high (>800 °C) growth temperatures often encountered in CNT synthesis.     

Thermal and ablative properties of binary carbon nanotube and nanodiamond reinforced carbon fibre epoxy matrix composites

The thermal and ablative properties of carbon nanotube (CNT) and nanodiamond (ND) reinforced carbon fibre epoxy matrix composites were investigated by simulating shear forces and high temperatures using oxyacetylene torch apparatus. Three types of composite specimens—(i) carbon fibre epoxy matrix composite (CF/Epoxy), (ii) carbon fibre epoxy matrix composite containing 0.1 wt-% CNTs and 0.1 wt-% NDs, and (iii) carbon fibre epoxy matrix composite containing 0.2 wt-% CNTs and 0.2 wt-% NDs—were explored. The ablative response of composites was studied through pre- and post-burnt SEM analysis and further related with thermogravimetric analysis, weight loss profile and thermal conductivity measurements. The novel nanofiller composites showed marked improvement in their thermal and ablative properties. A 22% and 30% increase in thermal conductivity was observed for composites containing 0.1 wt-% CNTs/0.1 wt-% NDs and 0.2 wt-% CNTs/0.2 wt-% NDs respectively. These nanofillers also improved the thermal stability of thermosetting epoxy matrix, and an increase of 13% and 20% was recorded in the erosion rate of composites containing 0.1 wt-% CNTs/0.1 wt-% NDs and 0.2 wt-% CNTs/0.2 wt-% NDs respectively. This improvement is due to the increased char yield produced by the increase in the loading of nanofillers, i.e. CNTs and NDs. Insulation index and insulation to density performance have also been improved due to increased thermal conductivity and char yield.     

Synergistic effect of graphene and carbon nanotube on lap shear strength and electrical conductivity of epoxy adhesives

In this study, synergy between graphene platelets (GnPs) and carbon nanotubes (CNTs) in improving lap shear strength and electrical conductivity of epoxy composite adhesives is demonstrated. Adding two-dimensional GnPs with one-dimensional CNTs into epoxy matrix helped to form global three-dimensional network of both GnPs and CNTs, which provide large contact surface area between the fillers and the matrix. This has been evidenced by comparing the mechanical properties and electrical conductivity of epoxy/GnP, epoxy/CNT, and epoxy/GnP-CNT composites. Scanning electron microscopic images of lap shear fracture surfaces of the composite adhesives showed that GnP-CNT hybrid nanofillers demonstrated better interaction to the epoxy matrix than individual GnP and CNT. The lap shear strength of epoxy/GnP-CNT composite adhesive was 89% higher than that of the neat epoxy adhesive, compared with only 44 and 30% increase in the case of epoxy/GnP and epoxy/CNT composite adhesives, respectively. Electrical percolation threshold of epoxy/GnP-CNT composite adhesive is recorded at 0.41 vol %, which is lower than epoxy/GnP composite adhesive (0.58 vol %) and epoxy/CNT composite adhesive (0.53 vol %), respectively. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48056.     

Effect of graphene and CNT reinforcement on mechanical and thermomechanical behavior of epoxy—A comparative study

Graphene‐nanoplateles (Gr) and multiwalled carbon nanotubes (CNTs) reinforced epoxy based composites were fabricated using ultrasonication, a strong tool for effective dispersion of Gr/CNTs in epoxy. The effect of individual addition of two different nanofillers (Gr and CNT) in epoxy matrix, for a range of nanofiller content (0.1–1 wt %), has been investigated in this study. This study compares mechanical and thermomechanical behavior of Gr and CNT reinforced epoxy. Gr reinforcement offers higher improvement in strength, Young's modulus, and hardness than CNT, at ≤0.2 wt %. However, mode‐I fracture toughness shows different trend. The maximum improvement in fracture toughness observed for epoxy‐Gr composite was 102% (with 0.3 wt % loading of Gr) and the same for epoxy‐CNT composite was 152% (with 0.5 wt % loading of CNT). Thorough microstructural studies are performed to evaluate dispersion, strengthening, and toughening mechanisms, active with different nanofillers. The results obtained from all the studies are thoroughly analyzed to comprehend the effect of nanofillers, individually, on the performance of the composites in structural applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46101.     

