The interfacial bonding between fiber and matrix played an important role for the mechanical property
of fiber reinforced composite. The SEM micrographs of fracture surface compared between untreated and
flexible epoxy treated composites of three different natural fibers are shown in Fig. 5. The layer of
flexible epoxy resin formed on the surfaces between natural fiber and matrix after treatment as the
flexible interphase is illustrated in Fig. 6. The interfacial structure to be formed on fiber surface was not
matrix were formed and can
interrupted the debonding and cracks propagation between fiber/matrix interfaces, which was reported by
Yoshikawa et al. [15]. However, in this study the gradient interface between PLA matrix and flexible
epoxy interphase was not clearly observed