where Sc and Sa are the area of crystal and amorphous diffraction peaks of samples, respectively. The tensile strength (b) and elongation at break (εb) of the films in dry state were measured on a universal testing machine(CMT6503, Shenzhen SANS Test Machine Co. Ltd., Shenzhen, China) according to ISO 527-2, 1993 (E) at a speed of 5 and 10 mm min−1, respectively. The b and εb values were the average of five measurements. Optical transmittance (Tr) of the films was measured with a UV–vis spectroscope (Shimadzu UV-160A, Japan) in the wavelength ranging from 400 to 800 nm.