Evaluation of PP/EPDM nanocomposites filled with SiO2, TiO2 and ZnO nanofillers as thermoplastic elastomeric insulators

Abstract

Thermoplastic elastomer, which has important characteristics for cable insulation, was developed by melt blending of polypropylene (PP) with ethylene propylene diene monomer (EPDM) at various blend ratios together with SiO₂, TiO₂ and ZnO nanofillers at fixed loading of 2 vol.-%. The influence of EPDM content and the presence of nanofillers in the blend on burning rate, hydrophobicity and dielectric breakdown strength were investigated. Burning rate of PP/EPDM/ZnO was significantly reduced, implying that there was an improvement in fire retardancy with the addition of ZnO nanofillers in the polymer blend. Both SiO₂ and ZnO filled system showed an improvement in hydrophobicity. Furthermore, dielectric breakdown strength showed higher value in EPDM rich blends. In addition, the presence of nanofillers deteriorated the dielectric breakdown strength of PP/EPDM nanocomposites.     

Properties of nanofillers/crosslinked polyethylene composites for cable insulation

In this work, we report the effect of nanofillers and filler loading on mechanical, physical, dielectric, and thermal properties of the crosslinked polyethylene (XLPE) matrix. XLPE filled with 0.5–2% of zinc oxide (ZnO), aluminium oxide (Al₂O₃), and organoclay (OMMT) nanofillers prepared by melt mixing with a single screw extruder followed by hot press moulding. Nanocomposites were tested as per ASTM standard methods and characterized with tensile test, water absorption, linear rate of burning, dielectric breakdown strength, and thermal stability. Scanning electron microscopy (SEM) was used to examine the surface morphology of the nanocomposites. The results showed that addition of nanofillers improved tensile strength, elongation at break, Young's modulus, burning rate, dielectric breakdown strength, and decomposition temperature. However, water absorption increased with time due to the hydrophilic properties of nanofillers. In general, based on the properties measured Al₂O₃ exhibits the highest properties than those of ZnO and OMMT nanofillers. Addition of 1.5% of Al₂O₃ in XLPE matrix has led to the improvement in tensile strength, elongation at break, Young's modulus, burning rate, and dielectric breakdown strength as compared to the unfilled polymer. J. VINYL ADDIT. TECHNOL., 25:E147–E154, 2019. © 2018 Society of Plastics Engineers     

Microstructure and physicomechanical properties of pressureless sintered multiwalled carbon nanotube/alumina nanocomposites

Multiwalled carbon nanotube (MWCNT)/alumina (Al₂O₃) nanocomposites containing CNT from 0.15 vol.% to 2.4 vol.% have been successfully fabricated by simple wet mixing of as-received commercial precursors followed by pressureless sintering. Extent of densification of nanocomposites sintered at low temperature (e.g. 1500 °C) was <90%, but increased up to ∼99% when sintered at 1700 °C and offered superior performance compared to pure Al₂O₃. Nanocomposites containing 0.3 vol.% MWCNT and sintered at 1700 °C for 2 h in Argon led to ∼23% and ∼34% improvement in hardness and fracture toughness, respectively, than monolithic Al₂O₃. In addition, the highest improvement (∼20%) in bending strength was obtained for 0.15 vol.% MWCNT/Al₂O₃ nanocomposite compared to pure Al₂O₃. Weibull analysis indicated reliability of nanocomposites increased up to 0.3 vol.% MWCNT, whereas, beyond that loading consistency was the same as obtained for pure Al₂O₃. Detailed microstructure and fractographic analysis were performed to assess structure-property relationship of present nanocomposites.     

