1. School of Chemical Engineering, Hanoi University of Science and Technology, No. 1, Dai co viet, Hai Ba Trung, Hanoi, Vietnam
2. Center for Science and Technology of Rubber, Hanoi University of Science and Technology, No. 1, Dai co viet, Ha Ba Trung, Hanoi, Vietnam
3. Faculty of Engineering, Nagaoka University of Technology, Nagaoka, Niigata 940-2188, Japan