Key Engineering Materials Vol. 694

Abstract: Corn starch has been used as hydrocolloids in kenaf filled natural rubber latex foam (NRLF). Kenaf filled NRLF was successfully prepared by using Dunlop method. This research was carried out to study the effects of hydrocolloid on compression and morphological properties of kenaf filled NRLF. From the graph of 50% compression, it was shown that kenaf filled NRLF with hydrocolloid has higher compression strength compared to kenaf filled NRLF without hydrocolloid. From the micrograph of Scanning Electron Microscope (SEM), it was observed that the pores size of kenaf filled NRLF with hdrocolloid was smaller than the pores size of kenaf filled NRLF without hydrocolloid. This showed the effect of hydrocolloid which contributes to the high compression strength.

Abstract: Polymer blend system of polylactic acid (PLA) and core shell as the impact modifier was studied. PLA was melt-blended with different amount of core shell impact modifier (0 to 30 wt.%). The PLA/core shell impact modifier was prepared by single screw extruder and injection molding machine into the required specimens. Morphological properties of the blends were investigated. Scanning electron microscopy (SEM) micrographs revealed that the addition of core shell impact modifier showed a coarser dispersed phase of voids. Dynamic mechanical analysis (DMA) tests confirmed that PLA/core shell impact modifier blends were partially miscible.

Abstract: Three different functionalized polydimethylsiloxane based probable self-healing materials were encapsulated by oil-in-water emulsion polymerization melamine-formaldehyde (MF) microcapsules for future applications in self-healing composites systems. The diameter and morphology, thermal properties, and structural analysis of the synthesized microcapsules were determined by scanning electron microscope (SEM), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR), and electron dispersive spectroscopy (EDS). The results showed that nature of core material plays an important role in the morphology and thermal stability of the microcapsules.

Abstract: In this study, silica spheres (SiO₂) nanomaterials were introduced as the support materials for glucose sensors. Glucose oxidase (GOx) was immobilized onto SiO₂ spheres (SiO₂/GOx) using physical adsorption (electrostatic interaction) method. The SiO₂ spheres were synthesized in-house using a nonsurfactant template of palm oil derived fatty alcohols (PODFA). Based on FT-IR analyses, SiO₂/GOx exhibited N-H absorbance at ca. 2990 cm^-1 and O-H absorbance at ca. 3330 cm^-1. One new absorbance peak was observed at ca. 2320 cm¹ attributed to the bending vibration (ν_bend)of silane molecules (Si-H) obtained by the interaction of GOx and the surface silanols (Si-OH). UV-Vis analysis results exihibited the presence of a new broad peak for GOx/SiO₂ sample at ca. 250 nm to 280 nm suggested to be assigned to H₂O_2, C=C and benzene ring from GOx. The optimum pH and optimum temperature for SiO₂/GOx for GOx activity were ca. 7.0 and ca. 50°C respectively. The increase of glucose concentration from 2mM to 5mM resulted to the increment of absorbance value for both GOx and SiO₂/GOx suggesting succesful immobilization of GOx on SiO₂ spheres. These materials were suitable for glucose detection at very small glucose concentrations particularly in salivary glucose detection.

Abstract: Freeze-dried β-wollastonite (β-CaSiO₃) powders were synthesized via sol-gel, combined with autoclaved, sintered and finally freeze-dried at -50 °C for 12 h using rice straw ash and calcined limestone as the starting materials. To prepare β-CaSiO₃, the precursor ratio of SiO₂:CaO was set at 45:55. Pure β-CaSiO₃ was obtained after sintering at 950 °C for 3 h. The bioactivity of freeze-dried β-CaSiO₃ was investigated by soaking the cylinderical shape samples in simulated body fluid (SBF) up to 21 days. The surface compositional, morphological and structural changes of the samples before and after soaking were analyzed via X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) coupled with EDS. Sintered freeze-dried β-CaSiO₃ has a porous structure and changed to cauliflower-like after soaking in simulated body fluid solution. After 21 days of soaking process, an amorphous calcium phosphate (ACP) and calcium deficient hydroxyapatite (CDHA) were formed with the molar ratio of Ca/P between 1.76 to 1.63.

