Novel polyacrylonitrile/Na-MMT/silica nanocomposite: Co-incorporation of two different form nano materials into polymer matrix

Polyacrylonitrile (PAN)/Na-montmorillonite (Na-MMT)/SiO₂ nanocomposites were synthesized via in-situ emulsion polymerization. The X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) observations show that the Na-MMT layers were exfoliated in polymerization and the nano materials are well dispersed in the polymer matrix. The thermogravimetric analysis (TGA) suggests that co-incorporating Na-MMT and SiO₂ into the polymer matrix significantly enhances the thermal stability of the polymer. At same nano material loading, the PAN/Na-MMT/SiO₂ nanocomposites show superior thermal stability with respect to the PAN/Na-MMT and PAN/SiO₂ nanocomposites. The mechanical properties of the nanocomposites were also examined. It was found that the PAN/Na-MMT/SiO₂ nanocomposites exhibit considerably enhanced moduli compared with the PAN/Na-MMT and PAN/SiO₂ nanocomposites due to the synergistic reinforcing effect.     

Effect of TiO2 and nanoclay on the properties of wood polymer nanocomposite

High density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP) and poly(vinyl chloride) (PVC) with Phragmiteskarka wood flour (WF) and polyethylene-co-glycidyl methacrylate (PE-co-GMA) was used to develop wood polymer composite (WPC) by solution blending method. The effect of addition of nanoclay and TiO₂ on the properties of the composite was examined. The exfoliation of silicate layers and dispersion of TiO₂ nanopowder was studied by X-ray diffractometry and transmission electron microscopy. The improvement in miscibility among polymers due to addition of compatibilizer was studied by scanning electron microscopy (SEM). WPC treated with 3 phr each of clay and TiO₂ showed an improvement in thermal stability. Mechanical, UV resistance and flame retarding properties were also enhanced after the incorporation of clay/TiO₂ nanopowder to the composites. Both water and water vapor absorption were found to decrease due to inclusion of nanoclay and TiO₂ in WPC.     

Thermal stability and tensile properties of sol-enhanced nanostructured Ni–TiO2 composites

A highly-dispersed TiO₂ nano-particles reinforced Ni–TiO₂ composite was prepared by sol-enhanced composite electroplating. The microstructure, thermal stability and tensile properties of the sol-enhanced and traditional Ni–TiO₂ composites were explicitly compared. TiO₂ nano-particles agglomerated to large clusters of ∼400 nm in the traditional Ni–TiO₂ composite. In contrast, nano-sized TiO₂ particles (∼15 nm) were distributed at grain boundaries in the sol-enhanced composite. The grain size, higher micro-strain (∼0.31%) and higher microhardness (∼407 HV₅₀) of the sol-enhanced Ni–TiO₂ composite were stabilized up to 250 °C compared to 150 °C of the traditional composite. The sol-enhanced Ni–TiO₂ composite showed a much higher tensile strength of ∼1050 MPa compared to ∼610 MPa of the traditional composite. The lattice diffusion dominated at high temperatures during grain growth for the sol-enhanced composite. The distribution and location of TiO₂ nano-particles played a significant role in determining the thermal stability and tensile behaviors.     

Interfacial enhancement of nano-SiO2/polypropylene composites

The authors proposed an approach for manufacturing nano-SiO₂/polypropylene (PP) composites by in situ reactive processing. The key issue lies in that the nanoparticles were covalently bonded to the matrix polymer via polyurethane (PU) elastomer and PP-g-NH₂. Unlike the previous techniques based on graft polymerization, the present one did not need to pretreat the nanoparticles. Taking the advantages of rubber-type grafting polymer (i.e. PU) and interfacial reactive compatibilization with PP-g-NH₂, a synergetic toughening effect was observed for the PP nanocomposites. Only very low concentrations of nano-SiO₂ (1.5–2.5 vol.%) and PU (<4 vol.%) were sufficient to greatly increase notched impact strength of PP. Meanwhile, tensile properties of the nanocomposites were also slightly enhanced.     

Micromechanical deformations in PP/lignocellulosic filler composites: Effect of matrix properties

Polypropylene composites were prepared from three different PP matrices, a homopolymer, a random and a heterophase copolymer, and corn cob to study the effect of matrix characteristics on deformation and failure. The components were homogenized in an internal mixer and compression molded to 1 mm thick plates. Mechanical properties were characterized by tensile testing, while micromechanical deformations by acoustic emission measurements and fractography. The results proved that the dominating micromechanical deformation process may change with matrix properties. Yield stress determined from the stress vs. strain traces may cover widely differing processes. Debonding is the dominating process when the adhesion of the components is poor, while matrix yielding and/or filler fracture dominate when adhesion is improved by the introduction of a functionalized polymer. The dominating deformation mechanism is determined by component properties and adhesion. Interfacial adhesion, matrix yield stress and the inherent strength of the reinforcement can be limiting factors in the improvement of composite strength. The properties of polymer composites reinforced with lignocellulosic fillers are determined by micromechanical deformation processes, but they are independent of the mechanism of these processes.     

