CHEMICAL RESISTANCE OF HNBR AND NBR IN PROPYLENE

ABSTRACT The chemical resistance of HNBR and NBR in propylene is considered as no resistance by many chemical compatibility handbooks and industry chemical resistance tables and charts. This situation drives the change of the elastomer compounds from cheap HNBR/NBR to expensive fluoroelastomer for applications involving propylene. However, in the literature, NBR and HNBR are rated as having good or excellent chemical resistance to all other hydrocarbons, such as ethylene, ethane, propane, butane, and butylene. It seems that there are some special or unknown characteristics of propylene that make it very harsh to both NBR and HNBR; therefore, it is important to investigate the chemical resistance of NBR and HNBR in propylene. In this study, the chemical resistance of HNBR and NBR in propylene is investigated according to ISO 23936-2 and ASTM Standard D 471. The test results are crucial for the applications of HNBR/NBR in contact with propylene. Based on the tests, we investigated tensile property changes, volume changes, and glass transition temperatures and chemical structures of HNBR/NBR after aging in high-pressure propylene at an elevated temperature. The Hansen solubility parameters (HSPs) of HNBR and NBR and many hydrocarbons such as ethylene, ethane, propylene, propane, butane, and butylene were estimated. Based on the HSP, the polymer–solvent interaction parameters between HNBR/NBR and hydrocarbons were also estimated to explain the chemical resistance of HNBR/NBR in propylene. An aging mechanism was proposed to explain the changes of HNBR and NBR in propylene aging. This study enhanced guidance on chemical resistance of HNBR/NBR in propylene to the elastomer industry.