MECHANODESTRUCTION OF ISOPRENE RUBBER. PART 3. KINETICS OF OXIDATIVE DESTRUCTION

Continuation of studies of changes in molecular parameters, in particular, the molecular weight (MM) during the plasticization (P) of SKI-3 isoprene rubber. The kinetics of oxidative destruction (OD) in the temperature range (T) 30-130 °C and time (t) 30–600 s were studied in detail. Plasticization of rubber, as before, was carried out in a laboratory rubber mixer of the company «NFM», and gel chromatographic studies were carried out on a gel chromatograph of the company «Waters». The speed constant OD K0 decreases in absolute value with a decrease in T and an increase in t. The calculated effective activation energy of OD Eeff decreases from 24,4 to 13 kJ/mol in the studied t range. The influence of the oxygen diffusion process on the kinetic features of the OD of SKI-3 at Р is pointed out.

COMPARISON OF THE PROPERTIES OF TREAD RUBBER FOR WHOLE WITH METAL CORD HEAVY-DUTY TIRES BASED ON NR AND ON SYNTHETIC POLYISOPRENE SKI-3 OF VARIOUS BRANDS

Technological properties of rubber compounds as well as viscous-elastic and strength properties of the tread rubber for heavy-duty tires whole with metal cord (MCT), based on blends of natural (NR) or synthetic polyisoprene of various trade marks (more than 80 %) and polybutadiene (more than 10 %) were studied. The new processing aid (PA), worked out in LLC «NPP QUALITET» under registered trade mark KVALISTROL® A100, was suggested instead of importing analogous of PA Polyplastol 6 type. It was established that replacement of NR in MCT formulation by the SKI-3S rubber produced with the use of a new anti-agglomerator of a crumb of KVANTISLIP® of the BM-2R, PA A100 brand, increased dosage of sulfur-accelerated group and the corrected dosage of the vulcanization inhibiter Santogard PVI and together with the worked out mixing mode at a stage of production of masterbatch allows to receive rubber compound close to reference on the basis of the NR on viscosity. At the same time the new rubber compound's strength and elastic properties practically don't differ, and in the lowered values of a hysteresis, surpass reference rubber compound with NR use.

Mechanodestruction of Isoprene Rubber. Part 1. Process Kinetics

A method is proposed that allows us to obtain the values of the rate constants (CR) of the processes of mechanodestruction (mechanical cracking) of kм, oxidative destruction of kо, and recombination of kр macromolecules, as well as the mass fractions of the corresponding fractions of φм, φо, and φр,r involved in the plasticization process (P) of SKI-3 isoprene rubber. The method is based on the selection of the values of these parameters that correspond to the previously obtained experimental data, using the previously obtained recurrent equations and a specially developed program. The dependences of the CR on the time P at 30oC are obtained, which allows us to describe the kinetics of the processes accompanying P at this temperature, and the changes in molecular mass (MM) in this process. It is shown that constant values of CR are established at large times of P. Refined explanations of the nature of the kinetics of the CR change at P are proposed. The MM value of SKI-3 macromolecules that have not undergone destruction is calculated, depending on the time of plasticization.

Comparative Assessment of Ozone and Weather Aging of Rubber by Laboratory and Field Testing Conditions

The authors compared the results of determining the ozone resistance (OR) and weather resistance (WR) obtained in laboratory and natural conditions of tropical climate. The samples were manufactured with unsaturated rubbers (nitrile butadiene rubbers BNKS-18AN, BNKS-28AN, BNKS-40AN and SKN-26PVC-30, styrene butadiene rubber SKMS-30 ARKM, isoprene SKI-3 and butadiene SKD-ND). All the samples were not filled with antioxidants or antiozonants. The curing process at 160 °C and the total crosslink density (νt) were studied using a MonTech MDR 3000 Professional rotorless rheometer. The physical and mechanical properties of the vulcanizates were determined with the using of a Zwick\Roell Z010 tensile testing machine at a test speed of 500 mm / min. Hardness and tear resistance were also determined. The numerical estimate of νt was obtained from the data on the dynamic shear modulus. Density of chemical bonds νch was determined from the data of equilibrium swelling in toluene according to the Flory-Rener equation. Full-scale climatic tests in tropical climate in the south of the Republic of Vietnam were carried out for 9 months in accordance with GOST 9.066-76 with initial deformations of 10, 20, 30, 40 %. The sample stand was oriented south, at a 45 degree angle. Cracks formed on the rubber surface were recorded by photography. The time before the onset of fracture Tof and the time until the appearance of the first cracks Tfc were determined. It is shown that samples of rubbers with high OR in laboratory tests had the best WR. A correlation of νch with Tof and Tfc was revealed. The obtained results show the possibility of using the express method for assessing the OR of rubbers in the development of formulations for tropical climates.

Results «Tires & Rubber-2021»

Post Show Report of 23-rd International Exhibition for Rubber Goods, Tires, Their Production, Raw Materials and Equipment. «Tires & Rubber» (Moscow, Expocenter, 2021, April).