New Elastomers by Reactive Processing. Part I. Vulcanizable Precured Alloys from NBR and ACM

Abstract

Abstract The dynamic vulcanization of ACM (the dispersed phase) during its mixing with NBR (the continuous phase) can produce a new type of millable specialty elastomer alloy. The millable dynamic vulcanizate containing the crosslinked dispersed phase can be later mixed with curatives for the continuous phase, fillers, antidegradants, etc. The completed mixture of millable dynamic vulcanizate with the additional curatives (for the NBR), fillers, stabilizers, etc. can then be vulcanized e.g., in a heated mold. Thus, the dynamic vulcanization technique is a means of separately controlling the vulcanization of individual phases of a blend of elastomers. Since the ACM can be completely vulcanized during the dynamic vulcanization stage of the mixing process, the usual postcuring associated with ACM technology is not necessary. Also, since the continuous or external phase is NBR, the prevulcanized millable alloy exhibits processability more similar to that of NBR than to that of ACM. Sticking and splitting on the roll mill is less of a problem after dynamic vulcanization than before dynamic vulcanization. The dynamic vulcanization of the ACM can be achieved by using the soap-sulfur type or the diamine-generator type curatives during the mixing process at elevated temperatures. Compositions filled either with carbon black (N326) or silica (Hisil 233) give compositions of excellent hot-oil resistance and room-temperature set. (Compression-set testing has not yet been done at this early stage of our research.) As in the case of conventional NBR stocks, the silica-filled compositions give excellent hot-air resistance whereas, carbon-black-filled compositions give fair hot-air resistance. In either the black-filled or the silica-filled compositions, provided that at least half of the rubber polymer is ACM, essentially complete resistance to ozone attack is obtained.