Surface Characterization. The functional groups were determined using a fourier transform infrared spectroscopy Spectrum TWO (Perkin Elmer, USA) at room temperature with a diamond window. The static water contact angle was determined using a contact angle meter Drop Master DM300 (Kyowa Interface Science, Japan). A 4.0 μL water droplet was fixed onto the surface of the PP samples, and the contact angle was determined at 1 s (scanning time) after the attachment of the droplet. The results were calculated as the average of five repetitions. The water absorption ability was tested by submerging the PP NWF samples (10-15 mg; 2 × 2 cm 2 ) in distilled water and incubating for 10 min at room temperature. The dry weight (Wdry) of the samples was measured before submersion in distilled water, while the wet weight (Wwet) was measured after. The water absorption rate was calculated using equation 1 (W = weight). The results were calculated as the average of three repetitions.