Preparation of nano‐zinc oxide/EPDM composites with both good thermal conductivity and mechanical properties

In this article, nano‐zinc oxide (ZnO) filled ethylene propylene diene monomer (EPDM) composites are prepared, and the mechanical (static and dynamic) properties and thermal conductivity are investigated respectively, which are further compared with the traditional reinforcing fillers, such as carbon black and nano‐silica. Furthermore, influence of in‐situ modification (mixing operation assisted by silane at high temperature for a certain time) with the silane‐coupling agent Bis‐(3‐thiethoxy silylpropyl)‐tetrasufide (Si69) on the nano‐ZnO filled composites is as well investigated. The results indicate that this novel reinforcing filler nano‐ZnO can not only perform well in reinforcing EPDM but can also improve the thermal conductivity significantly. In‐situ modification with Si69 can enhance the interfacial interaction between nano‐ZnO particles and rubber matrix remarkably, and therefore contribute to the better dispersion of filler. As a result, the mechanical properties and the dynamic heat build‐up of the nano‐ZnO filled composites are improved obviously by in‐situ modification, without influencing the thermal conductivity. In comparison with traditioanl reinforcing fillers, in‐situ modified nano‐ZnO filled composites exhibit the excellent performance in both mechanical (static and dynamic) properties and better thermal conductivity. In general, our work indicates that nano‐ZnO, as the novel thermal conductive reinforcing filler, is suitable to prepare elastomer products serving in dynamic conditions, with the longer expected service life. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of nanoparticles on the performance of thermally conductive epoxy adhesives

Microsized or nanosized α‐alumina (Al₂O₃) and boron nitride (BN) were effectively treated by silanes or diisocyanate, and then filled into the epoxy to prepare thermally conductive adhesives. The effects of surface modification and particle size on the performance of thermally conductive epoxy adhesives were investigated. It was revealed that epoxy adhesives filled with nanosized particles performed higher thermal conductivity, electrical insulation, and mechanical strength than those filled with microsized ones. It was also indicated that surface modification of the particles was beneficial for improving thermal conductivity of the epoxy composites, which was due to the decrease of thermal contact resistance of the filler‐matrix through the improvement of the interface between filler and matrix by surface treatment. A synergic effect was found when epoxy adhesives were filled with combination of Al₂O₃ nanoparticles and microsized BN platelets, that is, the thermal conductivity was higher than that of any sole particles filled epoxy composites at a constant loading content. The heat conductive mechanism was proposed that conductive networks easily formed among nano‐Al₂O₃ particles and micro‐BN platelets and the thermal resistance decreased due to the contact between the nano‐Al₂O₃ and BN, which resulted in improving the thermal conductivity. POLYM. ENG. SCI., 50:1809–1819, 2010. © 2010 Society of Plastics Engineers     

Development of highly reinforced maleated natural rubber nanocomposites based on sol–gel‐derived nano alumina

In the present study, sol–gel synthesized alumina (Al₂O₃) nanoparticles were characterized by Fourier transform infrared spectra, X‐ray diffraction, field‐emission scanning electron microscopy. Then, Al₂O₃ nanoparticles were employed to improve cure, mechanical, and thermal properties of maleated natural rubber (MNR) nanocomposites. The MNR nanocomposite with 2 phr nano Al₂O₃ exhibited excellent value of cure rate index and exceptionally high value of mechanical properties like modulus and tensile strength in comparison to unfilled MNR compound. Thermogravimetric analysis indicated that nano Al₂O₃ was able to improve the thermal stability of MNR composites to some extent. Additionally, the present study revealed that the interfacial interaction between MNR and nano Al₂O₃ was far better than that between NR and nano Al₂O₃ as confirmed from crosslinking degree measurement and morphological analysis. The present article offers a fresh approach to prepare high performance nano Al₂O₃‐based MNR compounds for future industrial application. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46248.     

