Mechanical and three‐body abrasive wear behaviour of SiC filled glass‐epoxy composites

Fiber/filler reinforced polymer composites are known to possess high strength and attractive wear resistance in dry sliding conditions. How these composites perform in abrasive wear situations needs a proper understanding. Hence, in this research article the mechanical and three‐body abrasive wear behaviour of E‐glass fabric reinforced epoxy (G‐E) and silicon carbide filled E‐glass fabric reinforced epoxy (SiC‐G‐E) composites are investigated. The mechanical properties were evaluated using Universal testing machine. Three‐body abrasive wear tests are conducted using rubber wheel abrasion tester wherein two different loads and four varying abrading distances are employed. The results showed that the wear volume loss is increased with increase in abrading distance and the specific wear rate decreased with increase in abrading distance/load. However, the presence of SiC particulate fillers in the G‐E composites showed a promising trend. The worn surface features, when examined through scanning electron microscopy, show higher levels of broken glass fiber in G‐E system compared to SiC‐ filled G‐E composites. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

On the ‘curiosity’ of electrical self‐heating,static charge and electromagnetic shielding effectiveness from carbon black/aluminium flakes reinforced epoxy‐resin composites

This paper shows the wide application range (such as electrical self‐heating and electromagnetic shielding effectiveness) of composites consisting of conductive carbon black/aluminum flakes (CBA) filler and epoxy insulative matrix. The effect of CBA content on the network structure of epoxy matrix was investigated in detail. Static electrical conductivity increases linearly with the increase of filler concentration at the interface in epoxy composites. The large decrease of the conductivity as a function of the temperature is analyzed in terms of the negative temperature coefficient of conductivity (NTCC) effect. The influence of viscosity, surface energy and barrier highest energy on the NTCC behaviour in the composite is also considered. Based on these results, a new interpretation is proposed to explain the NTCC phenomena by computing the swelling force among conductive phases. The correlations of conductivity during the temperature cycling and activation energy were analyzed. The effects of dynamic ageing at various temperatures on the resistivity are reported. Current–voltage–temperature characteristics for epoxy with different contents of CBA were examined in detail. A model based on the law of energy conservation is proposed to calculate the specific heat and amount of heat dissipation. The static charge of the epoxy–CBA composites was estimated. The correlation between electromagnetic wave‐shielding effectiveness (EMS), conductivity and frequency of epoxy composites with different filler contents is also discussed. Furthermore, the effect of annealing on EMS of epoxy composites was examined. © 2002 Society of Chemical Industry     

Flexural,compression, chemical resistance,and morphology studies on granite powder‐filled epoxy and acrylonitrile butadiene styrene‐toughened epoxy matrices

Granite powder is an inexpensive material that can reduce the overall cost of a composite if used as a filler in epoxy and acrylonitrile butadiene styrene (ABS)‐toughened epoxy matrices. Epoxy and ABS‐toughened epoxy resins filled with granite powder were cast into sheets. To enhance the properties of these composites, granite powder was treated with triethoxymethyl silane coupling agent. Flexural properties, compression properties, chemical resistance, and morphology of these composites were studied. The filler used varied from 0 to 60 wt %. Composites consisting of ABS‐toughened epoxy with treated granite powder were found to be superior in mechanical properties to composites with treated and untreated granite powder. Composites with 50 wt % of granite powder was found to have maximum mechanical properties in all cases. All the three composites, i.e., untreated, treated and ABS toughened composites showed good resistance toward, acids, alkalis, and solvents. Treating granite powder with silane coupling agent enhances its mechanical properties and improves the interfacial bond between granite powder and the matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 171–177, 2007     

Nonlinear electrical conductivity of tin‐filled urea‐formaldehyde‐cellulose composites

This work reports on the elaboration and characterization of composite materials prepared by compression molding of mixtures of tin powder and a commercial grade thermosetting resin of urea‐formaldehyde filled with alpha‐cellulose in powder form. The morphology of constituents and composites has been characterized by optical microscopy. The porosity rate of the composites has been determined from density measurements. These results show that the composites are homogeneous. Furthermore, it has been shown that the hardness of samples remains almost constant with the increase of metal concentration. The electrical conductivity of the composites is <10⁻¹¹ S/cm unless the metal content reaches the percolation threshold at a volume fraction of 18.6%, beyond which the conductivity increases markedly by as much as 11 orders of magnitude. The results have been well interpreted in the statistical percolation theory frame. POLYM. COMPOS., 26:401–406, 2005. © 2005 Society of Plastics Engineers     

