Dielectric,mechanical and electro-stimulus response properties studies of polyurethane dielectric elastomer modified by carbon nanotube-graphene nanosheet hybrid fillers

The typical nano-carbon materials, 1D fiber-like carbon nanotubes (CNTs) and 2D platelet-like graphene nanosheets (GRNs), that have attracted tremendous attention in the field of polymer nanocomposites due to their unprecedented properties, are used as conducting filler to induce a considerable improvement in the mechanical, thermal and electrical properties of the resulting graphene/polymer nanocomposites at very low loading contents. This study deals with the preparation and electro-stimulus response properties of polyurethane (PU) dielectric elastomer films with such 1D and 2D nanocarbon fillers embedded in the polymer matrix. The various forms of carbon used in composite preparation include CNT, GRN and CNT-GRN hybrid fillers. Results indicate that the dielectric, mechanical and electromechanical properties depend on the carbon filler type and the carbon filler weight fraction. Here, it has been also established that embedding CNT-GRN hybrid fillers into pristine polyurethane endows somewhat better dispersion of CNTs and GRNs as well as better interfacial adhesion between the carbon fillers and matrix, which results in an improvement in electric-induced strain. Therefore, the nanocomposites seem to be very attractive for microelectromechanical systems applications.     

Biodegradable Nanocomposites Based on the Polyester Poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) and Layered Silicate or Expanded Graphite

Novel nanocomposites based on the biodegradable polymer poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBHx) and layered fillers, specifically layered silicate (clay25A) and expanded graphite (EG), were prepared by melt intercalation. The dispersion of the fillers in the PHBHx was characterized by wide‐angle X‐ray diffraction (WAXD) and transmission electron microscopy (TEM). The effects of the fillers on the polymer structure, thermal stability and mechanical properties of the nanocomposites were also studied, by differential scanning calorimetry, thermogravimetric analysis, and strain‐stress measurements in elongation, respectively. The WAXD and TEM results showed that the clay25A and EG was exfoliated into well‐dispersed sheets in the polymer matrix, especially when the filler concentration were relatively low. This gave rise to considerable improvements in Young's modulus, and resulted in increases in the thermal degradation. It should be possible to convert the EG dispersions obtained thus far to ones yielding filler‐filler networks that show electrical conductivity.     

Comparisons Among Electrical and Rheological Properties of Melt-Mixed Composites Containing Various Carbon Nanostructures

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.     

Preparation and properties of chitosan nanocomposites with nanofillers of different dimensions

In this work, the chitosan ternary nanocomposites with two-dimensional (2D) clay platelets and one-dimensional (1D) CNTs have been successfully prepared by a simple solution-intercalation/mixing method in acid media. It was found that the thermal degradation temperature of chitosan (at 50% weight loss) could be only improved in about 20-30 °C by adding 3 wt% either clay or CNTs, however, almost 80 °C increase of degradation temperature could be achieved by adding 2 wt% clay and 1 wt% CNTs together. Dynamic mechanical measurement demonstrated an obviously improved storage modulus for chitosan/clay-CNTs than that for the corresponding binary chitosan/clay or chitosan/CNT nanocomposites with the same total filler content (3 wt%). For the solvent vapor permeation properties, a largely improved benzene vapor barrier property was observed only in chitosan/clay-CNT ternary nanocomposites and depended on the ratio of clay to CNTs. XRD, SEM and TEM results showed that both clay and CNTs could be well dispersed in the ternary nanocomposites with the nanotubes located around the clay platelets. FTIR showed an improved interaction between the fillers and chitosan by using both clay and CNTs. A much enhanced solid-like behavior was observed in the ternary nanocomposites, compared with the corresponding binary nanocomposites with the same total filler content, as indicated by rheological measurement. The unique synergistic effect of two-dimensional (2D) clay platelets and one-dimensional (1D) CNTs on the property enhancement could be tentatively understood as due to a formation of much jammed filler network with 1D CNTs and 2D clay platelets combined together. Our work demonstrates a good example for the preparation of high performance polymer nanocomposites by using nanofillers with different dimensions together.     

