Characterization of natural fibre-reinforced composites with advanced ultrasonic techniques

This paper presents an investigation of polypropylene composites reinforced with natural fibers (sisal, microfiber, and wheat straw) with ultrasonic methods. Results show a correlation between sound speed in composite and fiber content and water absorption. Fiber inhomogeneity and voids distribution were assessed with various ultrasonic imaging devices with different resolution. The obtained results justify the feasibility of using the ultrasonic technique for evaluation of the fiber´s volume fraction and water content and for visualization of voids and fibre homogeneity. The ultrasonic method provides quick feedback in optimizing the molding technological regime settings to produce composites with the required mechanical performance.