Effect of POSS‐grafted titanium dioxide on the electrical and thermal properties of LDPE/TiO2 polymer nanocomposite

Two types of nanocomposites have been fabricated by a ball‐milling technique. The first type consists of untreated titanium dioxide (TiO₂) incorporated into low‐density polyethylene (LDPE). For the second one, TiO₂ filler chemically treated with trisilanol phenyl–polyhedral oligomeric silsesquioxane (TP–POSS) as compatibilizing agent was ball‐milled with LDPE. All specimens were tested by microstructure analysis and thermal, dielectric characterization techniques. Microstructure analysis by atomic force microscopy and scanning electron microscopy show clearly an increased dispersion in presence of POSS. Scanning electron microscopy even shows the formation of a particular structure due possibly to interactions between functionalization. It was observed that the modification of the surface of TiO₂ by the POSS decreased the dielectric loss. All nanocomposites containing treated TiO₂ revealed an improvement in thermal conductivity, with the most distinct value of 19% in case of LDPE containing 5 wt % treated TiO₂. The incorporation of TiO₂ fillers seems to reduce the dielectric breakdown strength of the nanocomposites. However, nanocomposites containing 3 and 5 wt % treated TiO₂ have exhibited a slightly enhancement in dielectric breakdown strength up to 5%. The improvement in surface resistance to partial discharge was found in all nanocomposites specimens, especially for both types of composite containing 7 wt % untreated and treated TiO₂. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46095.     

SiO2/Al2O3 ratio dependence of microstructures and dielectric properties in barium strontium titanate glass ceramics

(Ba, Sr)TiO₃-Al₂O₃-SiO₂ glass ceramic system with various SiO₂/Al₂O₃ ratios was investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), dielectric spectroscopy and impedance spectroscopy. The XRD results demonstrated that the proper SiO₂/Al₂O₃ ratio could promote the crystallization of the major crystalline phase from the glass matrix. The dielectric property investigations showed that the dielectric constant passes through a maximum value while the dielectric breakdown strength has a minimum value with increasing SiO₂/Al₂O₃ ratio. Meanwhile, the complex impedance analyses suggest the resistance of the glass-crystal interface rapidly decreases and the capacitance of the crystal slightly decreases with the increase of SiO₂/Al₂O₃ ratio. The relaxation mechanisms of the (Ba, Sr)TiO₃ glass ceramics changed from localized relaxation to long range conductivity as the SiO₂/Al₂O₃ ratio was increased from 1.43 to 1.83. The variations in the dielectric response and the activation energy of the glass-crystal interface in the (Ba, Sr)TiO₃ glass ceramics with the ratio of 2.40 could be attributed to the crystallization of fresnoite phase.     

Enhanced dielectric breakdown strength in Ni2O3 modified Al2O3-SiO2-TiO2 based dielectric ceramics

Dielectric ceramics have raised particular interest since they enable pulsed-power systems to achieve high voltage gradient and compact miniaturization. In this work, x wt%Ni₂O₃ doped Al₂O₃-SiO₂-TiO₂ based dielectric ceramics were prepared using conventional solid-state reaction and the effects of Ni₂O₃ on the crystal structure, dielectric properties and dielectric breakdown strength were investigated. It was found that with the doping of Ni₂O₃, the Al₂O₃-SiO₂-TiO₂ based dielectric ceramics became denser and the distribution of each phase was more uniform. For the composition of x?=?2.0, the dielectric breakdown strength was increased into 82.1?kV/mm, more than twice compared with that of the undoped one. In addition, the relationship between the dielectric breakdown strength and the resistance of Al₂O₃-SiO₂-TiO₂ based dielectric ceramics was discussed. The results show that the doping of Ni₂O₃ is a very feasible way to improve the dielectric breakdown strength and optimize the dielectric properties for the Al₂O₃-SiO₂-TiO₂ based dielectric ceramics.     

