Black improvers

In 30% nitric acid, silica fillers impair the resistance of vulcanisates while all types of carbon black improved it. The silica filled compounds failed completely in one to five days at 20 °C whereas the unfilled vulcanisates retained 70% of their initial strength after 25 days immersion. The carbon black loaded compounds are unchanged after this treatment. At higher temperature (up to 70 °C) channel blacks gave the best resistance. The failure of the silica filled vulcanisates is due to the formation of holes and pits on the surface. For carbon blacks a protective layer is formed on the surface due to nitration of the polymer and the enhanced intermolecular attraction of the NO2 groups. In any case rapid failure occurs at temperatures of 90 °C to 100 °C. 

The incidence of cracking due to ozone attack has been investigated for NR-EPDM blends (Tokita, 1977 Avgeropoulos et al., 1976). Andrews (1966) showed that small zones of EPR in an EPR-NR blend provide a barrier that inhibits ozone crack growth. Ambelang et al. (1969) found the importance of small EPM domain size in EPDM-SBR blends. Matthew (1984) has shown that carbon black improves the ozone resistance of NR-EPDM. An improvement was obtained in the blends with a balanced carbon black phase obtained by phase inversion. This is because (1) there is better reinforcement of the EPDM phase and (2) carbon black in the EPDM expands the volume of that phase. In BIMS-BR blends, the ozone failure can be retarded by reducing the size of the BIMS dispersion (Tse et al., 1998). 

Features Rec. where high infrared reflecfance is required much lower heaf buildup fhan fradifional blacks improved heaf buildup props, over conventional infrared reflecting blacks... 

A suitable strategy to minimize the carbon corrosion issue is to use carbon materials which have higher graphite contents and therefore fewer structural defects at which the oxidation initiates [81]. Heat-treatment of carbon blacks at elevated temperature is known to be able to impart the graphitic character to the carbon black [77, 82, 83]. As seen from Fig. 22.5, graphitization of the carbon blacks improved the stability and catalyst durability, though at the expense of a significant decrease in the specific surface area of the support material. The specific surface area loss was found to be primarily due to the elimination of pores less than... 

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