Materials Science Forum Vols. 775-776

Abstract: The tensile properties of DGEBA/TETA epoxy matrix composites reinforced with different amounts of sisal fibers were evaluated. Composites reinforce with up to 30% in volume of long, continuous and aligned sisal fibers were room temperature tested in an Instron machine. The fracture was analyzed by SEM. The results showed significant changes in the mechanical properties with the amount of sisal fibers. These mechanical properties were compared with other bend-tested composites results. The fracture analysis revealed a weak fiber/matrix interface, which could be responsible for the performance of some properties.

Abstract: The objective of this work was to investigate the toughness behavior of epoxy matrix composites reinforced with up to 30% in volume of long, continuous and aligned sisal fibers by means of Charpy impact tests. The addition of sisal fibers results in a visible improvement in the energy absorption ability of the composites. Macroscopic observation of the post-impacted specimens and the SEM fracture analysis showed that longitudinal rupture through the sisal fiber interface with the epoxy matrix is the main mechanism for the higher toughness attended by these composites.

Abstract: The buriti (Muritia flexuosa) fiber are among the lignocellulosic fibers with apotential to be used as reinforcement of polymer composites. In recent years, the buriti fiber has been characterized for its properties as an engineering natural material. The toughness of buriti composites remains to be a evaluated. Therefore, the present work evaluated the toughness of epoxy composites reinforced with different amounts of buriti fibers by means of Charpy impact tests. It was found a significant increase in the impact resistance with the volume fraction of buriti fibers. Fracture observations by scanning electron microscopy revealed the mechanism responsible for this toughness behavior.

Abstract: To investigate the variation with temperature of the dynamic-mechanical parameters for the polyester matrix composites incorporated with up to 30% in volume of giant bamboo fiber was the motivation of this work. The analyzed parameters were the storage modulus, the loss modulus and the delta tangent. The investigation was conducted in the temperature interval from 25 to 195°C in a DMA equipment operating at 1 Hz of frequency under a flow of nitrogen. The results showed that the incorporation of long and aligned giant bamboo fibers tends to increase the viscoelastic stiffness of the polyester matrix. By contrast, only minor changes occurred in both the glass transition temperature and the damping capacity of the structure as measured by the tan δ peaks. These are indications that the polyester molecular mobility is not sensibly affected by interaction with the bamboo fibers in the composites.

Abstract: Fibers of the giant bamboo (Dendrocalmus giganteus) are amongst the strongest lignocellulosic fibers. Although studies have been already performed, limited information exists on the mechanical properties of polymeric composites reinforced with continuous and aligned giant bamboo fibers. This work evaluates the tensile strength of this type of composite. Standard tensile specimens were fabricated with up to 30% of fibers aligned along the specimen length. The fibers were press-molded with a commercial polyester resin mixed with a hardener and cured for 24 hours at room temperature. The specimens were tensile tested in an Instron machine and the fracture surface analyzed by scanning electron microscopy. The tensile strength increased significantly with the amount of giant bamboo fiber reinforcing the composite. This performance can be associated with the difficult of rupture imposed by the fibers as well as with the type of cracks resulting from the bamboo fiber/polyester matrix interaction, which prevents rupture to occur.

Abstract: Environmentally correct composites, made from natural fibers, are among the most investigated and applied materials today. In this paper, the mechanical behavior of epoxy matrix composites reinforced with continuous jute fiber was investigated through bending tensile tests. Specimens containing 0, 10, 20 and 30% in volume of jute fiber were aligned along the entire length of a mold to create plates of these composites. Those plates were cut following the ASTM standard to obtained bending tests specimens. The test was conducted in an Instron machine and the fractured specimens were analyzed by SEM. The results showed an increase in the materials tensile properties with the increase of fiber amount.

Abstract: Polymer composites reinforced with natural fiber that were obtained as industrial wastes, are of particular interest due to both the environmental benefits and economical advantages. In the present work sugarcane bagasse fibers, obtained as a waste from sugar and ethanol production, were incorporated in an amount of 25wt% into a polypropylene matrix. These fibers were previously alkali treated with NaOH to improve their adherence to the composite matrix. Thermal analyses were conducted in both types of composites, with untreated fibers and with alkali treated fiber. The result indicated that the alkali treatment improves the compatibility between the bagasse fiber and the polypropylene matrix, which then provides more thermal resistance.

Abstract: Natural fibers obtained from plants are being investigated as possible engineering materials with application in polymer composite reinforcement. For instance, the lignocellulosic fibers extracted from the leaves of the curaua plant (Ananas erectifolius) display a reinforcement potential owing to their relatively high strength. However, the curaua fiber has a poor adhesion with the polymeric matrix. In order to understand the curaua fiber interaction with a polymer matrix, the physical and chemical characteristics need to be evaluated. Among these characteristics, the Fourier transform infrared spectroscopy (FTIR) provides relevant information about the functional molecular groups and their possible interaction. Therefore, the objective of the present work was to analyze the FTIR of curaua fibers by means of transmittance spectrum obtained in the FTIR method with a 60o angle. The results showed peaks corresponding to specific molecular interaction that are discussed and compared to other results.

Abstract: The buriti palm tree (Mauritia flexuosa) has, in its petiole, natural fibers with great potential for reinforcement of polymer composites. This work attempts to evaluate the impact resistance of this type of fiber reinforcing polyester matrix. The fibers were mixed with polyester resin under pressure in a metallic mold, and cured at room temperature for 24 hours. Specimens were prepared with fiber percentages varying from 0 to 30% in volume. These specimens were tested in an Izod impact pendulum and the fracture surfaces were examined by scanning electron microscopy, SEM. The impact resistance increased substantially with the relative amount of buriti fiber reinforcing the composite. This performance was associated with the resistance imposed by the fibers and the crack propagation behavior.

Abstract: Artificial stones have recently been worldwide commercialized but are still not produced in Brazil. This has motivated efforts for the local fabrication of a similar stone. Thus, an artificial ornamental stone (AOS) was fabricated by means of a resin transfer molding (RTM) process. Marble residues were placed inside a hermetic mold under vacuum. A still fluid polyester resin, already mixed with a catalyst and a thinner, was injected into the mold. After curing, the density and water absorption of the AOS were evaluated. The material was also subjected to both compression and bend mechanical tests. The AOS microstructure was analyzed by scanning electron microscopy, which was then related to the obtained physical and mechanical properties.