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Effect of blending and nanoclay on dielectric properties of polypropylene
Abstract
This paper investigates the effects of organomodified montmorillonite (clay) and styrene-(ethylene-co-butylene)-styrene triblock copolymer (SEBS) on the morphological and electrical properties of polypropylene (PP). A series of binary PP-clay nanocomposites along with nanocomposites having a blend matrix were prepared. The nanofillers were found to be well-embedded into the polymeric matrix with a high degree of dispersion. The microstructure of the blend matrix revealed a co-continuous structure for the equal proportion of the two polymers. This was shown to control the localization of nanofiller by triggering them to migrate into the SEBS phase, mostly accommodating in the interface and creating a strong network which eventually resulted in more exfoliation of clay platelets and comparable/superior electrical properties comparing to binary nanocomposites. The incorporation of clay resulted in a solid-like rheological behavior which was more enhanced in blend nanocomposites due to the stronger network of nanofiller. The dielectric spectra of the nanocomposites revealed two major relaxation processes aroused by the presence of clay. A new relaxation process was observed for the nanocomposites with the blend matrix, related to the SEBS phase. Both blending and nanofiller inclusion resulted in less accumulated space charge. A significant improvement in the AC breakdown strength of PP was witnessed upon addition of clay. Despite the less inherent breakdown strength of SEBS, the blend nanocomposites showed even more enhanced breakdown properties confirming the further improvement of nanofiller network structure.
... The dielectric properties of nanocomposites also depend on the geometry of nanofillers. Beside 0D nanofillers, 1D and 2D nanofillers are also incorporated into PP for tailoring its dielectric properties [79][80][81][82][83][84][85][86][87]. Since the anisotropy of 1D and 2D nanofillers is different from 0D, they result in different interface adhesions. ...
... Nanoclay is also used to enhance the breakdown strength and suppress the space charge of PP. For instance, Eesaee et al. [86] investigated the AC breakdown strength of PP/SEBS blend nanocomposites containing 2D organomodified clay. It was reported that, by the addition of 5 wt% organoclay, an improvement of 25% was achieved in breakdown strength with suppressed space charge. ...
Abstract Cross‐linked polyethylene (XLPE) is commonly used as an insulation material in power cables. Due to the recent advancements in the field of high voltage power transmission and distribution, there is a need for novel cable insulation materials that have high performance, recyclability and high working temperature as alternatives for the conventional XPLE‐based insulation materials. Polypropylene (PP) shows excellent properties and has drawn considerable attention as a potential high voltage direct current (HVDC) insulation material. Therefore, the development of PP‐based HVDC cable insulation with improved electrical, thermal and mechanical properties is important in discovering a potentially recyclable cable insulation material. Due to the remarkable development in the field of nanodielectrics, nanotechnology can be a promising solution for enhancing the overall dielectric properties of PP‐based insulation materials. This review presents the important aspects of PP‐based nanocomposites for HVDC cable insulation with a special focus on understanding the effects of various parameters of nanofillers on the dielectric properties of PP‐based HVDC cable insulation. Based on the gathered information, future perspectives for improving the dielectric properties of PP‐based nanocomposites for HVDC cable are provided.
... Polypropylene nanocomposites have demonstrated improved dielectric properties, such as increased dielectric breakdown strength and space charge suppression [7]. Typically, a surfacemodified nanofiller is required to enhance nanofiller dispersion and its interaction with the polymer matrix. ...
This work studies the effects of surface-modified magnesium oxide (MgO) nanofiller on the mechanical properties and AC breakdown strength of polypropylene (PP) and ultra-high molecular weight polyethylene (UHMWPE) composites. The inclusion of nanoparticles results in improved interfacial interactions as a consequence of the transition from separate crystallization to co-crystallization. Thus, nano-MgO enhances the breakdown strength of PP/UHMWPE by acting as a compatibilizer between the PP/UHMWPE. UHMWPE decreases Young’s modulus and ultimate tensile strength while increasing elongation at yield point in the PP matrix. PP/UHMWPE has increased elasticity due to weak interfacial adhesion. The addition of nano-MgO, however, promotes stronger bonding between PP and UHMWPE phases, providing stiffer composites than those without MgO. There are no apparent differences between PP/UHMWPE and PP/UHMWPE/MgO regarding ultimate tensile strength. It is obvious that the dielectric breakdown strength and elastic enhancement are significantly influenced by the interfacial adhesion between the polymers.