Novel heat‐conductive composite silicone rubber

The silicone rubber with good thermal conductivity and electrical insulation was obtained by taking vinyl endblocked polymethylsiloxane as basic gum and thermally conductive, but electrically insulating hybrid Al₂O₃ powder as fillers. The effects of the amount of Al₂O₃ on the thermal conductivity, coefficient of thermal expansion (CTE), heat stability, and mechanical properties of the silicone rubber were investigated, and it was found that the thermal conductivity and heat stability increased, but the CTE decreased with increasing Al₂O₃ fillers content. The silicone rubber filled with hybrid Al₂O₃ fillers exhibited higher thermal conductivity compared with that filled with single particle size. Furthermore, a new type of thermally conductive silicone rubber composites, possessing thermal conductivity of 0.92 W/mK, good electrical insulation, and mechanical properties, was developed using electrical glass cloth as reinforcement. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2478–2483, 2007     

Autoclaved aerated concrete waste (AACW): An alternative filler material for the natural rubber industry

Material waste from the production of autoclaved aerated concrete, a porous material, should be considered as a valuable byproduct for use as a filler material for the rubber industry. Natural rubber (NR) composites filled with different loading (over the range of 0–60 phr) of autoclaved aerated concrete waste (AACW) as a new eco‐friendly material were produced using two roll mills and then were studied for their cure characteristics, mechanical and aging properties, and morphology, and also compared with commercial fillers, calcium carbonate (CaCO₃), and silica (SiO₂). In most cases, the cure characteristics and mechanical and aging properties of the SiO₂‐filled NR composites were significantly better than those of the AACW‐ and CaCO₃‐filled NR composites. However, these properties for AACW‐filled composites appeared to be higher than CaCO₃‐filled composites. The reason for this could be due to a larger surface area which is both porous and of an irregular shape of the AACW filler used. Scanning electron microscope images showed that the morphology of the rubber filled with SiO₂ was finer and more homogenous compared with the rubber filled with AACW or CaCO₃. Overall results revealed that the reinforcement ability of AACW‐filled NR composites was generally better when compared with CaCO₃‐filled NR composites; therefore, AACW can be used effectively as a cheaper filler for production of rubber products where end‐use properties of a rubber product is specifically required. POLYM. COMPOS., 36:2030–2041, 2015. © 2014 Society of Plastics Engineer     

Properties of thermally conductive silicone rubbers filled with admicellar polymerized polypyrrole-coated Al2O3 particles

Polypyrrole (PPy) nanolayers were introduced on the surface of alumina (Al₂O₃) particles via admicellar polymerization. The properties of silicone rubbers (SRs) filled with PPy-coated Al₂O₃ and pristine Al₂O₃ as thermally conductive fillers were studied and compared. The results demonstrate that the addition of PPy-coated Al₂O₃ leads to a better interfacial compatibility but lower cross-linking density of the composites than pristine Al₂O₃. The improvement in the compatibility and the decrease in the cross-linking density are paradoxes in affecting mechanical properties. The improvement in the compatibility shows a slight predominance on the strength at low-filler contents. Lower cross-linking density of modified-Al₂O₃/SR composites led to a better processing performance and a higher maximum filler loading amount than the pristine Al₂O₃/SR composites, which is beneficial to increasing the thermal conductivity and maintaining a relatively good strength. The PPy-coated Al₂O₃/SR composite with 83 wt% filler content has a thermal conductivity of 1.98 W/(m K) and a tensile strength of 2.9 MPa, and the elongation at break was 63%. Functionalized fillers by admicellar polymerization used in the fabrication of filler/SR composites not only improve the interfacial compatibility but also optimize and expand the functions of the composites, which has great significance for the production and application of thermally conductive SR in some branches of industry (automotive, electrical engineering, etc.) in the future.     

