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Nanocomposites of poly(lactic acid) (PLA)/poly(butylene adipate‐co‐terephthalate) (PBAT) blends with multiwalled carbon nanotubes (MWCNTs) were prepared and their morphology, as well as electrical, mechanical, and thermal properties were investigated. The motivation of this work is to prepare electrically conductive and environmentally benign polymer nanocomposites using biodegradable PLA/PBAT blends. The composites were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning and transmission electron microscopy, tensile and microindentation tests, and thermogravimetric analyses (TGA). Volume resistivity and resistance to tensile deformation were measured for electrical characterization. The nanocomposites films were integrated into an electrical circuit to confirm their electrical conductivity. The FTIR spectra revealed the physical mixing between the polymer matrix and the filler. TEM micrographs suggested selective localization of MWCNTs in the PBAT phase with partial agglomeration forming a co‐continuous morphology. TGA and derivative thermogravimetric curves suggested the overall decreasing thermal stability of composites than pure polymer blends regardless of the effects on individual blend components. A relatively low electrical percolation threshold (around 1 wt% of the fillers) compared to the literature works was achieved. Increasing electrical resistance of nanocomposites upon tensile deformation suggested their possibility of piezoresistive properties. Furthermore, the overall mechanical performance (i.e., elastic modulus, tensile strength, and hardness) of the materials was found to improve with increasing filler content. [ABSTRACT FROM AUTHOR]

The principles of large deformation rubber viscoelasticity are not new, but there is a need to make explicit certain theories or modify the available models for deeper understanding of behavior of rubber nanocomposites. The difficulties are chiefly due to the assumptions under which a given theoretical model fails to predict large deformation behavior of elastomer nanocomposites, as models are basically proposed for neat rubbers, and more critically they can hardly be supposed to remain valid for systems in which two or more nanofillers having different nature, shape, and size are used. This work attempts to apply nonlinear hyperelastic theoretical models proposed for hyperelastic behavior of rubbers for nanocomposites containing multi‐walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GnPs), and to explore the interplay between morphology, viscoelastic properties, and large deformation behavior of typical hydrogenated acrylonitrile butadiene rubber (HNBR)‐based rubber nanocomposites. Morphological observations used for knowing the localization of nanofillers, where dynamic mechanical and uniaxial tensile strength analyses exhibited a rise in both Young's modulus and tensile strength of composites by MWCNTs and GNPs content up to 200 and 160%, respectively. We applied Arruda‐Boyce model and appropriately predicted nonlinear hyperelastic behavior of HNBR model nanocomposites and interfacial interactions between phases, as recognized by comparing model parameters for nanocomposites containing only MWCNTs, or only GNPs, and their combinations varying filler content. POLYM. COMPOS., 40:E1548–E1558, 2019. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

ABSTRACT Electrical and melt rheological properties of melt-mixed polycarbonate (PC) and co-continuous PC/poly(styrene-acrylonitrile) (SAN) blends with carbon nanotubes (CNTs) are investigated. Using two sets of mixing parameters, different states of filler dispersion are obtained. With increasing CNT dispersion, an increase in electrical resistivity near the percolation threshold of PC-CNT composites and (PC + CNT)/SAN blends is observed. This suggests that the higher mixing energies required for better dispersion also result in a more severe reduction of the CNT aspect ratio; this effect was proven by CNT length measurements. Melt rheological studies show higher reinforcing effects for composites with worse dispersion. The Eilers equation, describing the melt viscosity as function of filler content, was used to fit the data and to obtain information about an apparent aspect ratio change, which was in accordance with measured CNT length reduction. Such fitting could be also transferred to the blends and serves for a qualitatively based discussion. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 79-88 [ABSTRACT FROM AUTHOR]

