Papers by Keyword: Crystallinity

Abstract: Anodizing is a surface modification technique that is applied to growing oxide films on Ti to accelerate the osseointegration of an implant. Besides the surface roughness, the crystalline structure of these films can affect its performance as a biomaterial. For this reason, this technique has been refined to produce crystalline films without requiring heat treatments. For this purpose, TiO₂ films were grown on Ti (grade 2) by anodizing with direct current at different potentials. Images obtained by optical microscopy with polarized light revealed a granular microstructure in various colors, as consequence of different crystalline orientations of the grains and films thickness. Raman spectroscopy showed that the films crystallinity is affected by variations in the applied potential and anodizing time.

Abstract: The isolation of microcryostalline cellulose (MCC) from rice husk (RH) via acid hydrolysis process has been successfully prepared by using different molarity of nitric acid (HNO₃) and hydrochloric acids (HCl). The properties of MCC obtained such as tapping and bulk densities, thermal stability and percentage crystallinity were studied. Tapping and bulk densities shown comparable results regardless of different acid used that reflecting the potential of MCC as reinforcement filler in composite fabrication. The usage of 2M HNO₃ gives highest percentage crystallinity (69%) in comparison with 2M HCl (49%). The result indicates the stability of MCC-RH obtained using HNO₃ has great potential to replace strong acid in acid hydrolysis process.

Abstract: Since the first observation of carbon nanotubes (CNTs) in 1991, their synthesis techniques has been extensively investigated. The chemical vapor deposition (CVD) process have attracted much attention because of both their versatility and easy large scale production for CNTs . This paper is focused on a catalytic CVD-based method for synthesis of whisker multiwalled carbon nanotubes (WMWCNTs). The new type of carbon nanotube is similar to the whisker. The morphology of the WMWCNTs are very different from traditional carbon nanotubes prepared by traditional chemical vapor deposition process. The traditional CNTs were twisted and entangled with each other. These suggested that there are a lot of deficiencies on the CNTs and are difficult to disperse in matrix materials. The as-produced WMWCNTs are very straight and not entangled with each other. The line structure means that WMWCNTs are easily dispersed in matrix materials than traditional CNTs which are twined together. The crystallinity of WMWCNTs increased to 96% which was much higher than traditional CNTs after graphitization treatment at 2800°C.

Abstract: Polyethylene terephthalate (PET) is usually used as food packaging materials. And the heavy metal introduced during the process of manufacture usually exists in the spaces between macromolecules as monomer form. When PET contacts with real food, some heavy metals will migrate into the food since the motion of these molecules overcomes the binding power. As a result, it does great harm to our health. In this article PET was disposed in different thermal ageing conditions in order to accelerate its aging process. Then the original and aged PET samples were tested by Different Scanning Calorimeter (DSC) to characterize its crystallinity. And migration experiments was conducted on them using 4% acetic acid (V/V) as food simulate, the heavy metal content in food simulates was detected by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), so that we can get the migration characteristics of heavy metal. The results show that different aging conditions can do harm to the structure of PET in varying degrees by changing its crystallinity and molecules arrangement. But the difference of crystallinity has no obvious effect on Sb migration characteristic of PET samples. While, the migration quantity of Sb increases significantly with the increase of migrate temperature. It will provide an important reference to the evaluation of use security and service life of PET in real usage to study the relation between heavy metal migration features and aging degree.

Abstract: In current research three different prepared calcium deficient hydroxyapatite samples were evaluated for dental application. Lyophilized (lyoCDHAp), spray dried (spCDHAp) powders and wet precipitates (pCDHAp) were characterized by XRD, FTIR, SEM and BET analysis. Results showed, that various drying processes did not affect initial crystallinity, phase and chemical composition of samples. Small agglomerates (up to 2 μm) beside separated particles for lyoCDHAp and spCDHAp were observed in SEM analysis. LyoCDHAp and spCDHAp powders could be used as desensitizing component in the dentifrice, while pCDHAp could be more resorbable due to smaller particle size and induce remineralization of caries sites in the enamel.

Abstract: Cellulose nanocrystals (CNCs) have generated increasing attention in the past few years as potential sources of innovative bionanomaterials. This study focuses on an alternative method of nanocellulose particle preparation, using ammonium persulfate, and compares this to existing techniques. Nanoparticles were prepared using 4 different methods: thermocatalytic method, TEMPO oxidation, the acid hydrolysis and oxidation with ammonium persulfate. With the ammonium persulfate method, the grinding time of the oxidised cellulose is reduced drastically to only 0.5h, and results in an average nanoparticles size of 404.5 nm, zeta potential of -26.4 and crystallinity degree of 80%. Based on comparison of these parameters to results from existing techniques, oxidising cellulose using ammonium persulfate appears to be a promising alternative.

