The influence of nano/micro hybrid structure on the mechanical and self-sensing properties of carbon nanotube-microparticle reinforced epoxy matrix composite

Nano/micrometer hybrids are prepared by chemical vapor deposition growth of carbon nanotubes (CNTs) on SiC, Al₂O₃ and graphene nanoplatelet (GNP). The mechanical and self-sensing behaviors of the hybrids reinforced epoxy composites are found to be highly dependent on CNT aspect ratio (AR), organization and substrates. The CNT–GNP hybrids exhibit the most significant reinforcing effectiveness, among the three hybrids with AR1200. During tensile loading, the in situ electrical resistance of the CNT–GNP/epoxy and the CNT–SiC/epoxy composites gradually increases to a maximum value and then decreases, which is remarkably different from the monotonic increase in the CNT–Al₂O₃/epoxy composites. However, the CNT–Al₂O₃ with increased AR ⩾ 2000 endows the similar resistance change as the other two hybrids. Besides, when AR < 3200, the tensile modulus and strength of the CNT–Al₂O₃/epoxy composites gradually increase with AR. The interrelationship between the hybrid structure and the mechanical and self-sensing behaviors of the composites are analyzed.     

Properties of calcium copper titanate and barium titanate filled epoxy composites for electronic applications: effect of filler loading and hybrid fillers

Inorganic ceramics such as calcium copper titanate, CaCu₃Ti₄O₁₂ (CCTO) and barium titanate (BaTiO₃) were used as fillers to produce epoxy thin film composites for capacitor application. The effects of filler types and loading range on the dielectric, tensile, morphology, and thermal properties of the epoxy thin film composites were determined. Results showed that epoxy thin film composites with 20 vol% filler loading of CCTO and BaTiO₃ showed good dielectric properties, thermal stability, and thermal conductivity. However, the tensile properties of the CCTO/epoxy thin film composite was reduced as the filler loading increased. On the other hand, the tensile properties of BaTiO₃/epoxy thin film composite improved as the filler loading increased. Hybrid fillers CCTO and BaTiO₃ filled epoxy composites were fabricated and the effect of hybrid fillers on the dielectric properties and morphology of the epoxy thin film composites were investigated. Results indicated that positive hybrid effect in dielectric constant and dielectric loss showed by the hybrid composites.     

Study on the effects of nanoparticulates of SiC,Al2O3, and ZnO on the mechanical and tribological performance of epoxy-based nanocomposites

In this research work, mechanical and tribological characteristics of ortho cresol novalac epoxy (OCNE)-based nanocomposites filled with nanoparticulates of SiC, Al₂O_3, and ZnO have been investigated. Also, in these investigations, the influence of wear parameters such as applied normal load, sliding velocity, filler contents, and sliding distance have been explored. The experimental plan for four factors at three levels using face centered composite design (CCD) has been employed by the response surface methodology (RSM) technique. The friction and wear tests were carried out using a pin on disc wear test apparatus under dry sliding conditions. The hardness and flexural strength of nano ortho cresol novalac epoxy composites filled with nano (SiC, Al₂O_3, and ZnO) particulates increases with an increase in the filler contents. Whereas, the tensile strength of these nanocomposites increases with an increase in the filler contents from 1 to 2 wt%, and with a further increase in filler contents the tensile strength decreases. The results of the study also showed that (2 wt%) filler contents bring superior mechanical and tribological properties. The lowest coefficient of friction and specific wear rate were found with nano Al₂O₃-filled composites. Also, the wear mechanisms of these nanocomposites were studied using a scanning electron microscope (SEM) equipped with an EDS analyzer.     

