Composites reinforced with natural lignocellulosic fibers (NLFs) are gaining relevance as the worldwide demand for renewable and sustainable materials increases. To develop novel natural composites with satisfactory properties, less common NLFs should also be investigated. Among these, the Cyperus malaccensis (CM), a type of sedge fiber, is already used in simple items like ropes, furniture, and paper, but has not yet been investigated as composite reinforcement for possible engineering applications. Therefore, the present work evaluated for the first time the properties of novel epoxy composites incorporated with 10, 20, and 30 vol.% of CM sedge fibers. Tensile, Izod-impact, and ballistic impact tests were performed, as well as Fourier transform infrared (FT-IR) spectroscopy and thermal analysis of the composites. Results disclosed a decrease (−55%) in tensile strengths as compared to the neat epoxy. However, the elastic modulus of the 30 vol.% sedge fiber composite increased (+127%). The total strain and absorbed ballistic energy did not show significant variation. The Izod impact energy of the 30 vol.% composite was found to be 181% higher than the values obtained for the neat epoxy as a control sample. An increase in both stiffness and toughness characterized a reinforcement effect of the sedge fiber. The thermal analysis revealed a slight decrease (−15%) in the degradation temperature of the CM sedge fiber composites compared to the neat epoxy. The glass-transition temperatures were determined to be in the range of 67 to 81 °C.

Kenaf (Hibiscus cannabinus L.) is one of the most investigated and industrially applied natural fibers for polymer composite reinforcement. However, relatively limited information is available regarding its epoxy composites. In this work, both thermal and chemical properties were, for the first time, determined in kenaf fiber reinforced epoxy matrix composites. Through XRD analysis, a microfibrillar angle of 7.1° and crystallinity index of 44.3% was obtained. The FTIR analysis showed the functional groups normally found for natural lignocellulosic fibers. TMA analysis of the composites with 10 vol% and 20 vol% of kenaf fibers disclosed a higher coefficient of thermal expansion. The TG/DTG results of the epoxy composites revealed enhanced thermal stability when compared to plain epoxy. The DSC results corroborated the results obtained by TGA, which indicated a higher mass loss in the first stage for kenaf when compared to its composites. These results might contribute to kenaf fiber composite applications requiring superior performance.

This article presents a comprehensive study on the physical, mechanical, thermal, and chemical properties of polypropylene (PP) composites reinforced with hemp fibers (HF) and compatibilized with maleic anhydride (MAPP). The composites were processed using a twin-screw extruder, followed by hot compression at 190 °C. Subsequently, the composites were analyzed using Izod impact and Shore D hardness tests to evaluate their mechanical properties. Thermal properties were investigated through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), while X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) were employed to study their chemical properties. Additionally, a statistical analysis was conducted to compare the average results of the impact and hardness tests. XRD analysis revealed that the addition of HF and MAPP led to the disappearance of peaks corresponding to the beta phase in pure PP. Hemp fibers exhibited an impressive crystallinity of 82.10%, surpassing other natural fibers, and had a significant molecular orientation angle (MFA) of 6.06°, making them highly desirable for engineering applications. The crystallite size was observed to be relatively large, at 32.49 nm. FTIR analysis demonstrated strong interactions between the fiber, compatibilizing agent, and polymer matrix. TGA tests showed that the addition of 5 and 10 wt.% MAPP resulted in complete degradation of the composites, similar to pure PP. DSC analyses indicated a reduction in crystallinity (X_c) due to the incorporation of HF and MAPP. Shore D hardness tests revealed an increase in hardness with the addition of 5 wt.% MAPP, while a steep decline in this property was observed with 10 wt.% MAPP. In terms of impact resistance, fractions of 3 and 5 wt.% MAPP in the composites exhibited improved performance compared to the pure polymer. Analysis of variance (ANOVA) was employed to ensure the statistical reliability of the mechanical test results. This comprehensive study sheds light on the diverse properties of PP composites reinforced with hemp fibers and compatibilized with MAPP, emphasizing their potential as sustainable materials for engineering applications. The results contribute to the understanding of the structural and functional aspects of these composites, guiding future research and developments in the field.

As destructive power of firearms raises over the years, ballistic armors are in continuous need of enhancement. For soft armors, this improvement is invariably related to the increase of stacked layers of high-strength fiber fabrics, which potentially restrains wearer mobility. A different solution was created in the early 2000s, when a research work proposed a new treatment of the ballistic panels with non-Newtonian colloidal shear thickening fluid (STF), in view of weight decreasing with strength reinforcement and cost-effective production. Since then, databases reveal a surge in publications generally pointing to acceptable features under ballistic impact by exploring different conditions of the materials adopted. As a result, several works have not been covered in recent reviews for a wider discussion of their methodologies and results, which could be a barrier to a deeper understanding of the behavior of STF-impregnated fabrics. Therefore, the present work aims to overview the unexplored state-of-art on the effectiveness of STF addition to high-strength fabrics for ballistic applications to compile achievements regarding the ballistic strength of this novel material through different parameters. From the screened papers, SiO${}_2$, Polyethylene glycol (PEG) 200 and 400, and Aramid are extensively being incorporated into the STF/Fabric composites. Besides, parameters such as initial and residual velocity, energy absorbed, ballistic limit, and back face signature are common metrics for a comprehensive analysis of the ballistic performance of the material. The overview also points to a promising application of natural fiber fabrics and auxetic fabrics with STF fluids, as well as the demand for the adoption of new materials and more homogeneous ballistic test parameters. Finally, the work emphasizes that the ballistic application for STF-impregnated fabric based on NIJ standards is feasible for several conditions.