Effect of phthalate-free plasticizer addition on thermal, mechanical, and aging properties of nitrile rubber (NBR)

Abstract

Nitrile rubber (NBR) is widely used in the automotive, aerospace, and chemical sectors due to its resistance to fuels, oil, thermal aging, and fatigue. A typical NBR compound is prepared with several components that are added to obtain a product to meet specific industry requirements. Plasticizer is one of the main components used in NBR compounds. Typically, phthalates like DBP (dibutyl phthalate) or DOP (dioctyl phthalate) are used for NBR plasticization. However, these phthalates-based plasticizers are associated with toxicity and often prohibited by international regulatory standards. In this way, in the pursuit of a non-toxic NBR compound, the use of phthalate-free plasticizer, namely dioctyl terephthalate (DOTP), has been proposed. In this work, NBR compounds with DOTP, DBP, or DOP were processed in an open mill and vulcanized in hydraulic press. The unvulcanized samples were tested in a moving die rheometer (MDR). Subsequently, thermal, mechanical, and aging analyses were conducted for the vulcanized samples. The lowest torque observed in the rheometric curve, the displacement value of glass transition temperature (Tg), the smaller Shore A hardness, and the high elongation at break indicate that the addition of DOTP results in higher plasticization. The better-aging properties indicate lower migration of the DOTP plasticizer. Thus, the use of DOTP as a plasticizer holds promise as a viable alternative to replace the phthalates-based plasticizer in NBR compounds.