A comparative study on the electrical,thermal and mechanical properties of ethylene–octene copolymer based composites with carbon fillers

Conducting polymer composites (CPC) were prepared with an ethylene–octene copolymer (EOC) matrix and with either carbon fibers (CFs) or multiwall carbon nanotubes (MWCNTs) as fillers. Their electrical and thermal conductivities, mechanical properties and thermal stabilities were evaluated and compared. CF/EOC composites showed percolation behavior at a lower filler level (5 wt.%) than the MWCNT/EOC composites (10 wt.%) did. Alternating current (AC) conductivity and real part of permittivity (dielectric constant) of these composites were found to be frequency-dependent. Dimensions and electrical conductivities of individual fillers have a great influence on the conductivities of the composites. CF/EOC composites possessed higher conductivity than the MWCNT-composites at all concentrations, due to the higher length and diameter of the CF filler. Both electrical and thermal conductivities were observed to increase with increasing filler level. Tensile moduli and thermal stabilities of both (CF/EOC and MWCNT/EOC) composites increase with rising filler content. Improvements in conductivities and mechanical properties were achieved without any significant increase in the hardness of the composites; therefore, they can be potentially used in pressure/strain sensors. Thermoelectric behavior of the composites was also studied. Accordingly, CF and MWCNT fillers are versatile and playing also other roles in their composites than just being conducting fillers.     

Influence of thermal conditions on the tensile properties of basalt fiber reinforced polypropylene–clay nanocomposites

In this paper, a comparative study on the tensile properties of clay reinforced polypropylene (PP) nanocomposites (PPCN) and chopped basalt fiber reinforced PP–clay nanocomposites (PPCN-B) is presented. PP matrix are filled with 1, 3 and 5 wt.% of nanoclays. The ultimate tensile strength, yield strength, Young’s modulus and toughness are measured at various temperature conditions. The thermal conditions are included the room temperature (RT), low temperature (LT) and high temperature (HT). The basal spacing of clay in the composites is measured by X-ray diffraction (XRD). Nanoscale morphology of the samples is observed by transmission electron microscopy (TEM). Addition of nanoclay improves the yield strength and Young’s modulus of PPCN and PPCN-B; however, it reduces the ultimate tensile strength. Furthermore, the addition of chopped basalt fibers to PPCN improves the Young’s modulus of the composites. The Young’s modulus and the yield strength of both PPCN and PPCN-B are significantly high at LT (−196 °C), descend at RT (25 °C) and then low at HT (120 °C).     

Mechanical and dielectric properties of epoxy–clay nanocomposites

Epoxy–clay nanocomposites were prepared using two types of surface-treated montmorillonite (Closite 30B and Nanomer I28E). Wide angle X-ray scattering showed that all the nanocomposites had an intercalated structure. Improvements in tensile and fracture properties were found. The pure epoxy polymer was very brittle with a fracture energy, G _c, of 131 J m^?2. The addition of the nanoclays significantly increased the value of G _c, up to 240 J m^?2 for 5 wt% C30B. The toughening mechanisms acting in the nanocomposites were identified using scanning electron microscopy as crack deflection and plastic deformation of the epoxy matrix around the clay platelets following debonding. From electrical testing, the permittivity and loss angle of the nanocomposites decreased, and their breakdown strength increased as desired for insulation applications. The breakdown strength of the pure epoxy was found to be 11.7 kV mm^?1, while for a 2 wt% C30B nanocomposite, it increased to 14.7 kV mm^?1. It was concluded that the restriction of chain mobility inhibited electrical polarisation and thus decreased the permittivity and loss angle. The electrical damage zone was analysed using scanning electron microscopy. It was found that the higher resistance-to-surface degradation by partial discharges and the creation of a tortuous electrical path, which delayed the propagation of the electrical tree, were the main factors which improved the breakdown strengths of the nanocomposites.     

