Pull-out method for direct measuring the interfacial shear strength between short plant fibers and thermoplastic polymer composites (TPC)

Thermoplastic polymer composites reinforced with short plant fiber are worldwide in focus of research activities. Interfacial shear strength (IFSS) is an important indicator for evaluating the bonding quality between the fiber and the matrix polymer. However, the direct measurement of IFSS is especially difficult in the case of short fibers. In the present article, a method is proposed to this purpose, which is related to the known "fiber pulling out" methodology. In the case of single bamboo fibers, the IFSS in a polypropylene (PP) matrix was on, an average, of 5 MPa, which can be considered as weak. Scanning electron microscopy images revealed a rough inner surface in PP cavities left after fiber pulling out. This is direct evidence that a mechanical interlocking mechanism is active in the interphase between the hydrophilic fibers and the hydrophobic matrix.