Elastomer solubility and stress relaxation in bio-lubricants

This study presents novel results from in-situ stress relaxation tests using rubber O-ring seals immersed in bio-lubricant base oils (jojoba, soybean and palm oil), with a mineral base oil used for comparison. Little information is available on the interaction of bi-lubricants and elastomers. The use of Hanson Solubility Parameter modelling methods was considered for assessing compatibility. Some correlation was found between experimental results for EPDM. Results were inconclusive for NBR and FKM. EPDM immersed in palm and soybean oil suffered minor shrinkage, caused by stress relaxation. Swelling occurred with EPDM immersed in jojoba and mineral base oil, caused by diffusion. Results for nitrile showed shrinkage for all oils. Less than 1% change in mass occurred for all oils and FKM