Influência de nanocristais de celulose nas propriedades térmicas, dielétricas e piezoelétricas em compósitos elastoméricos a base de poliuretano
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Data
2016-05-20
Autores
Sanches, Alex Otávio [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Compósitos particulados de conectividade 0-3 obtidos a partir de cerâmicas ferroelétricas são objetos de inúmeros estudos científicos. Tal fato decorre da necessidade da indústria eletrônica de materiais com altas constantes dielétricas e densidade de energia, para fabricação de componentes passivos integrados em circuitos impressos e fabricação de dispositivos de armazenamento de energia. Por outro lado, a constante dielétrica dessa combinação se limita a baixos níveis para algumas aplicações. A fabricação de compósitos trifásicos vem ganhando atenção devido às elevadas constantes dielétricas obtidas com a inserção de uma terceira fase condutiva. A literatura apresenta tais compósitos com um perfil bem comportado baseado na regra das misturas e na teoria da percolação. Por outro lado, em alguns casos as interações das fases de preenchimento com a matriz, bem como a possível geração de cargas durante o processo de fabricação impedem um comportamento previsível considerando a distribuição não aleatória das fases. Este trabalho teve como objetivo a obtenção e caracterização de compósitos trifásicos empregando-se como matriz o poliuretano a base de água, como segunda fase Titanato Zirconato de Chumbo (PZT) e como terceira fase, para efeito de comparativo, negro de fumo (NF) ou nanocristais de celulose (CNC). Os compósitos trifásicos foram preparados a partir da mistura dos componentes em solução aquosa de PU, e suas propriedades comparadas àquelas obtidas para compósitos bifásicos de PU_PZT e PU_NF e PU_CNC. As caracterizações foram realizadas por meio de Microscopia Eletrônica de Varredura (MEV), Calorimetria Exploratória Diferencial (DSC), análises termogravimétricas (TG), espectroscopia de impedância e infravermelho, condutividade dc, difração de raios X (DRX), e pela avaliação do coeficiente piezoelétrico. A presença de nanocristais de celulose na matriz PU, promoveu um aumento na transição vítrea e temperatura de início de degradação dos seguimentos soft em detrimento dos segmentos hard, demonstrando uma interação preferencial com os SS. A adição de CNC até 10% em massa impactou de forma substancial as propriedades mecânicas dos nanocompósitos, no entanto, estas foram afetadas consideravelmente em função da umidade. Medidas do coeficiente piezoelétrico (d33) dos compósitos PU_PZT ao longo de 30 dias, evidenciaram uma significante atenuação do seu valor. O fenômeno de redução do d33 também foi observado para os compósitos trifásicos com NF, embora nestes, a atenuação se restringiu a no máximo 30% dos valores iniciais. O decaimento nos valores do d33 foi atribuído não apenas a um fenômeno de não compensação de cargas durante a polarização, mas também à relaxação da matriz. Por sua vez, os nanocristais de celulose como terceira fase promoveram uma maior efetividade de polarização dos compósitos, resultando em um aumento do d33 superior a 400% comparativamente aos compósitos bifásicos PU_PZT dependente do conteúdo cerâmico e de nanocristiais. Um efeito de redução do volume livre para concentrações cerâmicas acima de 20% v/v ocasionou maior interação dos CNC com os segmentos hard do PU.
