Ramie fiber surface was physically fibrillated, and a bio based polyamide (PA) resin matrix composite material with a small amount (1 wt%) of the fibrillated fibers was produced via injection molding, and tested for tensile strength. When the results were compared with those of the untreated ramie fiber composite material, it was found that the tensile strength improved with increase in heat-treatment time. The strength was 24–28% higher than that of the neat PA. In contrast, the tensile strength of untreated ramie single fiber was significantly higher than that of the fibrillated fiber. Therefore, it can be concluded that the composite strength did not increase owing to fiber reinforcement. A sample wherein a single fiber was embedded in a PA was prepared, and the state of crystal formation with respect to heat-treatment time was observed. A new crystal that was neither a TCL nor a spherulite was observed around the fibril surface. It was speculated that the formation of this crystal promoted the strengthening effect of the PA resin. By applying this method, the PA resin was efficiently strengthened via crystallization through fibrillation of natural cellulose fibers without using individually produced cellulose nanofibers.
