Melting characteristic
The melting thermogram of the sample was determined using the DSC (Model D8000, Perkin-Elmer Co., USA). At t = 5, 15, 30, 45 and 60 min of the crystallization time, 3-5 mg of the sample was withdrawn from the glass cell and placed in an aluminum pan and hermetically sealed. An empty aluminum pan was used as a reference. The sample was heated from 25 °C to 60 °C at a rate of 5 °C/min. The melting profiles were analyzed by the software provided with the DSC (Pyris software, Perkin-Elmer, Shelton, CT, USA).