Preparation of photodegradable polypropylene/clay composites based on nanoscaled TiO2 immobilized organoclay

Photodegradable polypropylene (PP) composites were prepared via melting blending using PP and titanium dioxide (TiO₂) immobilized organically modified montmorillonite (organoclay). TiO₂ immobilized organoclay (TiO₂‐OMT) was synthesized by immobilizing anatase TiO₂ nanoparticles on organically modified clay via sol–gel method. The structure and morphology of TiO₂‐OMT were characterized by XRD and scanning electron microscope (SEM), which showed that anatase TiO₂ nanoparticles with the size range of 8–12 nm were uniformly immobilized on the surface of organoclay layers. Diffuse reflection UV–vis spectra revealed TiO₂‐OMT had similar absorbance characters to that of commercial photocatalyst, Degussa P25. The solid‐phase photocatalytic degradation of PP/TiO₂‐OMT composites was investigated by FTIR, DSC, GPC and SEM. The results indicated that TiO₂‐OMT enhanced the photodegradation rate of PP under UV irradiation. This was due to that immobilization of TiO₂ nanoparticles on organoclay effectively avoided the formation of aggregation, and thereby increased the interface between PP and TiO₂ nanoparticles. After 300 h irradiation, the average molecular weight was reduced by two orders of magnitude. This work presented a promising method for preparation of environment‐friendly polymer nanocomposites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers.     

Design and processing of Al2O3–Al2TiO5 layered structures

Al₂O₃–Al₂TiO₅ layered composites were manufactured by a colloidal route from aqueous Al₂O₃ and TiO₂ suspensions with 50 vol.% solids. The mechanical behaviours of individual monolithic composite materials were combined and taken as basis for the design of the layered structures. Residual stresses which are likely to occur due to processing and thermally introduced misfits were calculated and considered for the manufacture of the laminates.Monoliths with 10, 30 and 40 vol.% of second phase showed that increasing proportions of aluminium titanate decrease strength and increase the non-linear behaviour.In order to obtain the desired combination of mechanical behaviours of the layers, two laminate designs with external and central layers of one composition and the alternating internal layer of the other composition were chosen taking into account chemical compatibility and development of residual stresses. In the system AA10, external and central layers of monophase Al₂O₃ with high strength were combined with intermediate layers of Al₂O₃ with 10 vol.% of Al₂TiO₅. The system A10A40 was selected to combine low strength and energy absorbing intermediate layers of Al₂O₃ with 40 vol.% of Al₂TiO₅ and sufficient strength provided by external layers of Al₂O₃ with 10 vol.% of Al₂TiO₅.The stress–strain behaviour of the laminates was linear up to their failure stresses, with apparent strain for zero load after fracture larger than that corresponding to the monoliths of the same composition as that of the external layers. Moreover, the stress drop of the laminate samples occurred in step-like form thus suggesting the occurrence of additional energy consuming processes during fracture.     

In situ synthesis,mechanical and cyclic oxidation properties of Ti3AlC2/Al2O3 composites

ABSTRACT

Ti₃AlC₂/Al₂O₃ composite materials were successfully fabricated from TiO₂/TiC/Ti/Al powders by the in situ reactive hot pressed technique. The microstructure, mechanical and oxidation properties of the composites were investigated in the paper. Vickers hardness increased with the Al₂O₃ content. The relative density of Ti₃AlC₂/Al₂O₃ composites exhibits a declining tendency with Al₂O₃ content especially exceeds 10 vol.?%. The Ti₃AlC₂/Al₂O₃ composites show excellent electrical conductivity. The flexural strength and fracture toughness of Ti₃AlC₂/10 vol. % Al₂O₃ are 461 ± 20?MPa and 6.2?±?0.2?MPa m^1/2, respectively. The cyclic oxidation behaviour of resistance of Ti₃AlC₂/10 vol. % Al₂O₃ composites at 800–1000°C generally obeys a parabolic law. The oxide scale of sample consists of a mass of α-Al₂O₃ and TiO₂, forming a dense and adhesive protect layer. The result indicates that the Al₂O₃ can greatly improve the oxidation resistance of Ti₃AlC₂.     

