Abstract: Dense hydroxyapatite ceramic can be fabricated from hydroxyapatite (HA) powder prepared from cockle shells. The shell powder was treated at 900°C and co-precipitated with PO43- in NH4H2PO4 solution at Ca/P ratio of 1.67 in order to synthesize the HA powder. HA discs were formed by a hydraulic press machine and sintered at temperature of 1250°C for 2 h in an electric furnace which helps to dense ceramic. The results from FTIR analysis identified the functional groups of HA powder that has the ion stretching vibration around 3574, 2002 cm-1 for hydroxyl group (OH-), 1451 cm-1 for carbonate (CO32-), and phosphate groups (PO43-) were also observed around 1045 and 560 cm-1 respectively. XRD measurement showed that the ceramic contains hydroxyapatite crystals with β-tricalcium phosphate and calcium oxide as the secondary phase. Morphological evaluations by SEM measurement shows that the HA particles were agglomerated and showed the fractured surface of dense HA when sintered at 1300°C. Grain size ranges from 0.5–1 mm, with an apparent porosity of about 50% of the total area and the pore size ranges from 1–10 mm. Mechanical property measurements show that the dense ceramic contains bending strength of 135 MPa, which is close to the strength of human’s cortical bone (162 MPa).
Abstract: Insufficient endothelialization of stent grafts tends to cause a problem of thrombosis formation. Because the structure of nanofibers, generally defined as fibers with a diameter below 1 μm, resembles the structure of an extracellular matrix, nanofibers are applied to scaffolds for regenerative medicine. Using nanofibers as the covering material of the stent graft can be expected to solve the problem of the stent graft. Previous studies have shown that a porous scaffold offers better surfaces to anchor and culture endothelial cells than a nonporous scaffold. Therefore, fibers with nanoorder dimples are expected to promote endothelialization. As a method of forming the dimple shape on the surface of the PET fiber, there is a method utilizing a difference in the volatilization rate of the solvent in the high humidity environment in the electrospinning method. For practical application of the stent graft to artificial blood vessels, the mechanical properties of the dimpled PET fiber should be clarified. In this study, the mechanical properties of single nanofibers and nonwoven fabrics of PET fibers with dimples on their surface were evaluated by tensile test. By forming the dimple shape on the fiber surface, the tensile strength of single PET fibers with dimples was 90 % lower than that of single PET fibers with a smooth surface. In the fabrication process of nonwoven fabric, the addition of EG delayed the volatilization of the PET solution, and the fibers adhered to each other. The bonding between the fibers contributed to the tensile strength of the nonwoven fabric.
Abstract: The oral administration of pharmaceuticals is typically preferred over other methods due to its non-intrusiveness and convenience of administration. However, the varying chemical environments of the gastro-intestinal tract pose a challenge in ensuring the stability and inertness of a drug compound until it reaches its target. Polymers that are responsive to pH changes have potential as smart materials for the controlled oral administration of pharmaceuticals. In this study, linear and hyperbranched copolymers of methacrylic acid (MAA) and poly (ethylene glycol) methyl ether methacrylate (PEGMEMA) were synthesized by RAFT polymerization. High molecular weight polymers were produced with PDI values close to 1.0. These smart materials underwent phase changes at pH 5.15-5.6. This property enabled the amphiphilicity of the copolymers to be switched on or off. By doing so in in vitro drug release studies with ibuprofen as the model hydrophobic drug, the copolymers were able to inhibit drug release in simulated stomach conditions to up to 13% while enhancing drug release in simulated intestinal conditions to up to 75% within 6 hours. These indicate that copolymers based on MAA and PEGMEMA have potential as smart materials for drug delivery applications.
Abstract: The effects of the carbon fiber (CF), carbon black (CB) and nanosilica (SiO2) on the mechanical properties of the phenolic resin (PF) were studied and the optimum composition was selected for the preparation of quaternary composites (CF/CB/SiO2 phenolic composites). The incorporation of poly (acrylonitrile-co-butadiene) rubber (NBR) to strengthen the quaternary composites were also studied. The morphological, mechanical and thermo-mechanical properties of unmodified and NBR modified-quaternary phenolic composites were investigated. The phenolic compounds were mixed by ball milling and the phenolic composites were fabricated by hot compression molding. Scanning electron microscopy images of NBR modified-quaternary phenolic composites show the high fracture surface roughness. The results show that the addition of 5 wt% NBR in the quaternary composites offer the highest tensile strength and Young’s modulus which are significantly improved by 176% and 235%, respectively, and they also offer the high flexural strength, impact strength and flexural modulus which are improved by 79%, 29% and 12%, respectively, compared to neat PF. The glass transition temperature (Tg) of unmodified and NBR modified-quaternary phenolic composites are higher than that of neat PF (107.3 °C). The increase of NBR content does not deteriorate Tg of the quaternary phenolic composites. This study provides a new pathway for making advanced phenolic composites.