Mechanical properties,chemical and aging resistance of natural rubber filled with nano‐Al2O3

Al₂O₃ nanoparticles were introduced to natural rubber (NR) to investigate its reinforcement effect on filled NR vulcanizates. The results show that Nano‐Al₂O₃/NR nanocomposites exhibit significantly improved tensile strength, elongation at break, modulus, and tearing strength. Scanning electron microscopy analyses indicate that nanoparticles dispersed in NR matrix at nanoscale and show nano‐reinforcement effect on NR vulcanizates. The aging resistances of filled NR vulcanizates improve. After aging test, tensile strength, tearing strength, and modulus improved, and elongation at break decreased. These attribute to the crosslink maturation reactions, which result in the conversion of polysulfidic linkages into disulfidic and monosulfidic ones. The acid and alkaline resistances of nano‐Al₂O₃‐filled NR vulcanizates improve compared with that of unfilled NR systems. After acid and alkaline test, tensile strength and elongation at break improve, and modulus decrease. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Lap shear strength and thermal stability of diglycidyl ether of bisphenol a/epoxy novolac adhesives with nanoreinforcing fillers

Nanoreinforcing fillers have shown outstanding mechanical properties and widely used as reinforcing materials associated to polymeric matrices for high performance applications. In this study, a series of multiwalled carbon nanotubes (MWCNTs)‐, nano‐Al₂O₃‐, nano‐SiO₂‐, and talc‐reinforced epoxy resin adhesives composites were developed. The influence of different types and contents of nanofillers on adhesion, elongation at break, and thermal stability (under air and nitrogen atmospheres) of diglycidyl ether of bisphenol A (DGEBA)/epoxy novolac adhesives was investigated. A simple and effective approach to prepare adhesives with uniform and suitable dispersion of nanofillers into epoxy matrix was found to be mechanical stirring combined with ultrasonication. Transmission electron microscopic and scanning electron microscopic investigations revealed that nanofillers were homogeneously dispersed in epoxy matrix at optimized nanofiller loadings. Adhesion strength was measured by lap shear strength test as a function of nano‐Al₂O₃ and MWCNTs loadings. The results indicated that the lap shear strength was significantly increased by about 50% and 70% with addition of MWCNTs and nano‐Al₂O₃ up to a certain level, respectively. The highest lap shear strength was reached at 1.5 wt % of nano‐Al₂O₃ loading. MWCNTs at all loadings (except 3 wt %) and nano‐Al₂O₃ have enhanced onset of degradation temperature and char yield of the adhesives. By combined incorporation of 0.75 wt % nano‐Al₂O₃ and 0.75 wt % MWCNTs into the epoxy novolac/DGEBA blend adhesives a synergistic effect was observed in the thermal stability of the adhesives at high temperatures (800°C). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40017.     

Preparation and properties of nano‐Al2O3 particles/polyester/epoxy resin ternary composites

This article presents the results of an experimental study on the preparation and properties of new ternary composites composed of nano‐Al₂O₃ particles, polyester, and epoxy resin. The ternary composites were prepared by the addition of the nano‐Al₂O₃ particles in a binary matrix, with elevated viscosity, of the epoxy resin modified by the polyester. The nano‐Al₂O₃ particles were previously located and dispersed in the polyester phase. The study showed that the ternary system was a type of nanoscale dispersed composite with high strength and toughness as well as modulus, combined with excellent dielectric and heat‐resistance properties. All related properties of the composites were remarkably superior to those of both the binary matrix and the unmodified epoxy resin. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 70–77, 2002     

Effects of size and shape originated synergism of carbon nano fillers on the electrical and mechanical properties of conductive polymer composites

In this study, microstructural features, mechanical properties, and electrical conductivity behaviors of thermoplastic composites prepared by using of cyclic olefin copolymer (COC) as matrix and various types of carbon nano materials, expanded graphite (EG), carbon nanofiber (CNF), and multi walled carbon nanotubes (CNT) as conductive fillers were investigated. Effects of using of double and triple filler combinations on the electrical properties of composites were also quantified in detail by measuring the bulk resistance of samples under alternating current with an impedance spectrometer. The electrical percolation values of fillers were found to be 20, 10, and 5 phr for the series of composites prepared with the EG, CNF, and CNT, respectively. It was obtained that the bulk resistances of percolated samples were dramatically decreased from 10¹⁴ ohm.cm to 10³?10⁴ ohm.cm. On the other hand, it was also found that the using of double and triple filler combinations provided much lower (about 10¹ ohm.cm) bulk resistance which corresponded to higher conductivity values than the highly filled composites including of 30 and 40 phr of EG. Based on the DMA measurements and the quantifying of elastic modulus values of composites in the rubbery region, it was found that the reinforcing effects of carbon nano fillers on the elastic modulus of composites decreased in the order of CNT>CNF>EG, depending on the aspect ratio (A_f) values of fillers into the matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42313.     

