Key Engineering Materials Vols. 471-472

Abstract: Nanocomposites prepared from blend of high density polyethylene (HDPE), natural rubber (NR) and organoclay were melt compounded using an internal mixer. The phase morphology and mechanical properties of this thermoplastic natural rubber nanocomposites samples were examined. The transmission electron microscope (TEM) and wide angle X-ray scattering (WAXS) was used to determine the exfoliation of organoclay in this blend. The tensile and Izod impact test were used to evaluate the mechanical properties of HDPE/organoclay nanocomposites with and without the presence of NR. The Izod impact results shows an improvement more than 300% with addition of 10% NR content in the matrix. The X-ray diffraction results indicated intercalation of blend into the silicate interlayer of nano-filler I.44P and partially exfoliation of silicate layer into the blend. The SEM morphology revealed that there was some part of uneven dispersion of organoclay in the blend.

Abstract: The effect of nano-alumina and radiation on the mechanical properties of high density polyethylene hydroxyl apatite composite was investigated. The study showed that nano alumina as filler in the composite enhanced the strength of the polymer matrix and hence improved the mechanical properties of the composite. The study also showed that the mechanical properties of the composite depended on doses of nano alumina used and radiation dose of gamma ray. The maximum radiation dose used in this experiment 100 KGy is the best dose for the composite that enhances the tensile strength, impact, modulus and flexural strength. The interface behavior and strengthening mechanisms are discussed.

Abstract: Equal channel angular pressing (ECAP) is the one of the promising methods of severe plastic deformation to obtain bulk ultrafine grain structures. However, ECAP can also be used for powder consolidation. In the present study, fully dense bulk AA 4032 alloy was consolidated from nanocrystalline and microcrystalline powders. These materials were processed by ECAP until four passes at ambient temperature. It is observed that hardness and densification increased significantly with increase in number of ECAP passes. Transmission electron microscopic and scanning electron microscopic examinations evidenced that crystallite size of the nanopowders are unaltered, however a significant crystallite size reduction from around 50 µm down to submicron size is observed. Moreover, higher densification is achieved in microcrystalline powders than nano powders, whereas higher hardness in the case of nanopowders compared to microcrystalline powders.

Abstract: This research has been conducted to approach second-order shear deformation theory (SSDT) to analysis vibration characteristics of Functionally Graded Plates (FGP’s). Material properties in FGP's were assumed to be temperature dependent and graded along the thickness using a simple power law distribution in term of the volume fractions of the constituents. FGP was subjected to a linear and nonlinear temperature rise. The energy method was chosen to derive the equilibrium equations. The solution was based on the Fourier series that satisfy the simply supported boundary condition (Navier's method). Numerical results indicated the effect of material composition, plate geometry, and temperature fields on the vibration characteristics and mode shapes. The results revealed that, the temperature field and volume fraction distribution had significant effect on the vibration of FGPs. It was observed the second order theory was very close to the other shear deformation theorem as reported in the literature.

Abstract: Functionally graded metal-ceramic composite was fabricated by pressure-less sintering. The pure metallic component (Ti) and the pure ceramic component (HA) were located at the ends of a cylindrical specimen. Titanium and-Hydroxyapatite were utilized as a metallic and ceramic layer. The target sample thickness was 6 mm with radius cylindrical 20 mm. The sample was made from the cylindrical type of carbon die consisting of 5 layers. The composition of layers were 100%Titanium; 75 % Titanium +25% HA; 50% Titanium +50% HA; 25% Titanium+75% HA, and 100% Hydroxyapatite. The optimum thermal load mapping was obtained experimentally. The properties of all FGM products were characterized by shrinkage, optical-microscope, energy dispersive spectrometry (EDX) scanning electron microscope (SEM). The grade of the FGM material was proven by comparing amount of shrinkage after sintering. Result from optical micrograph, SEM and EDX indicated that the HA-Ti FGM could be produced successfully by using the optimal sintering procedure that was highlighted in this paper.

Abstract: Composites of palm fiber and polypropylene were compounded using a mixing device at various temperatures, mixing times, and mixing intensities. Two mixing options were utilized. Either the mixing device was mounted with a mixer or a single screw extruder. The composites were subsequently injection molded into standard tensile specimens for mechanical characterization. Tests were performed to determine the effects of processing parameters such as the mixing and molding temperatures, mixing speed, and mixing time on the mechanical performance of the palm-polypropylene composite. The optimum processing conditions for the mixer were determined to be: Mixing Speed = 50 rpm, Mixing Time = 8 min, and Processing Temperature = 200°C. Optimum extruder conditions, on the other hand, were determined as 40 rpm extruder screw speed and processing temperatures of Zone 1=195°C, Zone 2=200°C, Zone 3=205°C, and Nozzle 210°C. Use of the extruder resulted in higher composite strength with much shorter processing time. Further studies are also being conducted to include coupling agents in the processing to improve the interfacial adhesion between the palm fibers and the polypropylene matrix.

