An investigation of the effect of SiC particle size on Cu–SiC composites

In this study mechanical properties of copper were enhanced by adding 1 wt.%, 2 wt.%, 3 wt.% and 5 wt.% SiC particles into the matrix. SiC particles of having 1 μm, 5 μm and 30 μm sizes were used as reinforcement. Composite samples were produced by powder metallurgy method and sintering was performed in an open atmospheric furnace at 700 °C for 2 h. Optical and SEM studies showed that the distribution of the reinforced particle was uniform. XRD analysis indicated that the dominant components in the sintered composites were Cu and SiC. Relative density and electrical conductivity of the composites decreased with increasing the amount of SiC and increased with increasing SiC particle size. Hardness of the composites increased with both amount and the particle size of SiC particles. A maximum relative density of 98% and electrical conductivity of 96% IACS were obtained for Cu–1 wt.% SiC with 30 μm particle size.     

Mechanical and wear behaviours of nano and microfilled polymeric composite: Effect of filler fraction and size

The addition of ceramic reinforced material, SiC particles, to resin matrices, results in the improvement of the overall performance of the composite, allowing the application of these materials as tribo-materials in industries such as: automotive, aeronautical and medical. Particle-reinforced polymeric composites are widely used as biomaterials, for example as dental filler materials and bone cements. These reinforced composites have improved mechanical and tribological performance and have higher values of elastic modulus and hardness, and also reduce the shrinkage during the polymerisation compared with resin matrices. However, the effect of the filler level in mechanical and tribological behaviour is not quite understood.The aim of this work is to determine the influence of the particle volume fraction and particle size in the wear loss of the composites and their antagonists. Reciprocating wear tests were conducted using a glass sphere against resin polyester silica reinforced composite in a controlled medium, with an abrasive slurry or distilled water. For 6 μm average particle dimension, seven particles contents were studied ranging from 0% to 46% of filler volume fraction (FVF). Afterwards, filler volume fractions of 10% and 30% were selected; and, for these percentages, 7 and 4 average particle dimensions were tested and were evaluated regarding their wear behaviour, respectively. The reinforcement particle dimensions used ranged from 0.1 μm to 22 μm with the 10% filler fraction, and for 30% of filler content the range extended from 3 μm to 22 μm. The results allow us to conclude that in an abrasive slurry medium the composite abrasion resistance decreases with the increase of the particle volume fraction, in spite of the accompanying rise in hardness and elastic modulus. With constant FVF, and abrasive slurry, the composite wear resistance increases with increasing average particle dimension. In a distilled water medium and with several FVF values, the minimum wear was registered for a median particle content of 24%. In this medium and with constant FVF the highest wear resistance occurred for average reinforcement particles of 6 μm. The removal mechanisms involved in the wear process are discussed, taking into account the systematic SEM observations to evaluate the wear mechanisms.     

Preparation of zeolite-A/chitosan hybrid composites and their bioactivities and antimicrobial activities

Zeolite-A/chitosan hybrid composites with zeolite contents of 20–55 wt.% were prepared by in situ transformation of silica/chitosan mixtures in a sodium aluminate alkaline solution through impregnation–gelation–hydrothermal synthesis. The products were characterized by X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, scanning electron microscopy, thermogravimetric analysis, and mercury penetration porosimetry. Their in vitro bioactivities were examined using as-synthesized and Ca^2 +-exchanged hybrid composites in simulated body fluid (SBF) for hydroxyapatite (HAP) growth. Their antimicrobial activities for Escherichia coli (E. coli) in trypticase soy broth (TSB) were evaluated using Ag⁺-exchanged hybrid composites. The zeolite-A/chitosan hybrid composites could be prepared as various shapes, including cylinders, plates and thin films. They possessed macropores with pore sizes ranging from 100 to 300 μm and showed compressive mechanical strength as high as 3.2 MPa when the zeolite content was 35 wt.%. Fast growth on the Ca^2 +-exchanged hybrid composites was observed with the highest weight gain of 51.4% in 30 days. The 35 wt.% Ag⁺-exchanged hybrid composite showed the highest antimicrobial activity, which could reduce the 9 × 10⁶ CFU mL^? 1 E. coli concentration to zero within 4 h of incubation time with the Ag⁺-exchanged hybrid composite amount of 0.4 g L^? 1. The bioactivity and antimicrobial activity could be combined by ion-exchanging the composites first with Ca^2 + and then with Ag⁺. These zeolite-A/chitosan hybrid composites have potential applications on tissue engineering and antimicrobial food packaging.     