... The breakdown occurs via longer paths along spherulite boundaries and the strength of BD is therefore increased. Another possible mechanism is that the free charge densities surrounding the nanoparticle-polymer matrix interfaces decrease [14], resulting in modified samples having higher AC BD compared to unmodified references. The results on the different composites indicate further increase of AC BD, especially when using EA. ...
This work focuses on the effects of surface-modified nanofillers with various polar silane coupling agents on dielectric permittivity and dielectric breakdown strength of PP nanocomposites. Surface functionalization of nanofillers is implemented using an anhydrous technique with three different surfactants. These surface-modified nanofillers are mixed with polymers at fill grades of up to 5% by weight, prepared by a solution blending method. Thermogravimetric analysis confirms the presence of surface functionalization and the desired nanofiller amount. Dielectric permittivity values tend to rise as a function of filler content, and notably the dielectric loss of TiO 2 nanocomposites is significantly increased below 0.1 Hz. MgO nanocomposites have overall lower dielectric losses than TiO 2 . AC breakdown of PP is significantly improved with modified TiO 2 and MgO at 2.5%, while other fill grades have less pronounced effects. Ethoxy-modified nanoparticles with long chain hydrolysable group show overall the best dielectric properties.
... Others have found ways to create 2D layers of materials either through formal planar layering or through organization of fillers into sheets or strings that can also lead to interesting properties. 18,72,73 The naturally occurring 2D materials have also been explored with significant success when they can be well dispersed, 74,75 but there has been less emphasis on them. ...
This article provides a perspective on the development of polymer nanodielectrics for electrical insulation applications. It includes a short history of the development of the field, barriers to implementation, a chemical toolbox available for optimizing properties, some examples of potential commercial development, and the latest advances. It offers opinions on critical research needed to fully develop the models needed to predict the behavior and to develop design tools. Key findings include the need for quantification of nanofiller dispersion, investment in long term aging data research, better scale-up methods, a data resource that brings the broad data together in a format that enables faster scientific discovery, and a commercial entity willing to take the risk in implementing these promising materials.
... A recent publication on a PP-rubber blend containing an organically modified montmorillonite clay (organoclay) showed that the organoclay altered the dielectric properties of the immiscible blend [4]. Elsewhere, the dielectric properties of both PP and copolymer ethylene vinyl acetate (EVA) have been investigated thoroughly. ...
The addition of organoclay to a polypropylene-rubber blend, primarily introduced to compatibilise the immiscible polymer blend, invokes contrasting dielectric and charge dynamic behaviour depending on the filler loading level. We report that at 0.5 wt.% loading, the organoclay decreases the DC conductivity, causes no significant dielectric losses, makes no significant difference to the space charge results compared to the unfilled system, and increases the reproducibility of the breakdown strength results, and hence the reliability of the material. These somewhat surprising results, contrasted by measurements of samples with 2.5 and 5 wt.%, lead us to conclude that trace amounts of organoclay improve the otherwise immiscible polymer blend making organoclay a suitable additive for HVDC applications.
This paper discusses the charge transport and accumulation in clay-containing LDPE (low density polyethylene) nanocomposites. LDPE is shown to host charges of both polarities in the form of homo and heterocharge when subjected to high electric fields. The addition of nanoclays has been shown to always increase the high field DC conductivity of the nanocomposites. This is shown to actually work in favor of the ability of the material to prevent the accumulation of space charge by slowly, but persistently, allowing space charges to flow across the insulation wall. However, in severe conditions of a combined high electric field and high temperature, the current flow exceeds a threshold where massive injected charges negatively impact the charge profile and the electric field distribution is greatly distorted.
