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A growing environmental concern is increasing the search for new sustainable materials. In this scenario, natural lignocellulosic fibers (NLFs) became an important alternative to replace synthetic fibers commonly used as composites reinforcement. In this regard, unknown NLFs such as the caranan fiber (Mauritiella armata) found in South American rain forests revealed promising properties for engineering applications. Thus, for the first time, the present work conducted a technical characterization of caranan fiber-incorporated composites. Epoxy matrix composites with 10, 20 and 30 vol% of continuous and aligned caranan fibers were investigated by tensile tests, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Composites with more than 10% vol of caranan fibers significantly increase the elastic modulus and toughness in comparison to the neat epoxy. Indeed, the composite with 30 vol% was 50% stiffer, 130% tougher, and 100% stronger, which characterized an effective reinforcement. As for the elastic modulus, total strain and tensile toughness, there is a clear tendency of improvement with the amount of caranan fiber. The TGA disclosed the highest onset temperature of degradation (298 °C) with the least mass loss (36.8%) for the 30 vol% caranan fiber composite. It also displayed a higher degradation peak at 334 °C among the studied composites. The lowest glass transition temperature of 63 °C was obtained by DSC, while the highest of 113 °C by dynamic mechanical analysis (DMA) for the 30 vol% caranan composite. These basic technical findings emphasize the caranan fiber potential as reinforcement for polymer composites.

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Multilayered armor systems (MAS) with a front ceramic layer backed by a relatively unknown Amazonian guaruman fiber-reinforced (Ischnosiphon koem) epoxy composites, as second layer, were for the first time ballistic tested against the threat of 7.62 mm rifle ammunition. The amount of 30 vol% guaruman fibers was investigated in three distinct configurations: (i) continuous aligned, (ii) 0–90° cross-laid, and (iii) short-cut randomly dispersed. Additionally, single-target ballistic tests were also carried out in the best MAS-performed composite with cross-laid guaruman fibers against .22 caliber ammunition. The results disclosed that all composites as MAS second layer attended the US NIJ standard with corresponding penetration depth of (i) 32.9, (ii) 27.5, and (iii) 29.6 mm smaller than the lethal limit of 44 mm in a clay witness simulating a personal body. However, the continuous aligned guaruman fiber composite lost structural integrity by delamination after the 7.62 projectile impact. By contrast, the composite with cross-laid guaruman fibers kept its integrity for subsequent shootings as recommended by the standard. The single-target tests indicated a relatively higher limit velocity for .22 caliber projectile perforation, 255 m/s, and absorbed energy of 106 J for the cross-laid guaruman fibers, which are superior to corresponding results for other less known natural fiber epoxy composites.

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The Amazonian region of South America is known for its diversified number of plants from which food, medicine, wood and fibers have, since long time, been produced by local natives. A typical example is the guarumã ("guaruman"as suggested English spelling) scientifically identified as Ischinosiphon koem, an abundant plant found in the low lands alongside rivers of the state of Para in Brazil. Fibers extracted from the stem of the guaruman are used in ropes and baskets owing to their strength. In the present work, the possibility of applying guaruman fibers as reinforcement of polymer matrix composites is, for the first time, investigated. Amounts up to 30 vol% of continuous and aligned fibers were incorporates into epoxy matrix composites. Density measurements disclosed the guaruman to be one of the lightest natural fibers. Tensile tests indicate that the guaruman fiber addition was able to improve the composite elastic modulus. However, no significant change was found in the ultimate strength, total strain and resilience. On the other hand, a cost-effective analysis revealed a substantial reduction of ~29% in the epoxy composite price due to the incorporation of fibers. Preliminary ballistic evaluation disclosed a potential for application of guaruman epoxy composites in multilayered armor.