A brief survey on CLAYPEN and Nanocomposites based on unmodified PE and organo-pillared clays

New clay fillers are mixed with linear low-density polyethylene at 160 °C for 10 min to obtain clay-PE nanocomposites (CLAYPEN) by melt intercalation. Raw montmorillonite (Mt) was pillared (PMt) with partially hydrolyzed Al and Fe salt solutions and further reacted with hexadecyl trimethylammonium bromide (OPMt). For comparison, the hexadecyl trimethylammonium-montmorillonite (OMt) was prepared as a reference material. PE is not intercalated by organoclay. In investigating the pillared clay-PE nanocomposites, XRD is not an appropriate indicator of intercalation of PE, which penetrates into the mesoporous OPMt as shown by TEM. All the nanocomposites have higher Young modulus values than the pristine PE. The best compromise between the other mechanical properties (tensile strength and elongation at break) is obtained with the OPMt-PE nanocomposite. Cone-calorimeter study shows that peak heat release rate value of PE decreases substantially (34%) on addition of 5 phr of this novel OPMt filler.     

Properties of rubber filled with montmorillonite with various surface modifications

Layered silicate/natural rubber composites were prepared by direct polymer melt intercalation. Na‐montmorillonite Kunipia‐F and its organic derivates (organo‐clays) prepared by ion exchange were used as clay fillers. Silica (SiO₂) Ultrasil VN3, a filler commonly used in the rubber industry, was used in combination with clay fillers. The effect of clay or organo‐clay loading from 1 up to 10 phr without (0 phr) or with silica (15 phr) showed significant improvement of the tensile properties (stress at break, strain at break and modulus M100). Modification of montmorillonite by three alkylammonium cations with the same length of alkylammonium chain (18 carbons) and different structure resulted in altered reinforcing and plasticizing effects of the filler in composites with rubber matrix. Copyright © 2011 John Wiley & Sons, Ltd.     

Polymer nanocomposites based on polyamide 6 modified with fulleroid fillers

Polymer nanocomposites based on polyamide and fulleroid modifiers are synthesized through in situ polymerization, and their mechanical and electric properties are studied. After introduction of 0.001–0.1 wt % fulleroid modifiers, Young’s modulus and the strength of thermoplastic composites increases by 15–20%, practically independently of the amount of filler. This circumstance is due to the fact that the introduction of fulleroid fillers causes selective crystallization of polyamide 6 only in the α form. The introduction of fullerene fillers considerably improves the tribological characteristics of polymer nanocomposites, thereby decreasing the friction coefficient by a factor of 2. The electric properties of nanocomposites are studied also.     

Depth-Dependent Indentation Microhardness Studies of Different Polymer Nanocomposites

Continuous depth sensing indentation microhardness measurements were performed to investigate the effect of filler content and dimensionality on the mechanical behaviour of different polymer nanocomposites. In 1D filler reinforced nanocomposites (such as PP/MWCNT system), both the hardness and the indentation modulus were found to appreciably increase up to a filler weight fraction of 1.6 wt.-%. Further addition of the filler changed the properties only insignificantly. In the nanocomposites with 2D filler (such as in PA6/LS) both the hardness and the indentation modulus increase notably with the addition of the filler and showed intense plasticity. In the investigated systems and composition range, the 3D filler (such as PP/OS2) showed no reinforcing effect at all. In was concluded that the 1D and 2D nanofillers play much more effective reinforcing role to improve the mechanical properties than the 3D fillers.     

Click coupled graphene for fabrication of high‐performance polymer nanocomposites

An effective technique of using click coupled graphene to obtain high‐performance polymer nanocomposites is presented. Poly(ε‐caprolactone) (PCL)‐click coupled graphene sheet (GS) reinforcing fillers are synthesized by the covalent functionalization of graphene oxide with PCL, and subsequently the PCL‐GS as a reinforcing filler was incorporated into a shape memory polyurethane matrix by solution casting. The PCL‐click coupled GS has shown excellent interaction with the polyurethane matrix, and as a consequence, the mechanical properties, thermal stability, thermal conductivity, and thermo‐responsive shape memory properties of the resulting nanocomposite films could be enhanced remarkably. In particular, for polyurethane nanocomposites incorporated with 2% PCL‐GS, the breaking stress, Young's modulus, elongation‐at‐break, and thermal stability have been improved by 109%, 158%, 28%, and 71 °C, respectively. This click coupling protocol offers the possibility to fully combine the extraordinary performance of GSs with the properties of polyurethane. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Mechanical properties of polymers containing fillers