Enhanced conductivity behavior of polydimethylsiloxane (PDMS) hybrid composites containing exfoliated graphite nanoplatelets and carbon nanotubes

Polydimethylsiloxane (PDMS) hybrid composites consisting of exfoliated graphite nanoplatelets (xGnPs) and multiwalled carbon nanotubes functionalized with hydroxyl groups (MWCNTs-OH) were fabricated, and the effects of the xGnP/MWCNT-OH ratio on the thermal, electrical, and mechanical properties of polydimethylsiloxane (PDMS) hybrid composites were investigated. With the total filler content fixed at 4 wt%, a hybrid composite consisting of 75% × GnP/25% MWCNT-OH showed the highest thermal conductivity (0.392 W/m K) and electrical conductivity (1.24 × 10⁻³ S/m), which significantly exceeded the values shown by either of the respective single filler composites. The increased thermal and electrical conductivity found when both fillers are used in combination is attributed to the synergistic effect between the fillers that forms an interconnected hybrid network. In contrast, the various different combinations of the fillers only showed a modest effect on the mechanical behavior, thermal stability, and thermal expansion of the PDMS composite.     

PLA/algae composites: Morphology and mechanical properties

Bio-composites with poly(lactic) acid as matrix and various algae (red, brown and green) as filler were prepared via melt mixing. Algae initial size (below 50 μm and between 200 and 400 μm) and concentration (from 2 to 40 wt%) were varied. First, algae morphology, composition and surface properties are analysed for each algae type. Second, an example of algae particle size decrease during processing is given. Finally, tensile properties of composites are analysed. The surface of algae flakes was covered with inorganic salts affecting filler–matrix interactions. The Young’s modulus of composites increased at 40 wt% load of algae as compared with neat PLA although the strain at break and tensile strength decreased. In most cases the influence of algae type was minor. Larger flakes led to better mechanical properties compared to the smaller ones.     

Silane modification on mesoporous silica coated carbon nanotubes for improving compatibility and dispersity in epoxy matrices

A simple synthetic method for placing a mesoporous silica coating on multi-wall carbon nanotubes (CNTs@MS) was developed to improve the surface compatibility with regard to a polar epoxy matrix. In addition, the mesoporous silica shell with silanol groups on the CNTs provides a platform to attach silane molecules (e.g. 3-glycidoxypropyltrimethoxysilane, GPTMS) that enable the CNTs@MS to be incorporated into the epoxy matrix at a content of up to 20 wt.%. The viscosities of the CNTs@MS- and GPTMS-modified-CNTs@MS–epoxy composites are much lower than that of the CNTs–epoxy, and then the voids in the GPTMS-modified-CNTs@MS–epoxy composites are most significantly reduced. The effects of the CNTs@MS and GPTMS-modified CNTs@MS on the mechanical and thermal properties of the epoxy composite are investigated. The results show that the GPTMS-modified CNTs@MS improved the filler–epoxy matrix interaction, and has better compatibility in epoxy than the CNTs@MS. As the surface compatibility and interaction strength increase in the epoxy matrix, the enhancement in storage modulus, thermal conductivity and reduction in the coefficient of thermal expansion are in the following order: GPTMS-modified CNTs@MS > CNTs@MS ≫ CNTs.     