Study on thermally conductive ESBR vulcanizates

The thermal conductivities of emulsion polymerized styrene-butadiene rubber (ESBR) vulcanizates filled with alumina (Al₂O₃), zinc oxide (ZnO), carbon nanotubes (CNTs), silicon carbide (SiC), are measured by steady-state method. The effects of types and loadings of the fillers and their mixture on thermal conductivities of the ESBR vulcanizates are investigated. The results show that the thermal conductivity of ESBR vulcanizates filled with alumina or zinc oxide, increases nearly linearly with increasing loading when the filler loading exceeded 20 phr; the ESBR vulcanizates filled with CNTs have the highest thermal conductivity at a given filler loading in comparison with other composite vulcanizates. At a given loading of 100 phr, the ESBR vulcanizate filled with two different particle sizes SiC of 1–3 and 5–11 μm at the mass ratio of 1:1 has the highest thermal conductivity and relatively good mechanical properties. The experimental results are analyzed using Geometric mean model and Agari’s equation to explain the effect of filler types and particle sizes on the formation of thermal conductive networks. The thermal conductivity of the ESBR vulcanizates filled with Al₂O₃ or ZnO or CNTs could be well predicted by optimized parameters using Agari’s equation for a polymer composite filled with mixtures of particles.     

Application of lime kiln dust as a filler in the natural rubber industry

Lime kiln dust (LKD) obtained from kraft chemical recovery systems by conversion of calcium carbonate (CaCO₃) back into calcium oxide (CaO) for reuse in the causticizing process, is mainly composed of CaCO₃. A two‐stage conventional mixing procedure was used to incorporate LKD into natural rubber (NR). For comparison purposes, four commercial fillers, stearic acid coated CaCO₃, ground CaCO₃, silica, and carbon black, were also used. The effect of these fillers on the curing characteristics and mechanical properties of NR materials at various loadings ranging from 0 to 60 phr were studied. The results indicate that the use of LKD filler resulted in a lower Mooney viscosity and shorter curing time in the NR materials. The incorporation of LKD into NR improved the Young's modulus and hardness but decreased the tensile strength and tear strength. However, LKD was better in processability than the commercial fillers. Scanning electron micrographs revealed that the morphology of the rubbers filled with reinforcing fillers, such as silica and carbon black, was finer and more homogeneous compared to the those of the rubbers filled with LKD and commercial CaCO₃. The dispersion of LKD and commercial CaCO₃ fillers in the rubber matrix was discontinuous, which in turn, generated a weak structure compared with the reinforcing fillers. According to these observations, LKD could be used as a cheaper filler for NR materials where improved mechanical properties are not critical. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Tribological properties of micro‐ and nanoparticles‐filled poly(etherimide) composites

It has been found that nano‐ or microsized inorganic particles in general enhance the tribological properties of polymer materials. In the present study, 5 vol % nano‐TiO₂ or micro‐CaSiO₃ was introduced into a polyetherimide (PEI) matrix composite, which was filled additionally with short carbon fibers (SCF) and graphite flakes. The influence of these inorganic particles on the sliding behavior was investigated with a pin‐on‐disc testing rig at room temperature and 150°C. Experimental results showed that both particles could reduce the wear rate and the frictional coefficient (μ) of the PEI composites under the applied testing conditions. At room temperature, the microparticles‐filled composites exhibited a lower wear rate and μ, while the nano‐TiO₂‐filled composites possessed the lowest wear rate and μ at elevated temperature. Enhancement in tribological properties with the addition of the nano‐particles was attributed to the formation of transfer layers on both sliding surfaces together with the reinforcing effect. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1678–1686, 2006     