The addition of fillers can significantly change the mechanical characteristics of a material. In this paper, a general, mechanistic model is established to determine the moduli, relaxation moduli, break strengths, and break strains for polymer films containing liquid and solid micro fillers. Based on rigorous continuum mechanics principles, this model considers the filler/filler interactions, incorporates the nonlinear synergistic effects of fillers, and provides accurate predictions in comparison with experimental data. The analytical model developed provides information that is not available or extremely difficult to obtain experimentally. The model can be applied to determine the filler/matrix adhesion and filler modulus using measured modulus of a filled polymer film (a filled polymer is a polymer containing fillers). It is found that the compression moduli of polymer films containing liquid fillers differ significantly from the tension moduli, especially when the volume fraction of the filler is high. The difference in compression and tension Young's moduli normalized by the tension Young's modulus is as high as 35%. The relative error in maximum pressure calculation during Hertzian contact caused by using the tension moduli is as high as 48%. The relaxation modulus of a filled polymer film is determined through inverse Laplace transforms of its composite modulus in the s‐space. For a filled polymer film containing liquid phase fillers, a closed form solution for its relaxation modulus has been obtained. It is found that the composite relaxation modulus of the filled polymer is proportional to the relaxation modulus of the matrix polymer multiplied by a factor related to the volume fraction of the liquid filler. The break strength of the filled polymer is found to be proportional to the break strength of the polymer matrix material multiplied by a power function of the modulus ratio of filled polymer to polymer matrix, R. The break strain of the filled polymer is proportional to the break strain of the polymer matrix multiplied by a power function of 1/R. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 155–172, 1999     

Tensile modulus of polymer/CNT nanocomposites by effective volume fraction of nanoparticles as a function of CNT properties in the network

In this article, the effects of filler network and interphase between polymer matrix and nanoparticles on the tensile modulus of polymer/carbon nanotubes (CNT) nanocomposites are assumed by the effective volume fraction of nanoparticles. By this approach, the Takayanagi model is developed for polymer/CNT nanocomposites above percolation threshold. Also, the effective factors for filler network including the number (N ), aspect ratio (α ) and percolation threshold (? _p ) of CNT are correlated to three main parameters. The developed model is evaluated for some reported samples from previous papers, and the influences of main parameters on the modulus are examined. The acceptable predictability of the developed model for modulus of nanocomposites is illustrated by experimental results. The “α ” and “N ” parameters play positive roles in the modulus, while an inverse relation is observed between the modulus and the percolation threshold. The reasonable effects of these parameters on the tensile modulus of polymer/CNT nanocomposites are also discussed. Copyright © 2017 John Wiley & Sons, Ltd.     

Morphology and elastic modulus of novel poly[oligo(ethylene glycol) diacrylate]‐montmorillonite nanocomposites

Novel thermosetting poly[oligo(ethylene glycol) diacrylate]‐sodium montmorillonite nanocomposites containing a range of clay volume fractions were prepared by an in situ polymerization method. X‐ray diffraction showed that the basal plane spacing of the clay was increased to approximately 1.7 nm regardless of clay volume fraction. Transmission electron microscopy confirmed the basal spacing and intercalated structure. The elastic moduli of the composites were measured using ultrasonic pulse‐echo equipment. The results show that the Young's modulus and shear modulus increase with nominal clay volume fraction up to 0.22, and are in good agreement with the well‐established Christensen method and derived Hashin–Shtrikman bounds for conventional composites provided that the true volume fraction of clay reinforcement filler is calculated. At low clay volume fractions, the composites were transparent. When the nominal clay volume fraction was further increased, cracks and porous surfaces appeared, as observed by scanning electron microscopy. These defects decreased the elastic modulus, indicating an upper limit for clay additions in this preparation route. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1785–1793, 2005     

Development and thermo‐mechanical behavior of nanocomposite epoxy adhesives

Two kinds of organo‐modified (OM) clays were dispersed in an epoxy resin for the preparation of nanocomposite adhesives at various filler amounts. XRD tests evidenced the formation of intercalated structures, increasing the intercalation degree with the clay hydrophilicity. The original transparency of the samples was retained up to a filler content of 3 wt%, and then decreased due to filler agglomeration. The glass transition temperature of nanocomposites filled with the more hydrophilic clay (30B) raised up to a filler content of 3 wt% and then decreased, probably because of the concurrent and contrasting effects of the physical chain blocking and reduction of the cross‐linking degree. Also elastic modulus, stress at break, and fracture toughness were sensibly improved by nanoclay addition up to filler loadings of 0.5–1 wt%. For higher concentrations the positive contribution of clay nanoplatelets was counterbalanced by the presence of agglomerated tactoids in the matrix. Mechanical tests on single‐lap composite (epoxy/glass) bonded joints evidenced an enhancement of the shear strength by about 25% for an optimal filler content of 1 wt%. Therefore, it was concluded that the addition of a proper amount of OM clay to epoxy adhesives could represent an effective way to improve the shear resistance of adhesively bonded composite structures. Copyright © 2011 John Wiley & Sons, Ltd.     