Mechanical,sorption and adhesive properties of composites based on low density polyethylene filled with date palm wood powder

Low density polyethylene (LDPE) was blended with date palm wood powder (DPW) to prepare composites with concentrations of filler ranging from 10 to 70 wt.%. The Younǵs modulus of the composites significantly increased with an increase in the filler content in the entire concentration range. The maximum value of 1933 MPa for the composite filled with 70 wt.% of the filler is approximately 13 times higher than that for the neat LDPE.The presence of the filler improved the flexural strength, which was represented by the flexural stress at peak. The flexural strength of 17.8 MPa for the composite filled with 70 wt.% of the filler was two-times greater than that for the neat LDPE. The water absorption test revealed that the composites had a strong tendency to absorb water, which was dependent on the filler content. The experimental data were compared with several theoretical models.     

Thermal conductivity of Cu/diamond composites prepared by a new pretreatment of diamond powder

Cu/diamond composites were fabricated by spark plasma sintering (SPS) after the surface pretreatment of the diamond powders, in which the diamond particles were mixed with copper powder and tungsten powder (carbide forming element W). The effects of the pretreatment temperature and the diamond particle size on the thermal conductivity of diamond/copper composites were investigated. It was found that when 300 μm diamond particles and Cu–5 wt.% W were mixed and preheated at 1313 K, the composites has a relatively higher density and its thermal conductivity approaches 672 W (m K)⁻¹.     

Effect of electroceramic particles on damping behaviour of aluminium hybrid composites produced by ultrasonic cavitation and mechanical stirring

In this study, electroceramics PBN and PLZT along with SiC were included in Al–3.96 wt.% Mg (A514.0) master alloy. Ultrasonic cavitation (UST) and mechanical stirring (MS) were employed to improve wettability and dispersion during casting. Two composite systems were produced: PBN system (5 wt.% PBN + 1 wt.% SiC and 15 wt.% PBN + 1 wt.% SiC) and the PLZT system (follows the same designation). The influence of fabrication method on the microstructures, particle distribution and wettability as well as electroceramic impact on dynamo-mechanical properties of prepared composites were investigated. Optical microscope (OM) and scanning electron microscope (SEM) results indicate that the processing technique was effective as it promoted wettability and homogeneous dispersion of particles throughout the Al matrix. Dynamic mechanical analysis (DMA) study of the composites demonstrated that the addition of the functional particles to the Al alloy matrix improved damping capacity (Tan δ) at 200 °C. The composites exhibited an increase in Tan δ of 24.3 ± 0.3% and 91.4 ± 0.2% for 5 and 15 wt.% PBN + 1 wt.% SiC and an increase of 19.7 ± 0.5% and 42.5 ± 0.3% for 5 and 15 wt.% PLZT + 1 wt.% SiC, respectively, when compared to the aluminium alloy matrix.     

High performance cellulose acetate propionate composites reinforced with exfoliated graphene

This paper deals with the preparation, structural characterization, and physical performances of composites composed of biomass-based cellulose acetate propionate (CAP) and exfoliated graphene (EG). As a reinforcing nanofiller, EG is thus prepared by an oxidation/thermal expansion process of natural graphite flakes and it is characterized to consist of disordered graphene platelets. Structural features, thermal stability, mechanical modulus, and electrical resistivity of CAP/EG composites are investigated as a function of EG content. SEM and X-ray diffraction data demonstrate that graphene platelets of EG are well dispersed and exfoliated in the CAP matrix for the composites with up to ～1 wt.% EG, although they are partially aggregated in the composites with higher EG contents above ～3 wt.%. Thermo-oxidative stability of CAP/EG composites under active oxygen gas condition is improved substantially due to the gas barrier effect of graphene platelets of EG dispersed in the CAP matrix. Dynamic mechanical modulus of the composites is also enhanced significantly with increasing the EG content. This mechanical enhancement of CAP/EG composites is analyzed by adopting the Halpin–Tsai model. The electrical volume resistivity of CAP/EG composites prepared by melt-compounding is decreased dramatically from ～10¹⁵ to ～10⁶ Ω cm by forming the electrical conduction path at a certain EG content between 5 and 7 wt.%.     