Mill processing and properties of rubber–clay nanocomposites

The dispersion of nanoscale composites in elastomers, which generally have higher molecular weight and viscosity as compared to plastics, is a challenge. Several techniques have been proposed for improvement of the dispersion of nanofillers in the polymers [1]. For example, the interaction of natural layered silicates can be improved by ion-exchange of hydrated cation with organic cations such as introducing bulky alkylammoniums to obtain larger interlayer spacing and provide the galleries for the polymer chain diffusion. The resultant swollen nanoclay was dried and dispersed in the polymer matrix by means of high shear mixers [2–3]. In this paper we describe the results from a new method of incorporating nanofillers into solid rubber by use of a conventional two-roll mill, which we call the modified mill method. The properties of the resultant material are compared with that of the material prepared by a latex method. We also test processability parameters, tensile behavior and crosslink density of carbon black composites prepared by the same two methods to provide a comparison between the nanocomposites. The rubber–clay nanocomposites prepared by the mill method are shown to have a fine dispersed phase structure and good reinforcement properties.     

Effect of material and processing parameters on mechanical properties of Polypropylene/Ethylene–Propylene–Diene–Monomer/clay nanocomposites

Polypropylene/Ethylene–Propylene–Diene–Monomer (PP/EPDM) blends are well known for having a combination of favourable mechanical properties. In this paper, addition of organoclay to PP/EPDM to make PP/EPDM nanocomposites with enhanced mechanical properties is studied. PP/EPDM/organoclay nanocomposites were prepared using a lab scale twin-screw extruder. Maleic anhydride grafted polypropylene (PP-g-MA) was used to enhance the intercalation/exfoliation process and to create good adhesion at the polymer/polymer and polymer/filler interfaces. Taguchi method was employed to deign the experiments and optimize material and processing parameters for optimized mechanical properties. Organoclay (NC) and compatibilizer content were selected as material parameters and the main processing variables were feeding rate and average shear rate (RPM). X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) were used to study the microstructure of the nanocomposites samples. It was observed that NC content and shear rate in extruder improved the tensile strength and modulus. Another important result was the insignificant effect of NC content on impact strength while increasing shear rate first increased and then decreased the impact strength.     

Effect of ageing on the mechanical properties and the residual stress distribution of hybrid clay–glass fibre–polypropylene injection mouldings

The effects of ageing on the mechanical properties and thermal stresses distribution of injection moulded, short glass fibre/clay/polypropylene composites were studied. Two different clays were studied—talc and sepiolite. The results obtained indicate that the incorporation of short glass fibre into clay/polypropylene composites improves the mechanical properties, independently of ageing treatment. Larger elastic modulus values were obtained for talc-filled samples, whereas higher strength values were obtained with the sepiolite-filled ones. The impact strength increased as a result of the incorporation of glass fibre into the sepiolite-filled composite, while a small decrease was detected for the talc-filled polypropylene sample. Sepiolite-filled compounds show higher mould shrinkage in the bar-axis direction than equivalent talc-filled grades. In contrast, the shrinkage obtained on annealing at various temperatures between 100 and 160 °C was generally greater for talc-filled compounds than for the sepiolite-filled compounds. The shrinkage behaviour in the transverse direction was more complex. The residual stress levels of clay-filled polypropylene compounds were generally lower than those reported in the literature concerning short glass fibre polypropylene compounds under similar conditions. Hybrid composites showed much higher stress levels than the corresponding clay-filled samples independently of ageing conditions.     

Torsional,tensile and structural properties of acrylonitrile–butadiene–styrene clay nanocomposites

Torsional and tensile behaviour of acrylonitrile–butadiene–styrene (ABS)-clay nano-composites have been investigated and correlated with morphological and rheological characterisations. Nano-composites of ABS are prepared by melt compounding with different loading levels of nanoclay (Cloisite 30B) in a twin screw extruder and have been characterised in terms of torsional, axial and impact behaviour for their application in external orthotic devices. Tensile stress strain curve of nanocomposites are investigated to quantify resilience, toughness and ductility. Torque values of the nanocomposites are observed under torsion (10°–90°) and compared with that of neat ABS. Performance of ABS under torsional load improved by addition of nanoclay. Both modulus of elasticity and rigidity are found to improve in presence of nanoclay. State of dispersion in nano-composites is investigated using conventional methods such as transmission electron microscopy (TEM), X-ray diffraction (XRD), as well as by parallel plate rheometry. Addition of clay exhibits shear thinning effect and results in increase in storage modulus as well as complex viscosity of the nanocomposites. Zero shear viscosity rises tenfold with 1–2% addition of nanoclay, indicating the formation of structural network. It is found that state of dispersion of nanoclay governs the torsional and mechanical properties in ABS-clay nanocomposites.     

