Percolation Of Multiwalled Carbon Nanotubes Research Articles

Nonwoven Mats Based on Segmented Biopolyurethanes Filled with MWCNT Prepared by Solution Blow Spinning.

To prepare nonwoven mats constituted by submicrometric fibers of thermally responsive biopolyurethanes (TPU) modified with multiwalled carbon nanotubes (MWCNT), solution blow spinning (SBS) was used. The TPU was the product of synthesis using poly(butylene sebacate)diol, PBSD, ethyl ester L-lysine diisocyanate (LDI), and 1,3-propanediol (PD) (PBSe:LDI:PD) as reactants. TPU was modified by adding different amounts of MWCNT (0, 0.5, 1, 2, and 3 wt.%). The effect of the presence and amount of MWCNT on the morphology and structure of the materials was studied using field-emission scanning electron microscopy (FESEM) and Fourier-transform infrared spectroscopy (FTIR), respectively, while their influence on the thermal and electric behaviors was studied using differential scanning calorimetry (DSC) and capacitance measurements, respectively. The addition of MWCNT by SBS induced morphological changes in the fibrous materials, affecting the relative amount and size of submicrometric fibers and, therefore, the porosity. As the MWCNT content increased, the diameter of the fibers increased and their relative amount with respect to all morphological microfeatures increased, leading to a more compact microstructure with lower porosity. The highly porous fibrous morphology of TPU-based materials achieved by SBS allowed turning a hydrophilic material to a highly hydrophobic one. Percolation of MWCNT was attained between 2 and 3 wt.%, affecting not only the electric properties of the materials but also their thermal behavior.

Double percolation of multiwalled carbon nanotubes in polystyrene/polylactic acid blends

Abstract Selective localization of multi-walled carbon nanotubes (MWCNT) in polylactic acid/polystyrene (PLA/PS) bicontinuous blends is presented in this work. A masterbatch of PS with a 2 wt% content of MWCNT is prepared and then melt mixed with different amounts of PLA. This two-step process results in a double percolated morphology where PS percolates the PLA phase, and MWCNTs percolate the PS phase. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) evidence, respectively, the bicontinuous morphology and the high selectivity of MWCNT localization in the system. Double percolation leads to a very low electrical percolation threshold of about 0.45 vol% MWCNT on total volume and an electrical conductivity of 10 −9 S/cm.

폴리에틸렌/다중벽 탄소나노튜브 나노복합필름의 열적, 기계적 및 전기적 물성에 전자빔 조사가 미치는 영향

We report the effects of electron beam (EB) irradiation on the thermal, mechani- cal, and electrical properties of nanocomposite films, based on polyethylene (PE) and mul- tiwalled carbon nanotubes (MWCNTs), manufactured by solid mixing and melt- compression. For this purpose, the MWCNT content in the nanocomposite films was con- trolled to 1−10 wt% and the EB irradiation dose was 1−150 kGy. It was found that the melt- ing temperature and enthalpy of pristine PE and its nanocomposite film were improved on using low EB doses of 1 and 10 kGy because of irradiation-induced heating and crosslink- ing. In contrast, high EB doses of 50 and 150 kGy led to significant reduction in the melting temperature and enthalpy as well crystallization temperature and enthalpy of the films because of chain scission or degradation. The electrical resistivity of the nanocomposite films decreased from ~10 10 to ~10 1 Ω cm on increasing the MWCNT content, and regard- less of the EB irradiation dose, electrical percolation of MWCNTs in the PE matrix was attained at a MWCNT content between 3 and 5 wt%. Accordingly, PE/MWCNT nanocom- posite films with low electrical resistivity of 10 2 −10 1 Ω cm, which were subjected to moder- ate EB irradiation doses, exhibit excellent electric heating behavior, which depends on the applied voltage and MWCNT content.