Carbon nanotube film/epoxy composites with high strength and toughness

A strong and tough carbon nanotube (CNT)/epoxy composite was fabricated by resin solution impregnation process based on floating catalyst chemical vapor deposition (CVD)–growth CNT films, which had a tensile strength and toughness of 405 MPa and 122 J/g, respectively, and good damping properties as well. Evolution of the composite structure revealed that the CNTs aligned along the tension direction with decreasing orientation angle, and the CNT bundle size enlarged during the tensile test process, which contributed to efficient load transfer among the composite network. Results showed that the proper resin content could bring benefit for strong connections and dense packing of CNTs/bundles, but excessive resin content was unfavorable for improving mechanical properties and conductivities of the nanocomposite. In addition, the resin in CNT film/epoxy composites had a lower crosslink density than that in a neat epoxy system, which endowed the CNT composites with large deformation capability. POLYM. COMPOS., 38:588–596, 2017. © 2015 Society of Plastics Engineers     

炭黑/煤矸石/碳纳米管复合填料体系对天然橡胶性能的影响研究*

利用硝酸氧化法对碳纳米管(CNTs)进行纯化,并用环氧天然橡胶(ENR)进行改性处理。结合胶质量分数测定结果表明, ENR用量15%(质量)时效果最佳。采用胶乳凝聚法制备CNTs/天然橡胶(NR)母料。煤矸石粉(CG)经高温煅烧和表面改性处理。 将CNTs/天然橡胶(NR)母料、CG和炭黑(CB)通过机械混炼法与天然橡胶及配合剂混合,制备CB/CG/CNTs/NR复合材料,并对复合材料进行硫化特性及物理机械性能。结果表明： CNTs延迟硫化效应明显;相比炭黑,CG对硫化具有促进作用。硫化特性和甲苯溶胀法测定结果表明,在填料份数相同的条件下,单独由CB填充的NR有最大的交联密度,CNTs对交联密度影响不明显。物理机械性能测试结果表明,当CG：CB：CNTs=17.5:16.5:1(Phr)时,NR硫化胶的300%定伸应力和扯断伸长率明显高于单独由CB填充NR,而拉伸强度与之接近,复合填料样填充NR具有较好的综合性能。扫描电镜测试结果表明,复合填料在NR基体中分布均匀。     

Using supercritical carbon dioxide in preparing carbon nanotube nanocomposite: Improved dispersion and mechanical properties

Improvements in carbon nanotube (CNT) dispersion and subsequent mechanical properties of CNT/poly(phenylsulfone) (PPSF) composites were obtained by applying the supercritical CO₂ (scCO₂)‐aided melt‐blending technique that has been used in our laboratory for nanoclay/polymer composite preparation. The preparation process relied on rapid expansion of the CNTs followed by melt blending using a single‐screw extruder. Scanning electronic microscopy results revealed that the CNTs exposed to scCO₂ at certain pressures, temperatures, exposure time, and depressurization rates have a more dispersed structure. Microscopy results showed improved CNT dispersion in the polymer matrix and more uniform networks formed with the use of scCO₂, which indicated that CO₂‐expanded CNTs are easier to disperse into the polymer matrix during the blending procedure. The CNT/PPSF composites prepared with scCO₂‐aided melt blending and conventional melt blending showed similar tensile strength and elongation at break. The Young's modulus of the composite prepared by means of conventional direct melt blending failed to increase beyond the addition of 1 wt% CNT, but the scCO₂‐aided melt‐blending method provided continuous improvements in Young's modulus up to the addition of 7 wt% CNT. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Effect of coal gangue/carbon black/multiwall carbon nanotubes hybrid fillers on the properties of natural rubber composites

