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The use of vegetable fibers in the modern engineering industry represents a worldwide need for sustainable low-cost materials with desirable mechanical characteristics, such as high strength, modulus of elasticity and strain capacity. In order to be used as a reinforcement in composite systems, the Curauá fibers' durability and interface characteristics with the different matrices should be improved. The present work aims to characterize and compare the behavior of curauá filaments both in natural and treated conditions focusing on increasing their durability and bond performance. To minimize the degradation and high water absorption, two types of polymeric coatings were impregnated in the fibers: aluminum oxide and sand. Direct tensile tests were performed and correlated to the morphological observations of the fiber structure by SEM images. The adhesion between matrix and fiber was evaluated by pull-out tests. Volumetric changes due to the wetting and drying of the fibers were also analyzed. The results indicated an improvement of the fiber-matrix bond, fiber tensile strength and stiffness after the surface treatments. Additionally, the coating had a positive effect on the hydrophilic nature of the fiber, decreasing its water absorption capacity.

Microfibrillated cellulose (MFC) employed as reinforcement of polymeric matrices can increase elastic modulus, stiffness and strength of a composite. In this work, the assessment of the mechanical, thermal properties and tensile tests assisted by digital image correlation (DIC) was performed for curaua fiber MFC-reinforced polylactic acid (PLA) composites as a function of MCF content. First, MFC was incorporated into PLA using a solvent exchange technique and subsequent polymer solubilization to produce master batch composites. Then, more PLA was added to obtain composites with 0.5 and 1.5 wt% MFC by using double screw extrusion and injection molding. As a result, the addition of MFC caused the flexural, tensile, indentation, impact and modulus strengths to increase compared to those of pure PLA. The deformation gradient obtained from DIC verified that the 0.5 wt% MFC/PLA composite presented greater homogeneity in relation to load dispersion, corroborating the higher rigidity, maximum stress, and Poisson's ratio.

In the present work, two types of composites were produced, both reinforced with 30 vol% of curaua fibers (CF). In the first type, only the fiber was functionalized with graphene oxide (GO), producing the GOCF/EM composite. While in the second, only the epoxy matrix (EM) was functionalized, producing the CF/GOEM composite. The objective of the work was to investigate the influence of functionalization with GO on the tensile properties of these produced composites. In comparison with the non GO-functionalized composite, as control CF/EM, the results revealed an increase in yield strength (64%), tensile strength (40%), Young's modulus (60%) and toughness (28%) of the CF/GOEM composite. The GOCF/EM composites for which the fibers were functionalized with GO also performed better than the CF/EM composite. The ANOVA and Tukey tests confirm this increase. As for ductility, within the standard deviation, no change was observed between samples functionalized by GO and those from the control. For the first time, comparing the results of the composites, it was demonstrated that a polymer matrix functionalized by GO offers superior tensile performance compared to the other types, keeping the same GO concentration in the composite. This fact is corroborated by the analysis of the corresponding fracture mechanisms. Preliminary results of composite with simultaneous functionalization of both fiber and epoxy matrix failed to present superior properties. This might be attributed to high amount of GO, which is apparently not a good reinforcement as the curaua fiber.

The objective of this study was to obtain nanowhiskers from bleached and milled curaua fibers. Nanowhiskers were obtained via a TEMPO system. TEM micrographies proved the fibers were obtained. FTIR analysis showed characteristic peaks of the oxidation products for the samples submitted to the treatment, suggesting that the it was effective for cellulose. The results show that the TEMPO method increased crystallinity and decreased the degree of polymerization. As for thermal stability, the nanowhiskers were more thermally stable than the other samples. Based on our findings, the use of nanowhiskers may be suitable for a variety of applications, such as the production of nanocomposites.

With growing environmental concerns over synthetic polymers, natural polymeric materials, such as hemicellulose, are considered a good sustainable alternative. Curaua fibers could be an excellent source of biopolymer as they have a relatively high hemicellulose content (15 wt%) and only a small amount of lignin (7 wt%). In this work, hemicellulose was extracted by an alkaline medium using KOH and the influence of the alkali concentration, temperature, and time was studied. A hemicellulose film was produced by water casting and its mechanical, thermal, and morphological properties were characterized. The results show that the best method, which resulted in the highest hemicellulose yield and lowest contamination from lignin, was using 10% (w/v) KOH concentration, 25 °C, and time of 3 h. The hemicellulose film exhibited better thermal stability and elongation at break than other polymeric films. It also exhibited lower rigidity and higher flexibility than other biodegradable polymers, including polylactic acid (PLA) and polyhydroxybutyrate (PHB).

Natural fibers are increasingly used as composite reinforcement in different fields of engineering. Caraua fiber stands out for its good mechanical properties and adherence to resin; however, little is known about its behavior in the manufacture of a composite or whether classic failure theory applies in this case. The present study assesses the mechanical properties of two laminas reinforced with unidirectional curaua fiber containing fiber volume fractions of 30 % and 22 %, and compares the results with the values obtained for four failure criteria, using analysis of variance (ANOVA). To that end, tensile tests were conducted along the fiber direction and at other loading angles, in addition to iosipescu shear tests. The results show that the Hashin criterion was the best and the maximum stress criterion does not represent the failure behavior of these materials.

Over the last few years, great interest has been shown by researchers in presenting alternative proposals for the design and fabrication of materials with good mechanical properties and low cost for a variety of applications. With this in mind, a study was carried out on the addition of curaua fibers in a polypropylene (PP) matrix. These were extruded in the pellets form with curaua fiber content of 5, 10 and 20% (mass percentage). An injector was used to make the test specimens from these pellets, which were then subjected to mechanical tests (tensile and three point bending), physical and thermal tests (fluidity index and HDT). As a consequence, it was noted that the incorporation of fibers in composites of PP with curaua resulted in an increase in the elastic modulus and tensile strength improving therefore the mechanical properties of these materials. Another important point was to check if there was an increase in heat deflection temperature as the fibers were added. As a result, it has been found that it is feasible to use these materials in industry, facilitating its recycling and improving its final mechanical properties.

Composites with sustainable natural fibers are currently experiencing remarkably diversified applications, including in engineering industries, owing to their lower cost and density as well as ease in processing. Among the natural fibers, the fiber extracted from the leaves of the Amazonian curaua plant (Ananas erectifolius) is a promising strong candidate to replace synthetic fibers, such as aramid (Kevlar™), in multilayered armor system (MAS) intended for ballistic protection against level III high velocity ammunition. Another remarkable material, the graphene oxide is attracting considerable attention for its properties, especially as coating to improve the interfacial adhesion in polymer composites. Thus, the present work investigates the performance of graphene oxide coated curaua fiber (GOCF) reinforced epoxy composite, as a front ceramic MAS second layer in ballistic test against level III 7.62 mm ammunition. Not only GOCF composite with 30 vol% fibers attended the standard ballistic requirement with 27.4 ± 0.3 mm of indentation comparable performance to Kevlar™ 24 ± 7 mm with same thickness, but also remained intact, which was not the case of non-coated curaua fiber similar composite. Mechanisms of ceramic fragments capture, curaua fibrils separation, curaua fiber pullout, composite delamination, curaua fiber braking, and epoxy matrix rupture were for the first time discussed as a favorable combination in a MAS second layer to effectively dissipate the projectile impact energy.