There is a general principle describing the fact of swelling of the
elastomer in biodiesel, which is ‘‘like dissolves like’’. The polar substances
in elastomer are more likely to dissolve in polar solvents,
while the non-polar substances are more easily to dissolve in
non-polar solvents [16]. As mentioned above, NBR is a synthetic
rubber copolymer of acrylonitrile and butadiene, which is a polar
substance, thus, NBR samples when immersed in a solvent like biodiesel
tend to swell or degrade. The polar part of biodiesel (present
in esters) interacts with the polar part of NBR through dipole–
dipole interaction, and causes it to swell [17]. The degree of
dipole–dipole interaction in biodiesel for NBR seems to be stronger
than that of diesel fuel, because of the increased polarity of fatty
acid esters