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Assuming they’re polyester or nylon, and no cotton nor silk, then yes, generic oxiclean (dollar store) works with a bit of clear dish detergent as a surfactant.
I would soak in oxygen bleach according to the package directions. If the curtains are heavily stained, use twice the recommended amount. You may also add 1/2 cup of one of the following: vinegar, lemon juice, borax, washing soda, baking soda or hydrogen peroxide and then wash on gentle cycle in machine.
I use a little Tide and vinegar soak to wash them first then fill your basin with cool water and several drops of MRS. STEWART’S liquid bluing (follow instructions on bottle). It brings them back to bright whiteness but don’t ever add the curtains until you’ve mixed the blue drops in VERY WELL.
Soak them in Oxy Clean and then wash in cold water on the gentle cycle in your washing machine.