Polyaniline–sodium montmorillonite clay nanocomposites: effect of clay concentration on thermal, structural, and electrical properties

A simple and facile method was used to synthesize polyaniline (PANI) nanocomposites with sodium montmorillonite clay (Na⁺-MMT) using in situ intercalative oxidative polymerization. Aniline was admixed with Na⁺-MMT at various concentrations, keeping the aniline monomer in the reaction mixture constant. The intercalation of PANI into the clay layers was confirmed by X-ray diffraction studies in conjugation with electron microscope techniques and FTIR spectra, particularly by the narrowing of the Si–O stretching vibration band confirmed the interaction between PANI and the clay. The employed route offers the possibility to improve the thermal properties with simultaneously controlled electrical conductivity. Thermal studies show an improved thermal stability of the nanocomposites relative to the pure PANI. Depending on the loading of the clay, the room temperature conductivity values of these nanocomposites varied between 2.0 × 10⁻⁴ and 7.4 × 10⁻⁴ S cm⁻¹, with the maximum at 44 wt% PANI concentration. The decrease of electrical conductivity at high PANI concentration was ascribed to the decrease of the structural ordering of PANI in the nanocomposite.     

Structure and properties of nylon 6–clay nanocomposites: effect of temperature and reprocessing

Melt-compounding is a technique which has been commonly used for producing polymer–clay nanocomposites with enhanced mechanical, thermal, and physical properties. Twin-screw extruders have been found to effectively exfoliate the clay platelets due to their high shear intensity. However, concerns about polymer and organoclay degradation have been raised in some studies. In this investigation, a composite of nylon 6–Cloisite 30B with fully exfoliated and well-dispersed clay particles was produced using a single-screw extruder and hence with limited polymer degradation. We show that processing temperature plays an important role in enhancing dispersion and that reprocessing at a higher temperature can enhance both dispersion and exfoliation and thus can result in composites with superior properties. We attempt to elucidate how the change in melt viscosity—coupled with the change in processing temperature—affects clay exfoliation and dispersion.     

Microstructure,mechanical and wear properties of Cu–ZrO2 nanocomposites

Cu–ZrO₂ nanocomposites were produced by the thermochemical process followed by powder metallurgy technique. Microstructure development during fabrication process was investigated by X-ray diffraction, field emission scanning electron microscope and transmission electron microscope. The results show an improved distribution of zirconium dioxide (ZrO₂) nanoparticles (45?nm) in the copper matrix, which resulted in the improvement of mechanical properties of Cu–ZrO₂ composites. The nanocomposite with 9 wt-% ZrO₂ possesses the highest hardness (136.5 HV) and the superior compressive strength (413.5?MPa), resulting in an overall increase by 52 and 25%, respectively. The wear rate of the nanocomposites increased with increasing applied loads or sliding velocity.     

Mechanical properties and water uptake of epoxy–clay nanocomposites containing different clay loadings

Nanocomposites based on diglycidyl ether of bisphenol A (DGEBA) epoxy reinforced with 1–10 wt% I.30E nanoclay were fabricated using high shear mixing technique and characterized to determine the effects of clay loading on their mechanical, thermal, and water uptake properties. The XRD and TEM analyses revealed that the structures of the resultant nanocomposites were a combination of disordered intercalated and exfoliated morphologies. Tensile strength increased for nanocomposite containing 1 % clay loading and decreased for higher nanoclay loading. Unlike strength, the stiffness increased almost linearly with clay loading, showing 46 % improvement in modulus of elasticity for nanocomposites containing 5 % of nanoclay. Water uptake measurements indicated enhancement in the barrier properties of epoxy matrix as nanoclay loading increased from 1 up to 5 wt%.     

