Resistivity and PTC behaviour of electro-conductive PVOH/MWNT and EVOH/MWNT nanocomposites

Electro-conductive poly(vinyl alcohol)/multi-walled carbon nanotube (PVOH/MWNT) and poly(ethylene-co-vinyl alcohol) (EVOH)/MWNT nanocomposites were prepared by precipitation saponification method. The MWNT was functionalised by electron beam irradiation in air at 1200?kGy doses. The electrical resistivity, thermal and mechanical properties, and positive temperature coefficient (PTC) behaviour of these nanocomposites were investigated. The melting and crystallisation peak temperatures of both nanocomposite systems were shifted at a higher temperature with the increase in saponification time. Their crystallinity and mechanical strength also increased with saponification time, indicating an increase in intermolecular hydrogen bond between vinyl alcohol groups. With the saponification time, PTC peak temperature of EVA28/MWNT and EVA40/MWNT nanocomposites was shifted at a higher temperature and followed by a negative temperature coefficient (NTC) of resistivity. However, the saponified PVAc/MWNT nanocomposites showed only NTC behaviour over a temperature range of 30–140°C.     

Surface resistivity and rheological behaviors of carboxylated Multiwall carbon nanotube‐filled PET composite film

Multiwalled carbon nanotube (MWNT) nanocomposites with poly(ethylene terephthalate) (PET) were prepared via in situ polymerization. The refluxing time was more important factor than the sonication time for giving carboxylic groups onto the surface of MWNT. Acid‐MWNT prepared was well dispersed in ethylene glycol, whereas the neat‐MWNT agglomerated and sedimented at the bottom. The viscosity of the composites increased with the addition of MWNT, but PET/acid‐MWNT composite showed lower viscosity than PET/neat‐MWNT because of the damage of MWNT by acid treatment and copolymerization effect by the reaction between carboxylic groups of MWNT and PET. PET/acid‐MWNT composite film showed lower surface resistivity than PET/neat‐MWNT composite film. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 900–904, 2006     

Improvement of electrical conductivity with phase‐separation in polyolefin/multiwall carbon nanotube/polyethylene oxide composites

Electrical conductivity developments of polypropylene (PP)/multiwall carbon nanotube (MWNT) and polybutene (PB)/MWNT composites were carried out with polyethylene oxide (PEO) phase‐separation behavior for the polymeric materials. The low conductivity (8.47 × 10^?8 S cm^?1) of PP(98%)/MWNT (2%) was drastically increased up to 1.56 × 10^?3 S cm^?1 by only 2% PEO(96%)/MWNT(4%) loading. The drastic improvement originated from the formation of an electrical connector structure with the PEO/MWNT domain. The PB(93%)/MWNT(7%) conductivity was also improved by the PEO(92%)/MWNT(8%) loading although the conductivity improvement effect was lower than that of the PP/MWNT. The Raman spectra showed that the MWNT dispersity in the PB was poorer than that in the PP, resulting in the formation of a PEO/MWNT connector structure only at higher loading. In addition, a PEO/carbon black composite was able to produce the connector structure for the PP/MWNT as well as the PEO/MWNT. These results indicated that the highly conductive composites could be produced with smaller MWNT amounts. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and properties of multiwalled carbon nanotube/polycaprolactone nanocomposites

Multiwalled carbon nanotube/polycaprolactone nanocomposites (MWNT/PCL) were prepared by in situ polymerization, whereby as‐received MWNTs (P‐MWNTs) and purified MWNTs (A‐MWNTs) were used as reinforcing materials. The A‐MWNTs were purified by nitric acid treatment, which introduced the carboxyl groups (COOH) on the MWNT. The micrographs of the fractured surfaces of the nanocomposites showed that the A‐MWNTs in A‐MWNT/PCL were better dispersed than P‐MWNTs in PCL matrix (P‐MWNT/PCL). Percolation thresholds of the P‐MWNT/PCL and A‐MWNT/PCL, which were studied by rheological properties, were found at ～2 wt % of the MWNT. The conductivity of the P‐MWNT/PCL was between 10^?1 and 10^?2 S/cm by loading of 2 wt % of MWNT although that of the A‐MWNT/PCL reached ～10^?2 S/cm by loading of 7 wt % of MWNT. The conductivity of the P‐MWNT/PCL was higher than that of the A‐MWNT/PCL at the entire range of the studied MWNT loading, which might be due to the destruction of π‐network of the MWNT by acid treatment, although the A‐MWNT/PCL was better dispersed than the P‐MWNT/PCL. The amount of the MWNT at which the conductivity of the nanocomposite started to increase was strongly correlated with the percolation threshold. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1957–1963, 2007     

