I have just had the following back from Steve
"In principle I could do analogous experiments, but I don?t see a need.
"There is a reference book called the Polymer Handbook (ed. Brandrup & Immergut, pulished by Wiley-Interscience) which, among other things, lists solvents and non-solvents for thousands of polymers based on years of experimental data.
"For Nylon-6/Nylon-6,6 it lists (amongst many ? what follows it a bit of a generalisation):
SOLVENTS: phenols/cresols, methyl alcohol (methanol), diols/glycols, and most importantly, acids (any);
NON-SOLVENTS: hydrocarbons, aliphatic alcohols (so ethyl alcohol/ethanol, and higher homologues), chloroform, ethers, esters & ketones
"So on this information; keep your ropes away from coal tar products, creosote, antifreeze, meths, battery acid, even ant killer! But mineral oils or beer (or petrol ? what was that chap doing?!!!) shouldn?t be a problem, per se, though I agree with your point about the trapping of grit. Also remember that they use oils to reduce friction in the factory when spinning the yarns, and some of this will transfer to the fibres. Presumably they wouldn?t if it was harmful!
"There has been some work in the States looking at the effect of automatic transmission fluid on nylon. Wikipedia describes ATF as a ?highly-refined mineral oil?. That study saw some effects but ascribed them more to physical side-effects rather than chemical degradation (so not unlike the effect of plain water on nylon)."