Blends of polyethylene (PE) and polypropylene (PP) have always been the subject of intense reasearch for encouraging polymer waste recycling while producing new materials for specific applications in a sustainable way. However, being thermodynamically immiscible, these polyolefins form a binary system usually exhibiting lower performances compared with those of the homopolymers. Many studies have been carried out to better understand the PE/PP blend compatibilization for developing a high-performance and cost-effective product. Both nonreactive and reactive compatibilization promote the brittle to ductile transition for a PE/PP blend. However, the final product usually does not meet the requirements for high demanding commercial applications. Therefore, further PE/PP modification with a reinforcing filler, being either synthetic or natural, proved to be a good method for manufacturing high-performance reinforcend polymer blend composites, with superior and tailored properties. This review summarizes the recent progress in compatibilization techniques applied for enhancing the interfacial adhesion between PE and PP. Moreover, future perspectives on better understanding the influence of themodynamics on PE/PP synergy are discussed to introduce more effective compatibilization strategies, which will allow this blend to be used for innovative industrial applications.
Microstructure and electrical breakdown properties of blends and nanocomposites based on low-density polyethylene (LDPE) have been discussed. A series of LDPE nanocomposites containing different amount of organomodified montmorillonite (clay) with and without compatibilizer have been prepared by means of melt compounding. Two sets of blends of LDPE with two grades of Styrene-Ethylene-Butylene-Styrene block copolymers have been prepared to form cocontinuous structure and host the nanoreinforcement. A high degree of dispersion of oriented clay was observed through X-ray diffraction, scanning, and transmission electron microscopy. This was confirmed by the solid-like behavior of storage modulus in low frequencies in rheological measurement results. An alteration in the morphology of blends was witnessed upon addition of clay where the transportation phenomenon to the copolymer phase resulted in a downsizing on the domain size of the constituents of the immiscible blends. The AC breakdown strength of nanocomposites significantly increased when clay was incorporated. The partially exfoliated and intercalated clay platelets are believed to distribute the electric stress and prolong the breakdown time by creating a tortuous path for charge carriers. However, the incorporation of clay has been shown to diminish the DC breakdown strength of nanocomposites, mostly due to the thermal instability brought by clay.
Cross-linked polyethylene (XLPE) is commonly used in medium/high voltage insulation due to its excellent dielectric properties and acceptable thermomechanical properties. To improve both electrical and thermal properties to a point that would possibly avoid the need for crosslinking, nanoclay fillers can be added to polymer matrix to form nanocomposites materials. In this paper, PE/clay nanocomposites were processed by mixing a commercially available premixed polyethylene/O-MMT masterbatch into a polyethylene blend matrix containing 80 wt% low density polyethylene LDPE and 20 wt% high density polyethylene HDPE with and without compatibilizer using a corotating twin-screw extruder. Various characterization techniques were employed in this paper, including optical microscopy, AFM, TEM, TGA, DMTA, and dielectric breakdown measurements in order to understand the correlation between structure and short-term dielectric breakdown strength.
Nanocomposite formation, through the incorporation of high aspect ratio nanoparticles, has been proven to enhance the dielectric properties of thermoplastic polymers, when the mitigation of internal charges and the nature of the interfacial regions are properly adjusted. Here, we explore polyethylene/montmorillonite nanocomposites, and we specifically investigate how to impart desirable dielectric behavior through controlled nanoscale texturing, i.e., through control of the spatial arrangement of the high aspect ratio nanofiller platelets. In particular, it is shown that filler alignment can be used to improve the high electric-field breakdown strength and the recoverable energy density. The origins of the improved high field performance were traced to improved charge-trapping by a synergy of nanofillers and polar maleic anhydride (MAH) groups--introduced via polyethylene-MAH copolymers--as templated by the inorganic nanofillers. Further, it is conclusively demonstrated that the alignment of the two-dimensional nanoparticles has a measurable positive effect on the breakdown strength of the materials and, consequently, on the maximum recoverable energy density.
The peculiarities of moisture absorption of epoxy–nanoclay composite are estimated in the paper. Second Fick’s law of diffusion was used to predict moisture diffusivity and equilibrium moisture content using accelerated analytical procedure. It was experimentally confirmed that sorption process in NC passes more slowly than in pure epoxy resin, for the highest filler content diffusivity reduces about half of diffusivity as for epoxy resin. The deviation from mixture rule was obtained for the equilibrium moisture content and the estimation of interphase content in composite was undertaken. It was determined that the higher content of interphase consistently leads to greater moisture absorption.
