Sulfur

MoO₃ (99.5%) was purchased from Alfa Aesar (Yingong RD No. 229, Fengxian Chemical District, Shanghai, China), The other reagents were purchased from Sinopharm Chemical Reagent Co. Ltd. (Ningbo RD No. 22, Shanghai, China): Sulfur (99.999%), Ferrocene (98%), Ethanol (AR), HCl (37%, AR), and HNO₃ (66%, AR). All chemical reagents have been purchased from company and used without further purification.

Natural rubber (RSS1) consisting of cis-1,4-polyisoprene with a Mooney viscosity of ML (1 + 4) at 100 °C = 79.9, and butadiene rubber (BR9000) consisting of cis-1,4-polybutadiene with a Mooney viscosity of ML (1 + 4) at 100 °C = 50, were supplied by Shanghai Dukang Co., Ltd., (Shanghai, China). SiCB was produced by Jilin Kaiyu Biomass Development and Utilization Co., Ltd. (Changchun, China). Carbon black (N774) was obtained from Jiangxi Black Cat Carbon Black Co., Ltd. (Jingdezhen, China). Phenolic resin (2123) powder was supplied by Henan Xinxiang Co., Ltd. (Xinxiang, China). Stearic acid, zinc oxide (ZnO), and sulfur (S) in analytical grades were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All the other chemicals including N-1,3-dimethylbutyl-N’-phenyl-P-phenylenediamine (antioxidant 4020), poly(1,2-dihydro-2,2,4-trimethyl-quinoline) (antioxidant RD), wax, N-tertbutylbenzothiazole-2-sulphenamide (accelerator NS), and aromatic hydrocarbon oil (DAE) in chemical grade were supplied by Beijing Chemical Works. (Beijing, China) and used without further purification.

Natural rubber (RSS1) consists of cis-1,4-polyisoprene with a Mooney viscosity of 79.9 at ML (1 + 4) at 100 °C, and butadiene rubber (BR9000) consists cis-1,4-polybutadiene with a Mooney viscosity of 50 at ML (1 + 4) at 100 °C. Both natural rubber and butadiene rubber were from Shanghai Dukang Co., Ltd., (Shanghai, China). The pyrolytic rice husk ash containing biochar and silica (Trade Name as SiCB) were produced by Jilin Kaiyu Biomass Development and Utilization Co., Ltd. (Changchun, China). Milled SiCB (MSiCB) were prepared according to reported procedure using the XQM-2 planetary ball mill (Tianchuang Co., Changsha, China) [34 (link)], and the milling parameters of SiCB are described in Table S1. Maleic anhydride (MA), stearic acid, zinc oxide (ZnO), and sulfur (S) in analytical grades were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All the other chemicals including N-1,3-dimethylbutyl-N′-phenyl-P-phenylenediamine (antioxidant 4020), poly(1,2-dihydro-2,2,4-trimethyl-quinoline) (antioxidant RD), wax, N-tertbutylbenzothiazole-2-sulphenamide (accelerator NS), dicumyl peroxide (DCP, 98%), and aromatic hydrocarbon oil (DAE) in chemical grade were supplied by Beijing Chemical Works. (Beijing, China) and used without further purification.

The raw chemicals and solvents used in the experiment were analytical reagents without further purification: Cobalt Nitrate (Co(NO₃)2·6H₂O, Sigma-Aldrich LLC, Shanghai, China), Sodium thiosulfate (Na₂S₂O₃·5H₂O, Sigma-Aldrich LLC.), Iron disulfide (FeS₂, Sigma-Aldrich LLC.), Sulfur (S, Sinopharm Chemical Reagent Co., Ltd., Shanghai, China).