Rheological and electrical properties of polycarbonate/multi-walled carbon nanotube composites

Rheological and electrical properties of the polycarbonate (PC)/multi-walled carbon nanotube (MWNT) were studied. The MWNT was funtoinalized by treating with the hydrogen peroxide (H₂O₂). The H₂O₂ treated MWNT was dried by thermal and freeze drying methods. From the morphological studies, the degree of entanglement of the MWNT was decreased after treating with the H₂O₂. For the H₂O₂ treated MWNT (thermal drying), the length of the MWNT was shortened compared that of the H₂O₂ treated MWNT (freeze drying). The rheological and electrical properties of the PC/MWNT (H₂O₂ treated) composites increased compared that of the PC/MWNT (untreated) composites. Also, the electrical conductivity showed higher value for the PC/MWNT (H₂O₂ treated, freeze drying) composites compared that of the PC/MWNT (H₂O₂ treated, thermal drying) composites. From the results of the morphological, rheological, and electrical properties of the PC/MWNT composites, it is suggested that the electrical and rheological properties of the PC/MWNT composites are affected by the MWNT-MWNT network structure, which is related with the MWNT morphologies such as the degree of aggregation and aspect ratio of the MWNT.     

Dynamic mechanical and morphological properties of polycarbonate/multi-walled carbon nanotube composites

Dynamic mechanical and morphological properties of the polycarbonate (PC)/multi-walled carbon nanotube (MWNT) composites were studied by dynamic mechanical thermal analysis (DMTA) and X-ray diffractometry, respectively. For the without annealed PC/MWNT composites containing the higher content of the MWNT (≥7.0 wt%), double tan δ peaks were observed, which could be explained by the phase separation morphology model. For the annealed PC/MWNT composites, a broad single tan δ peak was observed. From the X-ray diffraction of the annealed PC/MWNT composites, it was observed that more regular structure of the PC was obtained, which was consistent with the result of the thermal analysis of the annealed PC/MWNT composites. From the dynamic mechanical properties, thermal analysis, and X-ray diffraction of the annealed PC/MWNT composites, it is suggested that PC/MWNT composites show a broad single tan δ peak and partially crystalline structure of the PC in the PC/MWNT composites by annealing.     

Amino functionalization and characteristics of multi-walled carbon nanotube/poly(methyl methacrylate) nanocomposite

To enhance adsorption of multi-walled carbon nanotube (MWNT) onto poly(methyl methacrylate) (PMMA) main chains, amino-functional modification was applied to the MWNT via chemical modification using thionyl chloride and hexamethylene diamine. Experimental results indicate that the amino-functionalized MWNT was covalently bonded to the PMMA. An uneven layer of the PMMA film was present on the MWNT surface, compared with smooth surface of pristine MWNT. Strong absorbance at 1570 cm^? 1 from FT-IR spectra for both MWNT-NH₂ and PMMA-g-MWNT was observed due to amino group, confirming further PMMA grafting onto the MWNT. Rheological characteristics of the MWNT/PMMA nanocomposite were also examined.     

表面活性剂对碳纳米管在水性体系中分散效果的影响

碳纳米管/水泥基复合材料(MWNT/CC)是一种新型功能材料,而MWNT在水中的分散性直接影响后续制备MWNT/CC的性能。以聚丙烯酸(PAA)、十六烷基三甲基溴化铵(C16TAB)、Triton x100(Tx)3种表面活性剂(SAA)单独或混合作为MWNT的分散剂,探讨了MWNT在水性体系中的分散性及其对Tx的吸附性。采用SAA超声分散法制备了14种MWNT分散液;用浇注成型法使MWNT与水泥复合。结合肉眼观察、TEM&SEM观察及电阻测试来评价MWNT在分散相液、水化产物中的分散性。V(Tx)∶V(PAA)=1∶3时,对MWNT分散效果最好,MWNT/CC的电阻值最低,离散性最小(105.76±5.06 kΩ);TEM及SEM观测表明,MWNT已较好地分散于基体中,两者界面结合紧密。FTIR分析表明,经酸氧化后的MWNT(AT-MWNT)表面带有许多MWNT所没有的亲水团。分光光度计测试得到MWNT和AT-MWNT对不同SAA溶液中Tx的吸附量:AT-MWNT对Tx吸附量达3.69mmol/g,明显比MWNT的2.14 mmol/g多;而PAA或C16TAB的加入使AT-MWNT对Tx吸附量分别降至1.55、1.60mmol/g。     

