Examining the impact from incorporation of fatty acid in nitrile-based synthetic rubber: film properties and biodegradability

Adverse environmental impacts from the increasing volume of synthetic rubber waste and the overexploitation of fossil fuels have heightened the awareness on sustainability in the synthetic rubber industry. The current use of synthetic rubbers is not sustainable, as they are primarily produced from fossil-derived monomers, are non-biodegradable, and are difficult to recycle. In this study, poly(isoprene-co-acrylonitrile) incorporated with oleic acid (XNIR OL) was synthesized using free radical emulsion polymerization. Oleic acid, a prevalent fatty acid in various vegetable oils, was used in the XNIR OL formulation instead of the typical fossil-derived acids found in carboxylated nitrile rubber. The incorporation of oleic acid in the synthetic rubber was confirmed through spectroscopic analyses and acid value test. Characterizations were conducted on the rubber film to investigate the effects of oleic acid incorporation on the mechanical properties, thermal properties, oil resistance and biodegradability. The vulcanized XNIR OL film exhibited rubbery behaviour at ambient temperature, with a glass transition temperature of − 21.9 °C and satisfactory thermal stability. XNIR OL demonstrated an elongation at break of 379% but subpar tensile strength of 0.53 MPa, attributed to the presence of bulky oleic acid pendant groups. Conversely, XNIR OL showed less than 5% swelling in mineral oil, indicating that the incorporation of 5 mol% oleic acid did not adversely affect its superior oil resistance. Additionally, XNIR OL exhibited significantly improved biodegradability, with a 28.2% mass loss after 180 days of soil burial, a level comparable to natural rubber.