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.     

Three-body abrasive wear behaviour of carbon and glass fiber reinforced epoxy composites

Three-body abrasive wear behaviour of carbon–epoxy (C–E) and glass–epoxy (G–E) composites has been investigated. The effect of abrading distance, viz., 270, 540, 810 and 1080 m and different loads of 22 and 32 N at 200 rpm have been studied. The wear volume loss and specific wear rate as a function of load and abrading distance were determined. The wear volume loss increases with increasing load/abrading distance. However, the specific wear rate decreases with increase in abrading distance and increases with the load. However, C–E composite showed better abrasion wear resistance compared to G–E composite. The worn surface features have been examined using scanning electron microscope (SEM). SEM micrographs of abraded composite specimens revealed the high percentage of broken glass fiber compared to carbon fiber and also better interfacial adhesion between epoxy and carbon fiber.     

Properties of polypropylene composites containing aluminum/multi-walled carbon nanotubes

Polypropylene/aluminum–multi-walled carbon nanotube (PP/Al–CNT) composites were prepared by a twin-screw extruder. The morphology indicates that the CNTs are well embedded or implanted within Al-flakes rather than attached on the surface. During preparation of composites, the CNTs came apart from Al–CNT so that free CNTs as well as Al–CNT were observed in PP/Al–CNT composite. The crystallization temperatures of PP/CNT and PP/Al–CNT composites were increased from 111 °C for PP to 127 °C for the composites. The decomposition temperature increased by 55 °C for PP/CNT composite and 75 °C for PP/Al–CNT composite. The PP/Al–CNT composite showed higher thermal conductivity than PP/CNT and PP/Al-flake composites with increasing filler content. PP/Al–CNT composites showed the viscosity values between PP/CNT and PP/Al-flake composites. PP/Al–CNT composite showed higher tensile modulus and lower tensile strength with increasing filler content compared to PP/CNT and PP/Al-flake composites.     

Optimization of tribological parameters in abrasive wear mode of carbon-epoxy hybrid composites

Abrasive wear performance of fabric reinforced composites filled with functional fillers is influenced by the properties of the constituents. This work is focused on identifying the factors such as filler type, filler loading, grit size of SiC paper, normal applied load and sliding distance on two-body abrasive wear behaviour of the hybrid composites. Abrasive wear tests were carried on carbon fabric reinforced epoxy composite (C-E) filled with filler alumina (Al₂O₃) and molybdenum disulphide (MoS₂) separately in different proportions, using pin-on-disc apparatus. The experiments were planned according to Taguchi L18 orthogonal array by considering five factors, one at two levels and the remaining at three levels, affecting the abrasion process. Grey relational analysis (GRA) was employed to optimize the tribological parameters having multiple-response. Analysis of variance (ANOVA) was employed to determine the significance of factors influencing wear. Also, the comparative specific wear rates of all the composites under dry sliding and two-body abrasive wear were discussed. The analysis showed that the filler loading, grit size and filler type are the most significant factors in controlling the specific wear rate of the C-E composite. Optimal combination of the process parameters for multi performance characteristics of the composite under study is the set with filler type as MoS₂, filler loading of 10 wt.%, grit size 320, load of 15 N and sliding distance of 30 m. Further, the optimal parameter setting for minimum specific wear rate, coefficient of friction and maximum hardness were corroborated with the help of scanning electron micrographs.     

Study on the mechanical properties,environmental effect,degradation characteristics and ionizing radiation effect on silk reinforced polypropylene/natural rubber composites

Natural silk fiber (20%) reinforced polypropylene (PP) composites were prepared by compression molding. Tensile strength, tensile modulus, bending strength, bending modulus, impact strength and hardness of the prepared composite were found 54.7 MPa, 1826.2 MPa, 58.3 MPa, 3750.7 MPa, 17.6 kJ/m² and 95 shore A, respectively. To improve the biodegradable character of the composite, natural rubber (NR) was blended (10%, 25%, 50% by weight) with PP. It was found that the mechanical properties of the composite decrease with increasing NR in PP (except IS which increased rather decreasing). Environmental effect on the composite and degradation in various media were investigated in this study. Gamma radiation was used to increase the mechanical properties of the prepared composites. Increase in TS and BS were maximum at 250 krad dose for silk fiber/PP, silk fiber/PP:NR (90:10), silk fiber/PP:NR (75:25) and silk fiber/PP:NR (50:50) composites.     