Effect of ultrasonic irradiation on the microstructure and the electric property of PP/CPP/MWNT composites

Poly(propylene) (PP)/chlorinated PP (CPP)/multiwalled carbon nanotube (MWNT) composites are prepared via melting blend with a MWNT masterbatch obtained by a solution process under ultrasonic irradiation. The effects of ultrasonic irradiation on the microstructure and the electric properties of the PP/CPP/MWNT composites are systematically investigated through a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), wide‐angle X‐ray diffraction (WAXD), and rheological measurements. Ultrasonic irradiation can remarkably decrease the volume resistivity of the PP/CPP/MWNT composites. The results of SEM and TEM show that the ultrasonic irradiation is beneficial to the dispersion of MWNTs in the PP/CPP/MWNT composites and the exfoliation of the MWNT agglomerates. When the MWNT content is more than 3.0%, ultrasonic irradiation can evidently increase the percent crystallinity of the PP/CPP/MWNT composites. The introduction of ultrasonic irradiation can increase the elastic modulus (G′), viscous modulus (G″), and complex viscosity (η*) of the PP/CPP/MWNT composites at low frequency. Ultrasonic irradiation is also shown to improve the interfacial adhesion of MWNT and the interaction between the PP matrix and MWNT. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A relationship between electrical conductivity and photodegradation in styrene-butadiene copolymer/multi-wall carbon nanotube composite

An effect of photodegradation on electrical conductivity of a styrene-butadiene copolymer (SBR)/multiwall carbon nanotube (MWNT) composite was studied with a TiO₂/polyethylene oxide/methyl linoleate paint photocatalyst under UV and/or visible light irradiation. An oxidative etching of impurities on the MWNT surface was caused by the UV or visible light irradiation, leading to an increase of quality of MWNT. On the other hand, the photocatalyst addition caused the degradation of MWNT structure. A relationship between the electrical conductivity and MWNT content showed that the MWNT dispersity in a SBR was superior to that in a polystyrene (PS). In addition, the PS addition to SBR matrix caused MWNT aggregation. The electrical conductivity decrease of the MWNT composite was due to electrical percolation structure loss caused by the photocatalyst under the visible light irradiation, and its rate depended on the MWNT dispersity. The PS molecular weight change behavior with the photocatalyst was consistent with the electrical conductivity one of the SBR/MWNT. The photocatalyst ability was estimated from the electrical conductivity of the SBR/MWNT.     

Low percolation thresholds of electrical conductivity and rheology in poly(ethylene terephthalate) through the networks of multi-walled carbon nanotubes

Coagulation method was first used to prepare nanocomposites of multi-wall carbon nanotubes (MWNT) and poly(ethylene terephthalate) (PET). The morphology of nanocomposites is characterized using transmission electronic microscopy and scanning electronic microscopy. A coating on MWNT by PET chains is observed by comparison of micrographs of purified MWNT and MWNT encapsulated by PET chains in the nanocomposites, and this coating is considered as evidence of interfacial interaction between MWNT and PET chains. Both electrical conductivity and rheological properties have been well characterized. With increasing MWNT loading, the nanocomposites undergo transition from electrically insulative to conductive at room temperature, while the melts show transition from liquid-like to solid-like viscoelasticity. The percolation threshold of 0.6 wt% (based on viscosity) for rheological property and 0.9 wt% for electrical conductivity has been found. The low percolation threshold results from homogeneous dispersion of MWNT in PET matrix and high aspect ratio of MWNT. The less rheological percolation threshold than electrical percolation threshold is mainly attributed to the fact that a denser MWNT network is required for electrical conductivity, while a less dense MWNT network sufficiently impedes PET chain mobility related to the rheological percolation threshold.     

Temperature dependence of oxygen diffusion into polymer/carbon nanotube composite films

This study examines the transport properties of polystyrene (PS)/multiwalled carbon nanotube (MWNT) composite films taking into consideration both MWNT composition and temperature, via fluorescence technique. Three different (3, 15, and 40 wt%) MWNT content films were prepared from PS/MWNT mixtures by annealing them at 170°C, above the glass transition temperature of PS for 10 min. The diffusivity of the PS/MWNT composite was determined by performing oxygen (O₂) diffusion measurements within a temperature range of 24 to 70°C for each film and pyrene (P) was used as the fluorescent probe. The diffusion coefficients (D) of oxygen were determined by the fluorescence quenching method assuming Fickian transport. Results indicated that D values are strongly dependent on both temperature and the MWNT content in the film and it was also observed that D coefficients obey Arrhenius behavior, from which diffusion energies were produced and increased along with increases of MWNT content. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Processing and properties of MWNT/HDPE composites