The objective of this study was to investigate three kinds of filler with completely different morphology on mechanical properties of natural rubber (NR). Coal gangue (CG) are derived from natural deposits are composed principally by illite and quartz. CG, carbon black (CB), and multiwalled carbon nanotube (CNT) were used as hybrid fillers in NR. CNTs were dispersed into NR latex by ultrasonic irradiation and then the mixed latex were coagulated to obtain the CNTs/NR masterbatch, then mechanical mixing method was employed to prepare the CG/CB/CNTs/NR composites. The addition of CG, CB, and CNTs to NR was varied with the total filler loading fixed at 35 phr. The mechanical properties of NR composites were studied in terms of tensile and dynamic mechanical analysis (DMA). The results showed that the tensile strength and modulus 300% (M300) of all hybrid samples were higher than the composites only loaded CG; and the highest tensile strength of NR loaded with hybrid fillers achieved at sample of loading amount of CG 17.5, CB 15.5, and CNTs 2 phr, whose M300 and elongation at break was obviously higher than that of only CB loaded NR composites; The inclusion CG improves the tensile strength of NR without the sacrifice of its extensibility, while CB and CNTs brings together the enhancement in the ultimate strength and the reduction in the extensibility. DMA results revealed that the existence of CG can improve the dispersion of CB and CNTs in NR matrix. POLYM. COMPOS., 37:3083–3092, 2016. © 2015 Society of Plastics Engineers     

Direct measurement of grafting strength between an individual carbon nanotube and a carbon fiber

Hierarchical structures consisting of carbon nanotubes (CNTs) grafted onto a carbon fiber (CF) have the potential to improve the performance of fiber/polymer composites. The strength between a CNT and a CF is a key factor that influences the load-transfer behavior and inter-laminar properties. Here, we directly measured the grafting strength of a chemically bonded CNT–CF hierarchical structure by detaching individual CNT from the CF substrate and simultaneously recording the force–displacement characteristics in a scanning electron microscopy equipped with a nano-manipulator. We observed a relatively wide distribution of the maximum forces at complete detachment for different grafted CNTs, which ranges from below the van der Waals (vdW) force existing at the CNT–CF interface up to 7 times higher than that. For a typical configuration where a CNT is partially anchored on a CF, we obtained grafting strengths in the range of 5–90 MPa, which are dominated by the vdW force as well as other factors such as chemical bonding. Our results, based on the measurements at individual nanostructure level, might be useful for designing and fabrication of high performance hierarchical composites.     

Hotmelts with improved properties by integration of carbon nanotubes

With the aim of the development of conductive and mechanically improved adhesives, carbon nanotubes (CNTs) were dispersed by melt mixing into a non-reactive polyolefine based hotmelt adhesive. The composite materials, containing 0.5 to 5.0 wt% multi-walled CNTs (MWNTs), showed electrical percolation at about 0.75 wt%. Investigations of the mechanical properties using tensile tests resulted in a significant enhancement of Young's modulus up to 372% and nearly doubling of tensile strength at 5.0 wt%. Even if the hotmelt material is highly elastic compared to typical thermoplastic matrices, the melt mixing resulted in suitable CNT dispersion. The melt viscosity increased with CNT loading, however near the observed electrical percolation threshold the processability was not notably reduced. Most important, next to conductivity at low CNT loadings, also a significant enhancement in the shear strength of bonded joints of AlMg3 up to values of 250% of the pure hotmelt could be obtained. The property profile can be tailored with CNT concentration, indicating the suitability of CNT addition into these hotmelt adhesives.     

