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	Downstream Engineering & Product   Design Unit Advanced Rubber   Technology Unit Latex Science &   Technology Unit Upstream Crop Management Unit Crop Improvement and   Protection Unit Biotechnology Unit			Advanced Rubber Technology Unit NR/EPDM blends NR vulcanisates have good elasticity and strength properties but poor resistance to heat and ozone. Ethylene-propylene-terpolymer rubber (EPDM) vulcanisates on the other hand have excellent heat ageing and ozone resistance. It has been a practice that NR is blended with EPDM in order to obtain the best characteristics of each component or for cost consideration. However, this practice often results in poor physical properties. This has partially been explained by migration of curatives from the EPDM to the NR phase resulting in the EPDM being undercured and the NR overcured. Recent study, adopting a ‘reactive mixing’ procedure for EPDM mastermatch mix, has shown that improved co-curability and good black distribution throughout the NR/EPDM blends can be obtained, resulting in improved physical properties. The ‘reactive mixing’ procedure involves the use of BAPD (bisalkylphenol disulphide) with DTDC (dithiodicaprolactam) for effective modification of the EPDM phase in the blend to give improved crosslinking, morphology and good interaction with black. Typical Properties of NR/modified EPDM blends for extrudate product and grommet Property NR/modified EPDM (60/40)   Extruded product Grommet Hardness, IRHD 53 55 Tensile Strength, MPa (min) 17.7 15.1 Elongation at Break, % (min) 585 575 Compression set, % 1 day @ 70°C (max) 28 23 Resilience, % Dunlop 72.4 - Ozone Resistance (50 pphm @ 40°C/72h/20% strain) No crack No crack Crescent Tear, N/mm - 25 The approach to material preparation was, firstly to prepare separately NR and EPDM masterbatches. The next step was to crossblend the two masterbatches using the ratio 60:40, NR:EPDM. This ratio was found to be optimal in maintaining complete ozone protection in the blend while maintaining the good set/elasticity performance. The work so far has shown that it is possible to compound and produce NR/EPDM blend compounds on large scale, and to satisfy most of the properties of a typical weatherstrip formulation. It is also possible to extrudate and vulcanise continuously through the microwave oven at temperature exceeding 180°C without any difficulty.
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