This work, conceived as a second step in the development of high-performance damping materials suitable for seismic application, describes the preparation and characterization of complex natural rubber-based composites containing hybrid nano- and conventional fillers. The cluster-cluster aggregation model was used to assess the apparent filler networking energy. The values obtained suggested that the presence of the hybrid nanofiller strengthens the filler networking. The same model was used to understand the mechanisms of energy dissipation. The damping coefficient was found to be in the sought range between 10% and 20% (at 0.5 Hz and high shear strain). [ABSTRACT FROM AUTHOR]

In this study, the development and characterization of an intrinsically self-healable material have been reported based on bromobutyl rubber (BIIR) modified with imidazole (Im) and loaded with carbon nanotubes (CNTs) as reinforcing and electrically conducting agent. The ionic imidazolium groups facilitate an ionic network, which imparts the composites a pronounced self-healing behavior. The cation-π bondings between modified BIIR and CNT surface improve the rubber-filler interaction leading to a better mechanical performance and a higher electrical conductivity of the composites. It has been demonstrated that the healing process can be accelerated by applying an electrical current across a damaged surface of a test specimen owing to the Joule heating effect. The recovery of the mechanical and electrical properties of the composites is investigated under different test conditions and specifically discussed in terms of the rubber-filler interactions and the filler dispersion. The applied scientific approach with the exploration of the unique nature of the imidazolium modified and CNT loaded BIIR may promote developments for a new class of rubber materials for different smart and technological applications. [ABSTRACT FROM AUTHOR]

Multiwalled carbon nanotube (MWCNT) filled poly(ether sulfone) (PES) and poly(ether imide) (PEI) composites were prepared with different MWCNT weight fractions (0.5-5wt%) by a solution mixing technique. Their electrical conductivities, electromagnetic interference (EMI), shielding effectiveness (SE), return loss (RL), and absorption loss (AL) were investigated. Morphologies of the fracture surfaces of nanocomposites studied by scanning electron and transmission electron microscopy showed relatively good MWCNT dispersion and distribution. The electrical conductivity of compression molded samples measured at room temperature indicated that the electrical percolation network was achieved already at 0.5% loading. The measurements of shielding effectiveness (SE) carried out in the frequency range of 8 to 12 GHz (X-band range) showed that SE increases with measurement frequency and with filler loading, whereby no significant differences could be observed between PES and PEI as matrices. The nanocomposites based on both matrices with 5 wt% loading of MWCNT exhibited shielding levels at 8 GHz between 42 and 45 dB in comparison with the pure polymers which showed value in the range of 1 to 2 dB. RL and AL showed significantly lower values for the composites as compared to unfilled polymers, but no systematic trends were observed on frequency. POLYM. ENG. SCI., 54:2560-2570, 2014. © 2013 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

ABSTRACT This article reports the preparation and characterization of multiwalled carbon nanotubes (MWCNTs)-filled thermoplastic polyurethane-urea (TPUU) and carboxylated acrylonitrile butadiene rubber (XNBR) blend nanocomposites. The dispersion of the MWCNTs was carried out using a laboratory two roll mill. Three different loadings, that is, 1, 3, and 5 wt % of the MWCNTs were used. The electron microscopy image analysis proves that the MWCNTs are evenly dispersed along the shear flow direction. Through incorporation of the nanotubes in the blend, the tensile modulus was increased from 9.90 ± 0.5 to 45.30 ± 0.3 MPa, and the tensile strength at break was increased from 25.4 ± 2.5 to 33.0 ± 1.5 MPa. The wide angle X-ray scattering result showed that the TPUU:XNBR blends were arranged in layered structures. These structures are formed through chemical reactions of NH group from urethane and urea with the carboxylic group on XNBR. Furthermore, even at a very low loading, the high degree of nanotubes dispersion results in a significant increase in the electrical percolation threshold. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40341. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) are mixed into SBR/NR and SBR/IR blends using a wet mixing process. The phase specific localization of CNTs in rubber blends is predicted theoretically using surface energy data of blend components and determined experimentally by means of the wetting concept. Almost all CNTs are found to be localized in the SBR matrix of SBR/IR blends due to the better affinity of CNTs to SBR than to IR. In contrast, a high CNT loading localized in the NR phase of SBR/NR blends results from the presence of phospholipids in NR. Electrical and mechanical properties of the rubber blends depend strongly on CNT localization. A lower CNT loading in SBR matrix of SBR/NR blends imparts a better wet grip and lower rolling resistance to tire tread compounds. [ABSTRACT FROM AUTHOR]

