Investigation of thermal aging of styrene butadiene rubber/ethylene propylene diene monomer blends

Rubber is one of the most important material in industry. It has significantly high elasticity and durability, good tear and abrasion resistance and low deformation. Having the structure which can return to original size and dimension when force is removed is the main distinctive characteristic from thermoplastics. Rubber is used in many vehicles and equipment such as automobile sector hose, door and glass seals, bonding solutions, windshield wipers, seals and conveyor belts in daily life. Styrene-butadiene rubber (SBR) is a type of synthetic rubber and it represents half of all synthetic rubber production. The most important properties of SBR is the mechanical properties. EPDM is a rubber has high mechanical properties, resistance against thermal, ozone and polar solvents. Blending is the common favored method that is used to improve properties of rubbers. Blend is defined as physical mixture of at least two different polymers without any chemical bonding. As a result of this method, the product has developed thermal and mechanical properties and can be produced with low cost. In this study, ethylene propylene diene monomer (EPDM) and styrene butadiene rubber (SBR) were blended prepared with different ratios and their properties were investigated. Two types of EPDM (EPDM 4460, EPDM 4465) were used in study. Compounds were prepared in laboratory type banbury and two roll mill, respectively. The curing time and curing characteristics of compounds were obtained by using moving die rheometer at 150 oC. Differential Scanning Calorimeter (DSC) was used determine glass transition (Tg) and curing peak (Tp) temperatures of compounds Curing times of rubber compounds did not change significantly. Minimum viscosity (ML), maximum torque value (MH) were affected by amount of SBR used in blends. All compounds were cured at hydraulic hot press at 150 oC for pre-determined curing times. Blends which were suitable for international test standards were treated at 125 oC for 168 h in hot-aging oven. After thermal aging, mechanical properties of blends (tensile strength, elongation at break) were obtained with a tensile test machine. Mechanical properties exhibited some differences depending on amount of SBR used in blends. Hardness values were measured by using a Shore A type durometer. Abrasion resistances were evaluated with abrasion resistance machine according to international standards. Hardness value of blends increased with increasing amount of SBR in blends. It has also been observed that the SBR rich blends showed low abrasion resistance.