In this work, a smectite clay from the State of Paraiba, Brazil, was treated with six different types of ammonium salts, which is an usual method to enhance the affinity between the clay and polymer for the preparation of nanocomposites. The clays, before and after modification, were characterized by X ray diffraction. The conformation of the salts within the platelets of the clay depended on the number of long alkyl chains of the salt. The thermal stability of the clays was also studied. The ammonium salts thermal decomposition was explained in light of their position within the organoclays.
Blends of polyethylene (PE) with nanocomposites of polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene grafted maleic anhydride (SEBS-MA) thermoplastic elastomer filled with Zinc Oxide (ZnO) nanoparticles have been studied as potential candidates for applications in HV insulation systems including HVDC cables. In particular, the dielectric and mechanical properties of PE/SEBS-MA/ZnO blend nanocomposites have been evaluated and compared to those of PE/ZnO homopolymer nanocomposites prepared as a reference. PE/ZnO materials were characterized by homogeneous distribution of nanoparticles and presence of agglomerations attributed to insufficient compatibility between the metal oxide nanoparticles and the polyolefin matrix. However, nanoscale dispersion was achieved in SEBS-MA/ZnO and PE/SEBS-MA/ZnO nanocomposites due to improved compatibility between the nanoparticles and SEBS-MA. Besides, in PE/SEBS-MA/ZnO blend nanocomposites, ZnO nanoparticles remained exclusively confined in SEBS-MA or at the interface between PE and SEBS-MA. In terms of dielectric properties, the unfilled blend PE/SEBS-MA featured reduced breakdown strength and resistance to surface erosion by partial discharges in comparison with neat PE. However, upon addition of ZnO the blend PE/SEBS-MA presented higher performance when compared to PE. At 1 wt% ZnO loading, the resistance to surface erosion of PE/SEBS-MA increased by 45% higher than neat PE/SEBS-MA, 38% higher than unfilled PE and 30% higher PE/ZnO nanocomposite containing the same ZnO loading. Besides, blend nanocomposites exhibited dielectric losses lower than PE/ZnO nanocomposites at power frequencies and temperatures up to 80 °C. The breakdown strength of both sets of nanocomposites decreased compared to unfilled materials, at large loadings of nanoparticles. However, smaller reduction was observed in the case of PE/SEBS-MA/ZnO nanocomposites due to improved nanoparticles dispersion. Finally, PE/SEBS-MA/ZnO nanocomposites featured enhanced mechanical flexibility when compared to PE/ZnO nanocomposites.
Having higher melting temperature than polyethylene, polypropylene has been expected as insulation material for power cable. But isotactic polypropylene used generally is unsuitable as cable insulation because it shows poor flexibility, low breakdown strength due to growing spherulites, and so on. But stereoregular syndiotactic polypropylene (s-PP) newly developed with metallocene catalyst shows quite different properties from i-PP. The authors had investigated the basic properties of s-PP and the initial properties as a cable which was manufactured using s-PP insulation, in the previous paper. As the results of this, it was revealed that s-PP had superior thermal and electrical properties to cross-linked polyethylene and the s-PP insulation cable showed satisfactory initial properties. However, in order to apply to an actual cable, the properties must be maintainable over 30 years after construction. In this paper, we estimated the long term and remaining properties for s-PP insulation cable. A series of experiments on long term properties gave following results. (1) S-PP cable shows longer life over 30 years. (2) The breakdown strength of s-PP cable after long term experiment equal to 30 years is slightly lower than initial breakdown strength, but it's sufficient as remaining property. Furthermore, water-tree resistivity of s-PP was investigated and it was revealed that s-PP significantly suppressed the water tree propagation compared with XLPE. These results suggested that s-PP cable would be available as next generation cable. © 2004, The Institute of Electrical Engineers of Japan. All rights reserved.