Properties of graphene nanopowder and multi-walled carbon nanotube-filled epoxy thin-film nanocomposites for electronic applications: The effect of sonication time and filler loading

Graphene nanopowder (GNP) and multi-walled carbon nanotube (MWCNT)-filled epoxy thin-film composites were fabricated using ultrasonication and the spin coating technique. The effect of sonication time (10, 20 and 30 min) and GNP loading (0.05–1 vol%) on the tensile and electrical properties of GNP/epoxy thin-film composites was investigated. The addition of GNP decreased the material’s tensile strength and modulus. However, among the tested samples, the GNP/epoxy composites produced using 20 min of sonication time had a slightly higher tensile strength and modulus, with a lower electrical percolation threshold volume fraction. The effect of sonication time was supported by morphological analysis, which showed an improvement in GNP dispersion with increased sonication time. However, GNP deformation was observed after a long sonication time. The GNP/epoxy composites at different filler loadings showed higher electrical properties but slightly lower tensile properties compared with the MWCNT/epoxy composites fabricated using 20 min of sonication time.     

The effect of interfacial interactions on the mechanical properties of polypropylene/natural zeolite composites

The effect of interfacial interactions on the mechanical properties of polypropylene (PP)/natural zeolite composites was investigated under dry and wet conditions. Interfacial interactions were modified to improve filler compatibility and mechanical properties of the composites by surface treatment of natural zeolite with a non-ionic surface modifier; 3 wt% polyethylene glycol (PEG) and three different types of silane coupling agents; 3-aminopropyltriethoxysilane (AMPTES), methyltriethoxysilane (MTES) and 3-mercaptopropyltrimethoxysilane (MPTMS), at four different concentrations (0.5–2 wt%). PP composites containing (2–6 wt%) zeolite were prepared by an extrusion technique. The tensile properties of the composites determined as a function of the filler loading and the concentration of the coupling agents were found to vary with surface treatment of zeolite. Silane treatment indicated significant improvements in the mechanical properties of the composites. According to the dry and wet tensile test results, the maximum improvement in the mechanical properties was obtained for the PP composites containing 1 wt% AMPTES treated zeolite. The improvement in the interfacial interaction was confirmed using a semi-empirical equation developed by Pukanszky. Good agreement was obtained between experimental data and the Pukanszky model prediction. Scanning electron microscopy studies also revealed better dispersion of silane treated filler particles in the PP matrix.     

Effect of matrix glass transition on reinforcement efficiency of epoxy-matrix composites with single walled carbon nanotubes,multi-walled carbon nanotubes,carbon nanofibers and graphite

This study compares the mechanical and thermal properties of glassy and rubbery epoxy–matrix composites reinforced with 1 and 4 wt.% single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), graphite, and carbon nanofibers (CNFs). The tensile modulus of most glassy composites was higher than that of the epoxy and increased with higher filler concentration and 4% graphite/epoxy and 4% SWCNT/epoxy exhibited approximately the same highest tensile modulus. The elongation of glassy composites was significantly lower than that of the epoxy and decreased with increasing filler loading. Most rubbery composites showed a higher tensile modulus and elongation than the epoxy and the modulus increased with rising filler content and 4% SWCNT/epoxy showed the highest tensile modulus and tensile strength. In the rubbery regime, glassy and rubbery composites displayed a higher storage modulus than the corresponding epoxy and 4 wt.% SWCNT/epoxy composites showed a 300% improvement in storage modulus compared to the epoxy.     

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.     

Tribological characteristics of innovative Al6061–carbon fiber rod metal matrix composites

Rods made of continuous carbon fibers are being extensively used as structural materials in light weight micro-air vehicles owing to their excellent specific modulus and strength. Further, they possess excellent tribological characteristics – low friction and wear coupled with high conductivity making them an ideal reinforcement in developing light weight, high strength aluminum based metal matrix composites. In the last three decades, researchers have focused mainly on the study of mechanical and tribological behavior of discontinuous carbon fiber reinforced metal matrix composites. However, no information is available regarding the tribological behavior of carbon fibers rod reinforced metal matrix composites, although it is interesting and will result in expanding the applications of metal matrix composites (MMC) where tribological failures are expected.In the light of the above, the present work focuses on development of innovative Al6061–carbon fiber rods composites by casting route and assessing their tribological characteristics. Carbon fiber rods of 4 mm and 6 mm diameters were surface sensitized to achieve electro less nickel coating. Copper plating on the electro less nickel coated carbon fiber rods were carried out. The copper plated carbon fiber rods were arranged in cylindrical array in the metallic mold to which molten Al6061 alloy after degassing was poured at a temperature of 700 °C. The developed innovative composites were subjected to density tests, microstructure studies, hardness, friction and wear tests. A pin on disk configuration was used with hardened steel as the counter face. Load was varied from 20 N to 60 N while the sliding velocity was varied between 0.12 m/s and 0.62 m/s. Scanning electron microscopy (SEM) studies on worn surfaces and wear debris have been carried out to validate the wear mechanism. The developed innovative composites (11 Vol.% & 25 Vol.%) have exhibited lower coefficient of friction and wear rates when compared with matrix alloy.     

