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Articles by Rike Yudianti
Total Records ( 3 ) for Rike Yudianti
  Rike Yudianti , Lucia Indrarti and Jun-ichi Azuma
  This study presents two types of natural gellous materials as cellulose resources including gellous material synthesized by Acetobacter xylinum in fermentation process of coconut water with common name Bacterial Cellulose (BC) and gellous material isolated from seed of Ocimum americanum called hydrogel. Morphological surface of BC and hydrogel was observed by Scanning Electron Microscope (SEM). These images show randomly arrangement of fibres in three dimensional network having length of 1-5 μm and 3-12μm, respectively in forming a dense reticulated structure. Hydrated fibres were observed evidently by Atomic Force Microscope (AFM) showing that BC and hydrogel have fibres in nanometer scale diameter, 7-10 and 2-3 nm, respectively. At glance, X-Ray diffraction profile of hydrogel shows broadening peaks at 2θ, 16° and 22°. While BC has peaks at 2θ, 14.7, 16.7, 20.5 and 22.5°, attributed to lattice diffractions (100), (010), and (110), respectively. The sharp profile present in BC lead to ordered structure, confirmed by higher crystallinity degree of BC (75%) compared to that’s of hydrogel (35%). Water Holding Capacity (WHC) of BC and hydrogel has values about 5.5 and 39.2 mL g-1, respectively while swelling ability of BC and hydrogel in water is 6.2 and 102.2%, respectively. Neutral sugar compositions of BC resulted in less 0.1% arabinose and rhamnose, 1.1% galactose, 98.5% glucose, 0.2 xylose and 0.2 mannose indicating high cellulose content. Meanwhile, hydrogel contains 11.9% (arabinose), 4.5% (rhamnose), 18.6% (galactose), 50.5% (glucose), 13.2% (xylose), 1.3% (mannose) indicating high hemicellulose contents leading to branching of arabinogalactan attached to cellulose.
  Rike Yudianti and Lucia Indrarti
  Bacterial Cellulose (BC) sheet has a remarkably high elastic modulus and crystallinity inhibiting its processing. Short fibers of homogenized BC are utilized in Bacterial Cellulose Composites (BCC) formation. Water Soluble Polymers (WSP) (Carboxymethyl Cellulose (CMC) and glycerol) present in homogenized BC fiber have significant effects on mechanical properties and structure. Increasing CMC concentrations from 0 to 0.75% causes crystallinity index reduction from 81 to 61, 76 to 53 and 70 to 50% when treated glycerol concentrations of 0, 0.25 and 0.5%, respectively. Increasing CMC concentrations from 0 to 0.75% enhances elastic modulus from 2907.5 to 6245, 180.4 to 1581.3 and 30.5 to 212.5 Gpa greatly under glycerol concentrations of 0, 0.25 and 0.5%, respectively. Increasing tensile strengths from 64.8 to 167.7, 52.7 to 78.2 and 17.5 to 41.3 MPa and elongation reduction from 4.9 to 2.5, 14.5 to 9.2 and 29.6 to 23% occurs at glycerol concentrations of 0, 0.25 and 0.5%, respectively when CMC concentrations increased from 0 to 0.75%. Conversely, effects of glycerol treatment on tensile strength, elastic modulus and elongation are also presented in this study. Combination of CMC and glycerol treatment into homogenized BC is quite possible to modify BC characteristic as good processing BC.
  Rike Yudianti , Lucia Indrarti and Holia Onggo
  Heating effect of purification on the structural integrity of multiwalled carbon nanotubes through acid treatment has been studied using classical oxidative treatment on the temperature variation of reflux (80, 100 and 120°C). The treatment was conducted to find a precise condition of oxidative treatment with monitoring structural carbon by means of its thermal behavior. Thermal behavior of the purified samples quantified by thermogravimetric analysis indicated enhancement of purity with removal of graphitic particles and non-oxidative compounds. Non-oxidative compounds as metal components reduced from 6.3% to 1.4, 1.5 and 1.2% under refluks 80, 100 and 120°C, respectively. During reflux, functionalization occurred, based on appearance of peak at 252.3°C (reflux 80°C) and 261.2°C (reflux 100°C). Exception in reflux 120°C, thermogravimetric analysis pointed out peak at 325.6°C which showed more unstable carbon on the result of a serious defect of side wall. The small number of particles seen on the images of Scanning Electron Microscope proved that the reflux was able to eliminate impurities attached on the side wall. In the generation of more unstable carbon tend to form densely-pack structure due to losses some of order hexagonal carbon ring. Heating of oxidative treatment was closely related to dispersibility of multiwalled carbon nanotubes in water. Removal of impurities certainly increased its dispersibility and tend to be lower with the generating unstable carbon due to excessive heating (120°C).
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