Mechanisms of antiozonant protection: antiozonant-rubber reactions during ozone exposure

• Published in: Rubber chemistry and technology Vol. 57; no. 5; pp. 1023 - 1035
• Main Authors: LATTIMER, R. P, LAYER, R. W, RHEE, C. K
• Format: Conference Proceeding Journal Article
• Language: English
• Published: Akron, OH American Chemical Society 01-11-1984
• Subjects: Applied sciences; Compounding ingredients; Exact sciences and technology; Polymer industry, paints, wood; Stabilizers (antioxydants, antiozonants, etc.); Technology of polymers; Ozone resistance; Vulcanizate; Butadiene polymer; Model compound; Elastomer; Reaction mechanism; Isoprene polymer; Antiozone
• ISSN: 0035-9475; 1943-4804
• DOI: 10.5254/1.3536041

Abstract
Rubber (IR or BR) vulcanizatcs containing DOPPD antiozonant have been aged under ozone, and the soluble constituents have been removed by acetone extraction. Small amounts of nitrogen from the antiozonant remain in the rubber after extraction; this nitrogen is presumed to be chemically attached to the polymer network. Some of this “unextractable nitrogen” may be due to reaction of ozonized rubber with antiozonant, but other explanations are possible. The amount of unextractable nitrogen in the vulcanizate before ozone aging is about the same, within experimental error, as the amount remaining after static ozone aging. Model compound experiments (with cis-9-tricosene or squalene) show that chemical reactions can take place between the ozonized olefins (or unsaturated rubber) and DOPPD. The chemical structure for a model reaction product has been determined. Despite these findings, it seems unlikely that these types of reactions will play a significant role in the overall protection of rubber vulcanizates from ozone attack. That is, these products can form only after the rubber starts to become ozonized, and it has been shown that ozone attack on the rubber does not occur until after the antiozonant is nearly completely consumed. The results of this work are consistent with previous studies in our laboratory that indicate a combined “scavenger-protective film” mechanism is principally responsible for antiozonant protection. There is no definitive evidence to date to show that ozonized rubber reacts with antiozonant during ozone aging of rubber vulcanizates.