Review of the mechanical properties of carbon nanofiber/polymer composites

In this paper, the mechanical properties of vapor grown carbon nanofiber (VGCNF)/polymer composites are reviewed. The paper starts with the structural and intrinsic mechanical properties of VGCNFs. Then the major factors (filler dispersion and distribution, filler aspect ratio, adhesion and interface between filler and polymer matrix) affecting the mechanical properties of VGCNF/polymer composites are presented. After that, VGCNF/polymer composite mechanical properties are discussed in terms of nanofibers dispersion and alignment, adhesion between the nanofiber and polymer matrix, and other factors. The influence of processing methods and processing conditions on the properties of VGCNF/polymer composite is also considered. At the end, the possible future challenges for VGCNF and VGCNF/polymer composites are highlighted.     

Mechanical properties of high density polyethylene/carbon nanotube composites

Carbon-nanotubes (CNTs) have been used with polymers from the date of their inception to make composites having remarkable properties. An attempt has been made in this direction, in order to enhance mechanical and tribological properties of the composite materials. The latter, were achieved through the injection molding of high density polyethylene (HDPE) reinforced with specific volume fraction of CNTs. A considerable improvement on mechanical properties of the material can be observed when the volume fraction of CNT is increased. The composite reinforcement shows a good load transfer effect and interface link between CNT and HDPE. The volumetric wear rate is calculated from the Wang’s model, Ratner’s correlation and reciprocal of toughness. The results obtained clearly show the linear relationship with CNT loading which supports the microscopic wear model. It is concluded that both Halpin–Tsai and modified series model can be used to predict Young’s modulus of CNT–HDPE composites. From thermal analysis study, it is found that melting point and oxidation temperature of the composites are not affected by the addition of CNTs, however its crystallinity seems to increase.     

Fabrication of aluminum matrix composites with enhanced mechanical properties reinforced by in situ generated MgAl2O4 whiskers

Aluminum matrix composite reinforced by in situ generated single crystalline MgAl₂O₄ whiskers was fabricated by chemical synthesis method in an Al-Mg-H₃BO₃ system. A large number of MgAl₂O₄ whiskers were generated during the sintering process and distributed homogeneously in the Al matrix. The whiskers penetrate into the matrix grains to form the framework of the materials, leading to an incredible increase in mechanical properties of the composites. The generation mechanism of the MgAl₂O₄ whiskers was also discussed.     

A low-temperature process to synthesize rutile phase TiO2 and mixed phase TiO2 composites

This works employed K₂Ti₄O₉, a novel Ti source, to prepare TiO₂ powders. By a “low-temperature dissolution-reprecipitation process” (LTDRP), rutile phase TiO₂ was successfully synthesized after reacting at 50 °C for 48 h. The obtained sample showed a specific surface area about 45 m²/g, and excellent activity in photo-destruction of NO_x gas. The coupling of rutile phase TiO₂ with commercial anatase TiO₂ showed significant effect in further enhancing the photocatalytic activity.     

Bounds on effective magnetic permeability of three-phase composites with coated spherical inclusions

An effective model is developed to bound the effective magnetic permeability of three-phase composites with coated spherical inclusions. In the present model, the trial magnetic potential for the upper bound and the trial magnetic induction field for the lower bound are constructed to satisfy continuity interface conditions. According to the variational principle, the upper and lower bounds on the effective magnetic permeability of three-phase composites with coated spherical inclusions are derived. In this paper, trial magnetic potentials with different function forms are taken and the optimal upper bound is obtained for the trail magnetic potential corresponding to the third-order function. When the three-phase model degenerates into the composite spheres assemblage model [1], it is interesting that the optimal upper and lower bounds are the same. The effects of the volume fraction of coated spherical inclusions and the thickness and magnetic permeability of coated layers between the matrix and spherical inclusions on the effective magnetic permeability of composites are analyzed. The upper and lower bounds are finite non-zero values when the magnetic permeability of spherical inclusions tends to ∞$\infty$ and 0, respectively.     

