*2.3. Composite Preparation*

The desired amount of filler, hybrid filler, and PP polymer were fed into a twinscrew extruder with an ellipse-blade type screw L/D 0.5 (IMC-1979, Imoto Machinery Co., Toyama, Japan). The rotation speed, temperature, and residence time for melt-mixing were controlled at 40 rpm, 180 ◦C, and 5 min, respectively. The films were prepared using a hydraulic hot-press (IMC-180C, Imoto Machinery Co., Toyama, Japan) at 180 ◦C for 3 min under a pressure of 30 MPa, and then cooled at room temperature.
