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Master's Dissertation
DOI
10.11606/D.3.2017.tde-26092017-141427
Document
Author
Full name
Leticia Mota de Oliveira
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2017
Supervisor
Committee
Valera, Ticiane Sanches (President)
Yee, Márcio
Possidonio, Shirley
Title in Portuguese
Caracterização do compósito de borracha natural reforçado com nanocristais de celulose.
Keywords in Portuguese
Borracha
Nanocompósitos
Abstract in Portuguese
Dentre os materiais de fontes naturais e renováveis, a celulose se destaca pela sua abundância, podendo ser encontrada em diversos organismos vivos, como plantas, amebas, bactérias, fungos e alguns animais marinhos. Suas dimensões podem ser reduzidas por quebra das cadeias amorfas, com possibilidade de atingir escalas nanométricas, obtendo-se assim as chamadas nanopartículas de celulose ou nanocelulose. Devido à alta cristalinidade, a nanocelulose possui altos valores de módulo elástico, proporcionando alta capacidade de reforço em matrizes poliméricas, combinados com baixo peso, área superficial elevada e biodegradabilidade. A borracha natural é uma matéria-prima de fonte natural, sendo extraída das seringueiras na forma de látex - dispersão coloidal de partículas de borracha e substâncias não-borrachas em um meio aquoso, com aspecto leitoso. No presente trabalho foram estudados compósitos de borracha natural e nanocelulose. Inicialmente, foi realizada uma análise do látex de nacionalidade brasileira, centrifugado, contendo 60% em massa de sólidos. Os resultados de caracterização do látex centrifugado comercial, a qual consistiu na análise de concentração de sólidos totais e na medida do pH, estavam de acordo com os dados apresentados pelo fornecedor. Além disso, a análise de distribuição de tamanho de partícula indicou que o material apresenta uma população, com tamanho médio de 1,0 ?m. A borracha coagulada com ácido acético apresentou, após mastigação em cilindro aberto, viscosidade Mooney e extrato acetônico igual a, respectivamente, 52,8 e 2,57%. As nanoceluloses foram obtidas por hidrólise com ácido ortofosfórico (NC P) e sulfúrico (NC S), sendo classificadas como nanocristal de celulose (NC). NC P apresentaram comprimento médio, razão de aspecto e cristalinidade igual a, respectivamente, 270 ± 89 nm, 50 ± 24 e 78%; e as NC S apresentaram 209 ± 51 nm, 29 ± 10 e 75%.. Os compósitos de borracha natural com nanocristais de celulose apresentaram, nos ensaios de tração, aumentos nos valores de todas as propriedades analisadas, quando comparados à borracha natural pura. Ao adicionar-se 10 phr de nanocelulose preparada com ácido fosfórico na borracha natural, os valores de resistência à tração na ruptura, alongamento na ruptura e módulo a 300% aumentaram, respectivamente, em 90%, 16% e 52%. Já com a adição de 10 phr de NC S, essas propriedades aumentaram, respectivamente, em 68%, 5% e 109%. O mesmo foi observado para a dureza Shore A. Com a adição de 10 phr de nanocelulose obtida por ácido fosfórico à composição da borracha natural, a dureza Shore A aumentou em cerca de 22%; já com a adição de 10 phr de NCs S, a dureza da borracha natural aumentou em 36%.
Title in English
Characterization of natural rubber cellilose nanocrystals composites.
Keywords in English
Acid hydrolysis
Nanocellulose
Nanocomposite
Natural rubber
Abstract in English
Among the natural and renewable sources' materials, cellulose stands out for its abundance, it can be found in many living organisms, such as plants, amoebas, bacteria, fungi and some marine animals. Its dimensions can be reduced by breaking the amorphous chains, with the possibility of reaching nanometric scales, obtaining the nanocellulose or cellulose nanoparticles. Due to the high crystallinity, the nanocellulose has high elastic modulus value, providing high reinforcement capacity combined with low weight, high surface area and biodegradability. Natural rubber is a raw material from a natural source, extracted from the latex - colloidal dispersion of rubber particles and non-rubbers in a milkylooking aqueous solution. At this work, composites of natural rubber and nanocellulose were studied. Initially, a Brazilian centrifuged latex with 60% of its weight in solids was characterized, by analyzing if the total solids concentration and the pH measurement is in agreement with the data presented by the supplier. In addition, particle size distribution analysis demonstrated that the material had an average size of 1.0 ?m. Then, the mastication in the open cylinder and the Mooney viscosity and acetone extract was measured and them were equal to, respectively, 52.8 and 2.57%. The nanocelluloses obtained by hydrolysis with phosphoric and sulfuric acids are classified as cellulose nanocrystal. NC P present average length, aspect ratio and crystallinity equal to 270 ± 89 nm, 50 ± 24 and 78%; and the NC S had 209 ± 51 nm, 29 ± 10 and 75%. In the tensile test, it was observed that there was an increase in all the mechanical properties analyzed for natural rubber when adding the nanocellulose in its composition. By adding 10 phr of prepared nanocellulose with phosphoric acid in the natural rubber the values of tensile strength at rupture, strain at rupture and modulus at 300% increased, respectively, by 90%, 16% and 52%. When added 10 phr of NC S, these properties increased, respectively, by 68%, 5% and 109%. The same was observed for Shore A hardness. When adding 10 phr of nanocellulose obtained by phosphoric acid in its composition, the Shore A hardness increased by about 22%; When adding 10 phr of NCs S, the hardness increased by 36%.
 
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Publishing Date
2017-09-29
 
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