Overall behavior and microstructural deformation of R-CNT/polymer composites

Carbon nanotubes (CNTs) are an excellent candidate for the reinforcement of composite materials owing to their distinctive mechanical and electrical properties. Reticulate carbon nanotubes (R-CNTs) with a 2D or 3D configuration have been manufactured in which nonwoven connected CNTs are homogeneously distributed and connected with each other. A composite reinforced by R-CNTs can be fabricated by infiltrating a polymer into the R-CNT structure, which overcomes the inherent disadvantages of the lack of weaving of the CNTs and the low strength of the interface between CNTs and the polymer. In this paper, a 2D plane strain model of a R-CNT composite is presented to investigate its micro-deformation and effective stiffness. Using the two-scale expansion method, the effective stiffness coefficients and Young’s modulus are determined. The influences of microstructural parameters on the micro-deformation and effective stiffness of the R-CNT composite are studied to aid the design of new composites with optimal properties. It is shown that R-CNT composites have a strong microstructure-dependence and better effective mechanical properties than other CNT composites.     

Determination of Young’s modulus in polyester-Al2O3 and epoxy-Al2O3 nanocomposites using the Digital Image Correlation method

Young’s modulus of nano-composite systems composed of unsaturated polyester and epoxy resins with alumina nanoparticles of different sizes has been experimentally estimated. The nanoparticles used were spherical alpha-Al₂O₃ having 30-40 and 200 nm in diameter. Young’s modulus was estimated using an inverse problem that is solved by means of the classical Levenberg-Marquardt technique. A cantilever beam under bending was used in the experiments and the experimental procedure was performed using the Digital Image Correlation method, which is a well-established optical-numerical method for estimating full-field displacement. Experimental results indicate that Young’s modulus increases with increasing nanoparticle volume fraction. Finally, the estimated Young’s moduli were compared with classical theoretical models, showing that the experimental results are in agreement with literature data.     

Estimation of modulus of elasticity of plastics and wood plastic composites using a Taber stiffness tester

This study measured the modulus of elasticity (MOE) of various plastics and composite materials with a Taber stiffness tester as an alternative to conventional universal testing machines. The proposed approach presents an expedited means to assess MOE for a wide range of plastics and wood plastic composites (WPCs) with various shapes. The Taber stiffness units and the geometry of the samples acted as the basis for the calculation of the MOE. The results showed a high correlation between the MOE calculated from Taber units and that obtained on a universal testing machine (Instron). Concurrently, Taber units showed the potential to assess stiffness of samples with irregular shapes, such as in the case of extruded rods, which exhibit this characteristic.     

Nitrogen-doped TiO2 nanotubes with enhanced photocatalytic activity synthesized by a facile wet chemistry method

Nitrogen-doped TiO₂ nanotubes with enhanced photocatalytic activity were synthesized using titanate nanotubes as raw material by a facile wet chemistry method. The resulting nanotubes were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and UV-vis absorption spectroscopy, etc. The photocatalytic activity of nitrogen-doped TiO₂ nanotubes was evaluated by the decomposition of methylene blue under artificial solar light. And it was found that nitrogen-doped TiO₂ nanotubes exhibited much higher photocatalytic activity than undoped titanate nanotubes.     

Macroporous TiO2/carbon composites prepared via a simple soaking process

A new-type composite photocatalyst of three-dimensional ordered macroporous (3DOM) TiO₂/C was prepared and tested in this paper. 3DOM carbon materials were first prepared by colloidal crystal templating process, and then the sols of TiO₂ from tetrabutyl titanate were infiltrated in the macroporous structures via capillary force. After calcinations at nitrogen flow, TiO₂/C composite materials were prepared. The obtained samples were analyzed by SEM, TEM, XRD and BET. The results indicated that macroporous TiO₂/C can remain the three-dimensional ordered structure and TiO₂ nanoparticles distributed in the interior of macropores uniformly. Eventually, 3DOM TiO₂/C materials were used as a new-type photocatalysts to decompose the methyl orange solution under ultraviolet light, which displayed excellent catalytic activity and regenerative ability.     

Microstructure and mechanical properties of in situ TiB reinforced titanium matrix composites based on Ti–FeMo–B prepared by spark plasma sintering

The in situ synthesized TiB reinforced titanium matrix composites have been prepared by spark plasma sintering at 800–1200 °C under 20 MPa for 5 min. The effects of sintering temperature and reinforcement volume fraction on flexural strength, Young’s modulus and fracture toughness of the composites are investigated. The titanium matrix consists of -Ti and β-Ti phases, and the volume fraction of β-Ti increases with increasing sintering temperatures. The in situ synthesized TiB reinforcements are distributed randomly and uniformly in matrix. The transverse section of TiB has a hexagonal shape aligned along [0 1 0] direction, and the crystallographic planes of the TiB needles are always of the type . The 10 vol% TiB reinforced composite sintered at 1000 °C exhibits excellent mechanical properties. The flexural strength, Young’s modulus and fracture toughness of this composite are 1560 MPa, 137 GPa and 8.64 MPa · m^1/2, respectively.     

