New phenylenediamine antiozonants for commodities based on natural and synthetic rubber

For protection of elastomeric materials against ageing, antioxidants such as UV-stabilizers and antiozonants are used. Although historically N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD) was the only approved antiozonant in Germany, a range of other phenylene diamine antiozonants (excluding 6PPD) are permitted for use in rubber articles intended for repeat food-contact use in the US (FDA regulations chapter 21 Part 177.2600). The biggest disadvantage of 6PPD is its partial decomposition during the vulcanization leading to the formation of toxic primary aromatic amines (PAA), such as aniline and secondary aromatic amines (SAA). A number of new PPDs have been developed and patented, that due to their chemical structures, are far less soluble in aqueous solutions but a lot more soluble within the rubber matrix. They therefore show significantly less migration of PAA and SAA. These new antiozonants were investigated and compared to 6PPD using commercial rubber materials with a certain content of antiozonant with regard to their migration of PAA and SAA into three different food simulants. The lowest concentration of PAA and SAA in all food simulants was measured in the RU 997 stabilized elastomer. Due to this fact RU 997 was permitted as a new antiozonant for commodities based on rubber according to the Recommendation XXI 'Articles based on natural and synthetic rubber' of the Federal Institute for Risk Assessment (BfR). RU 997 therefore represents an alternative for 6PPD with less migration of aromatic amines.     

Correlation between migration behaviors of antiozonants and temperature

Migration behaviors of antiozonants depending on temperature were studied using a carbon black‐filled NR vulcanizate containing N‐phenyl‐N′‐isopropyl‐p‐phenylenediamine (IPPD) and N‐phenyl‐N′‐(1,3‐dimethylbutyl)‐p‐phenylenediamine (HPPD) as antiozonants. The experimental temperatures were 100, 90, 80, and 70°C. Migration rates of them increased steeply by increasing the temperature. The correlation between the migration rates and the temperature was investigated using the half (t_1/2)‐ and quarter (t_1/4)‐lifetimes of the migrants remaining in the vulcanizate after the migration. The plot of log t versus 1/T was well fitted by the linear equation: The correlation coefficients were higher than 0.995. It was found that the migration behavior and temperature had a correlation of log t = b/T + c, where t and T are the migration time and temperature, b is E_a/R, and c is the constant. The activation energies for the migration were 36.48 and 37.93 kJ/mol for IPPD and HPPD, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1566–1570, 2001     

Migration behaviors of antiozonants to the surface in NR vulcanizates,depending on the season: The effect of wax

Influence of wax film on the surface of a rubber vulcanizate on migration of antiozonants was studied using NR vulcanizates containing various types of waxes. The waxes have different molecular weight distributions. N‐phenyl‐N′‐isopropyl‐p‐phenylenediamine (IPPD), N‐phenyl‐N′‐(1,3‐dimethylbutyl)‐p‐phenylenediamine (HPPD), N,N′‐di(sec‐butyl)‐p‐phenylenediamine (SBPPD), and N,N′‐di(1,4‐dimethylpentyl)‐p‐phenylenediamine (DMPPD) were used as antiozonants. Migration experiments were performed outdoors for two months in the summer, fall, and winter. The migration rates of the antiozonants in the vulcanizate without wax are faster than those in the vulcanizates with waxes. The antiozonants migrate slower in the vulcanizate containing wax with a high‐molecular‐weight distribution than in the vulcanizate with a low one. In the summer, the migration rates of SBPPD and DMPPD are faster than those of IPPD and HPPD, respectively. But, in the fall, the migration rates of SBPPD and DMPPD are slower than those of IPPD and HPPD, respectively. The differences of migration behaviors of the antiozonants, depending on season and wax type, was discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1987–1993, 1999     

Influence of rubber composition on migration behaviors of antiozonants in carbon black‐filled rubber vulcanizates composed of NR,SBR, and BR

Migration behaviors of antiozonants in carbon black‐filled rubber vulcanizates with different rubber compositions of natural rubber (NR), styrene–butadiene rubber (SBR), and butadiene rubber (BR) were studied at constant temperatures of 40–100°C and outdoors. Three single rubber‐based vulcanizates, three biblends, and three triblends were used. N‐Phenyl‐N′‐isopropyl‐p‐phenylenediamine (IPPD) and N‐phenyl‐N′‐(1,3‐dimethylbutyl)‐p‐phenylenediamine (HPPD) were employed as antiozonants. Migration rates of the antiozonants became faster with increasing the temperature. The order of the migration rates in the single rubber‐based vulcanizates was BR > NR > SBR. The migration rates in the vulcanizates containing SBR, on the whole, increased with decreasing the SBR content, while those in the vulcanizates containing BR decreased with decreasing the BR content. Difference in the migration behaviors of the antiozonants depending on the rubber composition was explained both by the intermolecular interactions of the antiozonants with the matrix and by interface formed between dissimilar rubbers in the blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 237–242, 2001