Influence of thermal conditions on the tensile properties of basalt fiber reinforced polypropylene–clay nanocomposites

In this paper, a comparative study on the tensile properties of clay reinforced polypropylene (PP) nanocomposites (PPCN) and chopped basalt fiber reinforced PP–clay nanocomposites (PPCN-B) is presented. PP matrix are filled with 1, 3 and 5 wt.% of nanoclays. The ultimate tensile strength, yield strength, Young’s modulus and toughness are measured at various temperature conditions. The thermal conditions are included the room temperature (RT), low temperature (LT) and high temperature (HT). The basal spacing of clay in the composites is measured by X-ray diffraction (XRD). Nanoscale morphology of the samples is observed by transmission electron microscopy (TEM). Addition of nanoclay improves the yield strength and Young’s modulus of PPCN and PPCN-B; however, it reduces the ultimate tensile strength. Furthermore, the addition of chopped basalt fibers to PPCN improves the Young’s modulus of the composites. The Young’s modulus and the yield strength of both PPCN and PPCN-B are significantly high at LT (−196 °C), descend at RT (25 °C) and then low at HT (120 °C).     

Effect of a novel coupling agent,alkyl ketene dimer,on the mechanical properties of wood–plastic composites

The objective of this study was to investigate the incorporation of poplar wood fibers both with and without a novel coupling agent, alkyl ketene dimer (AKD), on the mechanical properties of wood fiber/polypropylene (PP) composites. The resulting properties were compared to those obtained with the most commonly used coupling agent, maleic anhydride grafted PP (MAPP). Tensile and impact strengths of the composites decreased with increasing poplar wood fibers content. Tensile modulus of the composites increased by the incorporation of the wood fibers content up to 70 wt% but further increment in the wood fibers decreased the tensile modulus. At the constant content of poplar wood fibers (70 wt%), the tensile strength determined for the coupled composites with 5% AKD increased by 41% in comparison with the non-coupled composites while the tensile modulus increased by 45%, the impact strength of the coupled composites increased by 38%. The performance of 5% AKD on the mechanical properties of the composites is a little better than 3% MAPP. The good performance of 5% AKD is attributed to the enhanced compatibility between the poplar wood fibers and the polymer matrix. The increase in mechanical properties of the composites demonstrated that AKD is an effective coupling agent for wood fiber/PP composites.     

Investigations on the fabrication and the characterization of glass/epoxy,carbon/epoxy and hybrid composites used in the reinforcement and the repair of aeronautic structures

This paper reports the fabrication and the characterization of glass/epoxy, carbon/epoxy and hybrid laminated composites used in the reinforcement and/or the repair of aeronautic structures. These composites were manufactured by the hand lay-up process. Their physical, thermal and mechanical behaviors are discussed in terms of moisture absorption, thermal stability, tensile strength, elastic modulus, flexural strength, flexural modulus and abrasive wear resistance. The impact of hygrothermal aging on the mechanical properties of each composite group has been also investigated.The main results indicated that after water immersion, all composites showed significant moisture absorption especially for glass/epoxy composite. Thermogravimetric analysis showed that the hybrid composite presented the best thermal stability behavior while the glass/epoxy composite the bad behavior. The mechanical properties of the carbon/epoxy composites, in the bulk material, were considerably higher than those of the glass/epoxy; the hybrid structure presented intermediate mechanical properties. The same trend was also observed in terms of wear properties. Finally, a deleterious effect on the strength of all composites due to hygrothermal exposure was established. However, carbon/epoxy composites seem to be less susceptible to aging damage after 90 days at 90 °C.     

Fabrication of the new structure high toughness PP/HA-PP sandwich nano-composites by rolling process

In this study a designed rolling setup was used to fabricate new structure polypropylene/hydroxyapatite-polypropylene (PP/HA-PP) sandwich nano-composites. To check the effect of rolling process and PP layers content on the structure and mechanical properties of these sandwich composites, different mechanical tests and analysis were performed on these composites. Results of tensile, bending and buckling tests show the rolling process improves the strength, modulus and flexural rigidity of composites significantly while with increasing the PP layers content from 10 vol.% to 20 vol.% decreases the stiffness, flexural rigidity and modulus of composites slightly. Results of impact test demonstrate the rolling process and increasing the volume percentage of the PP layers in sandwich composites cause a dramatic improve in impact absorbed energy of the PP/HA-PP sandwich composites. The results of Differential Scanning Calorimetry (DSC) analysis confirm the rolling process increases the crystallinity and molecular alignment of polypropylene in composites. The results of mechanical tests and DSC analysis show the increasing of polypropylene molecular alignment by rolling process is the most dominant reason of improvement the mechanical properties of sandwich composites.     

