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Reinforcing natural fibers to polymer matrices provides an increase in mechanical properties. In addition, bio composite materials contribute to the sustainable ecosystem with its ease of recyclability. The effect of accelerated aging on the mechanical properties of PLA matrix bio composite specimens has been observed in previous research, but the effect of accelerated aging on the mechanical properties and the resulting mass loss of the material produced with fused filament fabrication (FFF) has been discussed for the first time in this study. Aging was applied to the bio composite consisted of 10% hemp and PLA matrix produced at a constant rate, parallel to the tensile direction and cross (+/– 45°) angle, and the results were examined as tensile stress and mass loss. The aging effect has been observed even from the first week. Specimens with parallel printing to tensile direction showed a lower tensile performance than cross printing one, since the structure in the laminates is quite durable, the adhesion performance in the laminate or through thickness direction has been low. Natural fibers are found so highly hygroscopic that chemical treatments will improve the interface and increase the mechanical properties.

The use of composite materials has seen many new innovations for a large variety of applications. The area of reinforcement in composites is also rapidly evolving with many new discoveries, including the use of hybrid fibers, sustainable materials, and nanocellulose. In this review, studies on hybrid fiber reinforcement, the use of nanocellulose, the use of nanocellulose in hybrid forms, the use of nanocellulose with other nanomaterials, the applications of these materials, and finally, the challenges and opportunities (including safety issues) of their use are thoroughly discussed. This review will point out new prospects for the composite materials world, enabling the use of nano- and micron-sized materials together and creating value-added products at the industrial scale. Furthermore, the use of hybrid structures consisting of two different nano-materials creates many novel solutions for applications in electronics and sensors.

The transportation industry with airways, road transportation, shipping, and railways is a huge market for composites both military and civil applications. The need for sustainable and lightweight solutions triggered the need for composite materials. There are many different approaches for composite materials design and manufacturing to optimize the properties in strength, acoustic, and many more like such as ballistic, thermal management, and so onetc. The use of various reinforcing elements for various resins created endless options for materials scientists and designers. Among a variety of possibilities, the use of hybrid reinforcement has been quite a new approach for the composites, which is analogous to composite to optimize the performance of the final properties, such as impact, ultimate tensile strength, modulus value, thermal properties, and other properties. In this review article, the future of the transportation sectors, the advantages of railway transportation in this area, and an overview of the railway and transportation industry are presented. Definitions of hybrid composites are made and examples of applications of hybrid composites used in the railway industry are shown. Studies and research in this field were examined and, in this perspective, the contribution of hybrid composites to future studies is stated.