Papers by Author: Francisco Rolando Valenzuela-Díaz

Abstract: The use of vulcanized rubber products is widely spread in the industry and in the society. Tires, shoes, tennis and other are examples of it. Most of the raw materials used in the formulations of vulcanized rubber products come from the synthesis of natural raw materials consuming time and energy and also generating CO₂ emissions during the respective transforming processes. The main reinforcing material used in rubber formulations is the carbon-black which is a petroleum derivative obtained by the incomplete burning of the fossil fuel. This paper show some results obtained after replacing all or part of the carbon-black by carbonaceous nanoparticle minerals in rubber formulations.

Abstract: The advantage of the incorporation of tire rubber powder and rice husk ash in the polymer compound is mainly due to the reduction of the products cost, as well as improving the essential properties for a great processing of the material, for example, its flow into a hole of a thin wall mold. The rice husk ash can replaces the carbon black in the new products, contributing with the improvement of the environment and the economy of the society. Main objectives of this work are: enhance the applications of the ashes from the rice husk and the waste from the tire rubber, as well as, study new methods of recycling of polymeric wastes, to incorporate an aggregated value to the recycled materials as well as obtaining compounds or nanocompounds materials.

Abstract: This paper has as main objective synthesize zeolitic materials in hydrothermal conditions using as the predominant source of Si and Al a waste in powder generated from kaolin processing industries for paper-coating from the Brazilian Amazon region, thus transforming a material of low commercial value in another with higher added value, and can thus be used in future in adsorption and catalysis. For this were tested compositions of the mixture with different molar ratios of Na₂O/Al₂O₃ and SiO₂/Al₂O₃ considering the effects time-temperature of crystallization. The starting material and the phases formed as synthetic products were characterized by XRD, SEM and FTIR. The results show that the methodology developed with metakaolinite from a thermically activated kaolin waste at 700 º C for 2h reacting in alkaline medium in the presence of an additional source of silica, zeolitic phases were obtained with structure FAU-type and GIS-type in the samples synthesized.

Abstract: Poly(vinyl butyral)-polyaniline-sodium montmorillonite nanocomposites were prepared via polymerization of aniline between clay mineral platelets at two different pH levels (2.0 and 5.0), followed by dispersion of the polyaniline-sodium montmorillonite nanocomposite in a poly(vinyl butyral) solution. A comparison was made of the effect of the pH levels and the polyaniline-sodium montmorillonite nanocomposite precursor on the final structures of the poly(vinyl butyral) nanocomposites and their electrical conductivities. X-ray diffraction patterns revealed the formation of nanocomposites at both pH levels. UV-Vis spectra indicated that the polyaniline formed at both pH levels was conductive, with the UV-Vis spectra presenting a band at 420 nm corresponding to the polaronic form and the beginning of a new band at 600 nm indicating the presence of polaronic segments. FTIR spectra revealed the peaks of the groups present in polyaniline and poly(vinyl butyral) nanocomposites. The electrical conductivities of the polyaniline and poly(vinyl butyral) nanocomposites prepared at pH 2.0 were lower than those of the same nanocomposites prepared at pH 5.0, probably due to the lower formation of polyaniline chains in a more acidic dispersion and to the final configuration of polyaniline in the nanocomposites.

Abstract: The paper describes the technique developed for applying garnet powder abrasive ultra-high pressure water jet advanced technology (AWJ) to build accurate models of artistic objects. The objects to be modeled have been selected through a cooperative initiative between the University of Sao Paulo and entities of the private sector. The first application was the reproduction of the artistic floor of marble at the St. Mark's Basilica, Venice, Italy. The other application was the production of official trophies for a technical awards ceremony for a national symposium that took place in Brazil. The trophies were made in stainless steel, whilst the floor reproduction was made in ceramic tiles. The floor was reproduced from high-definition photography of the original floor. The design concept and the blueprints of the trophies were originally conceived by the symposium organizers. Both models have been built using OMAX® CAD/CAM Software, which controls an AWJ unit installed at the University of São Paulo, where the procedures for building both models have been developed and executed with high success.