Carbon nanotube toughened aluminium oxide nanocomposite

This paper describes the mechanical properties of carbon nanotube-reinforced Al₂O₃ nanocomposites fabricated by hot-pressing. The results showed that compared with monolithic Al₂O₃ the fracture toughness, hardness and flexural strength of the nanocomposites were improved by 94%, 13% and 6.4% respectively, at 4 vol.% CNT additions. For 10 vol.% CNT additions, with the exception of the fracture toughness, which was improved by 66%, a decrease in mechanical properties was observed when compared with those for monolithic Al₂O₃. The toughening mechanism is discussed, which is due to the uniform dispersion of CNTs within the matrix, adequate densification, and proper CNT/matrix interfacial connections.     

Synergistic reinforcing of poly(lactic acid) by poly(butylene adipate-co-terephthalate) and alumina nanoparticles

Biodegradable poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate) (PBAT) blends and PLA/PBAT/Al₂O₃ nanocomposites were fabricated via solution blending. The influence of PBAT and Al₂O₃ content on the thermal stability, flexural properties, impact strength, and morphology of both the PLA/PBAT blends and the PLA/PBAT/Al₂O₃ nanocomposites were investigated. The impact strength of the PLA/PBAT/Al₂O₃ nanocomposites containing 5 wt% PBAT increased from 4.3 to 5.2 kJ/m² when the Al₂O₃ content increased from 0 to 1 wt%. This represents a 62% increase compared to the impact strength of pristine PLA and a 20% increase compared to the impact strength of PLA/PBAT blends containing 5 wt% PBAT. Scanning electron microscopy imaging revealed that the Al₂O₃ nanoparticles in the PLA/PBAT/Al₂O₃ nanocomposites function as a compatibilizer to improve the interfacial interaction between the PBAT and the PLA matrix.     

Enhanced dielectric constant and breakdown strength in dielectric composites using TiO2@HfO2 nanowires with gradient dielectric constant

To investigate the influence of modification of ceramic fillers on the dielectric properties of polymer-based composites, TiO₂ and core-shell structured TiO₂@HfO₂ nanowires were synthesized, and investigated in this study. TiO₂ nanowires/polyvinylidene fluoride (PVDF) and TiO₂@HfO₂ nanowires/PVDF nanocomposites were prepared using the solution casting method. The experimental results showed that the TiO₂@HfO₂ nanowires/PVDF composites had improved dielectric properties compared with that of the TiO₂ nanowires/PVDF composites. Owing to the enhanced interfacial polarisation by the multilevel interface, the composites with 10 wt % TiO₂@HfO₂ nanowires achieved the highest permittivity of 12.56 at 1 kHz, which was enhanced by ～72% compared to the PVDF matrix. The electric field was evenly distributed by building the fillers with a gradient dielectric constant. The characteristic breakdown strength of the composite with 5 wt % TiO₂@HfO₂ reached 377.76 kV/mm, compared with that of 334.37 kV/mm for the composite with 5 wt % TiO₂ nanowires. This study initiated a novel strategy for preparing dielectrics with high dielectric constant and improved breakdown strength.     

Spark plasma sintering technique for reaction sintering of Al2O3/Ni nanocomposite and its mechanical properties

Al₂O₃/Ni nanocomposites were prepared by spark plasma sintering (SPS) using reaction sintering method and the mechanical properties of the obtained nanocomposites are reported. The starting materials of Al₂O₃–NiO solid solution were synthesized from aluminum sulfate and nickel sulfate. These Al₂O₃–NiO powders were changed into Al₂O₃ and Ni phases during sintering process. The obtained nanocomposites showed high relative densities (>98%). SEM micrographs showed homogeneously dispersed Ni grains in the matrix. The 3-point strength and the fracture toughness of the composites significantly improved from 450 MPa in the monolithic α-Al₂O₃ to 766 MPa in the 10 mol% (2.8 vol.%) Ni nanocomposite and from 3.7 to 5.6 MPa m^1/2 in 13 mol% (3.7 vol.%) Ni nanocomposite. On the other hand, Young's modulus and Vickers hardness of the nanocomposites were mostly same as those of the monolithic α-Al₂O₃.     