Continuous growth of carbon nanotubes on the surface of carbon fibers for enhanced electromagnetic wave absorption properties

As electromagnetic wave (EMW) pollution has become a serious problem in daily life, lightweight, efficient, and mass-produced EMW-absorbing materials are urgently needed. Herein, we developed a novel method for the continuous growth of carbon nanotubes (CNTs) on the surface of polyacrylonitrile (PAN)-based carbon fibers (CFs) by chemical vapor deposition (CVD), which can be applied to mass production. The obtained CF/CNT composites demonstrate outstanding EMW absorption capability, exhibiting a -58.75 dB reflection loss (RL) at a thickness of 1.54 mm. An effective absorption bandwidth (RL < -10 dB) of 4.24 GHz (13.76–18.00 GHz) was achieved at a thickness as low as 1.25 mm, which almost covers the entire Ku band. The excellent EMW-absorbing performance can be attributed to the 3D conductive network constructed by the CNT forest, which effectively promotes multiple reflections and scattering, and further favors dipole and interface polarizations. The mechanical properties of CF, CF-electrochemical anodic oxidation (EAO), and CF/CNT composites were examined, the results showed that the single-filament tensile strength of CF/CNT@0.07 and CF/CNT@0.09 was effectively improved. Our work suggests that the novel CF/CNT composite is a promising material for EMW absorption and strength enhancement owing to its light weight, high strength, low thickness, and good scale-up ability.     

Fabrication and properties of carbon nanotube/styrene–ethylene–butylene–styrene composites via a sequential process of (electrostatic adsorption aided dispersion)‐plus‐(melt mixing)

Carbon nanotube (CNT)/styrene–ethylene–butylene–styrene (SEBS) composites were prepared via a sequential process of (electrostatic adsorption assisted dispersion)‐plus‐(melt mixing). It was found that CNTs were uniformly embedded in SEBS matrix and a low percolation threshold was achieved at the CNT concentration of 0.186 vol %. According to thermal gravimetric analysis, the temperatures of 20% and 50% weight loss were improved from 316°C and 352°C of pure SEBS to 439°C and 463°C of the 3 wt % CNT/SEBS composites, respectively. Meanwhile, the tensile strength and elastic modulus were improved by about 75% and 181.2% from 24 and 1.6 MPa of pure SEBS to 42 and 4.5 MPa of the 3 wt % CNT/SEBS composite based on the tensile tests, respectively. Importantly, this simple and low‐cost method shows the potential for the preparation of CNT/polymer composite materials with enhanced electrical, mechanical properties, and thermal stability for industrial applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40227.     

Comparison of the effect of carbon,halloysite and titania nanotubes on the mechanical and thermal properties of LDPE based nanocomposite films

In this study, titania nanotubes(TNTs) were prepared by hydrothermal method with the aim to compare the properties of these one-dimensional tubular nanostructures' reinforced nanocomposites with the carbon and halloysite nanotubes'(CNTs and HNTs, respectively) reinforced nanocomposites. Low density polyethylene(LDPE) was used as the matrix material. The prepared nanocomposites were characterized and compared by means of their morphological, mechanical and thermal properties. SEM results showed enhanced interfacial interaction and better dispersion of TNTs and HNTs into LDPE with the incorporation of a MAPE compatibilizer,however, these interactions seem to be absent between CNTs and LDPE, and the CNTs remained agglomerated.Contact angle measurements revealed that CNT filled nanocomposites are more hydrophilic than HNT composites, and less than TNT composites. CNTs provided better tensile strength and Young's modulus than HNT and TNT nanocomposites, a 42% increase in tensile strength and Young's modulus is achieved compared to LDPE.Tear strength improvement was noticed in the TNT composites with a value of 35.4 N·mm~(-1), compared to CNT composites with a value of 25.5 N·mm~(-1)·s~(-1). All the prepared nanocomposites are more thermally stable than neat LDPE and the best improvement in thermal stability was observed for CNT reinforced nanocomposites.CNTs depicted the best improvement in tensile and thermal properties and the MAPE compatibilizer effectiveness regarding morphological. mechanical and thermal properties was only observed for TNT and HNT systems.