2 mercaptobenzothiazole

(±)-α-Tocopherol, Methyl Viologen dichloride hydrate, DMEM 1 g/L glucose, Penicillin–Streptomycin Solution Hybri-Max (P/S), Fetal Bovine Serum (FBS), L-glutamine (L-Glut), 2-mercaptobenzothiazole, and 1,5-diaminonaphthalene, trypan-blue were purchased from Sigma-Aldrich (Saint Louis, MI, USA).

SBR (KER 1500) rubber containing 23.5% bonded styrene was obtained from Synthos SA (Oswiecim, Poland). Its Mooney viscosity was ML1+4 (100 °C): 50. SBR rubber was cured using a conventional curing system containing sulfur (Siarkopol, Tarnobrzeg, Poland) in the presence of 2-mercaptobenzothiazole (MBT) and N-cyclohexyl-2-benzothiazolesulfenamide (CBS) as accelerators (Sigma-Aldrich, Schelldorf, Germany). Microsized zinc oxide (ZnO) with a specific surface area of 10 m²·g⁻¹ (Huta Bedzin, Bedzin, Poland) was applied as activator only for the reference rubber compound. Organic zinc salts and complexes, i.e., GluZn with melting point M_p 175 °C (Merck, Darmstadt, Germany), RicZn with M_p 89 °C (Evonik Industries, Essen, Germany) and AAcZn with M_p 177 °C (Riedel-de Haën, Seelze, Germany) were used as alternative vulcanization activators to ZnO. Carbon black N550 provided by Brenntag Polska (Kedzierzyn-Kozle, Poland) was used as a filler. The structures of applied organic zinc activators are presented in Scheme 1, Scheme 2 and Scheme 3.

Styrene-butadiene rubber (SBR, KER 1500 type) was provided by Synthos SA (Oswiecim, Poland). It contains 23.5 wt.% of bonded styrene and exhibits the Mooney viscosity of ML1 + 4 (100 °C): 50. A conventional curing system containing sulfur as curing agent (Siarkopol, Tarnobrzeg, Poland) in the presence of two vulcanization accelerators, i.e., 2-mercaptobenzothiazole (MBT) and N-cyclohexyl-2-benzothiazolesulfenamide (CBS) (Sigma-Aldrich, Schelldorf, Germany) was applied for all rubber compounds. Microsized zinc oxide (M-ZnO) with a specific surface area of 10 m²·g⁻¹ (Huta Bedzin, Bedzin, Poland) was applied as standard activator only for the reference rubber compound. Zinc oxide nanopowder (N-ZnO) with a specific surface area of 25 m² g⁻¹ (Sigma-Aldrich, Schelldorf, Germany) and zinc complexes with 1–3-diketones were used as alternative vulcanization activators to reduce the content of zinc in rubber compounds as compared to M-ZnO. The procedure for the synthesis of zinc complexes from commercially available 1,3-diketones has been previously published [31 (link)]. Carbon black N550 supplied by Konimpex (Konin, Poland) was used as a filler. It was characterized by the surface area of 40 m²·g⁻¹ and pH in the range of 7–10. The structures of the zinc complexes employed as vulcanization activators are shown in Figure 1, Figure 2, Figure 3 and Figure 4.

MeHgCl, tiourea, 2-mercaptobenzimidazole (MBI), 2-mercaptobenzothiazole (MBT), acrylic acid (AA), ethylene glycol dimethacrylate (EGDMA) and azodiisobutyronitrile (AIBN) were purchased from Sigma-Aldrich (St. Louis, MO, USA); ethanol (EtOH) absolute (99.9%) was obtained from JT Baker (Radnor, PA, USA); MeHgCl standard solution 1000 mg L⁻¹ from Alfa Aesar (Tewksbury, MA, USA); and hydrochloric acid (HCl), sodium acetate (NaCH₃COO), acetic acid (CH₃COOH), sodium hydrogen phosphate (Na₂HPO₄), sodium dihydrogen phosphate (NaH₂PO₄), sodium hydroxide (NaOH), and sodium tetraborate (Na₂B₄O₇) were purchased from Merck (Darmstadt, Germany);. For the selectivity study, solutions were prepared from salt standards of lead nitrate, cadmium nitrate tetrahydrate, zinc sulfate monohydrate, and mercury dichloride (all acquired form Sigma-Aldrich). All the reagents used in this work were of analytical grade, and the solutions were prepared in ultrapure water (resistivity of 18.2 MΩ cm).
The samples were collected from the Batalha river (21.72 S, 49.20 W), and directly from the tap.
WARNING: MeHgCl appears as white microcrystals and is very toxic by inhalation, in contact with skin and if swallowed. Protection measures such as glasses, full face-shields, gloves and particulate respirators are required to manipulate it. Its disposal should also be carried out carefully.

Field natural rubber latex was obtained from the RRIM 600 clonal variety of rubber trees, in a rubber plantation located in Surat Thani province, Thailand. The chemicals for filler dispersion and bentonite were supplied by the BASF Company (Rhineland-Palatinate, Ludwigshafen, Germany). Vultamol, used as dispersant, was produced by S&B minerals GmbH (Kifissia, Athens, Greece). Chemicals for the determination of dirt content, 2-mercaptobenzothiazole and turpentine oil, were produced by Merck KGaA (Darmstadt, Germany) and Vidhyasom CO., Ltd (Phra Nakhon, Bangkok, Thailand), respectively. In addition, boric acid, sulfuric acid (H₂SO₄), and potassium sulfate (K₂SO₄), used to analyze nitrogen content, were manufactured by Merck KGaA (Darmstadt, Germany). The copper (II) sulfate (CuSO₄) was obtained from VWR (Fontenay-sous-Bois, France).

Tetraethyl orthosilicate (TEOS), cyclohexane, 1-penthanol, Cetylpyridinium Bromide hydrate (CPB), urea, 1H-benzotriazole (BTA), 2-Mercaptobenzothiazole (MBT), 3-Aminopropyl triethoxysilane (3-APTES), toluene anhydrous, ethanol, and water were purchased from Merck S.r.l. (Merck Life Science srl, Milan, Italy).