The present investigation compares different carbon-based nanoscaled materials with regard to their effectiveness in producing thermoplastic polymers with antistatic and electrically conductive behavior. The dispersed phases are carbon black (CB) as spherical particles, multiwalled carbon nanotubes (MWNT) as fiber-like filler, and expanded graphite (EG) as platelet-like filler. Each was incorporated into polycarbonate by small-scale melt mixing. The electrical percolation concentrations were found to be 2 wt% for MWNT, 4 wt% for EG, and 8.75 wt% for CB which parallels the aspect ratios of the fillers. For EG a strong dependence of morphology and electrical resistivity on mixing time was observed, indicating a structural change/destruction during intensive shear mixing. Rheological percolation thresholds were found to be lower than electrical percolation threshold for the MWNT and CB, but similar in the case of EG. The general impact on complex melt viscosity decreases in the order MWNT, CB, EG. For EG, at higher loadings (above 4wt%) the viscosity increase with filler content is delayed as is the decrease in resistivity. [ABSTRACT FROM AUTHOR]

An electromechanical response behavior is realized by nanostructuring the glass fiber interphase with different highly electrically conductive carbon allotropes like carbon nanotubes (CNT), graphene nanoplatelets (GNP), or conductive carbon black (CB). The operational capability of these multifunctional glass fibers for an online structural-health monitoring is demonstrated in endless glass fiber-reinforced polypropylene. The electromechanical response behavior, during a static or dynamic three-point bending test of various carbon modifications, shows qualitative differences in the signal quality and sensitivity due to the different aspect ratios of the nanoparticles and the associated electrically conductive network densities in the interphase. Depending on the embedding position within the glass fiber-reinforced composite compression, shear and tension loadings of the fibers can be distinguished by different characteristics of the corresponding electrical signal. The occurrence of irreversible signal changes during the dynamic loading can be attributed to filler reorientation processes caused by polymer creeping or by destruction of electrically conductive paths by cracks in the glass fiber interphase. [ABSTRACT FROM AUTHOR]

Front Cover: An intrinsically self‐healable elastomeric material based on reversible ionic clusters is reinforced with conducting carbon nanotubes. The electrical conducting nature was further exploited to enhance the self‐healing efficiency through application of electrical voltage across the damaged region. This is reported by Hong Hai Le, Frank Böhme, Aladin Sallat, Sven Wießner, Maria auf der Landwehr, Uta Reuter, Klaus‐Werner Stöckelhuber, Gert Heinrich, Hans‐Joachim Radusch and Amit Das, article number 1600385. [ABSTRACT FROM AUTHOR]

Electrophoretic deposition (EPD) is used to deposit multiwalled carbon nanotube networks (CNTs) onto electrically insulating glass fiber surfaces. We found that the thin networks on a single glass fiber surface exhibit semiconducting properties. This enables us to realize a single CNT-glass fiber as a probe with novel multifunctional capabilities forin-situmonitoring of various chemical/physical transitions, particularly in the interphase region between polymer and glass fiber. Because of the intimate interaction between CNTs and polymers in the vicinity of a glass fiber, our CNT probe can rapidly sense the local changes of fundamental polymer properties, such as glass transition, reaction activation energy, cross-linking reaction, and crystallization. [ABSTRACT FROM AUTHOR]