The electrical properties of nanocomposites are closely related to their nanostructures. In order to investigate the nanostructures and space charge characteristics of magnesium oxide (MgO)/low-density polyethylene (LDPE), samples of LDPE with nano-MgO from 0.1 to 2.0 wt% are prepared, as well as pure LDPE. The nanostructures of nanocomposites are investigated by the technology of synchrotron radiation small-angle x-ray scattering (SAXS), and the space charge distributions in nanocomposites and LDPE are measured by the pulsed electro-acoustic (PEA) method. Results of the synchrotron radiation SAXS experiments reveal that there is obvious interphase between the nano-MgO particle and the LDPE matrix, the thickness of which increases along with the increase in nano-MgO concentration. The agglomeration and mass fractal exist in all nanocomposites, and become more obvious at higher concentration. Results of space charge measurements indicate that the apparent trap-controlled mobilities and the apparent trap depths are respectively larger and smaller than those in LDPE during the initial phase of depolarization when the concentrations are 0.1 and 0.5 wt%, and are respectively smaller and larger than those in LDPE when the concentrations are 1.0 and 2.0 wt%. The space charge amount decreases after the addition of nano-MgO. This is mainly due to the introduction of shallow traps which promote the charge recombination in 0.1 and 0.5 wt% MgO/LDPE nanocomposites, and the introduction of deep traps which restrict the charge transportation in 1.0 and 2.0 wt% MgO/LDPE nanocomposites. The space charge characteristics of MgO/LDPE nanocomposites are explained combined with the nanostructures obtained from the synchrotron radiation SAXS experiments.
Thermoplastic elastomer nanocomposites based on respectively polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) and polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene grafted maleic anhydride (SEBS-MA) block copolymers and containing functionalized zinc oxide (ZnO) nanoparticles have been investigated as candidate materials for high voltage (HV) insulation systems. The dispersion of the organically modified ZnO nanoparticles has been successfully tuned through the MA graft and the block copolymer nanostructure. In particular, nanocomposites with signs of rheological percolation, indicating the formation of a network between individually dispersed nanoparticles and polymer chains, have been obtained at ZnO content as low as 5 wt% (0.9 vol%). This behavior resulted in an enhancement of the thermal conductivity and better control of the electrical conductivity while maintaining breakdown strength and dielectric losses in the same range of the unfilled insulating matrices. Furthermore, the resistance to surface erosion by partial discharges was significantly improved: in the presence of 5 wt% of individually dispersed ZnO nanoparticles, the eroded volume was reduced 10 times.
Polypropylene (PP) has been paid much attention due to its high melting point, excellent electrical insulting performance and thermoplastic property, which is potential to replace the XLPE as HVDC cable insulating material. Blending PP with polyolefin elastomer (POE) is an effective way to modify its stiffness and brittleness at room temperature. However, space charge behavior of PP/POE blend, as a great concern under dc stress, is not clear and needs further investigation. To research the space charge behaviors, pure PP, PP/POE blend and its nanocomposites with different contents were prepared. Then, mechanical properties, permittivity constant, breakdown strength, volume resistivity, space charge behaviors and trap level distribution were investigated. The results indicate the addition of POE enhances the mechanical flexibility of PP greatly, and nano-sized ZnO doping has little effect on the mechanical flexibility of PP/POE blend. The nanocomposites show lower permittivity constant, higher breakdown strength and higher volume resistivity than the PP/POE blend. Compared to pure PP, the space charge accumulation and electric field distortion get severe in PP/POE blend. However, by nanoparticles doping, space charges are remarkably suppressed, which is related to the increased trap level density in nanocomposites. It indicates the PP/POE/ZnO nanocomposites have much potential for HVDC cable application, which show high mechanical flexibility as well as excellent electrical performance.
Polypropylene (PP) has been paid much attention due to its high melting point, excellent electrical insulting performance and thermoplastic property, which is potential to replace the XLPE as HVDC cable insulating material. Blending PP with polyolefin elastomer (POE) is an effective way to modify its stiffness and brittleness at room temperature. However, space charge behavior of PP/POE blend, as a great concern under dc stress, is not clear and needs further investigation. To research the space charge behaviors, pure PP, PP/POE blend and its nanocomposites with different contents were prepared. Then, mechanical properties, permittivity constant, breakdown strength, volume resistivity, space charge behaviors and trap level distribution were investigated. The results indicate the addition of POE enhances the mechanical flexibility of PP greatly, and nano-sized ZnO doping has little effect on the mechanical flexibility of PP/POE blend. The nanocomposites show lower permittivity constant, higher breakdown strength and higher volume resistivity than the PP/POE blend. Compared to pure PP, the space charge accumulation and electric field distortion get severe in PP/POE blend. However, by nanoparticles doping, space charges are remarkably suppressed, which is related to the increased trap level density in nanocomposites. It indicates the PP/POE/ZnO nanocomposites have much potential for HVDC cable application, which show high mechanical flexibility as well as excellent electrical performance.