Morphology and Properties of Sulfonated Poly(styrene-b-(ethylene-co-butylene)-b-styrene)/Poly(4-styrene sulfonic acid) Blends Filled with Multiwalled Carbon Nanotubes

Nanocomposites based on poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) and multiwalled carbon nanotubes (MWNTs) were prepared. In order to facilitate the dispersion of MWNTs in the nanocomposites, the pristine MWNTs were reduced by Li to anions and SEBS was sulfonated. Poly(4-styrenesulfonic acid) (PSSA) was also added to either SEBS or S-SEBS and the morphology and properties of the nanocomposites were examined. Nanocomposites prepared from S-SEBS, PSSA, and the modified MWNTs showed a threshold decrease in electrical resistivity due to the percolation of MWNTs at a critical MWNT content (P(c)) lower than those for the nanocomposites based on SEBS, PSSA, and the MWNTs. It was found that the P(c) decreased with increasing the concentration of PSSA in the nanocomposites containing S-SEBS. The efficient percolation of MWNTs in the S-SEBS/PSSA nanocomposites was attributed to interactions between the ionic moieties of MWNTs and S-SEBS and the fine dispersion of the MWNTs. Nanocomposites based on S-SEBS showed large increase of rubbery plateau modulus compared with those based on SEBS. PSSA played the role of plasticizer of sulfonated PS blocks above T(g) of PS blocks in S-SEBS.

Thermal and Electrical Properties of Nanocomposites Based on Acrylic Copolymers and Multiwalled Carbon Nanotube

Nanocomposites based on multiwalled carbon nanotubes (MWCNT) and various acrylic copolymers, poly(methyl methacrylate-co-butyl acrylate) (PMBA) and poly(methyl methacrylate-co-butyl acrylate-co-acrylic acid) (PMAA), were prepared and the effects of the copolymer composition on the thermal and electrical properties of the nanocomposites were investigated. The results showed that there was a decrease in the glass transition temperature (T(g)) with increasing MWCNT content in the nanocomposites based on the acrylic copolymers. This decrease in T(g) was attributed to the characteristics of the nanocomposites in which the compatibility between the matrix polymers and MWCNT were relatively poor and there was an increase in free volume at the interface. It was found that the critical concentrations, P(c)s, for the percolation of MWCNTs in terms of the electrical resistivity decreased with increasing acrylic acid content in the matrix polymers. In addition, the thermal conductivity of the nanocomposites increased with increasing MWCNT content if there was good compatibility between the matrix polymer and MWCNT while those of the nanocomposites with relatively poor compatibility between the matrix and MWCNT showed little change.

Quantitative characterization of the formation of an interpenetrating phase composite inpolystyrene from the percolation of multiwalled carbon nanotubes

For the first time, an interpenetrating phase polymer nanocomposite formed by thepercolation of multiwalled carbon nanotubes (MWCNTs) in polystyrene (PS) has beenquantitatively characterized through electrical conductivity measurements andmelt rheology. Both sets of measurements, in conjunction with scanning electronmicroscopy (SEM) images, indicate the presence of a continuous phase of percolatedMWCNTs appearing at particle concentrations exceeding 2 vol% MWCNTs in PS.To quantify the amount of this continuous phase present in the PS/MWCNTcomposite, electrical conductivity data at various MWCNT concentrations,β, are correlated with a proposed degree of percolation, , developed using a conventional power-law formula with and without a percolationthreshold. To quantify the properties of the interpenetrating phase polymer nanocomposite,the PS/MWCNT composite is treated as a combination of two phases: a continuous phaseconsisting of a pseudo-solid-like network of percolated MWCNTs, and a continuous PSphase reinforced by non-interacting MWCNTs. The proposed degree of percolation is usedto quantify the distribution of MWCNTs among the phases, and is then used in arule-of-mixtures formulation for the storage modulus, , and the loss modulus, , to quantify the properties of the continuous phase consisting of percolated MWCNTs andthe continuous PS phase reinforced by non-interacting MWCNTs from the experimentalmelt rheology data. The properties of the continuous phase of percolated MWCNTs areindicative of a scaffold-like microstructure exhibiting an elastic behavior with a complexmodulus of 360 kPa at lower frequencies and viscoplastic behavior with a complex viscosity of6 kPa s rad−1 at higher frequencies, most likely due to a stick–slip friction mechanism at the interface ofthe percolated MWCNTs. Additional evidence of this microstructure was obtained viascanning electron microscopy. This research has important implications in providing a newmethodology based on the electrical and rheological properties of the polymernanocomposite for quantifying the continuous phase formed by the percolation of newfunctionalized nanostructures being developed for: (a) controlling the percolation ofthe nanostructures through self-assembly, (b) enhancing their interaction withthe continuous reinforced polymer phase, (c) enhancing the cohesion betweennanostructures.

