Lignocellulosic materials can significantly contribute to the development of composites, since it is possible to chemically and/or physically modify their main components, cellulose, hemicelluloses and lignin. This may result in materials more stable and with more uniform properties. It has previously been shown that chemically modified sisal fibers by ClO(2) oxidation and reaction with FA and PFA presented a thin coating layer of PFA on their surface. FA and PFA were chosen as reagents because these alcohols can be obtained from renewable sources. In the present work, the effects of the polymeric coating layer as coupling agent in phenolic/sisal fibers composites were studied. For a more detailed characterization of the fibers, IGC was used to evaluate the changes that occurred at the sisal fibers surface after the chemical modifications. The dispersive and acid-base properties of untreated and treated sisal fibers surfaces were determined. Biodegradation experiments were also carried out. In a complementary study, another PFA modification was made on sisal fibers, using K2Cr2O(7) as oxidizing agent. In this case the oxidation effects involve mainly the cellulose polymer instead of lignin, as observed when the oxidation was carried out with ClO(2). The SEM images showed that the oxidation of sisal fibers followed by reaction with FA or PFA favored the fiber/phenolic matrix interaction at the interface. However, because the fibers were partially degraded by the chemical treatment, the impact strength of the sisal-reinforced composites decreased. By contrast, the chemical modification of fibers led to an increase of the water diffusion coefficient and to a decrease of the water absorption of the composites reinforced with modified fibers. The latter property is very important for certain applications, such as in the automotive industry.
Cellulose nanocrystal (CNC)-reinforced poly(lactic acid) (PLA) nanocomposites were prepared by twin-screw extrusion followed by injection-molding using a masterbatch approach. Noncovalent modification of CNCs was performed with two different poly( l -lactide) (PLLA)-based surfactants to improve the filler/matrix compatibility. They both have a PLLA block that is expected to improve the compatibility with the PLA matrix and differ by the polar head. It consists of either a poly(ethylene glycol) (PEG) block (PEG- b -PLLA) or an imidazolium group (Im-PLLA), that is able to interact with the surface of the CNCs. The morphological, structural, thermal, rheological, and mechanical properties of the nanocomposites were investigated. The different modes of interaction of the polar head of the surfactant lead to different properties. However, the global decrease in the molecular weight of PLA, induced by the short PLLA blocks from the surfactants and the possible degradation during melt processing, results in a plasticization effect and impacts the crystallization of the matrix.
Resol type resins were prepared in alkaline conditions (potassium hydroxide or potassium carbonate) using furfural obtained by acid hydrolysis of abundant renewable resources from agricultural and forestry waste residues. The structures of the resins were fully determined by 1 H, 13 C, and 2D NMR spectrometries with the help of four models compounds synthesized specially for this study. MALDI-Tof mass spectrometry experiments indicated that a majority of linear oligomers and a minority of cyclic ones constituted them. Composites were prepared with furfural-phenol resins and sisal fibers. These fibers were chosen mainly because they came from natural lignocellulosic material and they presented excellent mechanical properties. Thermal analyses (dTG and DSC) and electron microscopy images indicated that the composites displayed excellent adhesion between resin and fibers. Impact strength measurement showed that mild conditions were more suitable to prepare thermosets. Nevertheless, mild conditions induced a high-diffusion coefficient for water absorption by composites. Composites with good properties could be prepared using high proportion of materials obtained from biomass without formaldehyde.
A Deus A família AGRADECIMENTOSA Prof a . Dr a . Elisabete Frollini pela orientação e compreensão durante o desenvolvimento deste trabalho;Ao Instituto de Química de São Carlos por ter proporcionado a infraestrutura;Aos funcionários da secretaria de pós-graduação do IQSC e setor financeiro pelos serviços prestados;Aos funcionários da biblioteca do IQSC pelos serviços prestados;Aos funcionários das oficinas eletrônica, mecânica, vidraria e setor de informática do IQSC pelo grande auxílio no desenvolvimento do trabalho;Aos funcionários da central de análises químicas do IQSC;A todos os colegas do laboratório do grupo de Físico-Química Orgânica e também ex-colegas do grupo.Aos colegas da linha da pesquisa em compósitos: Elaine e Cristina. Aziz pela amizade discussões, auxílio no desenvolvimento do trabalho e amizade durante meu estágio na Université Bordeaux I. Às Indústrias Tanac S.A. (pelo fornecimento dinâmico de tanino) eLwarcel (pelo fornecimento de fibras de sisal).CAPES pela concessão da bolsa e demais auxílios concedidos.Aos amigos pós-graduandos que direta ou indiretamente tornaram mais agradáveis minha estadia nesse instituto.A comunidade paranaense em São Carlos: Larissa (Borbi), Marcilene (minha irmã por adoção), Nelson, Priscila, Thaís, Elizangela, Junão.A Márcia Zambon técnica do grupo de Físico-Química Orgânica e pela sua grande amizade e discussões.A Marcinha e Edson pelas conversas descontraídas e auxílios durante o desenvolvimento deste trabalho.A ciência é à procura da verdade, não é um jogo no qual uma pessoa tenta derrubar seus oponentes, prejudicar outras pessoas. C para análise das resinas fenol-furfural. Fibras de sisal foram usadas como agente de reforço das matrizes termorrígidas do tipo fenol, tendo em vista suas excelentes propriedades mecânicas, assim como a disponibilidade da mesma no país, pois o Brasil é atualmente o maior produtor mundial dessas fibras. Foram utilizadas fibras de sisal (3,0 cm de comprimento, distribuição aleatória) em porcentagens diversas, sem tratamento e mercerizadas (tratamento com solução alcalina). Até 50% de fibras (em massa), a resistência ao impacto dos compósitos aumentou proporcionalmente a porcentagem de fibras. Ainda, foram utilizadas fibras tratadas com ar ionizado e tanino hidroximetilado, variando-se o tempo de exposição das fibras aos tratamentos usados. Os compósitos preparados com resina taninofenólica contendo fibras de sisal tratadas (mercerização, ar ionizado e tanino hidroximetilado), apresentaram uma diminuição no valor de resistência ao impacto, quando comparados aos compósitos preparados com fibras de sisal sem tratamento. Provavelmente, estes tratamentos degradaram as fibras de sisal, tornando-as mais frágeis mecanicamente. As imagens obtidas por Microscopia Eletrônica de Varredura (MEV) destes compósitos reforçados com fibras tratadas mostraram uma maior adesão entre fibra/matriz. Este resultado foi confirmado por experimentos de absorção de água, em que os compósitos contendo fibras de sisal tratadas absorveram, em geral, menores quan...
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