The effect of interfacial state on the thermal conductivity of functionalized Al2O3 filled glass fibers reinforced polymer composites

Rapidly increasing packaging density of electronic devices puts forward higher requirements for thermal conductivity of glass fibers reinforced polymer (GFRP) composites, which are commonly used as substrates in printed circuit board. Interface between fillers and polymer matrix has long been playing an important role in affecting thermal conductivity. In this paper, the effect of interfacial state on the thermal conductivity of functionalized Al₂O₃ filled GFRP composites was evaluated. The results indicated that amino groups-Al₂O₃ was demonstrated to be effective filler to fabricate thermally conductive GFPR composite (1.07 W/m K), compared with epoxy group and graphene oxide functionalized Al₂O₃. It was determined that the strong adhesion at the interface and homogeneous dispersion of filler particles were the key factors. Moreover, the effect of interfacial state on dielectric and thermomechanical properties of GFRP composites was also discussed. This research provides an efficient way to develop high-performance GFRP composites with high thermal conductivity for integrated circuit packaging applications.     

Preparation and characterization of maleimide–polystyrene/SiO2–Al2O3 hybrid nanocomposites by an in situ sol–gel process and its antimicrobial activity

Inorganic–organic nanocomposites have unlocked new opportunities in the design of innovative materials and compounds with enhanced and unique properties, based on soft chemistry. In the present study, a hybrid nanocomposite of maleimide–polystyrene (PSMA) with SiO₂ and Al₂O₃ (PSMA-SA) was synthesized by means of the sol–gel approach in the presence of γ-aminotriethoxysilane (γ-APTES), in which tetraethoxysilane (TEOS) and aluminum isopropoxide (AIP) were used as precursors. The Michael reaction led to bonding between the PSMA and SiO₂–Al₂O₃, giving a stable cross-linked network that prevented aggregation and mechanical mixing of the nanoparticles. XRD and FTIR analysis confirmed the effects of the coupling agent in promoting the Michael reaction. Thermal properties of the hybrid nanocomposites were tested through TGA and DSC. SEM, TEM and optical tests confirmed the controlled morphology and optical transparency of the composites. Additionally, the hybrid nanocomposites showed excellent solvent resistance and antimicrobial activity against pathogenic bacteria such as Bacillus cereus and Escherichia coli.     

Processing and mechanical properties of carbon nanotube-alumina hybrid reinforced high density polyethylene composites

Carbon nanotube-alumina hybrid reinforced high density polyethylene (HDPE) matrix composites were prepared by melt processing technique. Microstructure studies verified that the nanotubes consisting of well-crystallized graphite formed a network structure with Al₂O₃ in the hybrid, which was homogeneously dispersed in the HDPE matrix composites. Mechanical measurements revealed that 5% addition of nanotube-alumina hybrid results in 100.8% and 65.7% simultaneous increases in Young's modulus and tensile strength, respectively. Fracture surface showed homogenous dispersion of nanotubes and Al₂O₃ in the HDPE matrix and presence of interlocking like phenomena between hybrid and HDPE matrix, which might contribute to the effective reinforcement of the HDPE composites.     

Influence of nano-alumina and sub-micron copper on mechanical properties of magnesium alloy AZ31

Magnesium composites of AZ31–Al₂O₃–Cu formulations were produced using the disintegrated melt deposition technique following by hot extrusion. Microstructural characterization showed reasonable distribution of secondary phases up to 1 vol.% of copper. A tendency to form clustered agglomeration and longer shape of secondary phases was observed when the amount of copper was increased to 1.5 vol.%. Mechanical tests indicated remarkable improvements in 0.2%YS, UTS and microhardness when nano-alumina and sub-micron copper were added into AZ31. The ductility was increased up to 9.3% in the case of AZ31–1.5Al₂O₃–1.0Cu sample and significantly reduced (5.5%) when the amount of copper was increased to 1.5 vol.%. Heat treated sample of AZ31–1.5Al₂O₃–1.0Cu showed overall improvement in both tensile strength and ductility. The results suggest that the judicious selection of composition and heat treatment has the capability to enhance overall tensile response of Mg–Al₂O₃–Cu nanocomposites.     