Polymer dielectrics with high thermal conductivity and low dielectric loss are highly attractive for applications in electric and electronic industry. In this paper, surface modified aluminum nitride (AlN) nanoparticles were introduced into polypropylene (PP) matrix via melt blending to prepare thermoplastic dielectrics with enhanced thermal conductivity and low dielectric loss. The microstructure, DC conductivity, dielectric properties, breakdown strength, space charge behavior, thermal conductivity and thermal stability of the nanocomposites were investigated. It is found that the inclusion of surface modified AlN nanoparticles results in improved thermal conductivity and thermal stability of PP/AlN nanocomposites. The dielectric constant shows a slight increase with AlN nanofiller content, and the dielectric loss remains at very low level of below 0.003. DC conductivity of PP/AlN nanocomposites increases but shows desirable weak dependence on electric field. DC and AC breakdown strength slightly decrease with the AlN nanoparticle content but it is still high enough for dielectric applications. More importantly, the PP/AlN nanocomposites is a thermoplastic material which is potential to be recycled and has less impact on the environment.
In this work, the effect of controlling the morphology on the dielectric properties of triblock copolymers and their clay-containing nanocomposites was evaluated. Two different copolymers: polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) and SEBS grafted with maleic anhydride were used for that purpose. Morphologies with different degrees of intercalation, exfoliation and orientation were obtained and tested. At the highest state of dispersion, achieved at a clay loading equal to 5 wt%, 50% of clay nanoplatelets were individually dispersed and located within the soft domain of the block copolymer and a maximum of interfacial polarization and a minimum of dynamic mechanical damping factor were respectively exhibited. When the nanoclays were oriented, the dielectric loss due to nanoclays conductivity contribution was reduced up to 2 orders of magnitude at high temperatures and low frequencies and the AC short-term breakdown strength increased up to 45%.
The effect of poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) copolymer on the thermal and dielectric
properties of polypropylene (PP)—nanosilica (NS) composites in relation with morphological aspects
revealed by atomic force microscopy (AFM) was investigated in this article. SEBS hindered the crystallization
process of PP in PP/NS composites, leading to a smaller degree of crystallinity and lower perfection of
crystalline structure. Broader lamellar thickness distribution was obtained in nanocomposites containing
SEBS. Almost two times higher dielectric loss as compared to PP reference and two relaxation processes
were detected in e=r (f) curves of nanocomposites. The first peak, in the same frequency domain as for the
references, was assigned to a-relaxation of polymer components together with interfacial polarization. The
relaxation time follows the Arrhenius law with an activation energy of 80–90 kJ/mol. For the second process,
the temperature dependence of the relaxation times obeyed the VFT equation. The dielectric changes following the incorporation of SEBS support its tendency to hinder the motional processes in PP, in accordance with DSC results. A smooth transition from a phase rich in SEBS to one containing mainly PP was detected in the AFM image of the composite with the larger amount of SEBS, emphasizing the good compatibility at the PP/SEBS interface.
The dielectric properties of a number of polymeric nanocomposites (PNC) have been investigated and reported, and there are very good reviews available, for example, see [1]-[3]. CIGRE Working group D1.24 has also performed several collaborative investigations on mostly epoxy- and polyethylene-based nanocomposites, which are reported in CIGRE publications [4], [5] as well as in archived papers [6], [7]. Dielectric nanocomposites investigated in the literature include various polyolefins such as polyethylene (PE; and PE blends) and polypropylene, ethylene vinyl acetate, polyamine, epoxy, and elastomers such as silicone rubber, containing various nanofillers such as metallic oxides, silica, alumina, titanium oxide, zinc oxide, and layered silicates (clays). Due to the very high specific surface area of nano-sized fillers, a few percent addition can significantly affect the dielectric properties of a polymeric material. The most common and practical processing methods suitable for thermoplastic nanocomposites are melt compounding, using a mixer, extruder, or both, and mixing in the liquid phase prior to polymerization for thermosetting resins, a process commonly called the in situ polymerization process [8]. Figure 1 gives examples of typical microstructures of polyolefin-based nanocomposites processed by melt compounding. The striking similarity of the microstructure shown in Figures 1(b) and 1(c) should be noted as both were obtained in two different labs from the melt compounding of fumed silica and a thermoplastic resin using a twin screw extruder. Similar microstructures are also reported for isotactic polypropylene/SiO2 nanocomposites melt blended by extrusion [9].