Development of Natural Rubber-Fibrous Nano Clay Attapulgite Composites: The Effect of Chemical Treatment of Filler on Mechanical and Dynamic Mechanical Properties of Composites

Common nano clay fillers have layered structure. Some nano clays like Attapulgite (AT), Sepiolite have rod like fibrous structure. Compared to layered structured clay fibrous clay AT can undergo better dispersion in polymer matrix leading to better improvement in composite properties. Chemical modifications of AT are done through amine treatment as well as by amine+silane treatment to get chemically modified fillers AAT and SAT respectively. In the present investigation, nano composites are prepared using natural rubber (NR) filled with AT, AAT and SAT. Three different loadings of each filler are used namely 2.5, 5, and 10 phr (parts per hundred of rubber). Mechanical properties like tensile strength, elongation at break increase with the increase in filler loading up to 5 phr there after these properties marginally fall when loading is increased to 10 phr due to problem of filler dispersion at higher loading. However, modulus at 300% elongation and tear strength increases with the increase in filler loading up to 10 phr. Very similar trend can also be observed for composites with chemically modified fillers, AAT and SAT. But the degree of reinforcement is higher in the case of AAT and SAT compared to that of unmodified filler AT for the same filler loading. This difference is mainly due to better polymer-filler interaction and filler dispersion in the case of chemically modified clays AAT and SAT compared to unmodified AT. Tear strength of composites increases remarkably with the addition of AT and which is further enhanced when chemically modified clays AAT and SAT are added. Dynamic-mechanical analyses of different clay composites give idea about the difference in the degree of polymer–filler interaction due to chemical treatment of filler.     

Towards scalable production of polyamide 12/halloysite nanocomposites via water‐assisted extrusion: mechanical modeling,thermal and fire properties

In this study, polyamide 12 (PA12)/untreated halloysite nanotubes (HNTs) nanocomposites are prepared in a semi‐industrial scale extruder using a non‐traditional “one step” water‐assisted extrusion process. A morphological study is carried out using a combination of scanning electron microscopy and transmission electron microscopy analyses to evaluate the influence of water injection and filler content on the quality of clay dispersion. The use of water injection slightly improves the nanoscale dispersion at low HNTs content (<8 wt.%), while this effect is more pronounced at higher filler loading (16 wt.%). A mechanism explaining the physico‐chemical action of water during extrusion is proposed. The materials are characterized with respect to their mechanical, thermo‐mechanical, thermal and fire properties. A strong correlation is found between nanostructure and physical properties; the more uniform dispersion of the clay nanotubes, the higher mechanical reinforcement, thermal stability and fire retardancy of PA12 nanocomposites. Tensile tests results are interpreted in terms of three mechanical models: the Halpin–Tsai's model for stiffness and the interfacial strength model and the Pukanszky's equation for yield strength. Linear fits of the experimental data confirm that the superior reinforcement of nanocomposites prepared using water injection results from improved clay dispersion and better interfacial adhesion between PA12 and HNTs. In view of these promising results, the proposed direct melt compounding method could be easily scaled‐up towards the production of PA12–HNTs nanocomposites at an industrial scale. Copyright © 2013 John Wiley & Sons, Ltd.     

Amine‐cured epoxy/clay nanocomposites. II. The effect of the nanoclay aspect ratio

The thermophysical and mechanical properties of a nanocomposite material composed of amine‐cured diglycidyl ether of bisphenol A (DGEBA) reinforced with organomontmorillonite clay are reported. The storage modulus at 100 °C, which was above the glass‐transition temperature (T_g), increased approximately 350% with the addition of 10 wt % (6.0 vol %) of clay. Below the T_g, the storage modulus at 30 °C increased 50% relative to the value of unfilled epoxy. It was determined that the T_g linearly increased as a function of clay volume percent. The tensile modulus of epoxy at room temperature increased approximately 50% with the addition of 10 wt % of clay. The reinforcing effect of the organoclay nanoplatelets is discussed with respect to the Tandon–Weng and Halpin–Tsai models. A pseudoinclusion model is proposed to describe the behavior of randomly oriented, uniformly dispersed platelets in nanocomposite materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4391–4400, 2004     

Mechanical properties of polymer‐blend nanocomposites with organoclays: Polystyrene/ABS and high impact polystyrene/ABS

