Dynamic Mechanical Analysis and Ballistic Performance of Kenaf Fiber-Reinforced Epoxy Composites.

Several industry sectors have sought to develop materials that combine lightness, strength and cost-effectiveness. Natural lignocellulosic natural fibers have demonstrated to be efficient in replacing synthetic fibers, owing to several advantages such as costs 50% lower than that of synthetic fibers and promising mechanical specific properties. Polymeric matrix composites that use kenaf fibers as reinforcement have shown strength increases of over 600%. This work aims to evaluate the performance of epoxy matrix composites reinforced with kenaf fibers, by means of dynamic-mechanical analysis (DMA) and ballistic test. Through DMA, it was possible to obtain the curves of storage modulus (E'), loss modulus (E″) and damping factor, Tan δ, of the composites. The variation of E' displayed an increase from 1540 MPa for the plain epoxy to 6550 MPa for the 30 vol.% kenaf fiber composites, which evidences the increase in viscoelastic stiffness of the composite. The increase in kenaf fiber content induced greater internal friction, resulting in superior E″. The Tan δ was considerably reduced with increasing reinforcement fraction, indicating better interfacial adhesion between the fiber and the matrix. Ballistic tests against 0.22 caliber ammunition revealed similar performance in terms of both residual and limit velocities for plain epoxy and 30 vol.% kenaf fiber composites. These results confirm the use of kenaf fiber as a promising reinforcement of polymer composites for automotive parts and encourage its possible application as a ballistic armor component.

Evaluation of the Change in Density with the Diameter and Thermal Analysis of the Seven-Islands-Sedge Fiber.

Basic properties of sedge fibers from the seven-islands-sedge plant (Cyperus malaccensis) were investigated with possible application in reinforcing composite materials. A dimensional distribution and the effect of fiber diameter on density were investigated using gas pycnometry. The Weibull method, used to statistically analyze the acquired data from the diameter intervals, indicated an inverse dependence, where the thinnest fibers had the highest density values. The morphology of the fibers was obtained through scanning electron microscopy (SEM), in which a lower presence of defects was revealed in the thinner fibers, corroborating the inverse density dependence. In addition, the sedge fiber was characterized by differential scanning calorimetry and thermogravimetric analysis, which indicate an initial thermal degradation at around 241 °C. These results revealed for the first time that thinner sedge fibers might be promising reinforcement for polymer composites with a limit in temperature application.

Mechanical Properties, Critical Length, and Interfacial Strength of Seven-Islands-Sedge Fibers (Cyperus malaccensis) for Possible Epoxy Matrix Reinforcement.

The growing concern about the limitation of non-renewable resources has brought a focus on the development of environmentally sustainable and biodegradable composite materials. In this context, a trend in the development of natural fibers used as a reinforcement in composites is ever-increasing. In this work, for the first-time, fibers extracted from the seven-islands-sedge plant (Cyperus malaccensis) have been characterized by X-ray diffraction (XRD) to calculate the crystallinity index and the microfibrillar angle (MFA). Also, an evaluation of the ultimate tensile strength by diameter intervals has been investigated and statistically analyzed by both the Weibull method and the analysis of variance (ANOVA). Moreover, the maximum deformation and tensile modulus have been found from the data acquired. Pullout tests have been conducted to investigate the critical length and interfacial strength when sedge fibers, are incorporated into epoxy resin matrix. Microstructure analysis by scanning electron microscopy (SEM) was performed to observe the mechanism responsible for causing rupture of the fiber as well as the effective fiber interfacial adhesion to the epoxy matrix.