The industry is now increasingly looking for new materials that have strength and lower cost. Composite materials are designed to improve performance in certain applications, so fiber reinforced materials have attractive properties. This work aims to verify the influence of the length and mass fractions of composites with the insertion of synthetic glass fibers and natural jute yarn (Corchorus capsularis). The manufacturing process of the composites was by manual lamination associated with metal mold pressing. The polymeric matrix used was unsaturated isophthalic polyester resin homogenized with catalyst (1 %) and cobalt accelerator (1,5 %) in v/v. The proportions of fibers inserted in the composites were 2,5 % and 5 % by mass and in the lengths of 30 mm, 45 mm, 60 mm. Jute yarn and fiberglass were morphologically analyzed by Scanning Electron Microscopy (SEM) to verify their characteristics. The composites were evaluated according to their physical properties through apparent density – MEA (ASTM D-792), apparent porosity – PA (ASTM D-2734), and water absorption – AA (ASTM D570), in addition to the mechanical behavior of tensile strength (ASTM D3039). The fractures of the composites were analyzed by SEM. The morphological analysis showed a fiberglass with smooth and continuous areas, and the jute yarn with a tangle of fibers and rough surfaces characteristics that influenced the physical and mechanical performances. The physical properties of MEA, PA and AA increased from 5 % to 60 % with the additions of fiberglass (FV) and 4 % to 98 % with the addition of jute fiber (FJ). The greatest variation of the physical characterizations were the compositions of FV 60 – 2,5 % and FJ 45 – 5 %. The best results of mechanical tensile characterization showed that the FV 30 – 5 % and FJ 45 – 2,5 % composition presented tensile strength limit of approximately 28 MPa and 20 MPa respectively. The 5 % (FV) and 2,5 % (FJ) fractions had the best mechanical performances. Fracture surface analysis determined the failure mechanisms present in the materials such as occurrence of broken fibers, “river marks” and cracks. Generally, the physical and mechanical properties of the composites were superior to the full matrix making them suitable for possible applications such as general internal coatings.
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