Antioxidant properties of carbon black in unsaturated elastomers. Studies with cis-polybutadiene
✍ Scribed by J. T. Gruver; K. W. Rollmann
- Publisher
- John Wiley and Sons
- Year
- 1964
- Tongue
- English
- Weight
- 735 KB
- Volume
- 8
- Category
- Article
- ISSN
- 0021-8995
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✦ Synopsis
The thermal antioxidant behavior of carbon black was studied in vulcanized cispolybutadiene and related to the surface chemistry of the black. Continuous and intermittent stress-relaxation and oxygen absorption measurements were employed to determine the antioxidant ability of the carbon blacks. The blacks were characterized by the surface concentrations of oxygen-containing functional groups, using methods described in the literature. Antioxidant activity was found to be highest in carbons containing relatively large amounts of bound oxygen. These carbons are also acidic and decompose peroxides by the ionic mechanism. This was demonstrated with dicumyl peroxide. However, even though the acidity and ability to decompose dicumyl peroxide to phenol and acetone could be destroyed by methylation, this treatment did not seriously impair the antioxidant activity, so that the role of acidic groups appears to be minor. Evidence is presented which suggests strongly that the antioxidant behavior of carbon blacks is due to surface quinones, possibly hydrogen-bonded with adjacent hydroxyl groups. Measurements made on samples vulcanized in peroxide and sulfur curing systems indicate that the antioxidant behavior of carbon black is independent of the method of vulcanization in the absence of other antioxidants. A characteristic feature of the antioxidant action of carbon blacks is their tendency to repress the oxidative crosslinking reactions, the relative amount of compensation of chain scission by crosslinking being smaller than in gum vulcanizates.
* Stress-relaxation measurements made with vulcanizates which had never contained antioxidant were identical with those made with the extracted vulcanizates, indicating that complete extraction waa achieved.