Gallate ester of castor oil as a multifunctional additive in HAF carbon black–filled natural rubber composites

Abstract A multifunctional additive based on castor oil (gallate ester of castor oil [GECO]) for rubber composites was synthesized via esterification between castor oil (CO) and gallic acid (GA). Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were used to characterize the GECO. GECO was applied at different loadings (1, 2, and 4 phr) in high abrasion furnace (HAF) carbon black–filled natural rubber (NR) composite to study its effect on the curing, swelling, mechanical, and aging properties of the resulting composite. It was found that the use of GECO accelerated the curing process effectively and endowed the resulting composites with significantly better antiaging properties than the control composite containing the traditional antioxidant, N‐ isopropyl ‐ N ′‐ phenyl ‐ 1 , 4 ‐ phenylenediamine (IPPD). Additionally, it was found that the use of 1 phr of GECO enhanced the swelling and mechanical properties of the resulting composite, and after this level, a slight decrease in the properties was observed. Scanning electron microscopy results confirmed that the use of 1 phr of GECO caused a better dispersion of HAF within the NR matrix which resulted in an enhancement in the HAF reinforcement.