Abstract: Polychloroprene (CR) composites were prepared using unmodified and ionic liquid modified carbon nanotubes (CNTs) respectively. The composites with ionic liquid modified CNTs (M-CNTs) were found to exhibit high electrical conductivity, improved tensile modulus and thermal stability as opposed to the composites with unmodified CNTs (R-CNTs) [1,2]. The current article deals with the accelerated thermal aging of the aforementioned two different composites at various temperatures and time periods in aerobic conditions. Post-aging results are better for M-CNTs/CR composites: Enhanced retention of mechanical property (tensile strength) and reduced surface defects (as revealed by scanning electron microscopy pictures) were observed. It is inferred that ionic liquid (IL) acts as an anti-oxidant protecting the composites from surface oxidation. Fourier transform infrared (FTIR) spectroscopic studies confirmed the presence of hydroxyl and carbonyl regions in the aged samples; however, the intensity of the regions was least for the composites with M-CNTs. Surprisingly, the electrical conductivity of M-CNTs/CR composites increased upon aging and therefore, these composites can be used for applications where conductivity at elevated temperatures is required. [Copyright &y& Elsevier]

Abstract: A simplified and an eco-friendly approach to develop polychloroprene rubber composites with high electrical conductivity is reported. The usage of room temperature ionic liquid, 1-butyl 3-methyl imidazolium bis(trifluoromethylsulphonyl)imide and a low concentration (5phr) of commercial grade multi-walled carbon nanotubes (MWCNTs) in polychloroprene rubber exhibited an electrical conductivity of 0.1S/cm with a stretchability >500%. The physical (cation–pi/pi–pi) interaction between the ionic liquid and the MWCNTs is evidenced by Raman spectroscopy. Transmission electron microscopy images exhibit an improved dispersion of the BMI modified tubes in matrix at various magnification scales. The dependency of dynamic properties on the concentration of ionic liquid at constant loading of nanotubes supports the fact that ionic liquid assists in the formation of filler–filler networks. The tensile modulus of 3phr loaded modified MWCNT/CR composite is increased by 50% with regard to that of the unmodified MWCNT/CR composite. Mooney–Rivlin plot displays the existence of rubber–filler interactions. [Copyright &y& Elsevier]

In this paper some new aspects to the hybrid nano-filler networking in elastomer matrix under dynamic mechanical loading conditions and some new methods to reveal a hybrid nano-filler synergy are applied and discussed. Electron spin resonance (ESR) spectra of the multi-walled carbon nanotubes (MWCNT) present in the natural rubber (NR) based nanocomposites were investigated and the dependence of the double integral of resonance spectra on the amount of expanded organically modified montmorillonite (EOMt) present in the NR was established. Its decrease with an increasing amount of EOMt confirmed the synergy between these two nano-fillers. DMA temperature sweep measurements were performed and the cluster-cluster aggregation (CCA) model was used to assess the apparent filler networking energy. The obtained results suggest that the presence of the EOMt above a critical amount strengthens the hybrid-filler networking. In order to investigate how different ratios of these two nano-fillers influence the strain dependency of the storage modulus, strain sweep measurements were performed in tensile mode, and the CCA-model was used to describe the Payne effect. [ABSTRACT FROM AUTHOR]

Polycarbonate (PC)/multiwall carbon nanotube (MWCNT)/composites were prepared by melt mixing and subsequently melt spun to monofilament fibers. Electrical, mechanical and piezoresistive (strain sensing) properties of the fibers were evaluated as a function of the MWCNT weight concentration, which was varied up to 6 wt%. After the incorporation of MWCNTs, a decrease in electrical resistivity of the fibers was found for MWCNT concentrations as low as 2 wt%. Furthermore, an important effect of the draw down ratio (DDR) on the electrical properties of the fibers was observed. While the electrical percolation threshold (φ c ) for the bulk material was <1 wt% and ∼1 wt% for the undrawn-extruded rods, for the melt-spun fibers φ c was found to be highly dependent on the DDR. Stiffness and offset yield stress of the MWCNT/PC fibers were increased starting with the addition of 1 wt% of MWCNTs. However, decreased spinnability was observed for fibers with MWCNT concentrations above 4 wt%. The coefficient that relates the electrical resistance changes to the mechanical strain (strain gage factor S GF ) was estimated for fibers with MWCNTs amounts that range from 3.5 to 6 wt%. The highest S GF ∼16 was found at 3.5 wt% and the lowest S GF ∼2.5 at 6 wt% MWCNT. Smart multifunctional textiles, made from such conductive fibers, have wide applications such as structural health monitoring, detection of gases and liquids, sensor arrays and flexible sensors. [ABSTRACT FROM AUTHOR]

