How and why does black plastic fade?
The main ingredient in plastic is a derivative from crude oil, so it’s no surprise that all plastics contain lots of oil. The fading or chalking that you see is from the plastic drying out over time. Without getting too scientific, when UV rays are absorbed by plastic, the UV energy excites photos which can create free radicals and degradation occurs from the free radicals causing breaks in the polymer structure.
The reason your plastic trim pieces are more susceptible to this damage is they do not have a layer of UV inhibiting clear coat as your paint, wheels, and headlights do. This means that every plastic piece will inevitably fade, crack, and dry out unless protected. Now that we know how this process works, we have the knowledge to not only prevent it but to fix it.
So What should we do?