Abstract: Anodic oxidation is an electrochemical method that deposits ceramic coatings on the metal substrates to improve the bioactivity of implant. In this study, a novel approach was proposed to precipitate hydroxyapatite (HAP) directly on the surface of pure titanium through anodic oxidation approach. As part of the proposed approach, a new formulation of electrolyte was introduced, which consists of 0.04 M β-glycerophosphate (β-GP), 0.4 M calcium acetate (CA) and 1.0 M sulphuric acid (H₂SO₄). The approach herein only requires a single step to precipitate the HAP directly on the surface of titanium through anodisation process within the electrolyte. High purity titanium foils were anodised in 0.04 M β-GP + 0.4 M CA + 1.0 M H₂SO₄ at 350 V and 70 mA.cm^-2 for 10 minutes at varying fractions of mixture volumes of H₂SO₄ (0-100 vol%). The surface properties of anodised titanium were characterised by using several methods, namely the field emission scanning electron microscopy (FESEM), glancing angle X-ray diffractometer (GAXRD) and goniometer. The outcome of the characterisation showed that the needle-like HAP was precipitated on the titanium, whereby anodising in electrolyte contains 12.5 vol% H₂SO₄. Combinations of anatase, rutile, titanium, tricalcium phosphate (Ca₃O₈P₂) and calcium diphosphate (Ca₂O₇P₂) elements were detected within the anodised titanium, whereby the anodising in electrolyte contains 50 vol% H₂SO₄.

Abstract: The morphology and surface topography of calcium silicate coated on Ti6Al4V implant were studied using field emission scanning electron microscopy (FESEM) and X-ray diffraction analysis (XRD) respectively. The surface of titanium alloy plates was mechanically ground with 320, 800 and 1200 grits of SiC abrasive paper followed by surface polishing into mirror-like finish. The synthesized β-CaSiO₃ was deposited onto the Ti6Al4V substrate using electron beam evaporator. After coating, calcium silicate was heat treated at 500 °C for 1 hour. Characterization of the calcium silicate coated on Ti6Al4V substrate using e-beam evaporation technique demonstrated that 5 wt% of PVA addition was able to improve the coating-to-substrate adhesion.

Abstract: Sintering has major effect on the final properties of materials such as density, porosity and microstructure. Sintering of Mg-Si CHA in particular is a complex process since changes could occur during sintering, which include phase formation, grain size, pore size and carbonate content, and this in turn affects the mechanical properties. Improved mechanical properties of Mg-Si CHA is critical in load bearing implant applications. Poor control of thermal treatment of Mg-Si CHA during sintering would cause carbonate loss, leading to partial or total decomposition of Mg-Si CHA, subsequently would affect the physical and mechanical properties. The influence of powder properties (particle size, porosity, morphology) and sintering parameters (heating rate, firing atmosphere) on the sintered Mg-Si CHA microstructure was studied using scanning electron microscopy (SEM) characterization technique. The SEM results showed that we are able to produce sintered Mg-Si CHA without cracking of the compacted pellets, while keeping the carbonate level in the amount required (2 – 8%). X-Ray diffraction (XRD) was also performed on the sintered samples and the results indicated that a single phase Mg-Si-CHA was obtained, while Fourier transform infra-red (FTIR) spectroscopy result confirmed that as-synthesized Mg-Si CHA powder was a B-type.

Abstract: Porous beta-tricalcium phosphate (β-TCP) bioceramic has been reported as synthetic graft for cancellous bone substitute due to its biocompatibility and biodegradability properties. A highly porous and interconnected porosity architecture of bone scaffold facilitates attachment and in-growth of new bone tissue. β-TCP foam, a porous 3-dimensional scaffold was fabricated by employing polymeric foam replica method in this study. Polyurethane (PU) foam was used as the sacrificial template, in which β-TCP slurry with powder to water ratio of 10g:10ml was coated on PU template and sintered to 1100, 1200, 1250 and 1300°C. Observation on architecture of the foam, macrostructure and microstructure of pores and surface topography of porous strut showed that sintering at 1250°C produced sufficient densification of grains and micropores on the β-TCP strut. The β-TCP foams exhibited high porosity (92 – 97%) and large pore size (200 - 750um) that resemble cancellous bone structure.

Abstract: This work was carried out as a preliminary study of electrospun LiFePO₄/CA fibers. Cellulose acetate (CA) and LiFePO4 solutions were prepared separately using mixed solvent of acetone and water, prior to the electrospinning process. Then, electrospinning parameters including solution concentration, distance tip to collector, pump rate, and needle diameter size were optimized. Brunauer Emmett Teller (BET) was used to determine the surface area of CA fibers. Viscosity of CA solution was obtained by viscometer. LiFePO₄/CA fibers were stabilized and carbonized at different temperature. The surface morphology and microstructure of the obtained LiFePO₄/ CA fibers were then characterized using scanning electron microscope (SEM). In this work, it is shown that different electrospinning parameter, solution concentration and solution viscosity gives different fibers diameter and distribution. Moreover, the stabilization and carbonization temperature of LiFePO₄/CA fibers may also affect the fibers microstructure.