Full factorial design analysis and optimisation of mechanical behaviour of jute -flax reinforced epoxy composite

In the world of materials science, engineers have long sought a middle ground between the strength of synthetic plastics and the environmental friendliness of nature. For decades, the answer often lay in mixing natural plant fibers with tough chemical resins to create composites that are lighter and more sustainable than traditional metals or pure plastics. Think of these materials like a sandwich: the soft, sticky resin acts as the bread, holding everything together, while the stiff plant fibers act as the filling, providing the strength to resist breaking. However, making these natural fiber sandwiches work well is not as simple as just tossing ingredients into a bowl. The performance of the final material depends heavily on two specific details: how long the plant fibers are cut and how much of them are packed into the mixture. If the fibers are too short, they pull out easily; if they are too long, they tangle and create weak spots. Finding the perfect balance is essential for creating materials that can be used in cars, buildings, or everyday products without wasting resources.

A team of researchers set out to solve this balancing act by testing a specific combination of two common plants: jute and flax. These fibers were mixed into an epoxy resin, a strong type of plastic often used as a binding agent. The team wanted to know exactly how changing the length of the fibers and the amount of fiber in the mix would change the material's ability to stretch, bend, and absorb sudden hits. They did not rely on guesswork or computer simulations alone. Instead, they built eighteen different versions of the material in a laboratory, carefully controlling every variable. They cut the jute and flax fibers into six distinct lengths, ranging from very short pieces of 10 millimeters up to 35 millimeters. For each of these lengths, they created samples with three different amounts of fiber by weight: 20 percent, 30 percent, and 40 percent. Before mixing, the fibers were treated with a mild chemical solution to clean them and help them stick better to the resin, then they were pressed into molds to form solid blocks. Once cured, these blocks were tested to see how much force they could withstand before snapping or cracking.

The results revealed a clear and surprising pattern. While many people might assume that adding more fiber would always make the material stronger, the study showed that the length of the fiber mattered far more than the total amount used. In fact, the length of the fiber was the dominant factor, accounting for nearly all of the changes in performance. When the fibers were cut to 30 millimeters, the material reached its peak strength. At this specific length, the fibers were long enough to bridge gaps effectively and transfer force across the material, but not so long that they began to curl up or tangle within the resin. Once the fibers exceeded 30 millimeters, the performance actually started to drop. The longer fibers began to curl inside the mixture, creating tiny air pockets and preventing the resin from coating them evenly, which weakened the final product.

The amount of fiber in the mix played a much smaller role. The researchers found that increasing the fiber content from 20 percent to 40 percent did not significantly boost the strength. In some cases, adding too much fiber actually made the material slightly weaker because the resin could not fully wet the fibers, leaving dry spots that acted as weak points. The most successful combination turned out to be a mix with 20 percent fiber by weight and a fiber length of 30 millimeters. This specific recipe produced a material that could withstand a stretching force of 86.1 megapascals, a bending force of 92 megapascals, and an impact energy of 87 kilojoules per square meter. These numbers represent the highest performance achieved in the study, proving that precision in cutting the fibers is more critical than simply packing more of them into the mold.

This work highlights that optimizing natural fiber composites is about finding the sweet spot rather than maximizing quantity. The study confirms that for this specific mix of jute, flax, and epoxy, the length of the fiber is the key to unlocking strength, while the weight percentage has a minimal effect. The researchers noted that future work could explore adding other materials to the mix or testing how these composites hold up after being exposed to water and aging. For now, the findings offer a clear guide for engineers: if you want a strong, sustainable material made from these plants, focus your efforts on cutting the fibers to the right length, rather than just adding more of them.