1. a Department of Chemical Engineering, Pusan National University, Busan 609-735, Korea
2. b Department of Chemical Engineering, Pusan National University, Busan 609-735, Korea
3. c Department of Chemical Engineering, Pusan National University, Busan 609-735, Korea
4. d Department of Polymer Science and Engineering, Pusan National University, Busan 609-735, Korea
5. e Rubber Research Team, Korea Institute of Footwear & Leather Technology, Busan 614-100, Korea