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.     

Tensile modulus of carbon nanotube/polypropylene composites – A computational study based on experimental characterization

Micromechanical and computational models significantly over-predict the tensile modulus of composites, as they ignore many experimentally observed factors. Computational models that capture the effect of polymer-filler contact, the presence of carbon nanotube (CNT) agglomerates and the alignment of CNTs with respect to the applied load on the tensile modulus of CNT-reinforced polypropylene (PP) are proposed and discussed in detail in this study. The CNT/PP composites are made by melt mixing and injection molding. The CNT/PP contact area is characterized in terms of width and modulus using Atomic Force Microscope (AFM). The presence, including the size and distribution of CNT agglomerates, is characterized using Scanning Electron Microscope (SEM). The tensile modulus of CNT/PP composites, measured as a function of CNT content according to ASTM D638, is compared to predictions made using numerical methods based on Finite Element Analysis (FEA) within the composite’s elastic regime. The model over-predicts the modulus of the CNT/PP composites by 85% for 5 wt.% CNT/PP composites assuming perfect filler–polymer interfacial contact. When imperfect CNT/PP contact, CNT agglomerates and alignment are accounted for in the model the effective composite modulus predicted is in good agreement with the experimental data. The computational design tools proposed in this study by systematically incorporating experimentally observed characteristics, in combination with the manufacturing method used to make the CNT/PP composites, can lead to composites with engineered properties made by a scalable and cost effective method.     

Tribological behavior of Ni3Al matrix self-lubricating composites containing WS2, Ag and hBN tested from room temperature to 800 °C

Ni₃Al matrix self-lubricating composites (NMSC) containing varied amounts of WS₂, Ag and hBN (WAh) with weight ratio of 1:1:1 were fabricated by in situ technique using spark plasma sintering. The friction and wear properties of NMSC against the commercial Si₃N₄ ceramic ball at the load of 10 N and sliding speed of 0.234 m/s for 80 min from room temperature to 800 °C were investigated. The results showed that the tribological properties of NMSC strongly depended on the addition content of WAh. Moreover, NMSC with 15 wt.% WAh and 5 wt.% TiC exhibited the relatively lower friction coefficients and the less wear rates from RT to 800 °C. The excellent tribological behavior of NMSC with 15 wt.% WAh and 5 wt.% TiC was attributed to the synergetic action of composite lubricants of WAh and reinforced phase of TiC.     

Surface modification of wood flour and its effect on the properties of PP/wood composites

The surface of wood flour used as reinforcement in PP/wood composites was successfully modified by benzylation in NaOH solution of 20 wt% concentration at 105 °C. The time of the reaction was changed between 5 and 360 min in several steps. The progress of modification was followed by the measurement of weight increase and by diffuse reflectance infrared spectroscopy (DRIFT). The structure of the wood was characterized by X-ray diffraction (XRD) and its surface tension was determined by inverse gas chromatography (IGC). PP composites containing 20 wt% filler were prepared from a PP block copolymer and the modified wood flour. The mechanical behavior of the composites was characterized by tensile testing. The majority of the active hydroxyl groups at the surface were replaced by benzyl groups in about 2 h under the conditions used. Further increase in reaction time did not influence the properties of the filler. Both the structure of the wood flour and its surface tension changed as an effect of modification. The reduction of surface tension led to significant changes in all interactions between the wood flour and other substances resulting in a considerable decrease of water absorption, which is the major benefit of this modification. All measured mechanical properties of the composites decreased slightly with increasing degree of modification. A detailed analysis of the results proved that the dominating micromechanical deformation process of these PP/wood composites is debonding, which is further facilitated by the decrease in the surface tension of the filler. Chemical modification of wood flour slightly improved processability and the surface appearance of the composites prepared with them and considerably decreased the water absorption of these latter.     

Effect of W content on the compression properties and abrasive wear behavior of the (TiB2–TiCxNy)/(Ni + W) composites

The (TiB₂–TiC_xN_y)/(Ni + W) composites were fabricated successfully by the method of combustion synthesis and hot press consolidation in the Ni–W–Ti–B₄C–BN system. The effect of the content of W on the hardness, compression properties and abrasive wear behavior of the composites was investigated. The results indicate that with increasing W content from 0 to 8 wt.%, the average sizes of the TiB₂ and TiC_xN_y particles decrease firstly and then keep almost constant, while the hardness and the compression strength increase firstly and then change a little. The abrasive wear resistance of the composites increases firstly and then decreases with the increase in the W content.