Effects of post-annealing on the microstructure and mechanical properties of friction stir processed Al–Mg–TiO2 nanocomposites

Aluminum matrix nanocomposites were fabricated via friction stir processing of an Al–Mg alloy with pre-inserted TiO₂ nanoparticles at different volume fractions of 3%, 5% and 6%. The nanocomposites were annealed at 300–500 °C for 1–5 h in air to study the effect of annealing on the microstructural changes and mechanical properties. Microstructural studies by scanning and transmission electron microscopy showed that new phases were formed during friction stir processing due to chemical reactions at the interface of TiO₂ with the aluminum matrix alloy. Reactive annealing completed the solid-state reactions, which led to a significant improvement in the ductility of the nanocomposites (more than three times) without deteriorating their tensile strength and hardness. Evaluation of the grain structure revealed that the presence of TiO₂ nanoparticles refined the grains during friction stir processing while the in situ formed nanoparticles hindered the grain growth upon the post-annealing treatment. Abnormal grain growth was observed after a prolonged annealing at 500 °C. The highest strength and ductility were obtained for the nanocomposites annealed at 400 °C for 3 h.     

Fabrication and mechanical properties of silicon carbide–silicon nitride nanocomposites

A powder mixture of ultrafine –SiC–35 wt% –Si₃N₄ containing 6 wt% Al₂O₃ and 4 wt% Y₂O₃ as sintering additives were liquid–phase sintered at 1800°C for 30 min by hot–pressing. The hot–pressed composites were subsequently annealed at 1920°C under nitrogen–gas–pressure to enhance grain growth. The average grain–size of the sintered bodies were ranged from 96 to 251 nm for SiC and from 202 to 407 nm for Si₃N₄, which were much finer than those of ordinary sintered SiC–Si₃N₄ composites. Both strength and fracture toughness of fine–grained SiC–Si₃N₄ composites increased with increasing grain size. Such results suggested that a small amount of grain growth in the fine–grained region (250 nm for SiC and 400 nm for Si₃N₄) was beneficial for mechanical properties of the composites. The room–temperature flexural strength and fracture toughness of the 8–h annealed composites were 698 MPa and 4.7 MPa · m^1/2, respectively.     

Thermal and mechanical properties of hemp fabric-reinforced nanoclay–cement nanocomposites

The influence of nanoclay on thermal and mechanical properties of hemp fabric-reinforced cement composite is presented in this paper. Results indicate that these properties are improved as a result of nanoclay addition. An optimum replacement of ordinary Portland cement with 1 wt% nanoclay is observed through improved thermal stability, reduced porosity and water absorption as well as increased density, flexural strength, fracture toughness and impact strength of hemp fabric-reinforced nanocomposite. The microstructural analyses indicate that the nanoclay behaves not only as a filler to improve the microstructure but also as an activator to promote the pozzolanic reaction and thus improve the adhesion between hemp fabric and nanomatrix.     

Structure–morphology–mechanical properties relationship of some polypropylene/lignocellulosic composites

Natural lignocellulosic materials have an outstanding potential as thermoplastic reinforcement. Polypropylene composites were prepared using different types of lignocellulosic materials by melt blending of 70 wt% polypropylene (PP) and 30 wt% biomasses. The specimens were firstly evaluated for structural and morphological properties by infrared spectroscopy, X-ray diffraction, scanning electron and polarized optical microscopy. Depending on the biomass type, there were evidenced some particular shifts of the infrared bands and also crystallinity changes. An increase in crystallinity is explained by nucleating agent role of biomass. The morphological changes are directly related to variation in mechanical and rheological properties, an increase in Young modulus, melt viscosity and storage and loss moduli being recorded.     

Synergistic effect of montmorillonite–clay and gamma irradiation on the characterizations of waste polyamide copolymer and reclaimed rubber powder nanocomposites

A study on the mechanical properties and thermal evolution of waste polyamide copolymer/waste rubber powder and montmorillonite–clay (WPA/RRP/MMT) nanocomposites exposed to gamma-rays (0–200 kGy) has been carried out. TGA and DSC were used to investigate the influence of the exposure dose and the incorporation of montmorillonite–clay on the thermal parameters of the prepared composites. It was observed that both parameters were highly affected by the incorporated clay and dose. The structural and morphological studies were done by means of EDX and SEM to investigate the structural change imputed by the clay incorporation and irradiation. The chemical absorption behavior of MMT nanocomposites in HCl and NaOH media was investigated. The results show that irradiation markedly magnified the thermal stability and the tensile strength of the nanocomposite.     

