Kenaf composites have a high strength-to-weight ratio, but weak fiber-matrix interface bonding limits their automotive use. To address this, a novel technique was developed to fabricate multiphase composites using graphene nanoplatelets (GNPs), kenaf fibers, and an epoxy matrix. The composites were made using vacuum infusion molding, with the GNPs exfoliated using a bath sonicator for uniform dispersion. The composites modified with 0.2 wt% GNP showed the most significant improvement in mechanical properties. Specifically, these composites exhibited a 30.5% increase in tensile strength, a 61.5% increase in tensile modulus, a 17.6% increase in flexural strength, a 22.7% increase in flexural modulus, a 35.1% increase in interlaminar shear strength, and a 17.1% increase in fracture toughness. Additionally, the water absorption resistance of the multiphase composites improved by up to 7%. These improvements were attributed to the uniform dispersion of GNPs and improved interlocking with the fiber surface. The developed composite has the potential for interior parts (such as dashboards, interior walls, and luggage compartments) in the automotive vehicle.

Graphical abstract

The graphene sheets were aimed to be exfoliated for homogeneous dispersion into the polymer matrix, as illustrated in Fig. 1a. Firstly, GNPs were dispersed in ethanol with gentle mechanical stirring. Then, a coarse dispersion was done in the bath ultrasonic sonication (model: 040S, 240 W power, and 40 kHz frequency) [38] for 1 h in a closed glass beaker at 30-80 °C. The ethanol was completely evaporated after the sonication process by heating the GNPs/ethanol solution in an open beaker in an electric heater at 100-120 °C. After that, resin (EPOLAM 2040) was poured into a beaker containing the resultants GNPs (powder form) and mechanically stirred at 200 rpm for 0.5 h at room temperature. Once the GNPs and resin were uniformly dispersed, the hardener (EPOLAM 2042) was introduced and mechanically stirred at a speed of 120 rpm for 7 min at room temperature. Subsequently, the mixture was subjected to degassing in a vacuum chamber for 10 min. The resin and hardener were combined in a ratio of 100:32.

A) schematic diagram of dispersion process, and b) schematic diagram ofvacuum infusion molding (VIM).

Reduction in Emissions: Enhanced fuel efficiency contributes to meeting stringent environmental regulations and targets.

Sustainability: Increased use of natural fibers and recyclable materials supports sustainability and reduces the environmental footprint of manufacturing processes.

Cost Savings: Reduced fuel consumption leads to significant cost savings for consumers and industries.

Improved Fuel Efficiency: Use of advanced high-strength steels, aluminum, and synthetic fiber-reinforced polymer composites results in significant weight reductions (up to 90% in some cases), enhancing fuel efficiency.

Customization and Versatility: Natural fiber-based polymer composites can be tailored for specific applications in automotive, marine, and aerospace industries, providing versatile and adaptable material solutions.

To evaluate the composites' fracture performance, it is necessary to examine the processes of crack formation and delamination. After attaining maximum load and displacement, every composite showed constant crack propagation until a pre-cracked point and then snapped in the center. One possible explanation is the lower mechanical properties of kenaf fiber. Consequently, pre-cracked areas were discovered to have cracks running down to length. Delamination in the composite itself may be hard to spot while the fracture is loaded. Cracks and delamination that occur in composites under successive in-plane compressive loading can lead to local buckling and a decrease in in-plane compressive strength [64]. Compared to other composites, pure KNC0.0 may exhibit brittle behavior during testing. However, the addition of 0.1 wt% to the epoxy matrix can enhance the fracture toughness performance of pure KNC0.0. The crack formation was delayed by GNPs, which acted as additional reinforcement and improved the interlocking between the epoxy and kenaf fiber, as shown in Fig. 13a, b. Other GNPs combinations in the composites do not resist the crack formulation, leading to low applied load resistance and displacement; eventually, the fracture toughness becomes low. The amalgamation of GNPs particles makes weak interface bonding between the fiber and epoxy, which make speedy crack formation during the testing.

Crack formation mechanism a) pure kenaf/epoxy, b) GNPs toughened kenaf/epoxy, and c) failure behavior of the composites after fracture toughness (mode II).

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Automotive Industry:Synthetic fiber-reinforced polymer composites and natural fiber composites offer even more significant reductions, with potential weight reductions of up to 90%.

Marine Industry: Lightweight materials like aluminum and polymer composites reduce the overall weight of marine vessels, improving fuel efficiency and performance.

Aerospace Industry: The incorporation of advanced materials like graphene and carbon-based nanofillers can enhance the mechanical properties, thermal conductivity, and overall performance of aerospace components.

Fracture toughness (mode II) properties of pure and kenaf/GNPs/epoxy composites, a) load vs. displacement, and b) toughness values.

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