Development of expandable graphite reinforced acrylonitrile butadiene rubber composites and investigation of the properties

Acrylonitrile butadiene rubber (NBR) is a unique synthetic rubber widely used in the production of sealing elements such as gaskets and O-rings, especially in the automotive industry, due to its superior performance properties such as resistance to mineral oils, vegetable oils, petroleum, and various chemicals. Also, its ability to withstand extremely harsh operating conditions makes NBR an ideal material. However, NBR is a flammable material with a low limiting oxygen index (LOI) value. Expandable graphite (EG), a halogen-free mineral-based flame retardant, expands and forms a protective and gas-impermeable barrier layer, reducing the flammability of materials, and it is known as a sustainable and environmentally friendly material in terms of smoke reduction and prevention of toxic gas formation. In this study, various NBR rubber composites were prepared by simple two-stage blending method using carbon black as a reinforcing filler and expandable graphite as a flame-retardant filler. By keeping the main NBR rubber preparation procedure constant, the effect of 2, 4, 8, 10 and 20 phr EG addition on the material properties of NBR-based rubber composites was investigated in a versatile way. After determining the rheological properties, tensile strength, elongation at break, permanent deformation, hardness and density of NBR rubber composites, the flammability properties of the composites were investigated with the LOI and UL-94 horizontal combustion test. In addition, changes in hardness, tensile strength, elongation at break and weight loss values before and after aging tests were examined to determine their thermal oxidative properties against air, thermal aging properties against motor oil and their resistance to various solvents.