• JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
 
  Bookmark and Share
 
 
Doctoral Thesis
DOI
10.11606/T.23.2004.tde-17112004-172537
Document
Author
Full name
Milton Lazaro Filho
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2004
Supervisor
Committee
Ballester, Rafael Yague (President)
Demarquette, Nicole Raymonde
Giannini, Marcelo
Goes, Mario Fernando de
Kawano, Yoshio
Title in Portuguese
"Viscoelasticidade em função dos modos de fotoativação de compósitos"
Keywords in Portuguese
Dureza
Espectrofotomeria
Infravermelho
Resinas compostas
Teste de materiais
Viscosidade
Abstract in Portuguese
O escoamento viscoelástico pode contribuir ao alívio da tensão gerada durante a polimerização de compósitos aderidos em cavidades. O objetivo do estudo foi verificar a influência de dois modos de fotoativação contínua com diferentes intensidades (1000 mW/cm 2 e 250 mW/cm 2 ) e mesma densidade de energia final (24 J/cm 2 ) sobre propriedades viscoelásticas de dois compósitos comerciais (Filtek A110 e Herculite XRV) após a cura. Os parâmetros viscoelásticos avaliados foram: E’ (módulo de ar-mazenamento), tand (fator de perda) e as constantes reológicas t (tempo de relaxa-mento) e h (viscosidade).. Espécimes (50 x4 x 2 mm), de cada material em cada condição de fortoativação, (total de 51) foram confeccionados à temperatura ambiente e armazenados por 7 dias a 37 o C e submetidos então, a análise dinâmico-mecânica em aparelho DMA 242 (NETZSCH): varreduras de freqüência (50, 20, 10, 5, 2, 1 e 0,1 Hz) em ensaios isotérmicos (25 O C, 37 O C, 50 O C, 70 O C, 80 O C, 90 O C e Tg) em modo flexural (três pontos). Determinou-se também, a temperatura de transição vítrea (Tg). Os resultados de E’ e tand obtidos entre os 3 e os 7 minutos a cada temperatura permitiram a obtenção do módulo complexo E*. A aplicação do princípio de transposição tempo-temperatura de Williams-Landel-Ferry (TTS), resultou na curva mestra a 37 o C de E*(w). A aplicação de algoritmo de Laplace (RSI Orchestrator – Rheometrics), permitiu a obtenção da curva-mestra na mesma temperatura de E*(t). Através da aplicação do modelo matemático de Maxwell discretizado (n=10), obteve-se o espectro de relaxamento, que permitiu a obtenção de t e h de cada ma-terial em cada condição de fotoativação. Foi determinado também, em espécimes especialmente confeccionados para estas finalidades (n=3), o grau de conversão (GC) (análise de FTIR) e micro-dureza Knoop (KHN). Ambas propriedades foram analisadas antes (temperatura ambiente) e depois de tratamento térmico (aquecimento das amostras por 10 minutos a 110 o C). Os resultados do estudo permitiram concluir que: 1) Compósitos ativados com maior intensidade de luz produzem espécimes com menor t e h; 2) E’ e tand são significantemente afetados pelo aumento da intensidade da luz ativadora, diminuindo para Filtek A110 e aumentando para Hercu-lite XRV; 3) A Tg diminui com o aumento da intensidade para Filtek A110 e permanece inalterada para Herculite XRV; 4) Para Filtek A110, GC e KHN dos espécimes curados à temperatura ambiente não mudou com o aumento da intensidade, en-quanto que para Herculite XRV diminuiu; 5) GC e KHN melhoraram para Filtek A110 com o tratamento térmico adicional; para Herculite XRV, apenas KHN melhorou com o tratamento térmico, mas não o GC.
Title in English
Viscoelasticity as a function of fotoactivation mode
Keywords in English
Composite resins
Hardness
Infrared
Materials Testing
Rheology
Spectrophotometry
Viscosity
Abstract in English
Viscoelastic flow may contribute to the stress relief generated during composites po-lymerization adhered in cavities. The aim of this study was to verify how two modes of continuous photoactivation with different intensities (1000 mW/cm 2 and 250 mW/cm 2 ) and same density of the final energy (24 J/cm 2 ) affect viscoelastic properties after cure of two commercial composites (Filtek A110 and Herculite XRV). The evaluated viscoelastic parameters were: E’ (storage modulus), tand (loss factor) and rheologic constraints t (relaxation time) and h (viscosity). Specimens (50 x4 x 2 mm), of each material at each photoactivation mode (totaled 51) were built at room tem-perature and have been stored for 7 days at 37 o C to undergo the dynamic-mechanical analysis in DMA 242 (Netzsch) equipment. Frequency sweep was made (50, 20, 10, 5, 2, 1 and 0,1 Hz) in each of the isothermic testing (25 O C, 37 O C, 50 O C, 70 O C, 80 O C, 90 O C and Tg) in flexural test (3 points). It was also determined glass transition temperature (Tg). The results of E’ and tand obtained between 3 and 7 min-utes at each temperature allowed to obtain complex modulus E*. The application of time-temperature switch principle of Williams-Landel-Ferry (TTS) ended up in master-curve of E*(w) at 37 o C. The use of the Laplace algorithm (RSI Orchestrator – Rheometrics) allowed to obtain the master curve (at same temperature) of E*(t). By means of the using of discretized Maxwell’s mathematical model (n=10), relaxation spectrum was obtained, which resulted in t and h of each of the materials in each of the photoactivation conditions. Degree of conversion (DC) (FTIR analysis) and Knoop microhardness (KHN) were also determined in specially made specimens for these purposes (n=3). Both properties were analyzed before (room temperature) and after thermal treatment (heating of the specimens for 10 minutes at 110 o C). The results of the study allowed to conclude that: 1) Composites activated with higher intensity yield lower t and h specimens; 2) E’ and tand are meaningfully affected by the increase of the activating light intensity, decreasing for Filtek A110 and increasing for Herculite XRV; 3) Tg decreases with the intensity increase for Filtek A110 and remains un-changed for Herculite XRV; 4) For Filtek A110, DC and KHN of the cured specimens at room temperature, remained unchanged with the intensity increase, while for Her-culite XRV they decreased; 5) DC and KHN raised for Filtek A110 with additional thermal treatment – for Herculite XRV, only KHN improved with thermal treatment, but there were no changes for DC.
 
WARNING - Viewing this document is conditioned on your acceptance of the following terms of use:
This document is only for private use for research and teaching activities. Reproduction for commercial use is forbidden. This rights cover the whole data about this document as well as its contents. Any uses or copies of this document in whole or in part must include the author's name.
TeseToda.pdf (1.51 Mbytes)
Publishing Date
2005-02-02
 
WARNING: Learn what derived works are clicking here.
All rights of the thesis/dissertation are from the authors
Centro de Informática de São Carlos
Digital Library of Theses and Dissertations of USP. Copyright © 2001-2019. All rights reserved.