Hybrid natural rubber (NR) nanocomposites, containing 2 phr multiwalled carbon nanotubes (MWCNT) and different quantities (from 0 to 20 phr) of expanded organically modified montmorillonite (EOMt), were prepared in order to produce a NR based material with superior mechanical properties as a first step in obtaining a high-performance damping material suitable for seismic application. Initially a master batch of NR/MWCNT was prepared and then a dilution technique was used for the preparation of NR/EOMt/MWCNT nanocomposites. Raman spectra showed a strong interaction between the rubber matrix and MWCNT and the existence of an only physical mixture of the MWCNT and EOMt. This was reflected on the mechanical properties (both quasi-static and dynamic) which were found to change in the desired way. A remarkable improvement of the lower tensile modulus, tensile strength and storage modulus was achieved with the addition of MWCNT and then a gradual but permanent improvement of the above mentioned properties including improved elasticity and elongation at break with the addition of EOMt. DMA strain sweep measurements showed a pronounced non-linear dependence and a significant increase of the loss factor tan δ (a measure of the dissipation energy) for the nanocomposites with filler concentrations above the mechanical percolation threshold (16 phr). [ABSTRACT FROM AUTHOR]

Abstract: A simple and facile method for depositing multiwall carbon nanotubes (MWCNTs) onto the surface of naturally occurring short jute fibers (JFs) is reported. Hierarchical multi-scale structures were formed with CNT-networks uniformly distributed and fully covering the JFs (JF–CNT), as depicted by the scanning electron microscopy (SEM) micrographs. The impact of these hybrid fillers on the mechanical properties of a natural rubber (NR) matrix was systematically investigated. Pristine JFs were cut initially to an average length of 2.0 mm and exposed to an alkali treatment (a-JFs) to remove impurities existing in the raw jute. MWCNTs were treated under mild acidic conditions to generate carboxylic acid moieties. Afterward, MWCNTs were dispersed in an aqueous media and short a-JFs were allowed to react with them. Raman spectroscopy confirmed the chemical interaction between CNTs and JFs. The JF–CNT exposed quite hydrophobic behavior as revealed by the water contact angle measurements, improving the wettability of the non-polar NR. Consequently, the composite interfacial adhesion strength was significantly enhanced while a micro-scale “mechanical interlocking” mechanism was observed from the interphase-section transmission electron microscopy (TEM) images. SEM analysis of the composite fracture surfaces demonstrated the interfacial strength of NR/a-JF and NR/JF–CNT composites, at different fiber loadings. It can be presumed that the CNT-coating effectively compatibillized the composite structure acting as a macromolecular coupling agent. A detailed analysis of stress-strain and dynamic mechanical spectra confirmed the high mechanical performance of the hierarchical composites, consisting mainly of materials arising from natural resources. [Copyright &y& Elsevier]

