The effect of ureas and their sulfur and selenium-containing analogs on the vulcanization and thermo-oxidative resistance of elastomers based on nitrile butadiene rubber

Objectives. The study set out to investigate the effect of ureas and their sulfur- and selenium-containing analogs on the vulcanization of elastomeric materials based on nitrile butadiene rubber and their resistance to thermo-oxidative aging. Methods. The properties of the molecules of ureas under study were calculated by the MM+ quantum chemical method of molecular mechanics and PM3 semiempirical method using the HyperChem 8.0 software. Vulcanization of rubbers and total crosslink density were studied using the rotorless vulcanization method with a MonTech MDR 3000 Professional rheometer. The dynamic characteristics of vulcanized rubbers were investigated in accordance with ASTM D6601-02 and D5992-96 standards. The efficiency of the studied antioxidants against thermo-oxidative aging was evaluated in accordance with GOST 9.024-74. Infrared (IR) spectra of samples were recorded with an FT-801 Fourier-transform IR spectrometer (Russia) according to the attenuated total reflection method. Results. For the first time, a study was conducted on the efficiency of 1-(3-chlorophenyl)-3-phenylurea, 1-(3-chlorophenyl)-3-phenylthiourea, and 1-(3-fluorophenyl)-3-phenylselenourea as antioxidants for elastomers under conditions of thermo-oxidative aging. The effect of these substances on the vulcanization characteristics and total crosslink density of materials based on nitrile butadiene rubber was investigated. Conclusions. The values of electron affinity energy and its sign were shown to accurately predict the possibility of using individual molecules as accelerators of the vulcanization process or antioxidants. With a change in the electron affinity energy from 0.051 (urea) to −1.115 (thiourea) and −1.365 eV (selenourea), the time to the start of vulcanization was shown to change from 15 to 3 and 2 min, respectively. As a result of thermo-oxidative aging of rubbers based on BNKS-28 AN rubber without a stabilizer and with 1-(3-chlorophenyl)-3-phenylurea, 1-(3-chlorophenyl)-3-phenylthiourea, and 1-(3-fluorophenyl)-3-phenylselenourea, the total crosslink density changes by 33 %, 23 %, 25 %, and 29 %, respectively. In this connection, the use of 1-(3-chlorophenyl)-3-phenylurea somewhat improves the stability of rubbers to thermo-oxidative aging, whereas 1-(3-chlorophenyl)-3-phenylthiourea and 1-(3-fluorophenyl)-3-phenylselenourea do not worsen this property when introduced into the rubber compound.