Particulate polymeric composite with connectivity 0-3 obtained using ferroelectric ceramics as a filler are objects of numerous scientific studies. This is due to the need of the electronics industry materials with high dielectric constants and high energy density, for the manufacture of integrated passive components in printed circuits and manufacturing energy storage devices. On the other hand, the dielectric constant of this combination is limited to low levels for some applications. The manufacture of three-phase composite has gained attention due to the high dielectric constant obtained by inserting a third conductive phase. The literature shows such composites with a well behaved profile based on the rule of mixtures and percolation theory. Moreover, in some cases the interactions of the filling phase with the matrix, as well as the possible generation of charges during the manufacturing process prevents a predictable behavior considering the non-random distribution of phases. This study aimed to obtain and characterize three-phase composites employing as matrix water-based polyurethane, and as a second phase Lead titanate zirconate (PZT) and as a third phase, for comparative purposes, carbon black (NF) or cellulose nanocrystals (CNC). The three-phase composites were prepared adding the fillers in aqueous PU, and their properties compared with those obtained for biphasic composites PU_PZT, PU_NF and PU_CNC. The characterizations were performed by Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), thermogravimetric analysis (TG), impedance and infrared spectroscopy, dc conductivity, X-ray diffraction (XRD), and the evaluation of the piezoelectric coefficient. The presence of cellulose nanocrystals in PU matrix promoted an increase in the glass transition and onset temperature degradation of the soft segments (SS) to the detriment of hard segments, showing a preferential interaction with the SS. Adding CNC up to 10% (by weight) impacted substantially the mechanical properties of nanocomposites, however, they are considerably affected due to the moisture. Measurements of the piezoelectric coefficient (d33) of PU_PZT composites over 30 days showed a significant attenuation of its value. The d33 reduction phenomenon was also observed for the three-phase composites with NF, restricted to a maximum of 30% of initial values. The decay in the d33 values was not only attributed to a phenomenon of non-compensation of charge during polarization, but also to the relaxation of the matrix. In turn, the cellulose nanocrystals as the third phase promoted greater effectiveness composite polarization resulting in an increase d33 higher than 400% compared to biphasic composites PU_PZT dependent of the ceramic and nanocrystal contents. Above 20% v/v of ceramic content possible reduction of free volume occur resulting in a higher interaction of CNC with the hard segments of PU.
Particulate polymeric composite with connectivity 0-3 obtained using ferroelectric ceramics as a filler are objects of numerous scientific studies. This is due to the need of the electronics industry materials with high dielectric constants and high energy density, for the manufacture of integrated passive components in printed circuits and manufacturing energy storage devices. On the other hand, the dielectric constant of this combination is limited to low levels for some applications. The manufacture of three-phase composite has gained attention due to the high dielectric constant obtained by inserting a third conductive phase. The literature shows such composites with a well behaved profile based on the rule of mixtures and percolation theory. Moreover, in some cases the interactions of the filling phase with the matrix, as well as the possible generation of charges during the manufacturing process prevents a predictable behavior considering the non-random distribution of phases. This study aimed to obtain and characterize three-phase composites employing as matrix water-based polyurethane, and as a second phase Lead titanate zirconate (PZT) and as a third phase, for comparative purposes, carbon black (NF) or cellulose nanocrystals (CNC). The three-phase composites were prepared adding the fillers in aqueous PU, and their properties compared with those obtained for biphasic composites PU_PZT, PU_NF and PU_CNC. The characterizations were performed by Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), thermogravimetric analysis (TG), impedance and infrared spectroscopy, dc conductivity, X-ray diffraction (XRD), and the evaluation of the piezoelectric coefficient. The presence of cellulose nanocrystals in PU matrix promoted an increase in the glass transition and onset temperature degradation of the soft segments (SS) to the detriment of hard segments, showing a preferential interaction with the SS. Adding CNC up to 10% (by weight) impacted substantially the mechanical properties of nanocomposites, however, they are considerably affected due to the moisture. Measurements of the piezoelectric coefficient (d33) of PU_PZT composites over 30 days showed a significant attenuation of its value. The d33 reduction phenomenon was also observed for the three-phase composites with NF, restricted to a maximum of 30% of initial values. The decay in the d33 values was not only attributed to a phenomenon of non-compensation of charge during polarization, but also to the relaxation of the matrix. In turn, the cellulose nanocrystals as the third phase promoted greater effectiveness composite polarization resulting in an increase d33 higher than 400% compared to biphasic composites PU_PZT dependent of the ceramic and nanocrystal contents. Above 20% v/v of ceramic content possible reduction of free volume occur resulting in a higher interaction of CNC with the hard segments of PU.
Descrição
Palavras-chave
Poliuretano, Compósitos trifásicos, PZT, Nanocristais de celulose, Coeficiente piezoelétrico, Polyurethane, Three phase composites, Cellulose nanocrystals, Piezoelectric coefficient