The effect of poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) copolymer on the thermal and dielectric properties of polypropylene (PP)—nanosilica (NS) composites in relation with morphological aspects revealed by atomic force microscopy (AFM) was investigated in this article. SEBS hindered the crystallization process of PP in PP/NS composites, leading to a smaller degree of crystallinity and lower perfection of crystalline structure. Broader lamellar thickness distribution was obtained in nanocomposites containing SEBS. Almost two times higher dielectric loss as compared to PP reference and two relaxation processes were detected in εr ′′(f) curves of nanocomposites. The first peak, in the same frequency domain as for the references, was assigned to α-relaxation of polymer components together with interfacial polarization. The relaxation time follows the Arrhenius law with an activation energy of 80–90 kJ/mol. For the second process, the temperature dependence of the relaxation times obeyed the VFT equation. The dielectric changes following the incorporation of SEBS support its tendency to hinder the motional processes in PP, in accordance with DSC results. A smooth transition from a phase rich in SEBS to one containing mainly PP was detected in the AFM image of the composite with the larger amount of SEBS, emphasizing the good compatibility at the PP/SEBS interface.
Macromolecular dynamics of sulfonated poly(styrene-b-ethylene-ran-butylene-b-styrene) (sSEBS) triblock copolymers were investigated using broadband dielectric spectroscopy (BDS). Two main relaxations corresponding to the glass transitions in the EB and S block phases were identified and their temperature dependences were VFT-like. Tg for the S block phase shifted to higher temperature due to restrictions on chain mobility caused by hydrogen bonded SO3H groups. While the EB block phase Tg appeared to remain constant with degree of sulfonation in DMA experiments, it shifted somewhat upward in BDS spectra. A low temperature relaxation beneath the glass transition of the EB block phase was attributed to short range chain motions. The Kramers–Krönig integral transformation was used to calculate conductivity-free loss permittivity spectra from real permittivity spectra to enhance true relaxation peaks. A loss permittivity peak tentatively assigned to relaxation of internal S-EB interfacial polarization was seen at temperatures above the S block phase glass transition, and the temperature dependence of this relaxation was VFT-like. The fragilities of the EB and S block domains in sulfonated SEBS decreased after sulfonation. The temperature dependence of the dc conduction contribution to sSEBS loss spectra also followed VFT-like behavior and S block segmental relaxation time correlated well with conductivity according to the fractional Debye–Stokes–Einstein equation.
The synthetic routes and materials properties of polypropylene/montmorillonite nanocomposites are reviewed. The nanocomposite formation is achieved in two ways: either by using functionalized polypropylenes and common organo-montmorillonites, or by using neat/unmodified polypropylene and a semi-fluorinated organic modification for the silicates. All the hybrids can be formed by solventless melt-intercalation or extrusion, and the resulting polymer/inorganic structures are characterized by a coexistence of intercalated and exfoliated montmorillonite layers. Small additionstypically less than 6 wt %of these nanoscale inorganic fillers promote concurrently several of the polypropylene materials properties, including improved tensile characteristics, higher heat deflection temperature, retained optical clarity, high barrier properties, better scratch resistance, and increased flame retardancy.
The additive effects of the novel ethylene–propylene random (EP) copolymers with high isotacticity in propylene sequence on the morphology and mechanical properties of isotactic polypropylene (iPP) were investigated using polarized optical microscopy, transmission electron microscopy, dynamic mechanical analysis and tensile behavior. According to these results, the EP copolymers with a propylene content of more than 84 mol% were miscible with iPP, in which the crystallizable PP sequences in these EP copolymers were incorporated in crystal lattice of iPP and the other portions in the EP chains were excluded to the amorphous phases. Consequently, they act as tie molecules linking between adjacent lamellae, leading to enhancement of yield toughness of iPP. On the other hand, the EP copolymers with a propylene-unit content of less than 77 mol% were incompatible with iPP. The iPP/EP blends showed the phase-separated morphology.
