Effect of nano‐modified SiO2/Al2O3 mixed‐matrix micro‐composite fillers on thermal,mechanical, and tribological properties of epoxy polymers

Thermo‐mechanically durable industrial polymer nanocomposites have great demand as structural components. In this work, highly competent filler design is processed via nano‐modified of micronic SiO₂/Al₂O₃ particulate ceramics and studied its influence on the rheology, glass transition temperature, composite microstructure, thermal conductivity, mechanical strength, micro hardness, and tribology properties. Composites were fabricated with different proportions of nano‐modified micro‐composite fillers in epoxy matrix at as much possible filler loadings. Results revealed that nano‐modified SiO₂/Al₂O₃ micro‐composite fillers enhanced inter‐particle network and offer benefits like homogeneous microstructures and increased thermal conductivity. Epoxy composites attained thermal conductivity of 0.8 W/mK at 46% filler loading. Mechanical strength and bulk hardness were reached to higher values on the incorporation of nano‐modified fillers. Tribology study revealed an increased specific wear rate and decreased friction coefficient in such fillers. The study is significant in a way that the design of nano‐modified mixed‐matrix micro‐composite fillers are effective where a high loading is much easier, which is critical for achieving desired thermal and mechanical properties for any engineering applications. Copyright © 2016 John Wiley & Sons, Ltd.     

Combined effect of fibers and PTFE nanoparticles on improving the fretting wear resistance of UHMWPE‐matrix composites

Ultra‐high molecular weight polyethylene composites reinforced with carbon fibers (CF) and polytetrafluoroethylene (PTFE) were prepared. The effects of fillers on the microstructure and fretting wear behavior of composites were investigated. The results of X‐ray diffraction and scanning electron microscopy measurements indicated that the microstructure of composites were greatly changed, and the distinct interface between fillers and matrix had been formed with the incorporation of CF and PTFE. In addition, results also showed that the simultaneously filled with CF and PTFE at a proper weight fraction contributed to dramatically improving the friction reducing and wear resistance of ultra‐high molecular weight polyethylene. It can be found that there exists synergism between fillers. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of nano/micro‐mixed ceramic fillers on the dielectric and thermal properties of epoxy polymer composites

Nano/micro ceramic‐filled epoxy composite materials have been processed with various percentage additions of SiO₂, Al₂O₃ ceramic fillers as reinforcements selected from the nano and micro origin sources. Different types of filler combinations, viz. only nano, only micro, nano/micro, and micro/micro particles, were designed to investigate their influence on the thermal expansion, thermal conductivity, and dielectric properties of epoxy polymers. Thermal expansion studies were conducted using thermomechanical analysis that revealed a two‐step expansion pattern consecutively before and after vitreous transition temperatures. The presence of micro fillers have shown vitreous transition temperature in the range 70–80°C compared with that of nano structured composites in which the same was observed as ~90°C. Similarly, the bulk thermal conductivity is found to increase with increasing percentage of micron‐size Al₂O₃. It was established that the addition of micro fillers lead to epoxy composite materials that exhibited lower thermal expansion and higher thermal conductivity compared with nano fillers. Moreover, nano fillers have a significantly decisive role in having low bulk dielectric permittivity. In this study, epoxy composites with a thermal expansion coefficient of 2.5 × 10^?5/K, thermal conductivity of 1.18 W/m · K and dielectric permittivity in the range 4–5 at 1 kHz have been obtained. The study confirms that although the micro fillers seem to exhibit good thermal conductivity and low expansion coefficient, the nano‐size ceramic fillers are candidate as cofillers for low dielectric permittivity. However, a suitable proportion of nano/micro‐mixed fillers is necessary for achieving epoxy composites with promising thermal conductivity, controlled coefficient of thermal expansion and dielectric permittivity. Copyright © 2013 John Wiley & Sons, Ltd.     

Mechanical,thermal, and UV‐shielding behavior of silane surface modified ZnO‐reinforced phthalonitrile nanocomposites

In the present work, zinc oxide nanoparticles were treated with aminopropyl trimethoxy silane‐coupling agent and used as a new kind of reinforcement for a typical high performance bisphenol‐A‐based phthalonitrile resin. The resulted nanocomposites were characterized for their mechanical, thermal, and optical properties. Results from the tensile test indicated that the tensile strength and modulus as well as the toughness state of the matrix were all enhanced with the increasing of the nanoparticles amount. Thermogravimetric analysis showed that the starting decomposition temperatures and the residual weight at 800°C were highly improved upon adding the nanofillers. At 6 wt% nanoloading, the glass transition temperature and the storage modulus were considerably enhanced reaching about 359°C and 3.7 GPa, respectively. The optical tests revealed that the neat resin possesses excellent UV‐shielding properties, which were further enhanced by adding the nanofillers. Furthermore, the fractured surfaces of the nanocomposites analyzed by scanning electron microscope exhibited homogeneous and rougher surfaces compared with that of the pristine resin. Finally, the good dispersion of the reinforcing phase into the matrix was confirmed by a high resolution transmission electron microscope. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of solid lubricant particles on the tribological properties of PTFE composites lubricated with natural seawater

An orthogonal test was used to design different mixture ratios of molybdenum disulfide(MoS₂), graphite, and SiO₂ particles, which were filled with polytetrafluoroethylene (PTFE) composite. MoS₂-, graphite-, and SiO₂-modified PTFE was obtained by pressing and sintering, and the processing parameters were determined using progressive studies and experiments. The friction and wear properties of different PTFE composites lubricated with natural seawater were analyzed using an MMU-5G wear tester. A laser scanning confocal microscope was employed to examine the morphological characteristics of the worn surface. Moreover, the influence of particle proportions on the tribological property of composites was analyzed. Results show that the addition of SiO₂, MoS₂, and graphite can increase the bearing capacity, improve the wear resistance, reduce the friction coefficient, and increase the self-lubricating ability of the PTFE matrix.     

Probing the tribological behaviors in water of novel poly(phthalazione ether sulfone ketone) and its composites based on the state of aggregation and the microstructure

In this paper, novel poly(phthalazione ether sulfone ketone) (PPESK) and its composites reinforced with carbon fibers (CFs) were prepared, and their tribological behaviors in pure and sea water were comparatively investigated. Affected by the noncoplanar twisted aromatic structure in the molecular skeleton, the aggregation of the macromolecular chain in PPESK was amorphous, resulting in very high water absorption of PPESK matrix. The invading water molecules led to a sharp decrease in the hardness of PPESK surface, resulting in very high wear rate of PPESK in water. Although CF/PPESK composites had higher water absorption than pure PPESK, their wear processes in water were no longer dominated by high water absorption but by the load‐carrying effect of CFs, ascribed to the good CF/PPESK interfacial adhesion. Therefore, CF/PPESK composites exhibited very low wear rates in the order of 10^?7 mm³/Nm in water, which decreased with the CF content increasing until the content of CFs reached 50%. The results revealed that the most critical factor determining the wear behavior of a fiber‐reinforced polymer composite sliding in water is the fiber/matrix interface but not the water absorption of the polymer matrix. Copyright © 2017 John Wiley & Sons, Ltd.     

The direct architecture of carbon fiber‐carbon nanofiber hierarchical reinforcements for superior interfacial properties of CF/epoxy composites

A simple and efficient chemical method was developed to graft directly carbon nanofibers (CNFs) onto carbon fiber (CF) surface to construct a CF‐CNF hierarchical reinforcing structure. The grafted CF reinforcements via covalent ester linkage at low temperature without any usage of dendrimer or catalyst was investigated by FTIR, X‐ray photoelectron spectroscopy, Raman, scanning electron microscopy, atomic force microscopy, dynamic contact angle analysis, and single fiber tensile testing. The results indicated that the CNFs with high density could effectively increase the polarity, wettability, and roughness of the CF surface. Simultaneous enhancements of the interfacial shear strength, flexural strength, and dynamic mechanical properties as well as the tensile strength of CFs were achieved, for an increase of 75.8%, 21.9%, 21.7%, and 0.5%, respectively. We believe the facile and effective method may provide a novel and promising interface design strategy for next‐generation advanced composite structures.     

Synthesis of non‐destructive amido group functionalized multi‐walled carbon nanotubes and their application in antistatic and thermal conductive polyetherimide matrix nanocomposites

Thermal conductive and antistatic polyetherimide (PEI) nanocomposites were fabricated by encapsulating non‐destructive amido group functionalized multi‐walled carbon nanotubes (MWCNTs) into the PEI matrix. Briefly, nearly half of acyl chloride groups in poly (acryloyl chloride) reacted with sodium azide and formed acyl azide groups, which could conjunct with MWCNTs via non‐destruction nitrenes addition reaction. The remaining acyl chloride groups in poly (acryloyl chloride) hydrolyzed into carboxyl groups, therefore COOH‐rich MWCNTs (MWCNTs@azide polyacrylic acid) were synthesized without serious damage to the MWCNTs. Then, MWCNTs@azide polyacrylic acid were then reacted with p‐Phenylene diamine (PPD) and transformed to amido group functionalized MWCNTs (MWCNTs@PPD). MWCNTs@PPD could participate into the in situ polymerization of PEI matrix, where the conjunction between bisphenol A dianhydride and amido groups on MWCNTs@PPD guaranteed the strong covalent bonding at the PEI/MWCNTs interface, which directly avoided the aggregation of MWCNTs. Owing to the non‐destructive modification of MWCNTs and tight matrix/filler interface, the volume electric and thermal conductivity of as‐prepared nanocomposites was up to 6.4 × 10^?8 S/cm (1.0 wt%, MWCNTs@PPD) and 0.43 W/(m · K) (4.0 wt%, MWCNTs@PPD), respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

Mechanical hysteresis,interface and filler–filler structural breakdowns in ethylene vinyl acetate organoclay composites internally lubricated via radiolytically degraded PTFE microparticles

Inclusion of two or more distinct fillers (hybrid fillers) in a matrix is envisaged to entail synergetic advantages. This study reports synthesis and property evaluation of a novel hybrid filler‐based polymer composite containing two types of fillers with distinct attributes namely mechanical reinforcement and internal lubrication. Poly(tetrafluoroethylene) micro‐particles (PTFEMP) were synthesized via radiolytic‐mechanical degradation and used as an internal lubricant for organoclay (OC) reinforced ethylene vinyl acetate (EVA) matrix. Mechanical hysteresis, nonlinear and linear small amplitude oscillatory shear rheology, morphology, small angle X‐ray scattering (SAXS), dynamic coefficient of friction (DCoF), surface wetting and thermoxidative stability of binary and ternary composites were investigated. In EVA/OC composites, PTFEMP acted as an internal lubricant and reduced DCoF in a volume fraction‐dependent fashion. OC and PTFEMP both increased the mechanical hysteresis of EVA; though the magnitude of hysteresis was much less in PTFEMP. Intriguingly, PTFEMP reduced mechanical hysteresis of EVA/OC composites that is work done during loading and unloading stress–strain cycles was considerably reduced with the inclusion of PTFEMP in EVA/OC composites. SAXS results revealed mass fractals and the presence of an interfacial layer in EVA/OC composites but not in EVA/PTFEMP composites. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 509–519     

Infrared laser synthesis and properties of magnetic nano‐iron–polyoxocarbosilane composites

Nano‐magnetic, thermally stable iron‐based composites were obtained by a one‐step procedure consisting of continuous‐wave infrared laser‐induced and ethylene‐sensitized co‐pyrolysis of gaseous iron pentacarbonyl and hexamethyldisiloxane in argon. The simultaneously occurring formation of iron from iron pentacarbonyl and that of organosilicon polymer from hexamethyldisiloxane yield iron nanoparticles surrounded by an organosilicon polymer shell. The particles were characterized by spectral analyses, electron microscopy, thermal gravimetry and magnetic measurements. They become superficially oxidized in the atmosphere. Their composition, thermal behaviour and magnetic properties depend on the flow rates of the precursors and the total pressure of the procedure. Magnetization curves, exchange bias H_ex at T = 5 K and AC susceptibility were studied in the temperature range 5–400 K. The values of H_ex verified the observed degree of the particle surface oxidation. The system of the iron nanoparticles is in a ferromagnetic blocked state and the temperature dependence of the coercivity and susceptibility is in accord with the transmission electron microscopy data. Copyright © 2005 John Wiley & Sons, Ltd.     

Viscoelastic properties of poly(ε‐caprolactone) – hydroxyapatite micro‐ and nano‐composites

Various composites have been proposed in the literature for the fabrication of bioscaffolds for bone tissue engineering. These materials include poly(ε‐caprolactone) (PCL) with hydroxyapatite (HA). Since the biomaterial acts as the medium that transfers mechanical signals from the body to the cells, the fundamental properties of the biomaterials should be characterized. Furthermore, in order to control the processing of these materials into scaffolds, the characterization of the fundamental properties is also necessary. In this study, the physical, thermal, mechanical, and viscoelastic properties of the PCL‐HA micro‐ and nano‐composites were characterized. Although the addition of filler particles increased the compressive modulus by up to 450%, the thermal and viscoelastic properties were unaffected. Furthermore, although the presence of water plasticized the polymer, the viscoelastic behavior was only minimally affected. Testing the composites under various conditions showed that the addition of HA can strengthen PCL without changing its viscoelastic response. The results found in this study can be used to further understand and approximate the time‐dependent behavior of scaffolds for bone tissue engineering. Copyright © 2012 John Wiley & Sons, Ltd.     

Influence of heat treatment on electromagnetic properties of polyimide/carbon black composites

A kind of absorbing materials was prepared by hot pressing method using polyimide as matrix and carbon black (CB) as filler. The mechanical properties, the electromagnetic properties, and the thermal stability of polyimide/CB composites were studied. The results showed that the complex permittivity increased from 6.82 + 1.38i to 18.69 + 9.47i, whereas the flexural strength decreased from 108 MPa to 77 MPa, respectively, when the CB content increased from 2 wt% to 8 wt%. The reflection loss curves shifted to low frequency with increase of the thickness at the same content. The reflection loss below ?10 dB could be obtained in the X band with 6 wt% CB content and did not display significant difference before and after the heat treatment at 400°C for 5 h. When the content of CB was 8 wt%, the decomposition temperature (at 5% weight loss) increased approximately 42°C compared with pure polyimide matrix. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of homologous nano-composites on the thermal degradation of the silicone resin

Effect of homologous of nano-composites on the thermal degradation of the silicone resin was researched based on graphene oxide (GO)/polyhedral oligomeric silsesquioxane (POSS). First, the amino-POSS was grafted onto the GO surface (GO/POSS) via the amide bond. Second, GO/POSS was incorporated into the silicone with active epoxy group via chemistry grafting. The reaction kinetics of the thermal decomposition of the epoxy–silicone resin based on nano-composite homologous effect is developed. The initial decomposition temperature of the modified silicone resin is improved by 77.2°C. At high temperatures, GO/POSS-modified silicone molecular end forms homologous nano-structures, which can restrain silicone future degradation. The developed strategy has potential to restrain the degradation of the polymer molecular chain.     

Biomimetic chitosan‐treated clay–elastomer composites with water‐responsive mechanically dynamic properties

Biomimetic hydrophobic polymer composites with water‐responsive mechanically adaptive behaviors were successfully prepared using hydrophilic chitosan‐treated clay (chi‐clay) as the water‐activated, pH‐sensitive and reinforcing phase and elastomeric thermoplastic polyurethane (TPU) as the matrix. Structural characterization, swelling tests in three representative solutions with different pH values, and dynamic mechanical analysis under wet and dry conditions were performed on the resultant chi‐clay‐TPU composites with varying chi‐clay contents. The results showed that the equilibrium swelling degree of TPU increased significantly with increasing chi‐clay content and that water transportation in all the composites followed Fickian diffusion mechanism. The presence of chi‐clay provided remarkable enhancement of the storage modulus of TPU and offered water‐responsive changes of the modulus. Such changes increased with chi‐clay content and were pH‐sensitive, with the acidic condition rendering the largest modulus difference. These water‐responsive polymer composites may find potential applications in biomedical fields and beyond. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 55–62     

Investigation of sub‐micron size cenosphere fillers and filler loading on the mechanical and tribological peculiarity of polyester composites

This paper investigates the effect of sub‐micron size cenosphere filler and filler loading on mechanical and dry sliding wear property of polyester composites. Composites are fabricated by filling with 10 and 20 wt% of 800 and 200‐nm size of cenosphere filler particles. Neat polyester composite is also prepared for comparison analysis. Dry sliding wear test is conducted for these composites over a range of sliding distance with different sliding velocities and applied loads on a pin‐on‐disc wear test machine. Taguchi methodology and analysis of variance (ANOVA) is used to analyze the friction and wear characteristics of the composites. The artificial neural network (ANN) approach is implemented to the friction and wear data for corroboration. In this work, mechanical properties of composites such as hardness, tensile strength, tensile modulus, flexural strength, and compressive strength revealed that mechanical properties and wear resistance of the composites increase with a decrease in the particle size. The measured Young's moduli are comparable to standard theoretical prediction models. The morphology of worn composite specimens has been examined by scanning electron microscopy to understand the dominant wear mechanisms. Finally, optimal factor settings are determined using a genetic algorithm (GA). Copyright © 2017 John Wiley & Sons, Ltd.     