Platelet-reinforced polymer matrix composites by combined gel-casting and hot-pressing. Part I: Polypropylene matrix composites

Platelet-reinforced polymer matrix composites were fabricated by a combined gel-casting and hot-pressing method. Submicrometer-thin alumina platelets were dispersed in a highly diluted grafted maleic anhydride polypropylene solution. Upon cooling, the polymer formed a gel which trapped the platelets in their well separated positions. During subsequent solvent evaporation, the polymer–platelet gel densified and the platelets were oriented horizontally. The dried composites were hot-pressed to further improve the platelet orientation and increase the density of entanglements in the polymer. This method combines several advantages of large scale and lab-scale fabrication methods in that it is fast, simple but also versatile. Composites with platelet volume fractions up to 0.5 were easily fabricated. The maximal achieved yield strength and elastic modulus of the composites were 82% and 13 times higher, respectively, than the values of the polymer alone. The enhancement in the composites mechanical properties was caused by classical load transfer into the platelets as the crystallinity of the polymeric matrix was not affected by the platelets. Alumina platelets with an aspect ratio below the critical value allowed for the ductile platelet pull-out fracture mode enabling large plastic deformation of the composites prior to fracture. At high concentrations of platelets, the strength and stiffness decreased again and the ductility was almost lost due to out-of-plane misalignment of platelets and the increasing number and size of voids incorporated during the fabrication. The designing principles and fabrication method described in this work can potentially be extended to other types of polymers and platelets to create new composites with tailored properties.     

Effect of the SiO2/TiO2 ratio on the solid acidity of SiO2-TiO2/montmorillonite composites

SiO₂-TiO₂/montmorillonite composites with varying SiO₂/TiO₂ molar ratios were synthesized and the effect of the SiO₂/TiO₂ ratio on the solid acidity of the resulting composites was investigated. Four composites with SiO₂/TiO₂ molar ratios of 0, 0.1, 1 and 10 were synthesized by the reaction of colloidal SiO₂-TiO₂ particles prepared from alkoxides with sodium-montmorillonite at room temperature. The composites showed slight expansion and broadening of the XRD basal reflection, corresponding to the intercalation of fine colloidal SiO₂-TiO₂ particles into the montmorillonite sheets and incomplete intercalation to form disordered stacking of exfoliated montmorillonite and colloidal SiO₂-TiO₂ particles. The colloidal particles crystallized to anatase in the low SiO₂/TiO₂ composites but remained amorphous in the high SiO₂/TiO₂ composites. The specific surface areas (S_BET) of the composites measured by N₂ adsorption ranged from 250 to 370 m²/g, considerably greater than in montmorillonite (6 m²/g). The pore size increased with decreasing SiO₂/TiO₂ molar ratio of the composites. The NH₃-TPD spectra of the composites consisted of overlapping peaks, corresponded to temperatures of about 190 and 290 °C. The amounts of solid acid obtained from NH₃-TPD were 186-338 μmol/g in the composites; these values are higher than in the commercial catalyst K10 (85 μmol/g), which is synthesized by acid-treatment of montmorillonite. The present sample with SiO₂/TiO₂ = 0.1 showed the highest amount of acid, about four times higher than K10.     

Multifunctional properties of high volume fraction aligned carbon nanotube polymer composites with controlled morphology

Advanced composites, such as those used in aerospace applications, employ a high volume fraction of aligned stiff fibers embedded in high-performance polymers. Unlike advanced composites, polymer nanocomposites (PNCs) employ low volume fraction filler-like concepts with randomly-oriented and poorly controlled morphologies due to difficult issues such as dispersion and alignment of the nanostructures. Here, novel fabrication techniques yield controlled-morphology aligned carbon nanotube (CNT) composites with measured non-isotropic properties and trends consistent with standard composites theories. Modulus and electrical conductivity are maximal along the CNT axis, and are the highest reported in the literature due to the continuous aligned-CNTs and use of an unmodified aerospace-grade structural epoxy. Rule-of-mixtures predictions are brought into agreement with the measured moduli when CNT waviness is incorporated. Waviness yields a large (10×) reduction in modulus, and therefore control of CNT collimation is seen as the primary limiting factor in CNT reinforcement of composites for stiffness. Anisotropic electron transport (conductivity and current-carrying capacity) follows expected trends, with enhanced conductivity and Joule heating observed at high current densities.