I’m glad you posted this, as I have been reading more about it lately.
There are quite a few PW sites that that talk about oxidation, and several claiming that if left on the siding it actually causes damage. That part is somewhat suspect. I haven’t run into anything difinitive. It appears, from my limited understanding, that once it starts happening it is going to continuously occur, as it (PVC) has already begun to degrade. How long does it take to fully degrade, apparently it varies significantly based on too many variables from the manufacturing process to the application of any stabilizers (my term), but once it starts to occur the PVC will (my words here) become more brittle over time.
As it stands now, what I tell all my customers is this: It occurs due to the UV radiation, the PVC and oxygen reacting with one another (I don’t get more detailed). I tell them that if they want it removed it can be removed, but it will come back. I also tell them that it requires a lot of work and it is a little on the pricey side. I also usually show them the oxidation as I do in person estimates. Since you do a lot of volume, and are probably an online booker, I don’t know how you would approach that. I guess you could tell them (if they wanted to check) to go to the southern side or east side (depending on how their home is oriented) and wipe their hand on it. As you know, the darker shutters is where they would see it the easiest.
If any of my customers ask for more info, I direct them to this page and tell them to read number 14 and 15. Photostabilization of poly(vinyl chloride) – Still on the run - ScienceDirect I haven’t looked for another source of information since I found this one.
If you want to know how to fix it, so that it doesn’t degrade further, well, you will be rich. Here are the methods currently available from what I have read, but I haven’t read about any type of application, as this is largely in the production stage.
The photostabilization of polymers may be achieved in many ways. The following stabilizing systems have been developed, which depend on the action of stabilizer: light screeners, UV absorbers, excited state quenchers, peroxide decomposers and free radical scavengers, of these it is generally believed that excited state quenchers, peroxide decomposers and free radical scavengers are the most effective
I’m no scientist, just a guy with a keyboard and a curious monkey mind.
Good luck to you. If you run across anything that talks about oxidation removal increasing the longevity of the PVC, I would love to read it.