Effect of micro-sized lotus fibers on the fracture toughness of epoxy resin

Natural fiber-reinforced composites are gaining popularity due to their eco-friendliness, high fracture toughness, and biodegradability. A prime example is lotus fiber, derived from the lotus stem and often used in weaving towels and clothing, while the lotus flower is a symbol of Vietnam. Reinforcing epoxy resin with micro-sized lotus fibers (MLFs) to enhance its fracture toughness is a unique project with no prior work reported. This paper examines the influence of MLFs on the fracture toughness of epoxy resin by measuring Izod impact strength, critical stress intensity factor, and tensile strength. All tests were performed according to specified standards and measured at room temperature. The results showed that the content of MLFs significantly impacted the mechanical properties of composites, particularly the Izod impact strength and fracture toughness, as measured by the critical stress intensity factor (KIC). Specifically, increasing MLFs from 0 to 2.0% (by wt) enhanced the Izod impact strength by 242.71% (from 3.98 to 13.64 kJ/m2), the KIC by 139.59% (from 1.97 to 4.72 MPa.m1/2), and tensile strength by 41.43% (from 36.2 to 51.2 MPa). The fracture surfaces of epoxy resin and MLFs-reinforced composites were examined using scanning electron microscopy (SEM). Results indicated that the MLFs enhanced fracture toughness by creating rough and zigzag surfaces in the composite samples. The interaction between the MLFs and epoxy resin was primarily physical and assessed through Fourier transform infrared spectroscopy (FTIR). Thermogravimetric analysis (TGA) revealed that the composite sample exhibited better thermal stability compared to both lotus fiber and pure epoxy resin.