Thermal Aging and Abrasion Analysis of Natural Rubber Compounds

A model tire tread compound was prepared using NR (TSR20, 100 phr), carbon black (N234, 60 phr), processing oil (5 phr), stearic acid (3 phr), zinc oxide (4 phr), anti-degradants (total 4 phr), N-tert-butylbenzothiazole-2-sulfenamide (TBBS, 1.1 phr), N-(cyclohexylthio)phthalimide (CTP, 0.3 phr), and sulfur (1.6 phr). Mixing was performed in a Banbury-type mixer, and the initial temperatures of the mixer were 110 and 80 °C for the masterbatch (MB) and final mixing (FM) stages, respectively. The abrasion specimens were prepared by curing the rubber compound at 160 °C for the maximum cure time (t_max) in a compression mold (83 mm diameter and 19 mm thickness). Acetone, tetrahydrofuran (THF), n-hexane, and toluene were purchased from Aldrich Co. (Wyoming, IL, USA).
Three samples were prepared (Table 1): (1) untreated sample (sample code: NR0), (2) thermally aged sample (sample code: NRth), and (3) thermally aged sample after pre-abrasion (sample code: NRabth). Thermal aging was performed at 80 °C for 30 days in a convection oven. The aging temperature of 80 °C was determined by considering efficient thermal aging did not cause abnormal effects at high temperatures [41 (link),42 ,43 ]. The aging effect at 80 °C might correspond to about 16 times compared to that at 40 °C [44 (link),45 (link)].
An abrasion test was performed using a LAT100 tire tread compound tester of the VMI group (Gelderland, The Netherlands). Electro Corundum Disc Grain, 60 of VMI group (Gelderland, The Netherlands), was used as the abrasive disk. The load force was 75 N, and the velocity was 25 km/h. After the abrasion test, the wear particles were collected and separated by size using a sieve shaker of Octagon 200 (Endecotts Co., London, UK). Standard test sieves of 1000, 500, 212, 106, and 63 μm were used. The wear particles were divided into five groups; 63–106, 106–212, 212–500, 500–1000, and larger than 1000 μm.