A belt sander. Use a very very used belt, 150 or 180 grit. Best to mount the sander in a vice upside down and make light passes. Too easy to mess up. A shop with a belt grinder can do the same for you (not stone grind obivuously). Again, it's just not worth the trouble, just use a brass brush.
So my recollection is this: since the late 90s all commercially available ptex has polymer stabilizers added that suppress oxidation. Better quality ptex is provided with even more antioxidants, with the addition of other compounds that provide UV protection, repel water or enhance wax retention. Also many base materials are manufactured with processes designed to reduce oxidation. But if I remember correctly, some bases are infused with paraffins and other hydrocarbons that are themselves subject to oxidation, but it is not the base material itself. That's not disqualifying that poor quality ptex is out there suffering from severe oxidation and mechanical degradation, but I doubt it's something that would be met on equipment that uses a ptex topsheet.