Improvement in dielectric and mechanical performance of CaCu<Subscript>3.1</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12.1</Subscript> by addition of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

The properties of CaCu_3.1Ti₄O_12.1 [CC3.1TO] ceramics with the addition of Al₂O₃ nanoparticles, prepared via a solid-state reaction technique, were investigated. The nanoparticle additive was found to inhibit grain growth with the average grain size decreasing from approximately 7.5 μm for CC3.1TO to approximately 2.0 μm for the unmodified samples, while the Knoop hardness value was found to improve with a maximum value of 9.8 GPa for the 1 vol.% Al₂O₃ sample. A very high dielectric constant > 60,000 with a low loss tangent (approximately 0.09) was observed for the 0.5 vol.% Al₂O₃ sample at 1 kHz and at room temperature. These data suggest that nanocomposites have a great potential for dielectric applications.     

Enhanced performance in multilayer-structured nanocomposites using BaTiO3 and Ba0.8Sr0.2TiO3 decorated graphene hybrids

It is challenging to achieve high energy density in conductive fillers/polymer nanocomposites due to their extremely low breakdown strength. In this paper, a novel multi-component and multilayer-structured nanocomposite was designed and investigated, consisting of Ba_0.8Sr_0.2TiO₃ decorated graphene (BST @ RGO)/poly(vinylidene fluoride-chlorotrifluoroethylene) copolymer (P(VDF-CTFE)) composites (R-Layer) as interlayer, and BaTiO₃/P(VDF-CTFE) composites (B-Layer) as surface layer. The multilayer-structured nanocomposites were prepared through layer-by-layer solution casting method. Enhanced breakdown strength, energy density, dielectric constant and low dielectric loss were simultaneously obtained in the nanocomposites by the multilayer structure. The maximum dielectric constant of the composites with multi-layered structure was approximately 14, which was increased by 16.67% compared to the pure P(VDF-CTFE) layer, and the dielectric loss was as low as 0.047 at 1?kHz, even lower than pure P(VDF-CTFE) in frequency range from 10?kHz to 1?MHz. The breakdown strength and energy storage density of BRB-3 nanocomposites with 3 R-Layers reached to 220?kV?mm^?1 and 6.49?J?cm^?3, respectively. These results demonstrated that designing multi-component and multilayer-structured nanocomposites was an effective approach to fabricate high performance dielectric nanocomposites.     

Dielectric properties and energy-storage performance of two-dimensional molybdenum disulfide nanosheets/polyimide composite films

Flexible dielectric materials with high electric energy density and high-temperature resistant characteristic are of great importance for modern electronics and electrical systems. Herein, two-dimensional molybdenum disulfide (MoS₂) nanosheets were efficiently produced via liquid-phase exfoliation and then incorporated into polyimide (PI) to prepare MoS₂/PI dielectric nanocomposites. Compared to the pristine PI, MoS₂/PI nanocomposite films exhibited much larger dielectric permittivity while their dielectric losses still maintained relatively low levels. On the other hand, the Weibull breakdown strength of these nanocomposite films initially increased and then decreased with the increase in the MoS₂ content and gave rise to a maximum value of 395 MV m⁻¹ at 1 vol % loading. Combination of the improved dielectric permittivity and breakdown strength makes the MoS₂/PI nanocomposite film with 1 vol % MoS₂ possess an elevated energy density of about 3.35 J cm⁻³. Moreover, good tensile and thermal properties of the nanocomposite films hold great promise for their applications in high-temperature and harsh conditions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47991.     

Electrostatic self-assembly preparation of reduced graphene oxide-encapsulated alumina nanoparticles with enhanced mechanical properties of alumina nanocomposites

In this study, we employed facile self-assembly methods to synthesize reduced graphene oxide-encapsulated alumina (Al₂O₃/rGO) nanoparticles. The Al₂O₃/rGO nanoparticles were subsequently incorporated into an Al₂O₃ matrix as filler to prepare nanocomposites. The microstructural analysis showed that relatively thin rGO sheets were homogeneously dispersed in the matrix and bonded with the Al₂O₃ grains forming a three-dimensional rGO network structure. The specific structure caused the rGO sheets to be anchored and bound to the matrix grains, resulting in a high contact area between the rGO sheets and the matrix, whilst the fracture mode alteration, grain refinement and improved interfacial strength of the nanocomposites were related to the unique structure. The results indicated that the nanocomposites with 2.5?vol.% rGO exhibited outstanding mechanical properties, increasing both the flexural strength by 105%, with a maximum value of 636?MPa, and the fracture toughness by 90% (5.9?MPa?m^1/2) when compared with monolithic Al₂O₃.     

