Sisal fibers are among the natural lignocellulosic ones with great impact resistance for potential use in polymer composites. This work evaluates the ballistic efficiency of the distinct individual components of a multilayered armor. These include the front ceramic, the back metallic sheet and the intermediate layer as either the conventional aramid fabric or a novel sisal fiber reinforced epoxy composite. Sisal fibers incorporated in epoxy resin plates with volume fraction of 30% were ballistic tested using the 7.62 caliber ammunition. The fibers were embedded under pressure in the epoxy resin matrix and cured at room temperature for 24 hours. The tested specimens were examined by scanning electron microscopy.

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The world is ever more demanding materials that are not only less intensive in terms of processing energy but also environmentally friendly. Presently, issues like generalized pollution and global warming are renewing the interest of natural materials in substitution for synthetic ones. In fact, natural lignocellulosic fibers are today the subject of a growing number of studies. In particular, the jute fiber, has been investigated by various mechanical and thermal analyses. With the intention to further characterize this fiber, a specific method was considered in this work, the infrared spectroscopy. The Fourier Transform Infrared (FTIR) was used to reveal the most typical absorption bands of specific molecular components of jute fibers, in order to understand the interaction that occurs between the jute fiber and a polymer matrix.

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The present work compares the tensile properties of polyester and epoxy matrix composites reinforced with hemp fibers. Polyester and epoxy reinforced with different volume fractions of hemp fibers up to 30% were prepared according to ASTM D-638-14 and tensile tested. The epoxy matrix composites reinforced with 30% of fibers presented tensile strength of 53 MPa, while those of polyester matrix, 25 MPa. The elastic modulus of the epoxy matrix composites was 1.75 GPa and that of the polyester matrix 4.05 GPa. The tests showed that the resistance of the epoxy composites reinforced with hemp fiber is superior to those of polyester matrix. However, the stiffness of the polyester/hemp fiber composites is higher than the epoxy/hemp fiber ones.

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ResumoAs fibras sintéticas vêm sendo gradualmente substituídas por fibras naturais. Em comparação com a fibra sintética, fibra natural demonstrou vantagens econômicas e ambientais. Visto que apresenta características interfaciais com matrizes poliméricas que favorecem a absorção de energia de alto impacto pela estrutura. No entanto, até agora pouco foi avaliado sobre a fibra de cânhamo incorporada em matrizes poliméricas. Este estudo tem o objetivo de avaliar a resistência ao impacto deste tipo de compósito com matriz de poliéster reforçada com diferentes porcentagens de fibras de cânhamo. A resistência ao impacto aumenta proporcionalmente com a quantidade relativa de fibras incorporadas como reforço na matriz polimérica. Este desempenho foi relacionado com a dificuldade de ruptura imposta pelas fibras, resultante da interação da matriz de fibra de cânhamo / poliéster de forma a ajudar a absorção da energia de impacto. Palavras-chave: Charpy; Teste de impacto; Fibra de cânhamo; Compósitos. CHARPY IMPACT TEST IN POLYESTER MATRIX COMPOSITES REINFORCED WITH HEMP FIBER AbstractSynthetic fiber has been gradually replaced by natural fiber, such as lignocellulosic fiber. In comparison with synthetic fiber, natural fiber has shown economic and environmental advantages. The natural fiber presents interfacial characteristics with polymeric matrices that favor a high impact energy absorption by the composite structure. However, until now little has been evaluated about the hemp fiber incorporated in polymeric matrices. This study has the purpose of evaluate the impact resistance of this kind of polyester matrix composite reinforced with different percentages of hemp fibers. The impact resistance has substantially increased the relative amount of hemp fiber incorporated as reinforcement in the composite. This performance was associated with the difficulty of rupture imposed by the fibers resulting from the interaction of hemp fiber / polyester matrix that helps absorb the impact energy.