AGRADECIMENTOSAos meus pais, simplesmente por tudo! Pelo amor incondicional, carinho, dedicação e por terem me apoiado em todas minhas decisões. Ao meu irmão Augusto e meu namorado Bruno pelo companheirismo, toda compreensão e força nos momentos difíceis. Sem vocês nada disso faria sentido! Amo muito vocês! À Prof.ª Dra. Ticiane Sanches Valera pela orientação, atenção e apoio ao longo de todo este trabalho. Obrigada por ter me acolhido, por me apresentar este tema com o qual adorei trabalhar e, acima de tudo, obrigada pelo exemplo e pelos conhecimentos compartilhados! Ao meu coorientador Prof. Dr. Marcio Yee, Universidade Federal de São Paulo (UNIFESP), pela disponibilidade, mesmo trabalhando em outra cidade! Obrigada por ter me apresentado à Prof.ª Ticiane, pela paciência, compreensão e o enorme suporte que me proporcionou! Sem você tudo seria muito mais difícil!! Aos meus queridos amigos e colegas do Laboratório de Polímeros! Obrigada a todos por me ajudarem a fazer tudo isso dar certo! Obrigada a Fernanda, Nati e Kleber pelas conversas, pelas risadas, pelos chocolates (Kleber, nem um caminhão da Lacta poderia pagar por eles...), enfim, obrigada pela amizade única!! Às alunas mais novas Anita e Suellen. Su, obrigada por toda a ajuda no trabalho, espero que continuemos firmes e fortes para prosseguir com os trabalhos futuros! Obrigada Camila pela enorme ajuda em tudo que parecia que não ia dar certo, sua experiência no Laboratório é única e fez (e ainda faz) a diferença, muito Obrigada Palavras-chave: celulose, nanopartículas, biopolímeros, nanocompósitos, reologia. ABSTRACTCellulose is the renewable natural polymer currently available in greatest abundance. Cellulose is a semicrystalline polymer, and it is possible to extract its crystalline domains through a procedure that destroys its amorphous phase, such as acid etching, so obtaining crystalline cellulose particles called cellulose nanoparticles (NC). These nanoparticles have attracted great scientific interest because they have mechanical properties similar to those of many inorganic types of filler used in polymer matrix composites, like elastic modulus and tensile strength. Moreover, they have nanometric dimensions, which contribute to lower filler contents in the polymer matrix, due to its increased surface area when compared to the one of micrometric fillers. Nanocomposites formed by adding these fillers into polymeric matrices can present attractive commercial properties such as gas barrier, improved thermal properties, and low density, when compared to traditional composites. As NC are nanometric scale fillers, obtained from renewable sources, there is a great interest in their application into biodegradable biopolymer matrixes. Poly (lactic acid), PLA, is an example of biopolymer that presents improved thermal, mechanical and processing properties, when compared to the ones of other commercial biopolymers. In this work, cellulose nanoparticles (NC) were obtained, via acid hydrolysis, using three different methods, in order to study the most efficie...

There is growing interest in replacing the synthetic reinforcements used for natural rubber (NR) composites with natural fibers from renewable, environmentally sustainable sources. Jute fibers may be suitable reinforcements for NR because they have a high tensile strength, which is comparable to other fillers such as glass fibers. Thus, we studied the incorporation of bleached jute fibers into NR, characterizing the mechanical, dynamic mechanical, and morphological properties of the composites. The addition of fibers to the NR latex was achieved by chemical coagulation, followed by vulcanization in a laboratory two-roll mixing mill. The elastic modulus at 100 and 300% elongation of the NR doubled after the addition of 10 phr of fibers without significant loss in the tensile strength or the elongation at break. The hardness was increased by 47%, and the storage modulus also increased, indicating the excellent interactions between the surfaces of the fibers and the NR matrix.

A comparative study was conducted for three natural rubber (NR) composites: one containing raw jute fibers, one containing bleached jute fibers, and one containing cellulose nanocrystals (CNCs). The composites were prepared by adding each filler at 5 or 10 phr to the latex before chemical coagulation, and the composites were processed in a two-roll mixing mill. The mechanical, thermal, and vulcanization properties of the prepared composites were then determined. The NR stiffness increased with increasing fiber content, particularly when bleached fibers were added, as evidenced by the increased elastic moduli, maximum torques, glass transition temperature, and crosslinking density. Scanning electron microscopy showed agglomerates in the composite with 10 phr CNCs, which led to poorer mechanical performance compared to that of the bleached fiber-reinforced composite (10 phr). On the other hand, the addition of CNCs to the NR increased the cure rate index, thereby significantly advancing the optimum vulcanization time.