Highly mechanical strength and thermally conductive bismaleimide–triazine composites reinforced by Al2O3@polyimide hybrid fiber

Bismaleimide–triazine (BT) resins have received a great deal of attention in microelectronics due to its excellent thermal stability and good retention of mechanical properties. Thereafter, developing BT based composites with high mechanical strength, thermal conductivity and dielectric property simultaneously are highly desirable. In this study, one hybrid fiber of Al₂O₃ nanoparticle (200 nm) supported on polyimide fiber (Al₂O₃@PI) with core–shell structure was introduced into BT resin to prepare promising Al₂O₃@PI–BT composite. The results indicated that the resultant composites possessed high Young’s modulus of 4.06 GPa, low dielectric constant (3.38–3.50, 100 kHz) and dielectric loss (0.0102–0.0107, 100 kHz). The Al₂O₃@PI hybrid film was also conductive to improve thermal stability (T_d5% up to 371 °C), in-plane thermal conductivity (increased by 295% compared to that of the pure BT resin). Furthermore, the Al₂O₃@PI–BT composite were employed to fabricate a printed circuit substrate, on which a frequency “flasher” circuit and electrical components worked well.     

Nanostructured systems based on SBS epoxidized triblock copolymers and well-dispersed alumina/epoxy matrix composites

In the present research, the effect of addition of (1 wt.% and 3 wt.%) alumina nanoparticles (Al₂O₃) to epoxy modified by poly(styrene-b-butadiene-b-styrene) (SBS) epoxidized triblock copolymer was studied. The microstructure of final hybrid composites was studied with atomic force microscopy (AFM). Composites showed homogeneously dispersed Al₂O₃ nanoparticles in the epoxy matrix containing polystyrene (PS) microphase separated nanodomains. Dynamic mechanical analyses (DMA), flexural and fracture toughness investigations were carried out. The glass transition temperature of epoxy matrix has been retained unchanged by the addition of Al₂O₃ nanoparticles. The nanostructured epoxy systems based on SBS epoxidized triblock copolymer and well-dispersed Al₂O₃ nanoparticles allowed an increase in fracture toughness maintaining the transparency and stiffness of neat epoxy.     

Enhanced thermal conductivity of epoxy nanocomposites filled with hybrid filler system of triethylenetetramine-functionalized multi-walled carbon nanotube/silane-modified nano-sized silicon carbide

Multi-walled carbon nanotubes (MWCNTs) were first treated by a 3:1 (v/v) mixture of concentrated H₂SO₄/HNO₃, and then triethylenetetramine (TETA) grafting was carried out. Nano-sized silicon carbide particles (SiC_np) were modified by the silane coupling agent. Epoxy nanocomposites filled with hybrid filler system containing TETA-functionalized MWCNTs and silane-modified SiC_np were prepared. The investigation on the thermal conductivity of epoxy nanocomposites filled with single filler system and hybrid filler system was performed. Chemical surface treatment is conducive to the enhancement of thermal conductivity of epoxy composites. The thermal conductivity of epoxy composites with hybrid filler system is higher than that of epoxy composites with any single filler system (functionalized MWCNTs or modified SiC_np), which is due to the effective combination of MWCNT-to-MWCNT and SiC_np-to-SiC_np conductive networks. Hybrid filler system could provide synergistic effect and cost reduction simultaneously.     

Static and dynamic mechanical properties of poly(vinyl chloride) loaded with aluminum oxide nanopowder

A series of nanocomposites from poly(vinyl chloride) loaded with different concentrations of Al₂O₃ nanopowder was prepared. The tensile mechanical properties of these composites were studied at different temperatures namely; stress–strain curves. The elastic modulus was calculated and found to decrease with increasing both filler loading and temperature. The strain at a certain stress at different temperatures was studied and the thermal activation energy for polymer chains was calculated. The complex viscosity as well as the storage modulus was found to decrease with increasing the filler loadings at different frequencies. The relaxation time of the polymer matrix was calculated and found to independent on the concentration of the filler but it decreased linearly with increasing frequency. The glass transition temperature was found to increase with increasing both filler loading and frequency.     