Multi-walled carbon nanotube (MWNT) composites were fabricated using the screw extrusion and injection technique. The polymer-wrapped MWNTs were dispersed in fumed silicon dioxide with the help of ultrasonic stirring, and then further dispersed in a high density polyethylene (HDPE) matrix by a twin-screw extruder. It was found that there was a critical MWNT concentration around 1.0 wt% where a fine network of MWNT/SiO₂ was formed. This gives the MWNT/HDPE composites much improved mechanical properties. From the mechanical property, it was found that the surface treatment of MWNT/SiO₂ had a large effect on the performance of the composites. Thermogravimetric analysis (TGA) measurement showed that MWNT could stabilize HDPE when its weight content was greater than 2.0 wt%, whereas silicon dioxide accelerated thermo-oxidation of the composites.     

碳纳米管填充PDMS膜的渗透汽化性能

将碳纳米管（CNTs）填充到PDMS中制备出CNTs/PDMS杂化膜,并将其用于乙醇/水体系的分离,发现由多壁碳纳米管制备的膜分离性能优于单壁碳纳米管填充膜,在40℃下,进料乙醇浓度为5%（质量分数）时,膜的分离因子可由8.3提高到10.0,渗透通量为206.2 g·（m²·h）^-1;采用十二烷基三氯硅烷对多壁碳纳米管进行修饰,并对修饰前后碳纳米管的性能进行表征,研究表明修饰后碳纳米管表面形成疏水层,碳纳米管的疏水性增强;将修饰后的碳纳米管填充到PDMS中,可进一步提高杂化膜对乙醇的选择性,膜的分离因子可提高到11.3,渗透通量为130.9 g·（m²·h）^-1。     

Mechanical and electrical multifunctional poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)—multiwall carbon nanotube nanocomposites

In this work, nanocomposites of poly(hydroxybutyrate‐co‐hydroxyvalerate) PHBV and multiwalled carbon nanotubes (MWNT) were prepared by melt blending. Mechanical, thermal, morphological, and electrical properties of the prepared PHBV/MWNT nanocomposites were investigated. Differential scanning calorimetry (DSC) and X‐ray diffraction (XRD) results showed MWNT effectively enhanced the crystallization and nucleation of PHBV. Dynamic thermo‐mechanical and static uniaxial mechanical tensile and compressive properties were increased by the addition of MWNT. MWNT observed in the nanocomposites using transmission electron microscopy (TEM) showed dimensions similar to separated nanotubes inferring a good dispersion. The presence of nanotubes in close vicinity with each other formed an interconnecting network that led to the formation of electrically conductive nanocomposites. The electrical resistance of the nanocomposites was reduced with the addition of MWNT. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Microstructure and Multiwall Carbon Nanotube Partitioning in Polycarbonate/Acrylonitrile-Butadiene-Styrene/Multiwall Carbon Nanotube Nanocomposites

The multiwall carbon nanotube (MWNT) partitioning and its impact on morphology and electrical properties of Polycarbonate (PC)/Acrylonitrile-Butadiene-Styrene (ABS)/MWNT nanocomposites were studied. The rheological and TEM results indicated that the MWNT partitioning and state of dispersion of MWNT were determined by the affinity between MWNT and the blend components and MWNT concentration. In the PC/ABS (70/30: w/w)/2 wt.% MWNT sample the MWNTs were preferentially located in the ABS droplets and the interface due to the greater affinity between MWNT and ABS compared with PC. In the PC/ABS (30/70: w/w)/MWNT samples, however the MWNTs were mostly located in the ABS matrix.     

Effect of interfacial chemistry on crystallization of polypropylene/multiwall carbon nanotube nanocomposites

This study systematically investigates the polymer–carbon nanotube (CNT) interaction when the interphase is tailored. Maleic anhydride‐grafted‐polypropylene (MA‐g‐PP) or polypropylene (PP) was noncovalently coated onto acid functionalized multiwall nanotube (f‐MWNT) through solution mixing. These coated f‐MWNTs were melt microcompounded with neat PP to form PP/f‐MWNT nanocomposites. The effects of functional groups and the thin layer of solution processed polymers, namely, MA‐g‐PP or PP, at the PP/f‐MWNT interface on crystallization and on melting behavior of matrix PP were investigated. The results were compared with a pristine MWNT (p‐MWNT) incorporated system. It was shown that PP coated CNTs can serve as a strong nucleating agent for templated polymer crystal growth. Unlike other PP nanocomposites in the literature, a relatively high shift of 7°C in melting peak maximum (T_p), along with a sharp melt endotherm was achieved with the addition of 0.3 wt% f‐MWNT via PP/f‐MWNT master batch. This indicates refinement of matrix PP crystalline region due to the tailored f‐MWNT surface chemistry. With a designed self‐seeding and templated crystal growth approach, columnar crystalline interphases were found surrounding MWNT which melted at 10.5°C higher temperature than neat PP crystallized without undergoing the same heat treatment protocol. POLYM. ENG. SCI., 59:1570–1584 2019. © 2019 Society of Plastics Engineers     