Non‐linear electrical conductivity of urea‐formaldehyde‐cellulose loaded with powders of different carbon fillers

This article reports on the making and characterization of composite materials prepared by compression molding of a commercial grade thermosetting resin of urea‐formaldehyde filled with α‐cellulose in powder form mixed successively with carbon black, synthetic graphite, and activated carbon. The morphology of the constituents and the composites has been characterized by optical microscopy. The porosity effect has been discussed from density measurements. Furthermore, it has been shown that the hardness of the samples remains almost constant with the increase of filler concentration. The electrical conductivity shows clearly a non‐linear behavior. The observed values are lower than 10^?11 S/cm, unless the filler content reaches the percolation threshold beyond which the conductivity increases markedly by as much as ten orders of magnitude, indicating insulator‐conductor phase transition. The conduction threshold depends on the filler nature. The results have been interpreted by means of the statistical percolation theory. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 990–996, 2005     

Enhanced thermal conductivity of boron nitride epoxy‐matrix composite through multi‐modal particle size mixing

Castable particulate‐filled epoxy resins exhibiting excellent thermal conductivity have been prepared using hexagonal boron nitride (hBN) and cubic boron nitride (cBN) as fillers. The thermal conductivity of boron nitride filled epoxy matrix composites was enhanced up to 217% through silane surface treatment of fillers and multi‐modal particle size mixing (two different hBN particle sizes and one cBN particle size) prior to fabricating the composite. The measurements and interpretation of the curing kinetics of anhydride cured epoxies as continuous matrix, loaded with BN having multi‐modal particle size distribution, as heat conductive fillers, are highlighted. This study evidences the importance of surface engineering and multi‐modal mixing distribution applied in inorganic fillered epoxy‐matrix composite. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Optical properties of modified epoxy resin with various oxime derivatives in the UV‐VIS spectral region

Optical absorbance measurements have been performed on the epoxy resin and the composites prepared by its modification with two different oxime derivatives (benzaldoxime and 2‐furaldoxime) in the wavelength interval of 190–680 nm by unpolarized light. Using the experimental absorbance data, dielectric constant and refractive index dispersion have been determined by means of standard oscillator fit procedure. Moreover, based on the dispersion analysis, direct and indirect band gap energies of the samples have been calculated. It is found that direct band energy for epoxy is nearly 3.49 eV, while its value for the oxime derivatives has been increased up to the 4.15 eV. Another important result to be pointed out is that the absorbance for the 2‐furaldoxime doped resin has been greatly increased in a respectively, narrow interval (～ 30 nm wide) in the UV region, while in the case for the benzaldoxime doped sample, a decreasing has been observed in the absorbance at the same region. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and electrical properties of strontium-doped lanthanum ferrite with perovskite-type structure

In this study, we prepared strontium-doped lanthanum ferrites with the perovskite-type structure for application as solid oxide fuel cell (SOFC) cathodes. We used the Pechini method to prepare strontium-doped lanthanum ferrites with the strontium:lanthanum molar ratios of 20:80 and 40:60. The resulting doped materials were characterized using various analytical tools. The calcination process was conducted at 450 °C because above this temperature, the stabilization of mass loss occurred and no phase transformation was observed. The X-ray diffraction results confirmed the mixing of the powder phases after the calcination process and the presence of a single powder phase in the air-sintered samples. The high-resolution transmission electron microscopy results revealed the presence of agglomerated nanoparticles smaller than 20 nm in size in the samples. The electrochemical impedance spectroscopy results revealed that the sample with 20% strontium exhibited a conductivity of 3.9 × 10⁻³ S cm⁻¹ at 95 °C and activation energy of 0.37 eV. In contrast, the sample with 40% strontium exhibited a conductivity of 3.5 × 10⁻² S cm⁻¹ and activation energy of 0.29 eV. These results suggest that with an increase in the strontium content, the conductivity of the samples increased, where as the activation energy of the conduction process decreased. Therefore, the ferrites synthesized in this work are potential catalysts for SOFC cathodes.     

