Mill Processability of Brominated Isobutylene- Co-Paramethyl Styrene and Its Blends with Ethylene Propylene Diene Terpolymer (EPDM) in the Continuous Milling Operation BHUWNEESH KUMAR, 1 P. P. DE, 1 S. K. DE, 1 A. K. BHOWMICK, 1 D. G. PEIFFER 2 1 Rubber Technology Centre, Indian Institute of Technology, Kharagpur-721302, India 2 ExxonMobil Research & Engineering Company, Clinton Township, 1545 Route 22 East, Annandale, New Jersey 08801 Received 19 March 2001; revised 12 November 2001 Published online 29 May 2002 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/app.10752 ABSTRACT: The milling behavior of brominated isobutylene-co-paramethylstyrene (BIMS), ethylene propylene diene terpolymer (EPDM), and their blends was investi- gated over a range of temperatures and friction ratios using the continuous milling operation. At 30 °C, BIMS forms a loose nervy appearance and, as the temperature is increased to 90 °C, it gradually forms a tight elastic band. EPDM forms a loose band at all temperatures and friction ratios studied. For different blends of BIMS and EPDM, the milling behavior changes from a tight elastic band to a loose bagging band on increasing the EPDM content. Addition of different fillers results in lowering of the tendency to go to the back roll, even at lower temperatures. In all the filled systems, a smooth, regular, and tight elastic band is obtained at all the temperatures and friction ratios studied. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1484 –1495, 2002 Key words: friction ratio; front-to-back roll transition; continuous milling; milling behavior; processability INTRODUCTION In the manufacture of rubber products, one of the most important processing operations is milling. The great advantage of two roll mills is that it represents an open process to which additives can be easily introduced. Until internal mixers re- placed them, two roll mills have been the primary mixing equipment in the rubber industry. How- ever, in many industries, mixing on two roll mill is still routinely carried out. In large rubber in- dustries, mixing mills are mostly used in conjunc- tion with Banbury (or internal mixers), calendars, or extruders during normal processing opera- tions. Mills, although conjugational with internal mixers, are used to sheet off hot compounded rubber dumped onto them. This operation is necessary not only for instantaneous cooling of compounded polymer that is designed to avoid scorching and polymer degradation, but also for easier handling of the subsequent operations, such as mixing of curatives. In the case of extru- sion operation, mixing mills are used to warm up the compounded rubber stock to obtain a uni- form extrudate. Hence, it becomes very important that the compounded rubber stock forms a regu- lar continuous band on the front roll (slower) to Correspondence to: A.K. Bhowmick (anilkb@rtc.iitkgp. ernet.in). Journal of Applied Polymer Science, Vol. 85, 1484 –1495 (2002) © 2002 Wiley Periodicals, Inc. 1484