Abstract: Cellulose –Earth’s most abundant biopolymer–represent an enormous carbon-neutral renewable resource of biomaterials and bioenergy. The dissolution of cellulose with environmentally friendly and efficient solvents/methods is an important and challenging for further chemical processing. In recent years, room temperature ionic liquids (ILs)- a attractive “green” and “designer” solvent-have emerged as a potentially attractive “green” solvent for dissolution of cellulose for further processing. In general, dissolution of cellulose in ILs via conventional heating system requires high temperature and long pretreatment time. This study reports the effect of pressure on the dissolution of cellulose in IL [C₂mim][OAc] (1-ethyl-3-methylimidazolium acetate). The effects of temperature and pressure on cellulose dissolution time were investigated using high Pressure Solubility Measurement System (HPSMS). It was found that as the pressure and temperature increased, the dissolution time decreased significantly. For comparison, the original microcrystalline cellulose (MCC) and regenerated cellulose from ILs after dissolution were characterized using scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The results clearly revealed that the thermal stability of regenerated cellulose were reduced.

Abstract: The adsorption of ammonia gas on nanoparticle hydroxyapatite (HA) prepared from bovine bone was investigated. HA is well known as a good adsorbent for both of gas and liquid adsorbate. In this study, bovine bone was cleaned, calcined at 700 °C for 4 hrs and subsequently ground. The ground bovine bone powder was the starting material for synthesize of nanoparticle HA via precipitation. As-precipitated HA nanoparticles were filtered, washed and finally calcined at 500, 700, 1000 °C. Phase analyses were performed by X-ray diffraction (XRD) and the result showed that the higher the calcined temperature, the higher the degree of crystallinity. The result of ammonia (NH₃) gas adsorption indicated that as-precipitated HA with low crystallinity displayed better adsorption activity to NH₃ gas than calcined HA with high crystallinity.

Abstract: The pollution due to non-degradable material such as plastics, has led to studies about the development of environmental-friendly materials. Because of natural sources-based materials and their biodegradability, polylactid acid (PLA) and ijuk fiber are interesting to be modified into a composite. Furthermore this study is also expected to reduce the impact of environmental problems. Surface modification of ijuk fiber through alkalinization, was aimed to enhance compatibility between the ijuk fiber and the PLA, in order to improve properties of the composite such as crytallinity and thermal behavior. To investigate in detail about this modification, this research also studied effect of the alkalinized ijuk fiber and the PLA composition to the crystallinity and the thermal behavior of the composites. The experimental results were investigated by FTIR to qualitatively analyze compounds content in the ijuk fiber before and after alkalinization, DSC and TGA to study crystallinity and thermal stability behavior of the composite, respectively and FE-SEM to observe morphological behavior like compatibility between the ijuk fiber and the PLA. The FE-SEM observation showed that alkalinization of the ijuk fiber led to wettability enhancement between the ijuk fiber and the PLA. This may be caused by annihilating lignin and hemicellulose. Furthermore this treatment leads to expose micro-fibril cellulose (MFC) in the ijuk fiber and then to enhancement of bonding affinity with the PLA. This phenomenon gives a possibility for the PLA in the composite to increase its crystallinity due to nucleating effect of crystalline parts in the MFC. DSC measurements show that addition of the alkalinized ijuk fiber tends to increase the crystallinity of PLA in the composites.Keywords: alkalization, Arenga Pinnata, compatibility, crystallinity, PLA, thermal stability

Abstract: In this paper, the influence of synthetic conditions (the molar ratio of Mg²⁺ and Al³⁺; the concentration of cationic; the aging temperature and time) on the grain size and crystallinity of Mg-Al layered double hydroxide (LDH) has been investigated systematically based on the orthogonal experiment. Mg-Al LDH was prepared using magnesite through chemical precipitation and hydrothermal methods. The samples were characterized by X-ray diffraction (XRD). The grain size which along a and c axis were calculated through Scherrer formula. The experimental results showed that the grain size along a axis increased with the rise of synthesis temperature, while the grain size along c axis reduced. It was also found that the aging temperature and time had a great influence on the crystallinity of Mg-Al LDH.