Study on polycarbonate/multi-walled carbon nanotubes composite produced by melt processing

Multi-walled carbon nanotubes (MWCNTs) were filled into polycarbonate (PC) by large scale extruder, and some studies were carried out on as-produced composite. The results showed PC composite containing 1 wt.% of MWCNTs had a tensile strength 4.5% higher than neat PC, and the elastic modulus of PC/MWCNTs composite increased obviously with MWCNTs loadings. The electrical resistivity measurements indicated a percolation of MWCNTs near 5 wt.% (3.4 vol.%) for the composite. Either the decrease in the fluidity of the composite melts with the increase of carbon nanotubes (CNTs) loadings or the unexpected shortening of CNTs in extrusion was supposed to have weakened the effects of CNTs as a reinforcing agent or a conductive filler.

Melt process and performance of multi‐walled carbon nanotubes reinforced LDPE composites

PurposeTo develop a method for the preparation of multi‐walled carbon nanotube reinforced low density polyethylene (LDPE) composites (MWNTs/LDPE), based on ultrasonic vibration, solution casting and melt mixing.Design/methodology/approachThe preparation for MWNTs/LDPE composites was carried out by vibration of carbon nanotubes (CNT), solution casting and melt mixing for MWNTs and LDPE. The physical chemical properties of the composites were characterised using a variety of techniques including scanning electron microscopy, resistance and tensile measurement.FindingsIt was found that the preparation method reported had significantly improved the dispersion of multi‐walled carbon nanotubes (MWNTs) in LDPE matrix, resulting in the improvement of tensile strength of the composite. The percolation of MWNTs in LDPE matrix was between 10 and 15 wt% (1016‐108 Ω cm).Practical implicationsThe preparation method reported addressed a problem concerning the dispersion of CNT in polymer matrix. The method developed provided a practical and effective solution to such a problem.Originality/valueThe preparation method for MWNTs/LDPE composites involving vibration of CNT, solution casting and melt mixing for MWNTs and LDPE was novel. The method could be adapted for use in industrial scale.

Carbon nanotube-filled polycarbonate composites produced by melt mixing and their use in blends with polyethylene

This paper presents composites of polycarbonate (PC) having different amounts of multiwalled carbon nanotubes (MWNT). The composites were prepared by diluting a masterbatch of PC with 15 wt% MWNT using melt mixing in a DACA-Micro Compounder. Electrical resistivity measurements indicated percolation of MWNT between 1 and 1.5 wt%. Transmission electron microscopy (TEM) showed excellent dispersion of the MWNT and indicated no preferred orientation of MWNT in extrusion direction. In addition, a conductive PC-2 wt% MWNT composite was melt mixed with polyethylene in order to get co-continuous blends exhibiting double percolation. Significant reduction in electrical resistivity of the blends could be achieved in compositions down to 30 vol% filled PC in which the total MWNT content was only 0.41 vol%. These blends exhibited co-continuous structures.

Melt mixing of polycarbonate with multiwalled carbon nanotubes: microscopic studies on the state of dispersion

The focus of the paper is to investigate several issues related to the state of dispersion of multiwalled carbon nanotubes (MWNTs) in a polycarbonate (PC) matrix. A masterbatch of PC–MWNT (15 wt.%) was diluted with different amounts of PC in a small scale conical twin screw extruder (DACA Micro Compounder) to obtain different compositions of MWNT. In this system, electrical measurements indicated percolation of MWNT between 1.0 and 1.5 wt.%. We report TEM and AFM investigations of the state of dispersion of MWNT, in the entire volume of the matrix, in selected composites with compositions below (1 wt.% MWNT) and above the percolation threshold (2 and 5 wt.% MWNT). In addition, it was investigated if surface segregation of MWNT and flow induced orientation of nanotubes within the extruded strands had been occurred. It is found that the nanotubes dispersed uniformly through the matrix showing no significant agglomeration in the compositions studied. TEM micrographs seem to be able to detect the percolated structure of the carbon nanotubes. Furthermore, by comparing AFM micrographs from the core region and near to surface region no evidence of segregation or depletion of MWNT at the surface of the extruded strand was found. Comparison of TEM and AFM micrographs on surfaces cut along and perpendicular to the strand direction led to the conclusion that no preferred alignment had occurred as a result of extrusion. Aside from TEM technique, AFM is shown to be suitable to characterize the state of nanotube dispersion along with the issue of surface segregation and orientation of the nanotubes.