Multi-contact hybrid thermal conductive filler Al2O3@AgNPs optimized three-dimensional thermal network for flexible thermal interface materials

In this work, a multi-contact Al₂O₃@AgNPs hybrid thermal conductive filler was synthesized by in-situ growth method to fill high thermal conductivity polydimethylsiloxane (PDMS)-based composites to prepare TIMs. And the thermal conductivity, electrical conductivity, and mechanical properties of the composite materials were studied. During the synthesis process of the multi-contact hybrid filler, different concentrations of silver ions were reduced to generate silver nanoparticles and attached to the surface of Al₂O₃. Al₂O₃@AgNPs/PDMS thermally conductive composites were prepared by changing the filler addition. Using SEM, XPS, and XRD is used to characterize the morphology and chemical composition of Al₂O₃@AgNPs hybrid filler. The thermal conductivity of PDMS-based composites with different AgNPs content under 70 wt% filler loading was studied. The results show that the thermal conductivity of PDMS-based composites filled with 7owt%Al₂O₃@3AgNPs/PDMS multi-contact hybrid filler is 0.67 W/m·K, which is 3.72 times that of pure PDMS, and is higher than that of unmodified Al₂O₃ with the same addition amount. /PDMS composite material has a high thermal conductivity of 24%. This work provides a new idea for the design and manufacture of high thermal conductivity hybrid fillers for TIMs.     

Role of interface on dynamic modulus of high‐performance poly(etheretherketone)/ceramic composites

High‐performance printed circuit board or electronic packaging substrate with low warping particularly at high frequency is the key demand of manufacturers. In the present work, poly(etheretherketone) (PEEK) matrix composites reinforced with untreated micron size aluminum nitride (AlN) and alumina (Al₂O₃) particles have been studied for dynamic modulus in the temperature range varying from 30 to 250°C. At 48 vol % particles, the room temperature modulus of the PEEK/AlN composites increased by approximately fivefold (～ 23 GPa), whereas it increased by twofold for PEEK/Al₂O₃ composite. The reinforcing efficiency is more pronounced at higher temperatures. The significant improvement in modulus was attributed to the better adhesion between the matrix and the AlN particles. Scanning electron microscope (SEM) and Kubat parameter showed that the poor adhesion between the matrix and the Al₂O₃ particles resulted in comparatively smaller increase in modulus of PEEK/Al₂O₃, despite higher intrinsic modulus of Al₂O₃ than that of AlN. SEM showed almost uniform distribution of particles in the matrix. The experimental data were correlated with several theoretical models. The Halpin–Tsai model with ξ (xi) is equal to four correlates well up to 48 vol % AlN composites while ξ is equal to two correlates only up to 18 vol % Al₂O₃ composites. Guth–Smallwood model also correlates well up to 28 vol % AlN and 18 vol % Al₂O₃‐filled composites. Thereafter, data deviated from it due to the particles tendency to aggregate formation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Estimation of thermal conductivity of polymer multiphase composites

The thermal conductivities of a medium density polyethylene composites filled separately with two different thermal conductive fillers including graphite, cuprum, and aluminum oxide (Al₂O₃), an epoxy composites filled respectively with two different thermal conductive fillers including silicon nitride, aluminum hydroxide, Al₂O₃ and aluminum nitride, and a polypropylene composites filled with aluminum hydroxide and magnesium hydroxide were estimated using a thermal conductivity equation of polymer multiphase composites. This equation was based on a new heat transfer model, and the parameters were easily determined. It was found that the estimated thermal conductivities of the three composites systems were approximately close to the experimental measured data reported in literature. In addition, the predictions were roughly close to the estimations from the Agari model. POLYM. ENG. SCI., 57:965–972, 2017. © 2016 Society of Plastics Engineers     

Nano-BN/Nano-TiO2 and micro Mg(OH)2 loaded hybrid ethylene propylene diene monomer elastomer composites for outdoor high-voltage insulation application

