Polymers are materials of large use in the various sectors of the world economy. The use of polymeric materials in daily life, instead of the classic materials has increased in recent decades. However, for certain structural applications polymers need to get tougher. One of the principal toughening techniques based on physical mixture of two or more components, forming the so-called polymer blends. The addition of rubber or not vulcanized in polymer compositions is reported in the literature as a means of generating mixtures of easy processing, and economically advantageous to increase the toughness of the thermoplastic matrix of interest. Moreover, it can be an alternative for the recycling of waste tires and footwear coming from industries, as well reduce harmful effects on the environment. Therefore, the present study aims to present a review of the definitions, benefits, thermodynamic fundamentals and toughening polymers. ResumoPolímeros são materiais de grande utilização nos diversos setores da economia mundial. A utilização de materiais poliméricos no cotidiano, em substituição aos materiais clássicos vem crescendo nas últimas décadas. Porém, para determinadas aplicações estruturais os polímeros precisam ser tenacificados. Uma das principais técnicas de tenacificação se baseia na mistura física de dois ou mais componentes, formando as chamadas blendas poliméricas. A adição de borrachas ou desvulcanizados em composições poliméricas é apresentada na literatura como uma maneira de gerar misturas de fácil processamento, vantajosas economicamente e com aumento da tenacidade da matriz termoplástica de interesse. Além disso, pode ser alternativa para o reaproveitamento dos resíduos de pneus e calçados advindos de indústrias, bem como reduzir os efeitos nocivos sobre o meio ambiente. Portanto, o presente trabalho tem como objetivo apresentar uma revisão sobre as definições, vantagens, fundamentos termodinâmicos e tenacificação de polímeros.
Aiming to minimize the environmental pollution and reducing the production costs of the composite materials, the use of plant fibers improves their physical and mechanical properties. On the other hand, fibers have high water absorption, which may increase their volume and weaken the fiber/matrix interaction, affecting the mechanical features of the composites. Concerned with this problem, this research had the objective of making 3 and 10 millimeter-thick specimens, containing 23% (m/m) of Caroa fibers and 73% (m/m) of unsaturated polyester. Samples were withdrawn after 0, 2, 4, 7, 12 and 21 days of exposure at room temperature water (ASTM D570 − 98). Then, the test of tensile (ASTM D 3039), flexural (ASTM D 790-03) and impact (ASTM D 256) was realized and the mechanical properties were analyzed. The samples subjected to humidity had their fibers degraded and presented loss of mechanical properties, more significant in composite with 3 mm. For example, the reduction of the strengths tensile, after 21 days of test were 80% for composites with 3 mm and 60% for composites with 10 mm. Studies like this are important for long-term applications of such composites in humid environments.
Despite the ever-growing worldwide interest in the use of lignocellulosic fibers as reinforcement in either thermoset or thermoplastic matrices, the use of these fibers to replace synthetic ones, is limited. The reasons for these limitations are associated with the vegetable fiber’s heterogeneity, lower compatibility to most polymers, inferior durability, flammability, poorer mechanical properties and higher moisture absorption when compared with synthetic fibers. Nevertheless, despite these drawbacks, vegetable fiber reinforced polymer composites are lighter in weight, more sustainable and can be used for non-structural products. Strategies to minimize these drawbacks include fiber and or matrix modification, the use of compatibilizers, fiber drying and the concomitant use of vegetable and synthetic fibers, for the production of hybrid composites, the latter being an unquestionable way to increment overall mechanical and thermal properties of these hybrid systems. Here we present data on the water sorption of polymer composites having thermoset and thermoplastic matrices as a function of vegetable fiber identity, content and hybridization with glass fibers. Our data indicates that, regardless if the matrix is a thermoset of a thermoplastic, water absorption tends to be relatively independent of vegetable fiber identity and to be significantly dependent of its content. Fiber drying prior to composite manufacturing and hybridization with glass fibers leads to lower overall water absorption and higher mechanical properties.
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