Migration of antidegradants to the surface in NR and SBR vulcanizates

Abstract

Migration-generating equipment using a vacuum technique was constructed to measure the migration properties of antidegradants to the surface in compounded rubber in a short time. With this equipment, the migration of antidegradants to the surface is accelerated by the fast evaporation of organic molecules on the surface facing the vacuum and the pressure difference applied between two surfaces of the rubber vulcanizate. The effects of initial concentration and temperature on the migration of antidegradants such as 2,6-di-t-butyl-4-methyl phenol (BHT), N-phenyl-N-isopropyl-p-phenylenediamine (IPPD), and N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine (HPPD) were investigated with this equipment. The migration rate was found to be independent of the initial concentration of the antidegradants. BHT and IPPD migrate to the surface of an object faster than HPPD, which is due to molecular size. BHT migrates faster than IPPD at a low temperature of 40°C, while IPPD is faster than BHT at a high temperature of 60–100°C. Antidegradants in NR vulcanizates migrate faster than those in SBR ones. This is because interactions of antidegradants with SBR are stronger than those with NR. To explain the difference in rubber base, calculations with molecular mechanics and dynamics were tried, which gave the results that the interaction of IPPD with polystyrene is much stronger than those with cis-1,4-polyisoprene and cis-1,4-polybutadiene. Activation energies for migration to the surface of NR vulcanizate are 25.8, 30.7, and 38.6 kJ/mol, while those of SBR are 27.6, 36.5, and 51.7 kJ/mol for BHT, IPPD, and HPPD, respectively. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 117–125, 1997