Transcrystalline formation and properties of polypropylene on the surface of ramie fiber as induced by shear or dopamine modification

The key for fiber reinforced polymer composites is the interfacial interaction between fiber and polymer matrix. The crystallization of polymer on the surface of fiber as a possible way to enhance the interfacial interaction has received increasingly attention. In this work, the transcrystalline (TC) formation and properties of isotactic polypropylene (iPP) on ramie fiber surface, as induced either by fiber pulling or by dopamine modification, were investigated and compared. It was found that the growth rate of shear induced TC is faster than that obtained via dopamine modification. There exists α–β crystal form transition in the TC formation process as induced by pulling while only α-crystal form is obtained via dopamine modification. By using both dopamine modification and fiber pulling, a formation of TC with two step growth was observed for the first time: the first step growth has much enhanced rate than that induced by fiber pulling, and second step growth has the same rate with that induced by dopamine modification. Thus a unique TC structure was obtained, with α-crystal form presented in the inner layer and the outer layer, and β-crystal form in between. The result from single fiber fragmentation test indicated that interfacial shear stress (IFSS) between iPP and ramie fiber for dopamine modification induced TC is much higher than that of shear induced TC. Our work provides guidance for the preparation of polymer/fiber composites with enhanced interfacial interaction via formation of TC layer by using shear or fiber surface modification.