Kenaf and carbon fibers were used as reinforcement materials. Low-viscosity epoxy with two components (resin and hardener) was used as a matrix (Product datasheet S1). The various properties of fibers provided by manufacturers are given in Table 1. Both fibers were bidirectional, meaning the fibers were plain-woven in two directions (0° and 90°).

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Environmental Friendliness: Natural fibers like kenaf are biodegradable and nontoxic, contributing to environmental sustainability.

Cost-Effectiveness: Kenaf fibers are economical to produce, requiring only 15 MJ of energy per kilogram compared to 100-900 MJ for carbon fibers.

Mechanical Properties: Kenaf fibers have higher mechanical strength and specific modulus than glass fibers.

Mechanical Performance:Hybrid composites with carbon fibers show substantial improvements in tensile strength, flexural strength, and interlaminar shear strength compared to single-fiber composites.

Potential Replacement for Glass/Epoxy Composites: The enhanced mechanical properties of kenaf/carbon hybrid composites make them suitable for replacing glass/epoxy composites in building and construction applications, such as stairways, walkways, and bridges.

Moisture Sensitivity:One of the disadvantages of natural fibers is their sensitivity to humidity, which can reduce the mechanical performance of the composites and restrict their use in exterior applications.

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Single-fiber composite K1 showed 35.4% FVF, lower than that of Composite C2. By alternating two carbon layers with kenaf fibers in KC1, the VC reached 9% and VK was 28.2% with 37.2% total hybrid FVF. The VC in other hybrid composites (KC2-KC5) increased to approximately 16%, and VK decreased up to 25.9% with 39.3%-42.5% total hybrid FVF compared to that in KC1. As the number of kenaf and carbon layers was kept constant, the void contents were found between 2.1% and 4.9% in KC2-KC5 hybrids. The variation in FVF may occur because of instabilities in the epoxy amount impregnation, which is considered a process limitation of vacuum infusion molding (VIM) employed for the composites fabrication. Another possible reason may be the variation of vacuum pressure and flowability of epoxy during the infusion process in differently stacked fibers in the hybrid composites. The variation of void contents in the composites may be due to the nonuniform distribution of kenaf fibers with fiber cloth, high vacuum pressure (80 kPa) in VIM used in the current study, or the trapping of air during resin flow (Lundström et al. 1993). The reason for air entrapment may be, during the curing, gas is formed as a result of chemical reactions (Lundström and Gebart 1994) between resin and hardener and dissolved gas nucleation in the resin (Afendi et al. 2005). The primary source of air entrapment is the inhomogeneous fiber structure, which results in nonuniform permeability of the fiber preformed, causing local variations in resin velocity. The capillary effect, dominant at the microscale, exacerbates this local velocity variance (Kang et al. 2000).

Growing Demand for Sustainable Materials:Increasing environmental regulations and consumer preference for sustainable products drive demand for natural fiber composites.

Technological Advancements: Improvements in hybrid composite fabrication techniques, such as vacuum infusion molding, enhance product quality and performance.

Economic Viability: Lower production costs and competitive mechanical properties position kenaf fiber composites as a cost-effective alternative to traditional materials.

Regulatory Support:Government incentives for using eco-friendly materials in construction and manufacturing can further boost market adoption.