Effect of plasma treatment and graphite/carbon black addition on bending and electromagnetic shielding of hemp fiber/polylactic acid composites

As the global environmental problems of energy shortage and pollution are becoming prominent, the trend of using natural fibers as the reinforcement in the composite is increasing. In this study, the hemp fiber mat-reinforced polylactic acid (PLA) composite was designed and fabricated. As the fiber and matrix have different water affinity, the plasma treatment was used to improve the interfacial properties between them. After plasma treatment, scanning electron microscope (SEM), water contact angle and X-ray photoelectron spectroscopy (XPS) detection were conducted, and the results showed the effectiveness of plasma treatment. To further improve the interfacial properties and impart the electromagnetic shielding to the composites, the graphite and carbon black were respectively added into the interface by the spraying method. The results showed that the composite in which the fiber mat was plasma treated and 10wt% graphite added had the highest bending strength, and the after-fracture morphology of this composite showed good damage resistance. The reason lies in the synergistic effect from the combination of graphite and plasma treatment. Additionally, the electromagnetic shielding effectiveness of the above composite had the highest value of 20.25 dB in X-band frequency range.