Abstract: We investigated the effects of amount of antioxidants variability on selected mechanical and physical properties of wood plastic composites. Recycled high density polyethylene (rHDPE) and natural fibers were compounded into pellets by compounder, then the pellets were extruded using co-rotating twin-screw extruder and test specimens were prepared by hot and cold press process. From the study, samples with 0.5 wt% of antioxidants produce the highest strength and elasticity of composites. The effect of antioxidants presence on water uptake is minimal.

Abstract: Carbon nanotubes have excellent mechanical and electrical properties, and are also a good reinforcement material for composites than conventional materials. The matrix used in this study was epoxy and reinforcement filler in multi-walled carbon nanotubes (MWCNTs). The different MWCNTs loading concentrations (0 ~ 10 wt. %) were added into the epoxy resin. The dispersion of MWCNTs in epoxy resin was conducted using high speed mixer through mechanical shearing mechanism. The mixture of epoxy/MWNTs suspension was poured into the mold and compression molding was conducted for fabrication of MWCNTs/epoxy nanocomposites. The electrical conductivity of nanocomposite by variation of CNTs concentration was measured by the four point probe. Dispersion state of CNTs in epoxy matrix was observed on fractured surface by scanning electron microscopic. Hardness of the composite was tested using the Dinamic Ultra Micro Hardness machine. Non conductive epoxy polymer becomes conductor as addition of CNTs.. Electrical conductivity of nanocomposite plates increased with increasing CNTs concentration. Agglomerations of CNTs were observed on fractured surfaces. This phenomenon due to CNTs which used in this study was at as produced state where no modification is being done on it. Long and entanglement of individual CNTs easily lead to agglomerations. Van de Wall’s force interactions between CNTs also contribute to the agglomerations of CNTs. Hardness of the composite increases with the CNTs loading concentrations until it reaches a maximum peak at the composition of 5wt% of CNTs but the hardness decreases rapidly with loading greater than 5wt% of CNTs.

Abstract: Carbon nanotubes (CNTs) have excellent mechanical and electrical properties than conventional materials (carbon black and glass fibers), and are promising candidates as reinforcement material for composites. Formation of electrical conductive with effective dispersion of filler remains a main challenge in the polymer matrix and fillers in order to achieve a good electrical conductivity. Therefore, one of the solutions is to functionalize through wet oxidation of the CNTs besides adding surfactants or assisted liquids. Functionalization of CNTs involves the generation of chemical moieties on their surface that can improve the solubility and processibility. Any functionalization that is undertaken must preferably not influence other key properties such as strength and electrical conductivity of the nano-composite. The matrix used in this study was epoxy and reinforcement filler was multi-walled carbon nanotubes (MWCNTs). MWCNTs were treated with sulfuric acid and nitric acid at 3:1 (v/v) ratio. The present of functional groups on CNTS were investigated using Fourier Transform Infrared (FT-IR). Different weight percentages of MWCNTs (functionalized and as produced) / epoxy composite were prepared. The electrical conductivity of functionalized MWCNTs nanocomposites and as produced MWCNTs nanocomposites were measured by the four point probe. Dispersion state of CNTs in epoxy matrix was observed on fractured surface by scanning electron microscopic. Functionalized CNTs gave better dispersion stability in solvents than non-functionalized CNTs. As expected, non- functionalized CNTs (as produced MWCNTs) are not dispersed at all in all the solvents. However, functionalized CNTs composites give low electrical conductivity. Defects from acid treatment are assumed will damage the original chirality of as produced CNTs and give unbalance polarization on the CNTs, which are the reasons for no formation of conductive pathway networks of acid treated CNTs under electric field.

Abstract: Sugarcane bagasse is divided into two main components, pith and rind, with “pith” representing the inner part of the sugarcane bagasse and “rind” as the outer part. In this study, the tensile and impact properties of untreated pith/ poly(vinyl chloride) composites were compared to that of untreated rind composites using the same matrix with variation of fibre content. It was observed that the tensile strength and modulus of rind/PVC composites are higher than the unfilled PVC at composite fibre contents of 30% and 40%. Additionally, the rind composites exhibited superior strength and stiffness in comparison with the pith composites.