Antioxidant-loaded carbon nanotube to sustain a long-term aging-protection for acrylonitrile-butadiene rubber

Aging-resistance is an important property of rubber products for their long-term applications. Antioxidants are widely used in the rubber formula to prevent its oxidative aging. However, the blooming of antioxidants results in loss of aging protection and induces toxicity and pollution, which limit their amounts in the rubber. Herein, a novel strategy to avoid such a blooming and improve the aging-resistance of polar acrylonitrile-butadiene rubber (NBR) composites was proposed by doping sustainable carbon nanotubes (CNTs) with antioxidants. Phenolic antioxidants, 3,9-bis-{1,1-dimethyl-2[β-(3-tert-butyl-4-hydroxy-5-methylphenyl-)propionyloxy]ethyl}-2,4,8,10-tetraoxaspiro[5,5]-undecane (AO-80) were chemically grafted and then physically absorbed to CNTs, therefore CNTs with rich antioxidants (CNT-AO80) were prepared, whose total loading efficiency of AO-80 reached 10.3 wt%. In CNT-AO80, physical loading amounts of antioxidants were 3.7 wt% and strongly suppressed by those parts from chemically grafting (6.6 wt%), developing a distribution of antioxidant around CNTs. When 20 phr CNT-AO80 were added to NBR, they allowed a good dispersity and reinforcement for the composites. After naturally aging for 1 year and a 60-day thermal-oxidative test at 90 °C, the NBR composite with CNT-AO80 gave a low variation of mechanical property without AO-80 blooming, showing a good oxidative aging resistance. We believe that the design of loading antioxidants to CNTs may provide an effective solution to extend the service lifetimes of the rubber products.