The property of polycarbonate/acrylonitrile butadiene styrene‐based conductive composites filled by nickel‐coated carbon fiber and nickel–graphite powder

The filled conductive composites were prepared with a polycarbonate/acrylonitrile butadiene styrene matrix and both nickel‐coated carbon fiber (NiCF) and nickel–graphite powder (NCG) as fillers by using injection molding and injection‐compression molding. The effect of the NiCF content, NCG content, coupling agent, and molding methods on the properties of composites was studied. The results showed that the conductivity of the composites increased with raising the NiCF content and NCG content. NiCF treated with silane coupling agent could further improve the conductivity of the composites without any significant change in mechanical properties. Furthermore, compared with injection molding, the composites prepared by injection‐compression molding possessed better conductivity. POLYM. COMPOS., 38:157–163, 2017. © 2015 Society of Plastics Engineers     

Electrically conductive composites based on epoxy resin containing polyaniline–DBSA‐ and polyaniline–DBSA‐coated glass fibers

Four kinds of polyaniline (PANI)‐coated glass fibers (GF–PANI) combined with bulk PANI particles were synthesized. GF–PANI fillers containing different PANI contents were incorporated into an epoxy–anhydride system. The best conductivity behavior of the epoxy/GF–PANI composites was obtained with a GF–PANI filler containing 80% PANI. Such a composite shows the lowest percolation threshold at about 20% GF–PANI or 16% PANI (glass fiber‐free basis). The PANI‐coated glass fibers act as conductive bridges, interconnecting PANI particles in the epoxy matrix, thus contributing to the improvement of the conductivity of the composite and the lower percolation threshold, compared with that of a epoxy/PANI–powder composite. Particularly, the presence of glass fibers significantly improves the mechanical properties, for example, the modulus and strength of the conductive epoxy composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1329–1334, 2004     

A novel way of enhancing the electrical and thermal stability of conductive epoxy resin–carbon black composites via the Joule heating effect for heating‐element applications

The influence of Joule heating treatments and carbon black (CB) on the electrical and thermal behavior of epoxy resin composites is well described in this article. The effect of CB and Joule heating on network structure characteristics, such as shrinkability, interparticle distance between conductive particles, crosslinking density, hardness, thermoelectric power, thermal conductivity, the thermal expansion coefficient, and scanning electron microscopy, of epoxy composites was investigated. The electrical conductivity (σ) of epoxy resin correlated with the volume fraction of CB and Joule heating treatment. σ increased continuously with increasing CB content, and Joule heating increased the level of σ, which makes it attractive for electronic utilization. The σ for fresh and Joule heating samples was recorded during heating–cooling cycles. The conduction mechanism of σ for epoxy composites was identified. The activation energy and hopping energy for two batches of epoxy as a function of CB content were estimated. The hopping distance, the state density at the Fermi level, and the radius of localized wave function versus CB content were evaluated. The current–voltage–temperature characteristics of fresh and Joule heating samples of epoxy composites were demonstrated. The thermal reliability was tested by means of temperature–time characteristics when certain applied power was on and off for several cycles. The specific heat and amount of heat transfer by radiation and convection were calculated based on the energy balance model for two batches. The results indicate that the Joule heating effect is a very effective and prospective way of enhancing the electrical and thermal stability of epoxy–CB composites for consumer use as heaters and in other electronic areas such as electromagnetic shielding effectiveness. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 97–109, 2003     

Dielectric response of conducting carbon‐black‐filled ethylene–octene copolymer microcellular foams

Dielectric response of conducting carbon‐black‐filled ethylene–octene copolymer microcellular foams has been investigated with variation of blowing agent and filler loading in the frequency range of 100 Hz to 5 MHz and temperature range from 30 to 100°C. With increase in blowing agent loading, the dielectric permittivity increases for both unfilled as well as carbon‐black‐filled microcellular foams. The experimental complex impedance plots were compared with model‐fitted plots obtained by taking an equivalent circuit of (CQR) (CR).The values of R_b (bulk resistance), R_gb (grain boundary resistance), bulk capacitance (C_b), and grain boundary capacitance (C_gb) at different temperatures were calculated and compared with experimental values. The relaxation time due to bulk effect (τ_b) has been calculated from relaxation frequency (f_r). The dc conductivity (σ_dc) decreases with rise in temperature indicating the existence of positive temperature coefficient of resistance in the material. The activation energy (E_a) calculated from the relaxation time due to bulk effect (τ_b) was found to be 0.446 eV, whereas it was 0.363 eV from the dc conductivity plot in the temperature range of 30–100°C. POLYM. COMPOS., 37:3398–3410, 2016. © 2015 Society of Plastics Engineers     

