The main objective of this work was to investigate the effect of hybridization on the mechanical and thermal properties of intralaminar natural fiber-reinforced hybrid composites based on sisal. Ramie, sisal and curauá fibers were selected as natural fiber reinforcements for the epoxy matrix based composites, which were produced by the hand lay-up technique. Tensile, flexural and impact tests were carried out according to American society for testing and materials (ASTM) standards to characterize the hybrid composites, while differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to evaluate the thermal properties. It was found that the mechanical properties are improved by hybridization of sisal based composites. The thermal analysis showed that the hybridization did not significantly affect the thermal stability of the composites. A scanning electron microscopy (SEM) was used to examine the fracture surface of the tested specimens. The SEM images showed a brittle fracture of the matrix and fiber breakage near the matrix.

Nowadays, in order to increase the transport efficiency and reduce fuel consumption and emissions of contaminants, a reduction in weight associated with improved safety performance of the materials in use must be achieved. On the other hand, environmental concern has generated interest in research about new materials aligned with the principles of sustainability. Thus, this need for better performing and ecological structures has resulted in the development of a new variety of materials. Among these materials, currently, are the composites produced from resources of renewable sources. Natural fiber composites have recently attracted a great deal of attention by the industry due to their many attractive benefits (e.g., high strength-to-weight ratio, sustainable characteristics and low cost). Welding is highly impractical to use in these situations (i.e., thermoset polymer composites) and rivets or screws exhibit stress concentrations and offer a low fatigue resistance. Adhesive bonding is usually the preferred method since it allows for greater flexibility in design and is more efficient in mechanical and energy aspects. In this work, recent advances in development, characterization and joining of new sustainable materials, critical challenges and future perspectives are presented. The application of sustainable green composites may further increase in many structural and non-structural applications if their joining behavior is well-known and established.

The growing demand for sustainable alternatives to synthetic composites has increased the interest in natural-fibre-reinforced composites (NFRCs), due to their reduced environmental impact. This study presents a comparative investigation of the mechanical properties of mono-fibre and intraply sisal/flax hybrid composites as cost-effective bio-based solutions. Flax offers high tensile performance but is constrained by higher cost and geographical availability. Sisal, on the other hand, is widely available at lower cost, but exhibits a coarser morphology and reduced processing versatility. Mechanical testing demonstrated that intraply hybrids achieved well-balanced performance, with reduced flax content still delivering competitive tensile strength and stiffness when compared to the higher performing mono-fibre flax composites. However, sisal-rich and hybrid laminates outperformed mono-fibre flax composites in transverse and shear behaviour, with the 67% sisal/33% flax hybrid composite exhibiting the highest transverse properties and the 33% sisal/67% flax hybrid achieving the highest shear properties. Rule-of-mixtures models predicted longitudinal tensile behaviour effectively, while Halpin–Tsai models successfully estimated shear but not transverse and compressive properties. Compressive strength showed limited variation across configurations. Failure analysis identified intra-yarn fracture in flax, limited resin infiltration in sisal, and compressive failure modes such as brooming and microbuckling. Overall, intraply sisal/flax hybrid mats provide a structurally efficient, sustainable, and economically viable alternative to mono-fibre natural composites.