Thirty‐three polystyrene (PS)/acrylonitrile‐butadiene‐styrene (ABS) and high impact PS/ABS polymer blends with organoclay and copolymer additives were prepared by melt processing using different mixing sequences in order to test the putative capability of clay to perform a compatibilizing role in polymer blends. In general, the addition of clay increased the tensile modulus and had little effect on tensile strength. For the blends studied in this work, the addition of organoclays caused a catastrophic reduction in impact strength, a critical property for commercial viability. The polymer‐blend nanocomposites adopted a structure similar to that for ABS/clay nanocomposites as determined by X‐ray diffraction and transmission electron microscopy. It is suggested that clay reinforcement inhibits energy absorption by craze formation and shear yielding at high strain rates. Simultaneous mixing of the three components provided nanocomposites with superior elongation and energy to failure compared to sequential mixing. The clay pre‐treated with a benzyl‐containing surfactant gave the best overall properties among the various organoclays tested and of the two clay contents studied 4 wt % was preferred over 8 wt % addition. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Nanotailoring of sepiolite clay with poly [styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene]: structure–property correlation

Poly [styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS)/sepiolite clay nanocomposites are prepared by solvent casting method. Two types of schemes have been adopted to establish the compatibility between nonpolar polymer (SEBS) and needle‐like inorganic filler (sepiolite), either by polar modification of the nonpolar polymer or organic modification of the inorganic filler. Structure–property correlation of nanocomposites derived from two different approaches is compared. Structural and morphological analysis of nanocomposites has been investigated by Fourier transform infrared spectroscopy, X‐ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. Fourier transform infrared result shows better compatibility between SEBS and modified sepiolite clay compared to maleic anhydride grafted SEBS and pristine sepiolite in their nanocomposites. Tensile strength and % elongation are found to increase by 32 and 105%, respectively, with the addition of just 3 parts per hundred parts of resin (phr) modified sepiolite clay to pristine SEBS matrix. Moreover, thermal stability has also improved by 96°C with similar loading. This work provides a new insight into the structure and thermo‐mechanical properties of novel SEBS–sepiolite clay nanocomposites. Copyright © 2017 John Wiley & Sons, Ltd.     

Plasticized polylactide/clay nanocomposites. I. The role of filler content and its surface organo‐modification on the physico‐chemical properties

Polylactide (PLA)‐layered silicate nanocomposites plasticized with 20 wt % of poly(ethylene glycol) 1000 were prepared by melt blending. Three kinds of organo‐modified montmorillonites—Cloisite® 20A, Cloisite® 25A, and Cloisite® 30B—were used as fillers at a concentration level varying from 1–10 wt %. Neat PLA and plasticized PLA with the same thermomechanical history were considered for comparison. Nanocomposites based on amorphous PLA were obtained via melt‐quenching. The influence of both plasticization and nanoparticle filling on the physicochemical properties of the nanocomposites were investigated. Characterization of the systems was achieved by size exclusion chromatography (SEC), thermogravimetric analysis (TGA), thermally modulated differential scanning calorimetry (TMDSC), X‐ray diffraction (XRD), and dynamic mechanical analysis (DMTA). SEC revealed a decrease of the molecular weight of the PLA matrix with the filler content. Thermal behavior on heating showed one cold crystallization process in the reference neat PLA sample, while two cold crystallization processes in plasticized PLA and plasticized nanocomposites. The thermal windows of these processes tend to increase with the filler content. The crystalline form of PLA developed upon heating was affected neither by the plasticization nor by the type and content of Cloisite used. It was found that the series of organo‐modified montmorillonites with decreasing affinity to PLA is Cloisite® 30B, Cloisite® 20A, and Cloisite® 25A, respectively. The dynamic mechanical properties were sensitive to the sample composition. Generally, the storage modulus increased with the filler content. Glassy PEG, well dispersed within unfilled PLA matrix, exhibited also a reinforcing effect, since the storage modulus of this sample was higher than for unplasticized reference at temperature region below the glass transition of PEG. Moreover, loss modulus of all plasticized samples revealed an additional maximum ascribed to the glass transition of PEG–rich dispersed phase, indicating partial miscibility of organic components of the systems investigated. The magnitude of this mechanical loss was correlated with the filler content, and to some extent, also with the nanofiller ability to be intercalated by polymer components. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 299–311, 2006     

Largely improved tensile properties of chitosan film via unique synergistic reinforcing effect of carbon nanotube and clay

In this work, a great synergistic effect of 2D clay platelets and 1D carbon nanotubes (CNTs) on reinforcing chitosan matrix has been observed for the first time. With incorporation of 3 wt % clay and 0.4 wt % CNTs, the tensile strength and Young's modulus of the nanocomposites are significantly improved by about 171 and 124%, respectively, compared with neat chitosan. This could be understood as due to the formation of much jammed fillers network with 1D CNTs and 2D clay platelets combined together, as indicated by rheological measurement. Our work demonstrates a good example for the preparation of high performance polymer nanocomposites by using nanofillers of different dimension together.