Free‐standing aniline oligomer functionalized multiwalled carbon nanotube films from a filtration method

High electrochemical active free‐standing multiwalled carbon nanotube (MWNT) films have been synthesized from aniline oligomer functionalized MWNTs (MWNT‐AO), by using filtration of the acidic phosphate ester (APE) doped MWNT‐AO dispersions. The homogeneously distributed MWNTs endowed APE/MWNT films automatically releasing from the filter membrane. The sheet resistivity of MWNT‐AO (850 Ω sq^?1) showed a lower value than that of carboxyl MWNTs (1273 Ω sq^?1), due to the doping effect of MWNT on aniline oligomer, confirmed by the N1s X‐ray photoelectron spectrum. However, it showed a higher sheet resistivity value of 1526 Ω sq^?1 after further doped by APE, because of the presence of unreacted dopant. After removing the residual insulating dopant by the vacuum filtration, the resultant APE/MWNT films showed the sheet resistivity value as low as 131 Ω sq^?1. Thermogravimetric analysis showed that the MWNT loading in the film can be over than 77%, which showed the specific capacitance as high as 249 F g^?1. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40259.     

Development and characterization of solid and porous polylactide‐multiwall carbon nanotube composites

This article describes the fabrication of solid and porous polylactide (PLA)‐multiwall carbon nanotube (MWNT) composites prepared using melt blending and subsequent batch processing of porous structures. The morphology and thermal, rheological and electrical properties of the PLA‐MWNT composites prepared with MWNT concentrations of 0, 0.5, 1, 2, and 5 wt% were characterized. The composite structure consisted of identifiable regions of MWNT aggregation and MWNT dispersion. Increasing MWNT content was found to increase the thermal stability and crystallization kinetics of PLA. The addition of MWNT to PLA significantly increased the melt viscosity and electrical conductivity of the composites. Based on rheological and electrical measurements, a continuous MWNT network structure in PLA was found to form when the concentration of MWNT is increased from 0.5 wt% (0.33 vol%) to 1 wt% (0.66 vol%). As many current day applications of polymers and polymer composites require lightweight and low‐density materials, porous PLA‐MWNT composites were fabricated from a batch porous structure processing technique. Porous PLA‐MWNT composites containing 2 and 5 wt% MWNT had lower relative densities, which is attributed to the higher viscosity of the composites suppressing collapse of the porous structure during processing. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Dispersion of multiwall carbon nanotubes in blends of polypropylene and acrylonitrile butadiene styrene

State of dispersion of purified multiwall carbon nanotubes (p‐MWNT) in the presence of neutralized MWNT (n‐MWNT) in aqueous solution was assessed through UV–Visible spectroscopy, dynamic light scattering measurements, and solution experiments. Raman spectroscopic analysis revealed that debundling of p‐MWNT in the presence of n‐MWNT in aqueous solution was persistent even in the solid mixture, which was supported by transmission electron microscopic analysis. The proposed mechanism behind the improved dispersion of p‐MWNT in the presence of n‐MWNT in aqueous solution has been based on the electrostatic charge repulsion between negatively charged n‐MWNT. The state of dispersion of p‐MWNT in the presence of n‐MWNT in 45/55 polypropylene/acrylonitrile butadiene styrene (PP/ABS) blends was assessed through Raman spectroscopic analysis, bulk electrical conductivity measurements, solution experiment, and crystallization studies. Raman spectroscopic analysis indicated that the state of dispersion of MWNT was improved with increasing n‐MWNT content of the mixture. This strategy led to a remarkable increase in the bulk electrical conductivity of 45/55 PP/ABS blends at 3 wt% MWNT content and was strongly dependent on the concentration of n‐MWNT in the mixture. Differential scanning calorimetric measurements along with solution experiments revealed the subsequent migration of MWNT from the PP phase to the ABS phase in the blends during melt‐mixing in the presence of higher fraction of n‐MWNT. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers