Statistical analysis of mechanical properties of pressureless sintered multiwalled carbon nanotube/alumina nanocomposites

Mechanical properties of pressureless sintered 0.15–1.2 vol.% multiwalled carbon nanotube reinforced alumina matrix nanocomposites have been analyzed using the 2-parameter Weibull statistics. Electron microscopy and phase analysis of nanocomposites sintered at 1700 °C for 2 h in Argon revealed existence of interpenetrating network of nanotubes in alumina, formation of thin interface resembling stoichiometric aluminum monoxycarbide and matrix grain refinement by nanotubes. Statistical analyses indicated that with increasing Vickers hardness testing load (4.9–19.6 N) and flexural strength measurement temperature (room temperature to 1100 °C), Weibull modulus of nanocomposites increased significantly suggesting improved consistency at higher load and temperature. The highest Weibull moduli were obtained for nanocomposites containing either 0.15 or 0.3 vol.% nanotube which were ∼40% and ∼15% higher than single phase alumina for hardness and strength, respectively, supporting the specimen size effect on reliability of present brittle ceramic matrix nanocomposites. Superior mechanical reliability of nanocomposites over pure alumina was primarily attributed to the presence of structurally intact nanotubes forming effective interface region to ensure proper load sharing, matrix grain refinement, and especially, at higher testing load and temperature, overall averaging effect of flaws to yield higher Weibull moduli.     

Synergetic effects of radiolytically degraded PTFE microparticles and organoclay in PTFE-reinforced ethylene vinyl acetate composites

This article reports exceptional synergistic effects observed in organic–inorganic dual filler containing ethylene vinyl acetate (EVA) composites. Polytetrafluoroethylene microparticles (PTFEMP) were produced by mechanically grinding radiolytically degraded PTFE; composites of EVA containing PTFEMP and organoclay were prepared in different proportions by melt compounding and their mechanical, melt flow, morphological and crystallographic characteristics were examined. Mechanical properties of ternary composites demonstrated high synergy between fillers, leading to manifold increase in the modulus of dual filler filled composites in comparison to single filler systems. Nielsen model fitted well with EVA/PTFEMP system; however it predicted remarkably low values for EVA/PTFEMP/organoclay system, confirming exceptional synergy between two fillers. Melt viscosity of EVA increased substantially on the addition of either of the fillers. X-ray diffraction studies revealed around 10% intergallery expansion in organoclay, in the composites having high loading of PTFEMP; though the crystallinity of EVA did not change.     

Preparation and characterisation of polyamide 11/montmorillonite (MMT) nanocomposites for use in angioplasty balloon applications

With increased demands on catheter balloon functionality, there is an emphasis to blend new materials which can improve mechanical performance. Polymer nanocomposites were prepared by melt blending polyamide 11 (PA 11) with organically modified montmorillonite nanoclay. The effects of incorporating the nanoclay on the short-term mechanical properties of PA 11 were assessed using a design of experiments (DoEs) approach. X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis techniques (DMA) were used to characterise the morphology of the nanocomposites. Design of experiments studies revealed that the optimum nanocomposites properties can be achieved by carefully controlling the melt compounding parameters. XRD and TEM data proved that exfoliated clay morphologies existed within the matrix at low clay loading (2%). Whereas the interaction between the polymer matrix and nanoclay was quantified in the DMA spectra, showed a significant increase in storage modulus (up to 80%). The reinforcing effect of nanoclay within the PA 11 was further investigated using mechanical testing, where significant increases in the ultimate tensile strength and strain at break of reinforced tri-layer balloon tubing were observed.     

Comparisons of phase morphology and physical properties of PVDF nanocomposites filled with organoclay and/or multi-walled carbon nanotubes

Binary and ternary poly(vinylidene fluoride) (PVDF) nanocomposites filled with organoclay (15A) and/or multi-walled carbon nanotubes (MWNTs) were successfully prepared. MWNTs were dispersed more homogeneously than 15A within PVDF matrix, and the presence of MWNTs facilitated the dispersibility of 15A. The 15A addition induced β-form PVDF crystal formation, but MWNTs hardly changed the α-form crystal development. Both nanofillers facilitated the nucleation of PVDF (up to 12.3 °C increase), and the efficiency of enhancing PVDF crystallization followed the sequence MWNT > 15A/MWNT > 15A. The nanocomposites possess higher T_m° than neat PVDF. In particular, adding 15A led to a T_m° (β-form) increase of no less than 11 °C. A rheological percolation threshold at 1 wt.% MWNT loading was determined. The electrical resistivity dropped by more than 13 orders of magnitude at 5 wt.% MWNT loading. The nanocomposites exhibited enhanced tensile modulus (up to 83% increase with MWNTs inclusion) compared with neat PVDF.     

Structure, thermal properties and mechanical properties of sPS-based nanocomposites with and without styrenic elastomer inclusions

Syndiotactic polystyrene (sPS)-based nanocomposites with and without toughener inclusions were successfully prepared. One organo-montmorillonite (20A) and two styrenic elastomers (SBS and SEBS) served as the reinforcing filler and as tougheners, respectively. XRD and TEM results confirmed the achievement of intercalated and partially exfoliated sPS/20A nanocomposites. The presence of SBS or SEBS slightly depressed the dispersibility of 20A. DSC results indicated that 20A inhibited the crystallization of sPS. The presence of SBS or SEBS further retarded the crystallization of sPS; this effect was more apparent with SEBS. The presences of 20A and SBS/SEBS facilitated the formation of α-form sPS crystals. The thermal stability enhancement of sPS/20A nanocomposites was confirmed, and was further improved with the inclusion of SBS or SEBS. The stiffness of sPS increased with the sole addition of 20A. The addition of SBS or SEBS greatly increased the impact strength of the composites, especially with the addition of SEBS. The achievement of toughened sPS-based nanocomposites was confirmed.     

The effect of bagasse fibers obtained (from rind and pith component) on the properties of unsaturated polyester composites

In the present study, two major component of bagasse, namely rind (outer part) and pith (inner part) were used as reinforcement in unsaturated polyester (USP) composites. The bagasse fiber filled USP composites were produced by vacuum bagging method and the volume percentage of fiber was varied at 0%, 5%, 10% and 15%. Characterizations such as flexural, impact and water absorption were carried out to measure the properties of the composites. Based on the result, it was found that the rind fiber composites produced higher flexural and impact properties, and lowered water absorption rate compared to inner fiber composite. In short, the flexural, impact and water absorption properties of bagasse composites are governed by the two major component of bagasse; rind and pith.     

Effect of initial imbibed moisture content on flexural fatigue behavior of polyamide 66/hectorite nanocomposites at laboratory condition

Imbibed moisture affects the mechanical properties of polymers and influences the performance of products made out of them during service. Flexural fatigue tests were conducted under deflection control mode using a custom built, table-top flexural fatigue test rig at laboratory condition on PA66/hectorite nanocomposites (PA66CN). Dynamic mechanical analysis studies of PA66CN revealed significant plasticization effect of water on moduli and damping factor with increase in imbibed moisture content. A decrease in induced flexural stress amplitude and rise in temperature of specimen with increase in moisture content result in increased fatigue life at a constant cyclic end deflection. The microstructure of failed flexural fatigue specimens manifested a rubbery behavior. The extent of rubberiness is directly related to the difference between specimen temperature at cyclic steady state and glass transition temperature.     

Microstructural evolution and mechanical properties of Mg composites containing nano-B4C hybridized micro-Ti particulates

In this work, the microstructural evolution and mechanical properties of extruded Mg composites containing micro-Ti particulates hybridized with varying contents of nano-B₄C are investigated, and compared with Mg-5.6Ti. Microstructural characterization showed the presence of uniformly distributed micro-Ti particles embedded with nano-B₄C particulates that resulted in significant grain refinement. Electron back scattered diffraction (EBSD) analyses of Mg-(5.6Ti + x-B₄C)_BM hybrid composites showed that the addition of hybridized particle resulted in relatively more recrystallized grains, realignment of basal planes and extension of weak basal fibre texture when compared to Mg-5.6Ti. The evaluation of mechanical properties indicated improved strength with ductility retention in Mg-(5.6Ti + x-B₄C)_BM hybrid composites. When compared to Mg-5.6Ti, the superior strength properties of the Mg-(5.6Ti + x-B₄C)_BM hybrid composites are attributed to the presence of nano-reinforcements, the uniform distribution of the hybridized particles, better interfacial bonding between the matrix and the reinforcement particles and the matrix grain refinement achieved by nano-B₄C addition. The ductility enhancement obtained in hybrid composites can be attributed to the fibre texture spread and favourable basal plane orientation achieved due to nano B₄C addition.     

Mechanical properties of ABOw+MWNTs/Al hybrid composites made by squeeze cast technique

Multi-wall carbon nanotubes (MWNTs) have been considered a realistic kind of reinforcement for composite materials. In this paper, microstructure and mechanical properties of the aluminum borate whisker (ABOw) and MWNTs hybrid composites were investigated. The results show that MWNTs decrease the compressive deformation of the hybrid preforms and are kept intact in the matrix during squeeze cast processing. A small amount of MWNTs may effectively improve the modulus, strength and elongation of the hybrid composite. Decreasing micropores and strengthening the matrix, high strength MWNTs make the mechanical properties of the hybrid composite superior to the singularly reinforced ones. This makes MWNTs a promising material for novel micro/nanohybrid composite.     

Electrospun polymeric nanofibrous composites containing TiO2 short nanofibers

In this study, polymeric nanofibrous composites containing anatase TiO₂ short nanofibers (TiO₂-SNF) were successfully produced via electrospinning. The fabrication of the nanofibrous composite structure includes two steps. First, anatase TiO₂ nanofibers were obtained by calcination of electrospun PVP/TiO₂ nanofibers and then crushed into short nanofibers ranging from few microns in length. Second, these TiO₂-SNF were dispersed into polymer solutions and then electrospun into nanofibrous composites. We obtained nanofibers containing TiO₂-SNF from different polymer types including PMMA, PAN, PET and PC. The SEM and TEM imaging indicated that some of the TiO₂-SNF were fully covered by the polymeric matrix whereas some TiO₂-SNF were partially covered and/or stick on the surface of the fibers. The photocatalytic activity of nanofibrous composites containing TiO₂-SNF was evaluated by monitoring the photocatalytic decomposition of a model dye (rhodamine-6G) under UV irradiation.     

Mechanical properties and fracture behaviors of epoxy composites with multi-scale rubber particles

In this work, we developed a strategy to balance the toughness and thermal resistance of epoxy composites by incorporating the multi-scale rubber particles. Two types of rubber i.e. the phase-separation-formed submicron liquid rubber (LR) and preformed nano-scale powered rubber (PR) particles were chosen as tougheners. It was found that the combination of these multi-scale rubber particles not only provides superior efficiency in enhancing the impact resistance of epoxy composites, but also results in balanced glass transition temperature. In particular, the highest gain in impact strength was obtained for the ternary composites containing 9.2 wt% submicron liquid rubber and 9.2 wt% nano-sized powered rubber which were ∼112% higher than the maximum enhancements of ∼49% and ∼66% for the corresponding binary composite systems with the single-phase rubber, respectively. The damage zone observation and fracture surface analysis suggested that the combined use of multi-scale particles was effective to promote matrix plastic deformation including void growth and shear banding induced by the improved rubber cavitation/debonding, which is likely responsible for the highly improved impact resistance of the ternary composites.     

Creep behaviour of injection moulded polyamide 6/organoclay nanocomposites by nanoindentation and cantilever-bending

The creep behaviour of injection moulded PA 6/organoclay nanocomposites was studied by depth-sensing nanoindentation and DMA cantilever-bending. The glass transitions of PA 6 and its nanocomposites were decreased below room temperature upon saturation with water so that the materials could be tested in the rubbery regime. For nanoindentation creep on the skin and core regions of injection moulded samples, whilst organoclay improves the creep resistance of PA 6, the enhancement is due to the decrease of the initial compliance at zero time but the time-dependent creep is actually increased. In contrast, for cantilever-bending creep, organoclay reduces the creep compliance and the time-dependent creep in PA 6. It is suggested that the organoclay imparts a constraint effect on the PA 6 molecular chains, restricting their mobility in the bulk compared to the surface and hence improving their resistance to creep. A modified Halpin-Tsai equation was used to model their creep behaviour under these two loading configurations and compared to experimental data.     

Elastomeric epoxy nanocomposites: Nanostructure and properties

In polymer layered silicate nanocomposites, significant differences have been reported between the effects of the nano-reinforcement on rigid and elastomeric nanocomposites. In this paper, we have studied elastomeric nanocomposites based upon DGEBA epoxy resin filled with montmorillonite (MMT) and cured with a long-chain polyoxypropylene diamine, for comparison with analogous rigid nanocomposites. Ultrasonic mixing was used to disperse the MMT in the matrix to improve homogeneity and decrease the agglomerate size. Two different methods of nanocomposite preparation were used in which the MMT was first swollen with either the curing agent or the epoxy before the addition of, respectively, DGEBA or diamine. A better dispersion of the nanoclay in the matrix and a greater amount of intercalation occurred when the MMT was first swollen with the diamine. The effect of MMT concentrations up to 8 wt.% on the mechanical behaviour of the epoxy/MMT nanocomposites was investigated. It was found that the addition of MMT increased the tensile strength and modulus, although SAXS and TEM indicated that a significant fraction of the clay layers were not exfoliated. Nevertheless, the addition of the clay resulted in changes in the fracture surfaces, as indicated by SEM, consistent with the tensile results and indicative of toughening.     

Formation of friction layer of Ni3Al matrix composites with micro- and nano-structure during sliding friction under different loads

Research on friction layer is needed for mechanical systems and assemblies in order to control failure and wear of contacting materials. This study investigates the formation of friction layer of Ni₃Al matrix composites (NMCs) with multi-layer graphene (MLG) under different contact loads. The results show that, under 15 N condition, the friction layer with the ultrafine grain and nanocrystalline structure mainly consists of the thin debris re-embedded layer (DREL) and the matrix refinement layer (MRL). The build up of the DREL is a dynamic equilibrium recovery process. The severe plastic deformation induces the dislocations and twinning, as well as misorientation boundaries, resulting in the formation of the stress dissipative structure in MRL. The low friction coefficient (0.27–0.30) and wear rate (1.2–1.6 × 10⁻⁵ mm³N⁻¹ m⁻¹) of NMCs at 15 N load are attributed to the formation of friction layer with micro- and nano-structure during sliding friction.     

The intercalation of poly(methyl methacrylate)/aluminophosphate nanocomposites and the properties improvement

Poly(methyl methacrylate) (PMMA)/dodecylamine templated lamellar aluminophosphate (DDA-LAP) intercalated nanocomposites are prepared by in situ bulk polymerization of MMA. The intercalated structure is characterized. With the intercalation of DDA-LAP in PMMA matrix, the glass-transition temperatures of nanocomposites (T_g) are increased. The nanocomposites obtained keep relatively high transparency in optical property and have a significant improvement in mechanical properties and thermal stability. The mechanism for the properties enhancement is investigated. The strong interfacial interaction between the aluminophosphate layers and the PMMA chains, the homogeneously distribution and the graphitized char formation during heating are three key roles for the properties improvement.     

Observation of interactions between hydrophilic ionic liquid and water on wet agar gels by FE-SEM and its mechanism

In the present study, an attempt is made to understand the mechanism of field emission electron microscopy (FE-SEM) observation of wet agar gel using a typical hydrophilic ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate; [BMIM][BF₄]. The IL interaction with water molecules within agar gel during sample preparation condition for FE-SEM observation was investigated using Raman spectroscopy. Results showed that water molecules within agar gel form weak hydrogen bond such as BF₄⁻?HOH?BF₄⁻ by interaction with BF₄⁻ of IL, and, it remained stable even under vacuum condition at 60 °C, 24 h. This interaction was found to be helpful for IL displacement of the water molecules within agar gel. From this study, it was found that the exact morphology of gel materials in FE-SEM condition can be observed by optimization of water concentrations of IL and gel mixtures. Thus, using IL, agar gel or any other material under wet condition can be observed without drying in FE-SEM chamber, and, present result gives an insight to the mechanism of FE-SEM observation of agar gel using IL without any conducting coating.     

Cost-efficient high performance polyetheretherketone/expanded graphite nanocomposites with high conductivity for EMI shielding application

The cost efficient expanded graphite (EG) filled polyetheretherketone (PEEK) nanocomposites were prepared by hot pressing, which exhibited an electrical conductivity percolation threshold of 1.5 wt%. The electrical conductivity of the 1.5 wt% nanocomposite increased approximately eleven orders of magnitude than that of pure PEEK. The conductivities of 5 wt% and 10 wt% nanocomposites were increased to about 3.24 S cm⁻¹ and 12.3 S cm⁻¹, respectively. Scanning electron microscope showed 3-dimensional conductive network of EG across the PEEK matrix. The significant increase in electrical conductivity of the nanocomposites leads to the tremendous increase in electromagnetic interference shielding effectiveness.     

Biodegradable amylose films reinforced by graphene oxide and polyvinyl alcohol

Graphene oxide/amylose (GO/amylose) composite films with different amounts of graphene oxide (GO), glycerol and polyvinyl alcohol (PVA) were prepared by a solution casting method. The structure, morphologies, and properties of the films were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis, UV–vis spectroscopy and tensile tests. The results indicated good dispersion of the GO nanosheets in the GO/amylose composite films and consequently a significant improvement in their mechanical properties. The addition of GO increased the tensile strength of the GO/amylose films, significantly. When glycerol was used as a plasticizer, the elongation at break of the films increased. When PVA was also added to the composite films, the films were mechanically strong and flexible. The incorporation of GO also decreased the moisture absorbability and UV transmittance of the films. The stability of the GO/amylose films in acidic and alkaline solutions was also studied and the films had excellent stability in both acidic and alkaline aqueous mediums.     

Fabrication of toughened Cf/SiC whisker composites and their mechanical properties

In this paper, dense short carbon fiber reinforced silicon carbide matrix composites had been fabricated by hot-pressed (HP) sintering using Al₂O₃ and La₂O₃ as sintering additives. The results showed that the combination of Al₂O₃ and La₂O₃ system was effective to promote densification of short cut carbon fiber reinforced silicon carbide composites (Cf/SiC). The whisker structure of silicon carbide was formed during the annealed treatment at 2023 K for 1 h. However, it was noted that this structure was not observed in the as-received HP material. The mechanism of forming whisker structure was not clear, but this kind of whisker structure was helpful to improve mechanical properties. The combination of grain bridging, crack deflection and whisker debonding would improve the fracture toughness of the Cf/SiC composites.     

Quantum and dielectric confinements of sub-10 nm gold in dichroic phosphate glass nanocomposites

Blue shifts of the surface plasmon resonance band of sub-10 nm gold in dichroic phosphate glass nanocomposites are observed with increase in both size of gold nanoparticles and refractive index of the medium, which are contrary to the common trends. These phenomena have been enlightened with the electrodynamics theories (Mie and Drude models) and happened due to quantum and dielectric confinements. Nanocomposites have been synthesized by in-situ thermochemical reduction technique in reducing phosphate glass matrices. The plasmon bands are characterized by the UV–vis spectrophotometer, and shape and size of the nanogold by the transmission electron microscopy. All the nanocomposites are dichroic in nature.