Abstract: Co-continuous polycarbonate (PC)/poly(styrene-acrylonitrile) (SAN) = 60/40 wt.% blends were filled with 1 wt.% multi-walled carbon nanotubes (MWCNTs), which selectively localized within the PC component. To study the influence of the viscosity ratio, PCs with different viscosities were selected resulting in PC/SAN viscosity ratios (at 100 rad/s) between 1.2 and 4.5. With increasing viscosity ratio, smaller blend structures were observed. Furthermore, optical microscopy revealed that the filler dispersion was improved with decreasing PC viscosity. The highest electrical conductivity was achieved for the blend composite with the coarsest morphology, containing the low viscosity PC and having the lowest PC/SAN viscosity ratio. Transmission electron microscopy analysis indicated that for the composite prepared with high viscosity PC, not all of the incorporated MWCNTs were able to localize completely into the PC component. Instead, some MWCNTs were found to be stacked at the interface of the two polymers, indicating that the high PC melt viscosity had a restricting effect on the movement of the MWCNTs. Moreover, with electrical conductive atomic force microscopy, it was proven that small, spherical PC particles, even if filled with CNTs, do not take part in the conductive network of the blend composites. Rheological analyses showed a correlation with the morphological analysis and the electrical conductive behavior of the blend composites. In summary, a lower viscosity ratio between the blend components, in which upon addition due to thermodynamic reasons the CNTs localize (here PC), and the other component (here SAN) is favorable for high electrical conductivity values. [Copyright &y& Elsevier]

Abstract: Carbon nanotubes (CNTs) were modified using an ionic liquid (IL) and were admixed with a non-polar solution styrene butadiene rubber (SSBR). A local re-agglomeration of ionic liquid modified CNTs (m-CNTs) was found to occur in the SSBR composites, which was confirmed from transmission electron micrographs, as IL cannot couple CNTs and elastomer in order to maintain the disentangled state of the tubes. The conducting networks were established as a consequence of agglomerate-tube percolation and the maximum electrical conductivity of the investigated samples was found to be ∼0.01S/cm. The reinforcing effect of m-CNTs was not profound in the composites due to the plasticizing nature of IL in non-polar SSBR. [Copyright &y& Elsevier]

Abstract: Solution styrene butadiene rubber (S-SBR) composites reinforced with graphene nanoplatelets (GnPs), expanded graphite (EG), and multiwalled carbon nanotubes (MWCNTs) were prepared and the electrical and various mechanical properties were compared to understand the specific dispersion and reinforcement behaviours of these nanostructured fillers. The electrical resistivity of the rubber composite gradually decreased with the increase of filler amount in the composite. The electrical percolation behaviour was found to be started at 15phr (parts per hundred rubber) for GnP and 20phr for EG filled systems, whereas a sharp drop was found at 5phr for MWCNT based composites. At a particular filler loading, dynamic mechanical analysis and tensile test showed a significant improvement of the mechanical properties of the composites comprised of MWCNT followed by GnP and then EG. The high aspect ratio of MWCNT enabled to form a network at low filler loading and, consequently, a good reinforcement effect was observed. To investigate the effect of hybrid fillers, MWCNT (up to 5phr) were added in a selected composition of EG based compounds. The formation of a mixed filler network showed a synergistic effect on the improvement of electrical as well as various mechanical properties. [Copyright &y& Elsevier]

Abstract: An electrically conductive polymer composite (CPC) based on polycarbonate filled with 1.5 wt.% carbon nanotubes (CNTs) was investigated regarding its solvent selectivity when used as a sensor material for liquid detection. Based on the electrical response characteristics of the CPC when immersed in different solvents, “good” and “bad” solvents out of 59 test liquids were detected and the Hansen solubility parameters of the CPC were calculated using the “Hansen software” to be δ D = 18.4 ± 0.2 MPa0.5, δ P = 10.9 ± 0.8 MPa0.5, and δ H = 4.1 ± 0.5 MPa0.5. Based on the CPC''s and solvents'' Hansen solubility parameters the affinity between CPC and solvent represented by the distance in Hansen space was determined. As a second parameter the molar volume of the solvent molecules was used to describe the selectivity of the CPC by means of a quarter circle like area clearly separating “good” and “bad” solvents in a so-called solvent map. Whereas the Hansen solubility parameters are based on thermodynamics, the influence of the solvents'' molar volume on the CPC''s selectivity can be explained by diffusion processes. When increasing the molar volume of solvents having a similar chemical structure, a limiting value of the molar volume was found above which no solvent diffusion into the CPC was observed. Using this large number of solvents it could be clearly shown that the electrical response kinetics upon immersion into “good” solvents cannot be correlated with the Hansen solubility parameters of the CPC or their difference between CPC and solvent but is determined by the diffusion kinetics, which is governed by the solvents molecule size. [Copyright &y& Elsevier]

