Slightly off-topic, but for polypropylene nose cones I wet-sand (little bit of Dawn in the water) thoroughly with 320 wet/dry paper, rinse thoroughly with water followed by isopropyl alcohol, 91% or the pure stuff, not 70%. I hang the nosecone upside down and use a dropper to apply the isopropanol, allowing it to run down to the tip where a paper towel can remove any remaining alcohol.
Once the alcohol has
completely evaporated and the vapor has dispersed, a propane torch is run quickly over the entire surface---it generates reactive species that hold the paint better. Paint as soon as possible after the torch.
And if the nose has been held while painting by sliding it into a piece of tubing, don't remove it from the tubing till it's well-cured. Otherwise you can get this:
Gripped painted cone, twisted it (it was a tight fit in the tubing). Lovely fingerprints.