Multiple percolation in a carbon‐filled polymer composites via foaming

This article describes an investigation into the effects of foaming on the electrical conductivity for a carbon‐filled cyclic olefin copolymer (COC) composite incorporating both chopped carbon fibers (cCF) and carbon black (CB). Foamed and solid samples were injection molded and then analyzed for cell size, fiber length, fiber orientation, and electrical conductivity. Foamed samples exhibited higher electrical conductivity in the through‐plane direction for materials containing only CB or composites containing both filler types, and reduced electrical conductivity in the cCF‐filled composites. The increased electrical property gained by foaming was attributed to multiple percolation with CB aggregates forming more effective conductive clusters and networks in the continuous polymer phase during growth of the gas domains. A mechanism for the phenomenon was proposed based on these experimental observations. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of organo‐montmorillonite on the mechanical and morphological properties of epoxy/glass fiber composites

Epoxy composites filled with glass fiber and organo‐montmorillonite (OMMT) were prepared by the hand lay‐up method. The flexural properties of the epoxy/glass fiber/OMMT composites were characterized by a three‐point bending test. The flexural modulus and strength of epoxy/glass fiber were increased significantly in the presence of OMMT. The optimum loading of OMMT in the epoxy/glass fiber composites was attained at 3 wt%, where the improvement in flexural modulus and strength was approximately 66 and 95%, respectively. The fractured surface morphology of the epoxy/glass fiber/OMMT composites was investigated using field emission scanning electron microscopy. It was found that OMMT adheres on the epoxy/glass fiber interface, and this is also supported by evidence from energy dispersive X‐ray analysis. Copyright © 2007 Society of Chemical Industry     

Epoxy‐ and polyester‐based composites reinforced with glass,carbon and aramid fabrics: Measurement of heat capacity and thermal conductivity of composites by differential scanning calorimetry

The primary purpose of the study is to investigate the temperature dependence of heat capacity and thermal conductivity of composites having different fiber/matrix combinations by means of heat‐flux differential scanning calorimetry (DSC). The materials used as samples in this study were epoxy‐ and polyester‐based composites. Noncrimp stitched glass, carbon, and aramid fabric were used as reinforcements for making unidirectional composites. For the heat capacity measurements the composite sample and a standard material are separately subjected to same linear temperature program. By recording the heat flow rate into the composite sample as a function of temperature, and comparing it with the heat flow rate into a standard material under the same conditions, the temperature dependence of heat capacity of the composite sample is determined. Measurements were carried out over a wide range of temperatures from about 20 to 250°C. The differential scanning calorimeter was adapted to perform the thermal conductivity measurements in the direction perpendicular to the fiber axis over the temperature range of 45–235°C. The method used in this study utilizes the measurement of rate of heat flow into a sensor material during its first‐order phase transition to obtain the thermal resistance of a composite material placed between the sensor material and the heater in the DSC. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

The electrical properties of boron‐containing poly(vinyl alcohol) derived ceramic organic semiconductor

The direct and alternating current conductivity, space charge limited current, and thermoelectrical properties of boron‐containing poly(vinyl alcohol)‐derived ceramic have been investigated. The electrical conductivity of the sample increases with increase in temperature and the room temperature conductivity of the sample was found to be 3.82 × 10^?5 S/cm. The electrical conductivity and thermoelectric power results suggest that the PVAB polymer has p‐type electrical conductivity. The current–voltage characteristics indicate that at higher voltages, the space charge limited conductivity mechanism is dominant in the PVAB sample. The electronic parameters such as the position of the Fermi level bottom of the conduction band, E_F, the density of states in conduction band N_c, effective mass of holes m_s were found to be 0.44 eV, 2.12 × 10²⁵ m^?3, and 0.59 m_o, respectively. Alternating current conductivity results suggest that the correlated barrier hopping conductivity is dominant in AC conductivity mechanism of the sample. The imaginary part of the dielectrical modulus at different temperatures shows a relaxation peak, indicating a temperature‐dependent non‐Debye relaxation. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Electrical charge transport and optical properties of a poly(methacrylate) with a new side chain and its Ni(II) complex