High performance cellulose acetate propionate composites reinforced with exfoliated graphene

This paper deals with the preparation, structural characterization, and physical performances of composites composed of biomass-based cellulose acetate propionate (CAP) and exfoliated graphene (EG). As a reinforcing nanofiller, EG is thus prepared by an oxidation/thermal expansion process of natural graphite flakes and it is characterized to consist of disordered graphene platelets. Structural features, thermal stability, mechanical modulus, and electrical resistivity of CAP/EG composites are investigated as a function of EG content. SEM and X-ray diffraction data demonstrate that graphene platelets of EG are well dispersed and exfoliated in the CAP matrix for the composites with up to ∼1 wt.% EG, although they are partially aggregated in the composites with higher EG contents above ∼3 wt.%. Thermo-oxidative stability of CAP/EG composites under active oxygen gas condition is improved substantially due to the gas barrier effect of graphene platelets of EG dispersed in the CAP matrix. Dynamic mechanical modulus of the composites is also enhanced significantly with increasing the EG content. This mechanical enhancement of CAP/EG composites is analyzed by adopting the Halpin–Tsai model. The electrical volume resistivity of CAP/EG composites prepared by melt-compounding is decreased dramatically from ∼10¹⁵ to ∼10⁶ Ω cm by forming the electrical conduction path at a certain EG content between 5 and 7 wt.%.     

Utilization of natural montmorillonite modified with dimethyl,dehydrogenated tallow quaternary ammonium salt as reinforcement in almond shell flour–polypropylene bio-nanocomposites

The main goal of this work was to evaluate the technical feasibility of almond shell flour (ASF) as wood substitute in the production of wood–plastic composites (WPCs). The effects of organically modified montmorillonite (OMMT), as reinforcing agent, on the mechanical and physical properties were also investigated. In order to improve the poor interfacial interaction between the hydrophilic Lignocellulosic material and hydrophobic polypropylene matrix, maleic anhydride grafted polypropylene (MAPP) was added as a coupling agent to all the composites studied. In the sample preparation, OMMT and ASF contents were used as variable factors. The morphology of the specimens was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The results of mechanical properties measurements indicated that when 3 wt.% OMMT were added, tensile and flexural properties reached their maximum values. At high level of OMMT loading (5 wt.%), increased population of OMMT lead to agglomeration and stress transfer gets blocked. The addition of OMMT filler decreased the water absorption and thickness swelling of composites. SEM study approved the good interaction of the almond shell flour with the polymer as well as the effectiveness of OMMT in improvement of the interaction. TEM study revealed better dispersion of silicate layers in WPCs loaded with 3 wt.% of OMMT. The improvement of physico-mechanical properties of composites confirmed that OMMT has good reinforcement and the optimum synergistic effect of OMMT and ASF was achieved at the combination of 3 and 50 wt.%, respectively. The findings indicated that almond shell as agro-waste material is a valuable renewable natural resource for composite production and could be utilized as a substitute for wood in composite industries.     

Influence of redmud on the mechanical,damping and chemical resistance properties of banana/polyester hybrid composites

A novel hybrid composite was developed with the addition of redmud as secondary reinforcing filler with banana fiber reinforced polyester composites (BFRPCs). The effect of varying parameters such as particle size (4, 6 and 13 μm) and weight percentage (2, 4, 6, 8 and 10 wt%) of redmud were analyzed on static mechanical, free vibration and chemical resistance properties of hybrid composites. The addition of redmud shown enhanced performance compared to the virgin BFRPCs in all the above said properties. The maximum increase of 50% in mechanical strength was observed for the BFRPCs with the addition of redmud having 4 μm particle size and 8 wt% of filler content compared to pure BFRPCs. The increased value of fundamental natural frequencies with associated modal damping characteristics of redmud filled BFRPCs were found using half-power band width method. All the fabricated composites performed well against various chemicals and it indicates that the resistance to the weight loss is due to the uniformly distributed redmud. To study the effect of redmud on interfacial bonding between the banana fiber and polyester matrix the Scanning Electron Microscope (SEM) image analysis was performed.     