A comparative study of the effect of different rigid fillers on the fracture and failure behavior of polypropylene based composites

Polypropylene (PP) composites with 5 wt% of different rigid particles (Al₂O₃ nanoparticles, SiO₂ nanoparticles, Clay (Cloisite 20A) nanoparticles or CaCO₃ microparticles) were obtained by melt mixing. Composites with different CaCO₃ content were also prepared. The effect of fillers, filler content and addition of maleic anhydride grafted PP (MAPP) on the composites fracture and failure behavior was investigated. For PP/CaCO₃ composites, an increasing trend of stiffness with filler loading was found while a decreasing trend of strength, ductility and fracture toughness was observed. The addition of MAPP was beneficial and detrimental to strength and ductility, respectively mainly as a result of improved interfacial adhesion. For the composites with 5 wt% of CaCO₃ or Al₂O₃, no significant changes in tensile properties were found due to the presence of agglomerated particles. However, the PP/CaCO₃ composite exhibited the best tensile behavior: the highest ductility while keeping the strength and stiffness of neat PP. In general, the composites with SiO₂ or Clay, on the other hand, displayed worse tensile strength and ductility. These behaviors could be probably related to the filler ability as nucleating agent. In addition, although the incorporation of MAPP led to improved filler dispersion, it was damaging to the material fracture behavior for the composites with CaCO₃, Al₂O₃ or Clay, as a result of a higher interfacial adhesion, the retardant effect of MAPP on PP nucleation and the lower molecular weight of the PP/MAPP blend. The PP/MAPP/SiO₂ composite, on the other hand, showed slightly increased toughness respect to the composite without MAPP due to the beneficial concomitant effects of the presence of some amount of the β crystalline phase of PP and the better filler dispersion promoted by the coupling agent which favor multiple crazing. From modeling of strength, the effect of MAPP on filler dispersion and interfacial adhesion in the PP/CaCO₃ composites was confirmed.     

Performance properties of pigmented polyvinyl chloride nanocomposites

This work highlighted the role of blue CoO·MgO·Al₂O₃ pigments in changing some properties of PVC composites such as electrical, mechanical and thermal properties. The pigments were prepared by doping different ratios of magnesium in cobalt aluminate crystals using solid–solid interaction. The prepared pigments were characterized by different instrumental analysis (e.g. XRD, SEM and TEM). The influences of different concentrations of nanosized CoO·MgO·Al₂O₃ pigment on PVC prepared by solution blending were studied. The obtained data revealed that PVC nanocomposites containing 1CoO·1MgO·Al₂O₃ pigments show the most promising results. The composites containing 5 wt% of the three compositions of pigments exhibit the optimum electrical, mechanical as well as thermal properties.     

Fabrication of nano-sized Al2O3 reinforced casting aluminum composite focusing on preparation process of reinforcement powders and evaluation of its properties

In this study, a novel approach was used to fabricate Al₂O₃ nanoparticle reinforced aluminum composites to avoid agglomeration of nanoparticles in matrix. Al₂O₃ nanoparticles were separately milled with aluminum and copper powders at different milling durations and incorporated into A356 alloy via stir casting method. The effects of milling process and milling time on mechanical properties of the composites were evaluated by hardness, tensile, and compression tests. Based on the results, some of the composites, reinforced with Al₂O₃-metallic mixed powders, showed higher mechanical performance compared with that of the pure Al₂O₃ nanoparticle reinforced composite. This enhancement is related to uniform distribution of individual nanoparticles and grain refinement of A356 matrix, shown in microstructural studies. Moreover, the results showed that an increase in milling time, led to a gradual decrease in mechanical performance of the samples. It can be related to further oxidation of metallic powders that can act as inclusions and also further probable contamination of nanoparticles with increase in milling time. Studies on the fracture surfaces revealed that the failure of matrix was the basic mechanism of fracture in the composites. Agglomerated nanoparticles were observed on dendrites in the fracture surface of the Al₂O₃–Al reinforcement samples.     

Microstructure and mechanical properties of SiC-platelet reinforced Al2O3/SiC-particle hybrid composites

SiC-platelet reinforced Al₂O₃/SiC-particle nanocomposites were fabricated by hot-pressing the mixture through the conventional powder mixing process. The mechanical properties of Al₂O₃/SiC-particle/SiC-platelet hybrid composites were evaluated. Fracture toughness and work of fracture were increased by the incorporation of SiC-platelets into Al₂O₃/SiC-particle nanocomposites. The typical rising R-curve was shown during crack growth for these hybrid nanocomposites, whereas Al₂O₃/SiC-particle nanocomposites showed the constant K _R value and no rising R-curve. The further improvement of Al₂O₃/SiC-particle nanocomposites in the creep resistance was observed by the addition of SiC platelets. The relationship between the microstructure and mechanical properties for Al₂O₃/SiC-particle/SiC-platelet hybrid composites was discussed.     