Abstract: Thermal degradation of polychloroprene rubber (CR) composites based on unmodified and ionic liquid modified multi-walled carbon nanotubes (MWCNTs) is studied using thermogravimetric analysis (TGA) in aerobic and anaerobic (nitrogen) conditions. The CR and its composites exhibit three stage and four stage degradation in nitrogen and air respectively. The presence of unmodified CNTs alone does not improve the thermal stability of composites to a great extent whereas a reasonable enhancement is observed in case of modified CNTs/CR composites which can be attributed to the interfacial interactions of ionic liquid/modified tubes with CR and to the fine dispersion of modified tubes in CR. The degradation products of CR and its composites were analysed using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and the mechanism of degradation is discussed. Non-isothermal degradation kinetics were studied using Kissinger and Flynn-Wall-Ozawa methods and the activation energy of thermal decomposition is found to be high for modified CNTs/CR composites. Isothermal degradation of modified CNTs/CR composites at 290 °C for 30 min in nitrogen reveals decreased weight loss (14%) as opposed to CR (31%) and unmodified CNTs/CR composites (30%). The combustion behaviour of the composites was dealt using microscale combustion calorimeter (MCC) and the flame retardancy of the composites is discussed. [Copyright &y& Elsevier]

Abstract: The complete transfer of multiwalled carbon nanotubes (MWCNTs) from a poly(styrene acrylonitrile) (SAN) precompound into an initially unfilled polycarbonate (PC) phase during 5 min of discontinuous melt mixing in a microcompounder has been observed recently. However, the typical time scale of the occurring transfer is presently still unknown. Morphological investigations within our study revealed that similar results can be obtained when the SAN-MWCNT-precompound is melt blended with neat PC by continuous twin-screw extrusion. Additionally, the kinetics of the CNT transfer was also investigated in a kneading chamber. We found that the CNT transfer rate turned out to be strongly coupled to the development of the interfacial area of the blend. Furthermore, we evaluated the interplay and significance of the possible and presently only insufficiently understood transfer mechanisms. We proposed for the first time a correlation between major processing and blend parameters and the probability of carbon nanotube transfer due to the development of a nanoscaled wetting angle. [Copyright &y& Elsevier]

Abstract: This paper focuses on the influence of ionic liquid on carbon nanotube based elastomeric composites. Multi-walled carbon nanotubes (MWCNTs) are modified using an ionic liquid at room temperature, 1-butyl 3-methyl imidazolium bis (trifluoromethylsulphonyl) imide (BMI) and modified MWCNTs exhibit physical (cation–π/π–π) interaction with BMI. The polychloroprene rubber (CR) composites are prepared using unmodified and BMI modified MWCNTs. The presence of BMI not only increases the alternating current (AC) electrical conductivity and polarisability of the composites but also improves the state of dispersion of the tubes as observed from dielectric spectroscopy and transmission electron microscopy respectively. In addition to the hydrodynamic reinforcement, the formation of improved filler–filler networks is reflected in the dynamic storage modulus (E′) for modified MWCNTs/CR composites in amplitude sweep measurement upon increasing the proportion of BMI. Hardness and mechanical properties are also studied for the composites as a function of BMI. [Copyright &y& Elsevier]