The electronic conductivity of poly[2‐(2‐hydroxybenzyliden hydrazino)thiazole‐4‐yl methyl methacrylate] bearing a thiazole ring, Schiff base, and hydroxyl group in its side chain and its Ni(II) complex were measured as functions of temperature and frequency. The electrical measurements show the semiconducting nature of the samples as their electrical conductivity increased with increased temperature. Also, the activation energies were below 2 eV, which places them in the semiconductor regime. The conduction mechanism in the samples is discussed. Although extrinsic conduction mechanism occurs in the polymer, intrinsic conduction mechanism take places in its metal complex. The optical absorption spectra were recorded at room temperature and the optical energy gaps of samples were determined by optical spectra. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 741–746, 2003     

Thermophysical properties of anhydride‐cured epoxy/nano‐clay composites

Polymer nano‐composites made with a matrix of anhydride‐cured diglycidyl ether of bisphenol A (DGEBA) and reinforced with organo‐montmorillonite clay were investigated. A sonication technique was used to process the epoxy/clay nano‐composites. The thermal properties of the nano‐composites were measured with dynamic mechanical analysis (DMA). The glass transition temperature T_g of the anhydride‐cured epoxy was higher than the room temperature (RT). For samples with 6.25 wt% (4.0 vol%) of clay, the storage modulus at 30°C and at (T_g + 15)°C was observed to increase 43% and 230%, respectively, relative to the value of unfilled epoxy. The clay reinforcing effect was evaluated using the Tandon‐Weng model for randomly oriented particulate filled composites. Transmission electron microscopy (TEM) examination of the nano‐composites prepared by sonication of clays in acetone showed well‐dispersed platelets in the nano‐composites. The clay nano‐platelets were observed to be well‐intercalated/expanded in the anhydride‐cured epoxy resin system. POLYM. COMPOS., 26:42–51, 2005. © 2004 Society of Plastics Engineers.     

Epoxy/nano‐silica composites: Curing kinetics,glass transition temperatures,dielectric, and thermal–mechanical performances

Nano‐silica particles were employed for enhancement of epoxy vacuum pressure impregnating (V.P.I.) resin. The influences of nano‐silica particles on the curing reaction, glass transition temperatures, dielectric behavior, and thermomechanical performances were investigated. The activation energy (E) for the epoxy curing reaction was calculated according to Kissinger, Ozawa, and Friedman‐Reich‐Lev methods. The glass transition temperatures were determined by means of differential scanning calorimetry, dynamic mechanical analysis, dc conduction, and ac dielectric loss analysis. Relationships between the glass transformation behaviors, the thermomechanical performances, and the dielectric behaviors were discussed. The influences of nano‐silica particles on the mechanical properties were also discussed in terms of non‐notched charpy impact strength and flexural strength. The morphologies were studied by means of SEM and TEM. The results indicated that nano‐silica particles could effectively increase both the toughness and strength of epoxy resin at low loadings (no more than 3 wt %) when nano‐silica particles could be well dispersed in epoxy matrix without any great aggregations. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The thermal properties of a carbon nanotube‐enriched epoxy: Thermal conductivity,curing, and degradation kinetics

Multiwalled carbon nanotube‐enriched epoxy polymers were prepared by solvent evaporation based on a commercially available epoxy system and functionalized multiwalled carbon nanotubes (COOH–MWCNTs). Three weight ratio configurations (0.05, 0.5, and 1.0 wt %) of COOH–MWCNTs were considered and compared with neat epoxy and ethanol‐treated epoxy to investigate the effects of nano enrichment and processing. Here, the thermal properties of the epoxy polymers, including curing kinetics, thermal conductivity, and degradation kinetics were studied. Introducing the MWCNTs increased the curing activation energy as revealed by differential scanning calorimetry. The final thermal conductivity of the 0.5 and 1.0 wt % MWCNT‐enriched epoxy samples measured by laser flash technique increased by up to 15% compared with the neat material. The activation energy of the degradation process, investigated by thermogravimetric analysis, was found to increase with increasing CNT content, suggesting that the addition of MWCNTs improved the thermal stability of the epoxy polymers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2722–2733, 2013