Abstract: This paper presents a study of a stabilization/solidification (S/S) process of a tannery waste containing chromium. In this process a mixture of cement, water and the waste is solidified during hydration of the former. Stabilization occurs by the reaction of the chromium components of the waste with the calcium hydroxide formed during the process. A rigid block is obtained with low hazardous of contamination of soil and groundwater after its disposal into industrial landfill. Mixtures were prepared adding dried tannery waste in 10, 15 and 20% of the Portland cement mass. Sodium bentonite and organoclays in 5 % of cement mass were used as additives. Solidified specimens were analyzed after 28 days of hydration time by solid-state 29Si nuclear magnetic resonance (NMR) spectroscopy and unconfined compressive strength analysis. The increase of tannery waste content and the presence of the additives reduce silica polymerization as well as the mechanical strength of the solidified bodies.

Abstract: The organo-clays have important industrial uses between others are: rheological additives for drilling fluids in oil bases, inks, glues, lubricants and cosmetics. At the moment and in a growing way, these materials are considered as important reinforcement fillers in the structuring of nano-composites clays/polymers. They are obtained by the smectite clay reaction with quaternary ammonium salts. In this work an organophillic clay sample prepared by a dry process at the PMT – EPUSP – Metallurgic and Materials Engineering Department of the Polytechnic School at the University of São Paulo, had been characterized basically by techniques of XRD, IR, Thermal Analysis, and by swell capacity of the clays in some oils and organic solvents.

Abstract: Smectites are clay mineral with a layered structure and nanometric thickness, high specific area and a huge variety of uses. Consisting on stacked layers of about 1nm thickness, including two silica tetrahedral and one octahedral sheet. Properties of natural Smectites can be enhanced by organic modification, due to the substitution of the exchangeable cations in the interlayer area. In fact, the properties of the modified smectite (organophilic clay) are related to its modified chemical composition and structural parameters. The interaction of smectite clays with surfactants has an important interest in the fields of drilling fluids, paints, cosmetic, ceramic industries and others. Recent applications are: remediation of contaminated areas and polymer/clay nanocomposites. The aim of this paper is to obtain organophilic clays using a bentonite from the Chiqui Gómez deposit in Central Cuba. The raw and organophilic clays were analyzed by DRX, SEM, swelling capacity in organic solvents and others.

Abstract: The addition of a fourth component in the system composed by polymer/ solvent/ non-solvent is a technique generally employed to enhance membrane properties. Since polysulfone presents low hydrophilicity, which can hamper filtration performance, the addition of a hydrophilic material can be an important technique to improve this property. Therefore, the main purpose of this work is to understand the influence of addition of the activated carbon in the system polysulfone/ NMP/ water in terms of membrane morphology, hydrophilicity, thermal and mechanical resistance. From scanning electron micrographs, it could be seen that membrane surface became denser with the addition of higher activated carbon contents and the cross-section morphology was not changed. Acid-base interactions were favored with the activated carbon addition and the availability of Lifshtiz-van Der Waals interactions was decreased, being these two properties very important to avoid fouling formation onto membrane surface. The glass transition temperatures of the polysulfone composite membranes with higher activated carbon contents were increased. However, all activated carbon contents brittled the composite membranes in relation to the pristine polysulfone membrane.

Abstract: Drug delivery systems involving microcapsules provide an attractive way to improve the performance of many chemical and biological substances. These systems may be used for several industrial segments, especially medical, pharmaceuticals and cosmetics. PHB is a polyhydroxyalkanoate available in powder form, biocompatible, biodegradable and inert towards animal tissues. The obtained PHB/smectite clay nanocomposite improved the physical-chemical properties of PHB, including its biodegradability. In this work, we describe the preparation of microcapsules from two nanocomposites systems: a) PHB and Cloisite 20A organoclay (PHB1) and b) PHB and natural Brazilian green policationic clay (PHB2). When analyzed by XRD, the films and microcapsules did not show a d(001) peak, demonstrating an exfoliated structure for the nanocomposites. The films have shown by SEM an homogeneous distribution with the clay mineral particles spread homogeneously by the PHB film. The new microcapsules/nanocomposites showed an “hydrangea” morphology. The diameter of the microcapsules was variable between 0.5-15 µm.