PP/sugarcane bagasse fiber composites were prepared by injection molding from two fractions of fibers with different particle characteristics. The mechanical properties of the composites were characterized by tensile and impact measurements, while local deformation processes by acoustic emission testing and microscopy. The determination of fiber dimensions after processing showed that considerable attrition takes place during melt processing in both the length and the diameter of the fibers. Interfacial adhesion can be improved considerably by coupling. The strength of adhesion was estimated quantitatively and adhesion was ten times stronger (1600 mJ/m2) in the presence of the coupling agent than without it (140 mJ/m2) leading to larger composite strength in the former case. Local deformation processes also change with the strength of adhesion, debonding dominates without the coupling agent, while fiber fracture takes place at good adhesion. Fiber fracture consumes energy that leads to an increase in impact resistance. The size of the fibers must be reduced in order to achieve better properties, but the application of coupling cannot be avoided even in that case.