Retention of Mechanical and Thermal Properties of Hydrothermal Aged Glass Fiber-Reinforced Polymer Nanocomposites

The combined effect of nano-Al₂O₃ and TiO₂ fillers on residual mechanical and thermal properties of glass fiber-reinforced polymer composites has been evaluated. The results reveal that the addition of 0.1?wt% of Al₂O₃ and 0.1?wt% of TiO₂ into the epoxy matrix reduces the water diffusivity by 12%. The residual flexural and interlaminar shear strength of the nanocomposite have been increased by 19 and 21%, respectively, as compared to those of neat epoxy glass fiber-reinforced polymer composite. In spite of reduction in water diffusivity and increase in strength, there was no improvement in glass transition temperature of the nanocomposites.     

Polyimide dielectric nanocomposites containing functional nanofillers based on multilayer structure: Design,preparation, and properties

Polyimide (PI) dielectric nanocomposites containing functional nanofillers based on layered structure (single-layer: BT@Al₂O₃@PI, double-layer: PI/BT@Al₂O₃@PI, three-layer: PI/BT@Al₂O₃@PI/PI) were designed and prepared by using PI as matrix, barium titanate (BT)@alumina (Al₂O₃) as nanofillers through in-situ polymerization compounding technology. FTIR tests indicated that PI and PI dielectric nanocomposites have been synthesized successfully. The molecular mass of BaTiO₃@Al₂O₃@PAA oligomer was higher than that of pure PAA when BT and Al₂O₃ nanofillers were incorporated simultaneously, as verified by GPC and intrinsic viscosity tests. XRD analysis showed that the addition of nanofillers destroyed the order of PI molecular structure and reduced the arrangement density of PI molecular chains. Both FESEM and HRTEM observations showed that the nanofillers were homogeneously dispersed in the PI matrix, contributing to the property improvements of PI dielectric nanocomposites. TGA results indicated that adding nanofillers improved the thermal stability and heat resistance of PI dielectric nanocomposites. The dielectric constant of PI/BT@Al₂O₃@PI double-layer nanocomposites was between the single-layer nanocomposites and pure PI. Due to the effective medium theory, the dielectric constant of three-layer PI/BT@Al₂O₃@PI/PI nanocomposites containing 5 wt% BT@Al₂O₃ reached 5.43. This work can be expected to provide an effective strategy to fabricate PI dielectric nanocomposite films for energy storage applications.     

Thermal aging on ethylene–propylene–diene rubber composites reinforced by samarium oxide,samarium borate and Sb in Sb doped SnO2

Abstract

Ethylene–propylene–diene monomer (EPDM) rubber composites reinforced with 50 phr samarium oxide (Sm₂O₃), samarium borate (SmBO₃) and Sb in antimony doped tin oxide (ATO) are aged at 150°C for different intervals. It is found that neutral Sm₂O₃ and alkaline SmBO₃ can retard the oxidative degradation of EPDM by blocking radical passage. The acidic ATO particles can accelerate the oxidative degradation of EPDM. The trend of tensile strength of EPDM composites is consistent with that of cross-link density of EPDM composites. SmBO₃ and ATO can retard the increase of dielectric loss until 10 days of aging, while Sm₂O₃ can keep the dielectric loss at low level until 14 days of aging. The increased surface charge of filler can make surface and volume resistivity decrease sharply. Antimony doped tin oxide can deteriorate the dielectric strength of EPDM, while SmBO₃ and Sm₂O₃ can keep the dielectric strength of EPDM at a constant level.