Microstructure and mechanical properties of Si3N4–TiC nanocomposites

Abstract

Si₃N₄–TiC nanocomposites are fabricated by hot press sintering from silicon nitride nanopowders and ultrafine TiC powders. The microstructure and mechanical properties are analysed and discussed. Scanning electron microscopy images show that the microstructure consists of equiaxed grains and grain boundary phase. The TiC added as a dispersed phase reacts with the nitrogen from Si₃N₄ during the liquid phase sintering, with the formation of TiC_0.7 N_0.3 , trace of SiC and N₂. The adding of a proper amount of TiC powders increases the flexural strength and has little influence on fracture toughness. The hardness increases with increasing TiC content.     

The relationship between the electrical and mechanical properties of polymer–nanotube nanocomposites and their microstructure

A range of polymer–nanotube nanocomposites were produced using different processing routes. Both polymer-grafted and as-grown nanotubes were used and latex and polystyrene matrices investigated. The microstructures of the nanocomposites were studied, mainly by electron microscopy, in terms of the dispersion state of the nanotubes and the polymer–nanotube interface. The mechanical and electrical properties of the composites were also measured. The relationship between the microstructures observed and the resulting physical properties are discussed. It is found that composites with apparently similar microstructures can exhibit similar mechanical properties but very different electrical behaviours. Moreover, the nanocomposites produced using polymer-grafted nanotubes exhibit a clear improvement of the stress at large deformation. Thus, from our results, it appears that the mechanical and electrical properties do not necessarily depend on the same microstructural parameters. However it is still a challenge to simultaneously improve both physical properties.     

Preparation and characterization of polypropylene–wheat straw–clay composites

Preparation of polypropylene hybrid composite consisting of wheat straw and clay as reinforcement materials was investigated. The composite samples were prepared through melt blending method using a co-rotating twin-screw extruder. The composition of constituents of hybrid composite such as percentages of wheat straw, clay and maleic anhydride grafted polypropylene as a coupling agent was varied in order to investigate their influence on water absorption and flexural properties. The XRD analysis of composite samples containing clay showed shift in d₀₀₁ peak to lower 2θ indicating slight intercalation of polymer in clay sheets. The results of the study indicate that the increase in wheat straw and clay content in a composite increases the flexural modulus and reduces the resistance for water absorption. The increase in PP-MA coupling agent also increases the flexural modulus and resistance for water absorption. The morphological study by scanning electron microscope reveals that the addition of coupling agent increases the interfacial adhesion between the fibers and polymer matrix which is evidenced further from increased flexural modulus. Further, the particle size of wheat straw was analyzed before and after extrusion in order to investigate the effect of extrusion on wheat straw dimensions. The addition of clay as additional filler had no significant role on water absorption and flexural properties of the composite.     

Influence of short glass fibres and weldlines on the mechanical properties of injection-moulded acrylonitrile–styrene–acrylate copolymer

The present study investigated the dependence of various mechanical and fracture properties on the volume fraction, f, of reinforcing glass fibres in acrylonitrile–styrene–acrylate (ASA) copolymer. The addition of glass fibres enhanced the ultimate strength and modulus as measured in both tension and flexure but reduced the total work of fracture. The elastic modulus was not affected by the loading mode. The ultimate strength in flexure was found to be always greater than in tension by a factor of about 1.3. Both properties were found to be a linear function of f following the rule of mixtures:Pc=Pff+Pm(1–f)where Pc is the measured property for the composite, Pf and Pm are the corresponding values for the fibre and the matrix, respectively, and is the overall efficiency of the reinforcing fibres. Addition of glass fibres to ASA polymer reduced both the notched and the unnotched impact strengths. Linear elastic fracture mechanics were used to determine values of the fracture toughness and the strain energy release rate. The fracture toughness did not change significantly with f, whereas the strain energy release rate decreased with increasing f. The presence of weldlines in the specimens had an adverse effect on all tensile properties except for the elastic modulus. The weldline integrity parameter for the modulus was between 1 and 0.95, and for strength it was between 0.87 and 0.20, decreasing linearly with increasing f. © 1998 Kluwer Academic Publishers