Wear behavior of light-cured resin composites with bimodal silica nanostructures as fillers

To enhance wear behavior of resin composites, bimodal silica nanostructures including silica nanoparticles and silica nanoclusters were prepared and proposed as fillers. The silica nanoclusters, a combination of individually dispersed silica nanoparticles and their agglomerations, with size distribution of 0.07–2.70 μm, were fabricated by the coupling reaction between amino and epoxy functionalized silica nanoparticles, which were obtained by the surface modification of silica nanoparticles (~ 70 nm) using 3-aminopropyl triethoxysilane (APTES) and 3-glycidoxypropyl trimethoxysilane (GPS) as coupling agents, respectively. Silica nanoparticles and nanoclusters were then silanized with 3-methacryloxypropyl trimethoxysilane (γ-MPS) to prepare composites by mixing with bisphenol A glycerolate dimethacrylate (Bis-GMA) and tri (ethylene glycol) dimethacrylate (TEGDMA). Experimental composites with various filler compositions were prepared and their wear behaviors were assessed in this work. The results suggested that composites with increasing addition of silica nanoparticles in co-fillers possessed lower wear volume and smoother worn surface. Particularly, the composite 53:17 with the optimum weight ratio of silica nanoparticles and silica nanoclusters presented the excellent wear behavior with respect to that of the commercial Esthet-X, although the smallest wear volume was achieved by Z350 XT. The introduction of bimodal silica nanostructures as fillers might provide a new sight for the design of resin composites with significantly improved wear resistance.     

Effect of the temperature on surface modification of silica and properties of modified silica filled rubber composites

The modified silica at different temperature (MSaDT) with bis(3-triethoxysilylpropyl)tetrasulfide (TESPT), and MSaDT filled solution styrene butadiene rubber (SSBR) composites were prepared to investigate the effect of temperature on surface modification of silica. The results showed that TESPT was successfully bonded on the surface of silica by chemical bonds. The grafting degree (K) of MSaDT of 50 °C was 62.2% and higher than that at the other temperatures. The thermal weight loss and the size distribution of MSaDT showed that the silanol of TESPT hydrolysates reacted with the surface hydroxyl groups of silica, decreasing the average size and agglomeration of modified silica. For 50 °C modified silica/SSBR composite, the static mechanical properties and rubber–filler interaction of the composite were better than those of the others. As far as dynamic mechanical properties are concerned, the 50 °C modified silica/SSBR composite owned a best combination of low rolling resistance and high wet skid resistance.     

Enhancement of fracture toughness,mechanical and thermal properties of rubber/epoxy composites by incorporation of graphene nanoplatelets

Carboxyl terminated butadiene acrylonitrile (CTBN) was added to epoxy resins to improve the fracture toughness, and then two different lateral dimensions of graphene nanoplatelets (GnPs), nominally <1 μm (GnP-C750) and 5 μm (GnP-5) in diameter, were individually incorporated into the CTBN/epoxy to fabricate multi-phase composites. The study showed that GnP-5 is more favorable for enhancing the properties of CTBN/epoxy. GnPs/CTBN/epoxy ternary composites with significant toughness and thermal conductivity enhancements combined with comparable stiffness to that of the neat resin were successfully achieved by incorporating 3 wt.% GnP-5 into 10 wt.% CTBN modified epoxy resins. According to the SEM investigations, GnP-5 debonding from the matrix is suppressed due to the presence of CTBN. Nevertheless, apart from rubber cavitation and matrix shear banding, additional active toughening mechanisms induced by GnP-5, such as crack deflection, layer breakage and separation/delamination of GnP-5 layers contributed to the enhanced fracture toughness of the hybrid composites.     