Commercial clays Cloisites®Na+, 30B and 20A were labelled with the fluorescent dye Rhodamine B and used as fillers of polypropylene in order to prepare composites to be studied with confocal fluorescence microscopy. The dye uptake by clays was monitored by X-ray powder diffraction and spectroscopic analyses and clear evidences of intercalated dye in the organically modified montmorillonites Clo30B and Clo20A were obtained. Clay–Rhodamine B hybrids were investigated by steady-state absorption and emission spectroscopy to explore the effect of dye arrangement on the optical properties. The obtained information was used to rationalize fluorescence behaviour of composites. Confocal fluorescence imaging gave rise to bright fluorescent images of Cloisite aggregated labelled with the dye allowing to easily and directly visualize the 3-D dispersion of the labelled fillers in the polymer matrix in a non-invasive manner. The images were analyzed in terms of size distribution of the fluorescence grains to quantify the dispersion degree. The data indicate that Clo20A is able to homogeneously distribute in the polymer matrix forming a composite material.
Polypropylene (PP)/organo-montmorillonite (Org-MMT) nanocomposites toughened with maleated styrene-ethylene-butylene-styrene (SEBS-g-MA) were prepared via melt compounding. The structure, mechanical properties, and dynamic mechanical properties of PP/SEBS-g-MA blends and their nanocomposites were investigated by X-ray diffraction (XRD), polarizing optical microscopy (POM), tensile, and impact tests. XRD traces showed that Org-MMT promoted the formation of β-phase PP. The degree of crystallinity of PP/SEBS-g-MA blends and their nanocomposites were determined from the wide angle X-ray diffraction via profile fitting method. POM experiments revealed that Org-MMT particles served as nucleating sites, resulting in a decrease of the spherulite size. The essential work of fracture approach was used to evaluate the tensile fracture toughness of the nanocomposites toughened with elastomer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3112–3126, 2005
Polymer nanocomposites possess promising high performances as engineering materials, if they are prepared and fabricated properly. Some work has been recently done on such polymer nanocomposites as dielectrics and electrical insulation. This was reviewed in 2004 based on the literatures published up to 2003. New significant findings have been added since then. Furthermore, a multi-core model with the far-distance effect, which is closely related to an "interaction zones", has been proposed from consideration of mesoscopic analysis of electrical and chemical structures of an existing interface with finite thickness. It is speculatively examined in the paper how the model works for various properties and phenomena already found in nanocomposites as dielectrics focusing on electrical characteristics, resistance to high voltage environment, and thermal properties.
Polymer nanocomposites are defined as polymers in which small amounts of nanometer size fillers are homogeneously dispersed by only several weight percentages. Addition of just a few weight percent of the nanofillers has profound impact on the physical, chemical, mechanical and electrical properties of polymers. Such change is often favorable for engineering purpose. This nanocomposite technology has emerged from the field of engineering plastics, and potentially expanded its application to structural materials, coatings, and packaging to medical/biomedical products, and electronic and photonic devices. Recently these 'hi-tech' materials with excellent properties have begun to attract research people in the field of dielectrics and electrical insulation. Since new properties are brought about from the interactions of nanofillers with polymer matrices, mesoscopic properties are expected to come out, which would be interesting to both scientists and engineers. Improved characteristics are. expected as dielectrics and electrical insulation. Several interesting results to indicate the foreseeable future have been revealed, some of which are described on materials and processing in the paper together with basic concepts and future direction.
The different components that make up extruded, high-voltage cables, conductors, semiconductive shields, insulation, sheaths, and jackets are described. Transmission of bulk power over long distances requires high-voltage cable systems for use in urban areas and for underground and submarine crossings. Polymer insulated electrical cable consists of a metallic, low resistance conductor covered with polymeric insulation, and a sheath or jacket formulated according to their mechanical properties to protect the cable from the environment. The other major components include semiconductive layers, metal screen, reinforcing metal wire, and water blocking tape.