Enhancement of the thermal and mechanical properties of a surface‐modified boron nitride–polyurethane composite

Thermoplastic polyurethane (PU) elastomer, prepared from poly(tetramethylene glycol) and methyl diphenyl diisocyanate, was blended with boron nitride (BN) to fabricate a thermally conductive interface material. BN treated by a silane coupling agent (BN―NH₂) and PU‐grafted BN were prepared to fabricate a composite that has better thermal conductivity and mechanical strength. The surface‐modified filler showed enhanced dispersibility and affinity because of the surface treatment with functional groups that affected the surface free energy, along with the structural similarity of the doped crystallized diisocyanate molecule with the matrix. The thermal conductivity increased from 0.349 to 0.467 W mk^?1 on 20 wt% PU‐grafted BN loading that is a 1.34‐fold higher value than in the case of pristine BN loading at the same weight fraction. Moreover, the number of BN particles acting as defects, thereby reducing the mechanical strength, is decreased because of strong adhesion. We can conclude that these composite materials may be promising materials for a significant performance improvement in terms of both the thermal and mechanical properties of PU‐based polymers. Copyright © 2014 John Wiley & Sons, Ltd.     

Investigation of processing,thermal, and mechanical properties of a new composite matrix‐benzoxazine containing aldehyde group

A new benzoxazine aldehyde group containing monomer 3‐phenyl‐6‐formyl‐3, 4‐dihydro‐2H‐1, 3‐benzoxazine (Ald‐B) was synthesized via the Mannich reaction of formaldehyde, p‐hydroxybenzaldehyde, and aniline. The viscosities and curing behavior of the resins were studied. The results indicated that Ald‐B has an initial viscosity lower than 0.110 Pa s at 90°C and the maximum temperature of the exotherm was at 196°C. Dynamic mechanical analysis (DMA) of the copolymer of Ald‐B and methylenedianiline‐type bis‐benzoxazine (B‐BOZ) showed only one T_g of 251°C and high crosslink density in the matrix. The thermal stability of the copolymer was improved noticeably and the char yield at 800°C is 68.4%. The tensile strength and flexural strength of this resin cast are 72 and 137 MPa, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Mechanical and thermal properties of green polylactide composites with natural fillers

Green composites of PLA with micropowders derived from agricultural by-products such as oat husks, cocoa shells, and apple solids that remain after pressing have been prepared by melt mixing. The thermal and mechanical properties of the composites, including the effect of matrix crystallization and plasticization with poly(propylene glycol), have been studied. All fillers nucleated PLA crystallization and decreased the cold-crystallization temperature. They also affected the mechanical properties of the compositions, increasing the modulus of elasticity but decreasing the elongation at break and tensile impact strength although with few exceptions. Plasticization of the PLA matrix improved the ductility of the composites.     

Thermoelectrical and optical properties of double wall carbon nanotubes:polyaniline containing boron n‐type organic semiconductors

The electrical conductivity, thermoelectrical, and optical properties of the polyaniline containing boron/double wall carbon nanotubes (CNTs) composites have been investigated. The electrical conductivities of the composites prepared with 1%, 5%, and 8% CNT concentrations at 300 K were found to be 5.31 × 10^?6, 2.72 × 10^?4, and 1.12 × 10^?3 (S/cm), respectively. The thermoelectrical results indicate that all the samples exhibit n‐type electrical conductivity. The optical band gaps of the samples were found to be 3.71 eV for 0% DWNT, 3.32 eV for 1% DWNT, 3.15 eV for 5% DWNT, and 3.12 eV for 8% DWNT. The obtained results suggest that the electrical conductivity of PANI‐B polymer is improved by DWNT doping. Copyright © 2008 John Wiley & Sons, Ltd.     

Mechanical and electrical properties of the phosphor‐doped nano‐silicon film under an external electric field

The mechanical and electrical properties of the phosphor‐doped nano‐silicon film (nc‐Si:H) prepared by the plasma‐enhanced chemical vapor deposition (PECVD) method under electric field have been studied by Tribolab system, which is equipped with nano‐electrical contact resistance (ECR) tool. During indentation, different voltages and loads were applied. The topography of the sample surface was studied by atomic force microscopy (AFM). The experimental results show that the roughness of the film is 5.69 nm; the electric current was measured through the sample/indenter tip with different loads at a fixed voltage, and it increased nonlinearly during the indentation. The maximum current value depth was shallower than the maximum depth of each indent due to the plasticity of the film. When the loading speed is increased to 250 µN/s, the microcrack occurred on the film; the hardness (H) and elastic modulus (E) changed with the voltage applied both in open circuit and in short circuit case, which resulted in different values of H/E rate from 0.082 to 0.096. Copyright © 2009 John Wiley & Sons, Ltd.