Abstract: Electrically conductive polymer composites (CPCs) based on carbon nanotubes (CNTs) and polycarbonate were investigated regarding their electrical resistance change in different solvents like tetrahydrofuran, acetone, and ethyl acetate. CPCs containing 0.086 to 2.778 vol.% CNT were melt mixed using a twin-screw extruder under optimised conditions and subsequently compression-moulded. All sensing experiments revealed a resistance increase of CPCs having a U-shaped sample geometry during solvent immersion. Light microscopy investigations have shown that the diffusion of solvents into CPCs can be monitored in terms of a pronounced diffusion front, separating a swollen skin from the dry core. Based on this observed skin-core morphology, a model allowing the calculation of the time depending relative resistance change has been proposed considering several factors like diffusion parameters, composite characteristics, and geometrical values. Simulated response curves based on the model were compared with experimental data obtained on the CPCs and very good agreement was observed. Using this model the influence of CNT content and kind of solvent could be described exactly. [Copyright &y& Elsevier]

Abstract: In order to study the influence of melt viscosity and molecular weight on nanotube dispersion and electrical volume resistivity, three different polycarbonates (PCs) varying in molecular weight were melt compounded with 1 wt% multiwalled carbon nanotubes (MWCNTs, Baytubes® 150 HP) using a small-scale compounder. The experiments were performed at constant melt temperature but at varying mixing speeds, thereby applying different magnitudes of shear stress. Light transmission microscopy was used to access the state of agglomerate dispersion, and electrical resistivities of the composites were measured on pressed plates. The results indicate that with increasing matrix viscosity the agglomerate dispersion gets better when using constant mixing conditions but worse considering comparable shear stress values. To study the effect of molecular weight, in a second set of experiments melt temperatures were adjusted so that all PCs had similar viscosity and mixing was performed at constant mixing speed. As investigated on two viscosity levels, the composites based on the low molecular weight matrix showed smaller sized un-dispersed primary agglomerates as compared to composites with higher molecular weight matrices, highlighting the role of matrix infiltration into primary nanotube agglomerates as the first step of dispersion. The resistivity values of composites prepared using low viscosity matrices were lower than those of composites from high viscosity matrix. [Copyright &y& Elsevier]

Abstract: The interphase between reinforcing fibre and matrix is a controlling element in composite performance. We deposited multi-walled carbon nanotubes (MWCNTs) onto electrically insulating glass fibre surfaces leading to the formation of semiconductive MWCNT–glass fibres and in turn multifunctional fibre/polymer interphases. The deposition process of MWCNTs onto glass fibre surfaces involved both electrophoretic deposition (EPD) and conventional dip coating methods. The EPD coating method produces a more homogeneous and continuous nanotube distribution on the glass fibre surface compared with the dip coating. According to fragmentation test results, the interphase with a small number of heterogeneous MWCNTs in the EPD fibre/epoxy composites, mimicking a biological bone structure, can remarkably improve the interfacial shear strength. We found that the semiconductive interphase results in a high sensitivity of the electrical resistance to the tensile strain of single glass fibre model composites. This material provides a possible in situ mechanical load sensor and early warning of fibre composite damage. [Copyright &y& Elsevier]

Abstract: Dispersion of primary nanotube agglomerates in polymer melts is one of the difficult tasks when applying melt mixing for nanocomposite preparation. Hence, there is a need for a better understanding of the ongoing processes. Filler agglomerates generally undergo dispersion by rupture and erosion mechanisms, which usually occur simultaneously. To analyse these mechanisms and their corresponding dispersion kinetics 1 wt% multiwalled carbon nanotubes (MWNT) were incorporated into polycarbonate using a microcompounder. Different mixing speeds at constant melt temperature were applied thereby changing the applied stress. The states of MWNT agglomerate dispersion at different mixing times were assessed by quantifying the agglomerate area ratio and particle size distribution using image analysis of optical transmission micrographs. A model is proposed to estimate the fractions of rupture and erosion mechanisms during agglomerate dispersion. At low mixing speeds, the dispersion was found to be governed by both mechanisms, whereas rupture dominance increases with increasing mixing speed. Further, the relationship between electrical resistivity and dispersion was studied indicating a critical behaviour. A dependency on the amount of dispersed nanotubes was found only in a certain range of state of dispersion. [Copyright &y& Elsevier]