Abstract: Graphene oxide was synthesized from graphite by Hummer method and connected with (3-aminopropyl) triethoxysilane to form graphene oxide-aminosilane (GO-Si) linkage. The solution was centrifuged and washed with acetone to remove unreacted aminosilane before grafting with epoxidized natural rubber (ENR). ENR dissolved in toluene solution was mixed with GO-Si particle and dried at room temperature. Then, it was grafted to form graphene oxide grated with ENR via aminosilane linkage (GO-Si-ENR) by heat treatment. GO-Si-ENR was washed in toluene to remove unconnected ENR molecule. The synthesized GO particle in each step was characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The possible reaction mechanism was proposed in this research. The aim of this synthesis is to improve natural rubber - graphene interfacial interaction thus the dispersion of GO and GO-Si-ENR particle in natural rubber matrix by solvent mixing process was observed by transmission electron microscopy (TEM).
Abstract: Molybdenum disulfide (MoS2) catalyst on carbon support from varying ratio of sawdust and sugarcane bagasse has been successfully synthesized by hydrothermal carbonization and calcination process. Hydrothermal carbonization of lignocellulosic structure into carbon support is investigated at 200 oC for 24 hr and calcination at 600 °C for 2 hr. The precursor of MoS2 catalyst is prepared using thiourea (CH4N2S) and ammonium molybdate tetrahydrate ((NH4)6Mo7O24 . 4H2O) loaded on carbon support. The lignocellulosic structure as hemicellulose and cellulose is changed at high temperature via hydrothermal carbonization and calcination. The distribution of molybdenum disulfide on carbon support is varied based on morphology and functional group of carbon support. The morphology and functional group were analyzed using Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). It shows that carbon support at equal ratio (1:1) of sawdust and sugarcane bagasse is an optimum ratio with high distribution of molybdenum disulfide catalyst on carbon support.
Abstract: The effects of temperature and electrolyte concentration on the reaction of graphite electrodes in propylene carbonate (PC)-based solutions were investigated. In the case of natural graphite, it was confirmed that the reaction leading to the insertion of lithium ions into the graphite, which does not proceed at 25°C in a solution with a concentration of 0.85 mol kg–1, proceeds by lowering the reaction temperature to –15°C. The temperature at which lithium ions were inserted increased as the concentration increased. That is, lithium ions were electrochemically inserted into the interior of the natural graphite at 5°C in a solution of 1.63 mol kg–1 and at 15°C in a solution of 2.45 mol kg–1, indicating that the temperature and the electrolyte concentration greatly affect the properties of the solid electrolyte interphase produced by the decomposition of the PC-based electrolyte. Similar and slightly different electrochemical behavior was observed for synthetic graphite in terms of changes in temperature and the electrolyte concentration factor. In synthetic graphite, the temperature at which lithium ions were inserted was lower than in natural graphite: –25°C and 5°C in solutions of 0.85 mol kg–1 and 2.45 mol kg–1, respectively.
Abstract: This paper reports the synthesis, characterizations, microstructure and properties of forsterite powder produced in Thailand from talc and magnesite as raw materials by using mechanical activation with subsequent calcination. The synthesis forsterite powder were mixed by using talc and magnesite at 1:5 mole ratio. The maximum milling time was 24 h in a planetary zirconia ball mill. Afterward, the mixtures were calcined in an electric furnace for 1 h at 900, 1000, 1100, 1200 and 1300°C respectively. The synthesized powder was characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and physical properties. Results of the physical properties of synthesized forsterite showed an increased in density as the calcining temperature increased. In contrast, porosity was decreased with an increase of the calcining temperature. Therefore, forsterite that was calcined at 1300°C provided the best results which were 2.96 g/cm3 of true density and 15.41% of true porosity. Results of XRD of synthesized powder indicated that the forsterite crystallization was constant for which sharpen appeared after 5 h of mechanical activation. Fraction of forsterite was appeared after being calcined at 1000°C for 1 h with an increasing of calcination temperature, the fraction of forsterite phase increased. Based on the mentioned characteristics, the forsterite produced from Thai talc and magnesite exhibited properties of an insulator and can potentially be used as refractory devices.
Abstract: The welding thermal simulation of 2507 Super Duplex Stainless Steel (SDSS) was investigated using Gleeble-3800 thermo-mechanical simulator. The morphology evolution of austenite and ferrite under different t8/5 and t12/8 were observed and compared. The impact tests and pitting corrosion tests under different t8/5 and t12/8 were conducted. The results showed that the austenite content increased and the austenitic morphology changed from allotriomorphic structure to strip or coarse-blocky structures with the increase of t8/5 and t12/8. The effect of t12/8 on the microstructure of welding Heat Affect Zone (HAZ) was more distinct than that of t8/5. The impact toughness of HAZ with the increase of t12/8 was improved due to higher austenite content, while that with the increase of t8/5 was slightly decreased due to the formation of intermediate phase, such as σ phase. The corrosion tests showed that the pitting resistance of HAZ was improved with the increase of t8/5 and t12/8, while the effect of t12/8 was especially evident.