1. College of Material Science & Engineering, Qingdao University of Science & Technology, Qingdao, P. R. China
2. School of Mechanical, Electrical & Information Engineering, Shandong University, Weihai, Weihai, P. R. China
3. Key Laboratory of Rubber-Plastics Ministry of Education, Qingdao University of Science & Technology, Qingdao, P. R. China