This work deals with the synthesis, characterization of hybrid ethylene propylene diene monomer (EPDM) composites loaded with nano-boron nitride (nano-BN)/nano-titanium dioxide (nano-TiO₂) and micro Mg(OH)₂ particles for its suitability towards high-voltage insulation application. The elastomer samples were prepared by carefully dispersing the micro and nano fillers during the mastication process of EPDM polymer using a two roll mill, followed by vulcanization. The samples were characterized for mechanical, morphological, thermal, and electrical insulation properties. The highest tensile strength among the composite samples was noted for 1 phr nanoparticles loaded samples. Fourier Transform Infrared (FTIR) results show no change in the chemical moiety upon addition of nano-BN/nano-TiO₂ in EPDM composites. Enhancement in hydrophobicity is observed for 3 phr nano-TiO₂ loaded composites, which shows a maximum static contact angle of 110°. Meanwhile remarkable enhancement in the thermal conductivity and volume resistance of the composites are contributed to the addition of nano-BN, thereby achieving maximum dielectric breakdown voltage (i.e., ~21 kV/mm for EMB3). Scanning electron microscope images and atomic force microscopy (AFM) topography highlight that low concentration (i.e., 1 phr) based composites have homogeneous dispersion in matrix and excessive nano filler addition deteriorates properties by forming filler aggregates and increasing surface roughness.     

Tribological behavior of the polyamide composite coating filled with different fillers under dry sliding

The polyamide (PA) composite coating filled with the particles of microsized MoS₂, microsized graphite, and nano‐Al₂O₃, respectively, were prepared by flame spraying. The friction and wear characteristics of the PA coating and composite coating filled with the varied content of filler under dry sliding against stainless steel were comparatively investigated using a block‐ring tester. The morphologies of the worn surfaces and transfer films on the counterpart steel ring were observed on a scanning electron microscope. The result showed that the addition of fillers to the composite coatings changed significantly the friction coefficient and wear rate of the coatings. The composite coatings filled with a low level content of fillers showed lower wear rate than did pure PA coating under dry sliding; especially the MoS₂/PA composite coating had the lowest wear rate among these composite coatings. The composite coatings with a high level content of fillers had higher wear rate than did pure PA coating, except of the Al₂O₃/PA composite coating. The bonding strengths between the polymer matrix and fillers changed with the content of the fillers, which accounted for the differences in the tribological properties of the composite coatings filled with the varied content fillers. On the other hand, the difference in the friction and wear behaviors of the composite coatings and pure coating were attributed to the difference in their worn surface morphologies and transfer film characteristics. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Aluminum oxide particles/silicon carbide whiskers’ synergistic effect on thermal conductivity of high-density polyethylene composites

Aluminum oxide (Al₂O₃) particles and silicon carbide (SiC) whiskers improved the thermal conductivity of high-density polyethylene (HDPE). To improve the dispersion of inorganic fillers in the matrix, 5 wt% of maleic anhydride-modified polyethylene was added into HDPE as a compatibilizer, and the hybrid matrix was denoted as mHDPE. The thermal conductivity, heat resistance, and tensile properties of resulting HDPE composites were characterized. The results showed that the thermal conductivity reached its maximum value of 0.8876 W/(m K) at 1/4 weight ratio of Al₂O₃/SiC, which was 110.3, 54.8, and 8.8% higher than that of pure HDPE, mHDPE/Al₂O₃, and mHDPE/SiC composites, in the order given, indicating that hybrid fillers have synergistic effect on the thermal conductivity of HDPE composites. Moreover, they also have a synergistic effect on the heat resistance and Young’s modulus. As the SiC content increases, the heat resistance of the composites increases at first and then falls, and the maximum VST is reached at an Al₂O₃/SiC weight ratio of 3/2, which is 5.4 °C higher than that of HDPE. The maximum Young’s modulus of the composites (1160 MPa) is obtained at an Al₂O₃/SiC weight ratio of 1/4, and the yield strength increases gradually as the SiC whiskers’ content increases.