I wear Dickies t shirts at work. I often get grease or oil stains on them. I pretreat with Spray&Wash, let it sit while another load finishes, then wash. The oil stains will still be visible, but running through the wash again won't fix it unless I dry them first, then run the load.
Why?
That is contrary to my experience.
For me, if I don't get the stain entirely out before I dry the clothing, then it is never going away.
I will say that a 5-minute soak in Pine-Sol before washing will get even stubborn grease stains out.
Pretreat with hand cleaner (no pumice or scrubbers) works good for getting oil and grease out the first wash.
Spot treat and wash with some dawn helps as well. Agreed on if you do heated dry it's much harder to get out. If questionable washing, line dry.
You seeing the opposite is a little odd. If you are using a heated dry it may be baking off low molecular weight stuff that the wash can't get to. Heavier molecules the heat won't do a thing and actually lock it harder into the fibers.
Not a chemist or a physicist.
But I do remember some of high school science class. Not sure if this is what is going on, but doesn't heat tend to alter the structure of big molecules? Maybe something like that makes them more susceptible to solvents later?
Not really a chemist, but brewing school covered a fair amount of the chemistry of lipids, surfactants, and cleaning/sanitizing.
There's a strong possibility this has to do with the fibers used in the shirts. What kinds of shirts? What material are they made from? 100% cotton t-shirts? Are these the poly-blend work-shirts?
Different materials hold water and oils differently. E.g. Microfiber wicks water away, but holds onto oils.
My guess is this is something to do with fibers changing their orientation in drying bringing the oils to the surface instead of being trapped inside. Then when washing, the surfactants in the detergent are better able to get to and lift away the oil.
Or could be to do with the heat used changing the structure of the lipids, but I think that's unlikely with a motor oil which is formulated to remain stable in the temperatures of a hot car engine.
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