New alignment procedure of magnetite–CNT hybrid nanofillers on epoxy bulk resin with permanent magnets

The main properties of epoxy composites reinforced with aligned carbon nanotubes (CNTs) have been studied. The alignment was carried out in a specific designed device applying a weak magnetic field (0.3 T) with permanent magnets. CNTs were modified with magnetite nanoparticles (Fe₃O₄) functionalized, in a one-stage-process which does not require use of strong acids or aggressive treatments which could affect the structural integrity of CNTs. The study by transmission electron microscopy confirmed that the Fe₃O₄ nanoparticles were closely bonded over CNT surfaces. The thermo-mechanical and tensile properties of composites measured were higher than neat epoxy resin and were similar for both composites: reinforced with neat CNTs and magnetite–CNT hybrid nanofillers. The electrical behaviour indicates a high anisotropy for aligned composites, showing an increase of one order of magnitude for the electrical conductivity in the direction of aligned nanotubes.     

Tensile,dielectric, and thermal properties of epoxy composites filled with silica,mica, and calcium carbonate

The minerals silica, mica, and calcium carbonate (CaCO₃) were used as fillers to produce epoxy thin film composites for capacitor application. The effects of filler loading and type on the morphology, tensile, dielectric, and thermal properties of the epoxy thin film composites were determined. Results showed that epoxy thin films with 20 vol% filler loading showed good dielectric properties, thermal conductivity, and thermal stability. However, the tensile properties of the thin films were reduced as the filler loading was increased due to brittleness. Dielectric constant and dielectric loss of epoxy/inorganic composite films generally increased with increasing mineral filler loading. Meanwhile, the presence of mineral filler improved the thermal stability of the thin film composites. The highest dielectric constant of 5.75 with 20 vol% filler loading at a frequency of 1 MHz was exhibited by the epoxy/CaCO₃ composite, followed by epoxy/mica and epoxy/silica. Therefore, the epoxy/CaCO₃ composite is the most potential candidate for capacitor application. Moreover, precipitated CaCO₃ provided better tensile properties and slightly improved the dielectric properties compared with mineral CaCO₃.     

Mechanical properties of carbon nanotube–alumina nanocomposites synthesized by chemical vapor deposition and spark plasma sintering

Carbon nanotubes–alumina (CNT–Al₂O₃) nanocomposites with variable CNT content were directly synthesized by chemical vapor deposition (CVD). The as-grown CNT–Al₂O₃ mixture was densified by spark plasma sintering (SPS) at 1150 and 1450 °C. Vickers hardness of 9.98 GPa and fracture toughness of 4.7 MPam^1/2 were obtained for 7.39 wt.% CNT–Al₂O₃ nanocomposite. The addition of CNTs gives rise to 8.4% increase in hardness and 21.1% increase in toughness over that of the pure Al₂O₃. The optimum amount of CNTs is considered to be able to significantly enhance the mechanical property of ceramics in composites.     

Mechanical and thermal behavior of non-crimp glass fiber reinforced layered clay/epoxy nanocomposites

Mechanical and thermal properties of non-crimp glass fiber reinforced clay/epoxy nanocomposites were investigated. Clay/epoxy nanocomposite systems were prepared to use as the matrix material for composite laminates. X-ray diffraction results obtained from natural and modified clays indicated that intergallery spacing of the layered clay increases with surface treatment. Tensile tests indicated that clay loading has minor effect on the tensile properties. Flexural properties of laminates were improved by clay addition due to the improved interface between glass fibers and epoxy. Differential scanning calorimetry (DSC) results showed that the modified clay particles affected the glass transition temperatures (T_g) of the nanocomposites. Incorporation of surface treated clay particles increased the dynamic mechanical properties of nanocomposite laminates. It was found that the flame resistance of composites was improved significantly by clay addition into the epoxy matrix.