Interfacial adhesion in fully and partially biodegradable polymer composites examined with microdroplet test and acoustic emission

The interfacial adhesion of three different natural reinforcing fibers and three different matrix materials was examined by the microdroplet method and the process of acoustic emission. Flax, hemp and sisal reinforcing fibers and synthetic polypropylene, biodegradable MaterBi and PuraSorb PL matrix materials were used. Based on a large number of measurement results the strength of adhesion between the fiber and the matrix, as well as the critical fiber lengths were determined besides the strength properties of single fibers. The characteristic failure modes were also revealed from the microdroplet test and analysis of acoustic emission signals. The different material combinations were qualified with the help of comparative analysis. It was found that due to the relatively large diameters and deviations - characteristic of the structure of natural fibers - critical fiber length values turned out to be large as well. The sisal fiber and PuraSorb matrix droplet showed the highest interfacial shear strength out of the nine examined combinations. The acoustic emission results revealed that the starting of drops is preceded by the slipping of elementary fibers. The results were also supported by scanning electron microscopic examinations.