2.2. Compounding, curing characteristics and vulcanisation
All materials were used as supplied. The compositions were prepared according to the formulations presented in Tables 1 and 2. A semi-efficient sulphur vulcanisation system (semi-EV) was employed for the study on the accelerator types (the chemical structures of respective accelerators used in this study are shown in Fig. 1). Then, the CBS-vulcanised blend was again selected to study various vulcanising systems on the thermal stability of the blends. A fixed blend ratio of 70/30 (phr/phr) was produced using a laboratory-sized two-roll mixing mill (Model XK-160). N330 grade carbon black was also incorporated into the blends. The blended compounds were then compression moulded at 150 C with a force of 10 MPa using a hot press according to the respective curing times (tc90), determined by the MDR 2000. In addition to this study, conventional vulcanisation (CV) was not selected because the purpose of blending of natural rubber and recycled ethylene–propylene–diene-monomer is mainly to reduce compounding cost as well as eliminate the waste rubber. The minor objective is to improve the thermal properties towards natural rubber by using recycled EPDM in the second phase. In natural rubber, semi-efficient vulcanisation (semi-EV) and efficient vulcanisation (EV) can provide remarkable resistance to reversion and ageing. Therefore, semi-EV, EV, peroxide and mixed vulcanizing systems (semi-EV/Peroxide & EV/Peroxide) were employed and observed.