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Volta Redonda, Brazil

Mulinari D.R.,UniFOA | Cruz T.G.,Sao Paulo State University | Cioffi M.O.H.,Sao Paulo State University | Voorwald H.J.C.,Sao Paulo State University | And 2 more authors.
Carbohydrate Research | Year: 2010

Surface modification of natural fibers has been made using different methods. In this paper, cellulose fibers from sugarcane bagasse were bleached and modified by zirconium oxychloride in situ. The chemically modified cellulose fibers were compared to those of bleached ones. Cellulose fibers were modified with ZrO2·nH2O nanoparticles through the use of zirconium oxychloride in acidic medium in the presence of cellulose fibers using urea as the precipitating agent. The spatial distribution characterization of hydrous zirconium oxide on cellulose fibers was carried out by combining both processing and image analyses obtained by SEM and statistical methodologies. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TG) were also used to characterize the nanocomposite. Results indicated that ZrO2·nH2O nanoparticles of about 30-80 nm diameter deposited on cellulose fibers were heterogeneously dispersed. © 2010 Elsevier Ltd. All rights reserved. Source

Pereira P.H.F.,Sao Paulo State University | Voorwald H.C.J.,Sao Paulo State University | Cioffi M.O.H.,Sao Paulo State University | Mulinari D.R.,UniFOA | And 2 more authors.
BioResources | Year: 2011

Cellulose fibers were isolated from sugarcane bagasse in three stages. Initially sugarcane bagasse was subjected to a pre-treatment process with hydrolyzed acid to eliminate hemicellulose. Whole cellulosic fibers thus obtained were then subjected to a two-stage delignification process and finally to a bleaching process. The chemical structure of the resulting cellulose fibers was studied by Fourier Transform Infrared (FTIR) spectroscopy. Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) were used to analyze the effects of hydrolysis, delignification, and bleaching on the structure of the fibers. Two different thermal analysis techniques were used to study the bleaching cellulose fibers. These techniques confirmed that cellulose fibers were isolated from sugarcane bagasse. A future goal is to use these fibers as reinforcement elements in composites, organic-inorganic hybrid, and membranes for nanofiltration. Source

Melo-Silva C.L.,Federal University of Fluminense | Melo-Silva T.C.F.,Federal University of Fluminense | Carvalho C.F.,Federal University of Fluminense | Sudre J.P.S.,Federal University of Juiz de fora | And 3 more authors.
Materials Science Forum | Year: 2015

The aim of the study was to evaluate the difference in the surface of dental ceramics, the basis of lithium disilicate, varying the concentration and time of application of the acid. Samples of IPS e. max Press (Ivoclar) were divided into: G1-control; G2 hydrofluoric acid 10% - 20 sec; G3 hydrofluoric acid 10% - 40 sec; G4 hydrofluoric acid 5% - 20 sec G5 and hydrofluoric acid 5% - 40 sec. The samples were analyzed under SEM (Carl Zeiss) confocal microscope and (Carl Zeiss). The qualitative morphologic analysis showed that 40 seconds of conditioning promoted the dissolution of the vitreous component and the ceramic crystal display for the two concentrations. Hydrofluoric acid 10% showed higher values of roughness. One can conclude that conditioning for 40 seconds is more effective than the 20 seconds for the two concentrations hydrofluoric acid and 10% promoted a higher surface roughness in the ceramic. © (2015) Trans Tech Publications, Switzerland. Source

Dos Santos C.,UniFOA | Dos Santos C.,State University of Rio de Janeiro | Habibe A.F.,UFF EEIMVR | Rodrigues D.,University of Sao Paulo | And 3 more authors.
Materials Science Forum | Year: 2014

In this study, the effect of ball/powder ratios for grinding particles of a dental alloy consisting of 66%Co-28%Cr-6%Mo was investigated. Metal powders were obtained from SPEX mill, with tungsten carbide balls, setting the milling time to 60 minutes, 50% of volume of grinding vessel filled with powder and argon inert atmosphere. The ball/powder ratio was varied between 4:1, 6:1, 8:1, 10:1.The powders were characterized by XRD indicating Co as only crystalline phase present, which indicates that Cr and Mo enter into solid solution with the matrix Co. Measurement of crystallite size conducted using the Scherrer equation indicate the crystallite size about 10 to 6nm, due to the increase of the ball/powder ratio of 4:1 to 10:1. The morphology of the milled powders were analyzed by scanning electron microscopy (SEM) and indicate that the agglomerates created by the grinding process must have average sizes varying between 100μm and 200μm with the modification of the ball/powder. © (2014) Trans Tech Publications, Switzerland. Source

Mulinari D.R.,UniFOA | Baptista C.A.R.P.,University of Sao Paulo | Souza J.V.C.,UniFOA | Voorwald H.J.C.,Sao Paulo State University
Procedia Engineering | Year: 2011

Actually, studies about the utilization of natural fibers as reinforcement in polymeric composites are increasing due to the improvements that fibers can provide to the product. In this work, chemical modification of the coconut fibers by alkaline treatment was studied in order to use them as reinforcement in polyester resin. Coconut fibers were modified during 1 hour with sodium hydroxide solution 1% wt/v. The modified fibers were evaluated by scanning electron microscopy, X-ray diffractometry, thermal analysis and Fourier Transform infrared spectroscopy. The composites were prepared by compression molding technique using 10% wt of fibers. The mechanical properties were evaluated by tensile and fatigue tests. The surfaces of the fractured specimens were examined in order to assess the fracture mechanisms. Results presented a decrease in fatigue life of composites when applied greater tension, due to bonding interfacial, which was not adequate. © 2011 Published by Elsevier Ltd. Source

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