No abstract

Due to environmental problems and exhaustion related to materials provided from non-renewable sources, the development of recycling technologies using residue as raw material has grown increasingly. Polypropylene (PP), a thermoplastic polymer, despite be easily recycled, presents a decrease in their mechanical properties after reprocessing cycles. In order to solve this problem, reinforcements may be added, producing a composite with better properties. The choosing of the dispersed phase aimed to consider, especially, its mechanical properties. Moreover, it was also considered the orientations of the incorporated fibers at the composite mechanical strength. In this scenario, a composite material of polymer matrix from recycled PP reinforced unidirectionally and bidirectionally with bamboo fibers were prepared. The fibers were treated with modifiers in order to increase the adhesion between polymer/fiber. The results showed that the use of reinforcement improves the mechanical properties of the polymer. Also, the superficial treatments were effective, indicating that there was an increase of the compatibility between the materials. It can be also inferred that the orientation of the fibers has directly influence at the final properties of the composite.

ResumoSabendo da necessidade do homem de desenvolver trabalhos com novos materiais, o uso de compósitos das mais variadas fontes cresce de forma proporcional aos avanços tecnológicos. Com isso, materiais como fibras naturais têm-se destacado, sendo utilizadas como reforço em compósitos estruturais, a fim de incrementar suas propriedades mecânicas. Nesse contexto, o objetivo principal deste trabalho é analisar as mudanças superficiais das fibras de bambu após terem passado por tratamentos químicos de mercerização e de acetilação. Estes foram realizados com o intuito de retirar ceras, hemicelulose e parte da lignina, que se encontram na superfície de fibras lignocelulósicas, a fim de incrementar a adesão das fibras com as matrizes poliméricas. Para analisar se os tratamentos propostos foram bem sucedidos na retirada desses compostos, as fibras foram avaliadas através da Microscopia Eletrônica de Varredura (MEV) antes e após os tratamentos. Os resultados apresentaram que os tratamentos, quando realizados de forma adequada, mostraram-se eficazes sem proporcionar prejuízos estruturais às fibras. Palavras-chave: Fibras lignocelulósicas; Fibras de bambu; Modificação superficial; Reforço estrutural. EVALUATION OF SPECTROSCOPIC CHARACTERISTICS OF BAMBOO FIBERS AFTER SUPERFICIAL MODIFICATION AbstractKnowing the man's need to develop work with new materials, the use of composites of the most varied sources grows in proportion to technological advances. With this, materials such as natural fibers have been highlighted, being used as reinforcement in structural composites, in order to increase their mechanical properties. In this context, the main objective of this work is to analyze the superficial changes of bamboo fibers after having passed through mercerisation and acetylation chemicals. These were carried out in order to remove wax, hemicellulose and part of the lignin, which are found on the surface of lignocellulosic fibers, in order to increase the adhesion of the fibers with the polymeric matrices. To analyze whether the proposed treatments were successful in the withdrawal of these compounds, the fibers were evaluated through the Scanning Electron Microscopy (SEM) before and after the treatments. The results showed that treatments, when performed properly, proved effective without providing structural damage to the fibers.

Resumo É notório que a utilização de materiais compósitos é amplamente difundida e abrangente. Sendo assim, faz-se necessário a busca por novas tecnologias que auxiliem o desenvolvimento de compósitos cada vez mais fortes e resistentes, tendo em vista a otimização da relação custo-benefício. O objetivo desse trabalho, portanto, é estudar materiais compósitos de polietileno reforçados com fibras naturais de bambu e de sisal, avaliando as propriedades mecânicas destes. As fibras passaram por tratamentos químicos e, após a montagem dos corpos de prova, foram realizados ensaios de tração. Ademais, utilizando-se da Distribuição de Weibull, realizou-se uma análise estatística da resistência à fratura. Ao final dos procedimentos, averiguou-se que houve uma melhoria significativa nas propriedades mecânicas, quando em comparação com corpos de prova não reforçados com sisal ou bambu. Palavras-chave:Fibras Naturais; Materiais Compósitos; Propriedades Mecânicas; Distribuição de Weibull.

ResumoAs fibras de bambu são ricas em celulose, hemicelulose e lignina. Elas apresentam altos módulos de elasticidade e alta resistência mecânica, o que as tornam bastante eficazes como reforço em compósitos. Com o intuito de aprimorar as propriedades mecânicas de materiais poliméricos em escalas diminutas, tem-se buscado a aplicação desses reforços em sua forma nano. A extração de nanocelulose tem sido bastante estudada e, em nosso trabalho, foram feitas adaptações de métodos que mostraram-se mais eficazes. Os nanowhiskers a base de bambu foram obtidos por hidrólise ácida a 64%, após tratamento químico prévio de limpeza e branqueamento. Os materiais obtidos foram então caracterizados por FTIR, TG, DTG e tamanho de partícula por Potencial Zeta, onde seus resultados indicaram que o método de produção utilizado foi eficaz. Palavras-chave:Bambu; Nanowhiskers; Nanopartículas de celulose; Nanocompósitos. OBTAINING OF NANOWHISKERS FROM BAMBOO FIBERS FOR USE IN NANOCOMPOSITES AbstractBamboo fibers are rich in cellulose, hemicellulose and lignin. They present high elastic modulus and high mechanical strength, which makes them very effective as reinforcement in composites. In order to improve the mechanical properties of polymeric materials in very small scales, the application of these reinforcements in their nano form has been investigated. The nanocellulose extraction has been studied a lot and, in our work, adjustments in some methods that showed to be more effective were done. The nanowhiskers made from bamboo was obtained by 64% of acid hydrolisis after prior chemical treatment of cleaning and bleaching. The materials were then characterized by FTIR, TG, DTG and particle size by Zeta Pontential, which indicated that the production method was effective.

No abstract

We address the production of a musical tone by a very simple musical instrument of the Brazilian tradition: the berimbau-de-barriga. The simple physics of vibrations of the string and of the air mass inside the gourd are reviewed. Simple measurements, which illustrate the basic physical phenomena, are performed using a PC based Soundcard Oscilloscope. The inharmonicity of the string and the role of the gourd are discussed in the context of known results in the psychoacoustics of pitch definition.

The development of more resistant and inexpensive materials were important for the emergence of composites, materials that are the result of the mixing of two or more distinct components with improved properties. Vegetable fibers reinforced polymer matrix composites help to reduce costs as well as to preserve product quality. Sisal fibers are important due to good impact resistance and availability. Thus, the characterization used infrared spectroscopy and UV-Vis diffuse reflectance. The main purpose was to adapt the methodology used, in order to improve fiber-matrix adhesion, but without risks of fiber defibrillation. Scanning electron microscopy was used to obtain the morphological characterization and the energy-dispersive X-Ray spectroscopy to describe the elemental chemical composition of the fibers. Chemical treatments using NaOH 2% and acetylation with acetic acid and acetic anhydride in the ratio (1:1,5) were important to observe the main changes such as the removal of impurities and the smaller amount of water absorbed in the acetylated fiber, which allows a better adhesion of the fibers with a polymer. After this, the fibers can be used to the production of polypropylene and polyethylene composites that are expected to apply in automotive parts such as bumpers, fuel tanks and internal coatings.