High-performance silica nanoparticle reinforced poly (vinyl alcohol) as templates for bioactive nanocomposites

Silica nanoparticle reinforced poly (vinyl alcohol) cast sheets 40 μm thick were tested for mechanical and biological properties. The films were characterized using X-ray diffraction, scanning electron microscopy, and infrared spectroscopy. The crystallinity decreased with increased silica content. Changes in the morphology and structure upon the addition of silica suggest the formation of cross-linking. The modulus increased from 300 MPa for PVA to 7.2 GPa for 120 wt.% silica nanoparticle in the blend and the tensile strength increased from 3.5 MPa to 35 MPa. The modulus estimated using dynamic tests, tensile tests, and nanoindentation was comparable and was predicted well using the Halpin-Tsai's equation. The nanocomposites were an order of magnitude tougher than the pure polymer. Silica based nanocomposite was also found to be an excellent template for the deposition of calcium hydroxyapatite when immersed in simulated body fluid. The modulus and tensile strength of apatite coated silica nanoparticle (120 wt.%)–PVA composite increased to 11 GPa and 65 MPa respectively, close to that of cortical bone. The results represent one of the largest increases in mechanical properties of nanocomposite mimicking the properties of human bone. The addition of silica can also aid in osseointegration.     

Improved mechanical properties of recycled linear low-density polyethylene composites filled with date palm wood powder

Recycled linear low-density polyethylene (RLLDPE) was blended with date palm wood powder to prepare composites in which the concentration of the filler ranged from 10 to 70 wt.%. The cross-linking of composites was performed in some selected cases. The Young’s modulus of the composites significantly increased as the filler content increased over the entire concentration range. A maximum value of 1989 MPa was observed for the composite filled with 70 wt.% filler, which was approximately 6.5 times higher than that observed for neat RLLDPE. The presence of filler increased the flexural strength from 11.4 MPa for unmodified RLLDPE to 17 MPa for the composite containing 70 wt.% filler. The Young’s modulus and stress at break measured at 50 °C decreased significantly compared with those values measured at 25 °C. The ratio between the stress at break at 25 °C versus 50 °C (σ₂₅/σ₅₀) was between 2.7 and 3.8, whereas the ratio of Young’s modulus of E₂₅/E₅₀ was between 1.6 and 2.6.     

Thermal conductivity of graphene nanoplatelets filled composites fabricated by solvent-free processing for the excellent filler dispersion and a theoretical approach for the composites containing the geometrized fillers

The thermal conductivity of polymer composites containing nanofillers such as GNP (graphene nanoplatelet) and carbon black (CB) was investigated using experimental and theoretical approaches. We developed a fabrication method that allows different shapes and sizes of nanofillers to be highly dispersed in polymer resin. When the bulk and in-plane thermal conductivities of the fabricated composites were measured, they were found to increase rapidly as the GNP filler content increased. The in-plane thermal conductivity of composites with 20 wt.% GNP filler was found to reach a maximum value of 1.98 W/m K. The measured thermal conductivities were compared with the calculated values based on a micromechanics model where the waviness of nanofillers could be taken into account. The waviness of the incorporated GNP filler is an important physical factor that determines the thermal conductivity of composites and must be taken into consideration in theoretical calculations.     

Morphology and thermal conductivity of polyacrylate composites containing aluminum/multi-walled carbon nanotubes

Polyacrylate composites with various fillers such as multi-walled carbon nanotube (CNT), aluminum flake (Al-flake), aluminum powders and Al–CNT were prepared by a ball milling. The thermal decomposition temperature increased by as much as 64 °C for polyacrylate/Al-flake 70 wt% composite compared to polyacrylate. The thermal conductivity of polyacrylate/Al–CNT composites increased from 0.50 to 1.67 W/m K as the Al–CNT content increases from 50 to 80 wt%. The thermal conductivity of the composite sheet increases with the sheet thickness. At the given filler concentration (90 wt%), the composite filled with aluminum powder of 13 μm has a higher thermal conductivity than the one filled 3 μm powder, and the composite filled with mixture of two powders showed a synergistic effect on the thermal conductivity. The morphology indicates that the dispersion of CNT in the polyacrylate/Al-flake + CNT composite is not perfect, and agglomeration of CNTs was observed.