Just because something can be made out of plastic, doesn't mean it should be.
Go check out any uber-high end camera and see how much plastic they have chosen to use.
Lens for cameras and glasses can be made out of plastics (I use the term for any polycarbonate based material). Barring shock/impact resistance for shrapnel type applications, I'd rather have glass, even though it is heavier to use.
Sadly, most plastics lose their good properties if mixed with other types. PVC house pipes use to have recycled material until homeowners found out that the recycled material acted only as a filler, not as a structural bonding molecular unit. The filler reduced the amount of high dollar material and made a structurally inferior tube.
You want long term structural stability? Steel
Worried about rust? High Chromium Steel
Low weight? Aluminum
Strength/Weight Ratio? Titanium
Money not as important? Magnesium
Money really not important and weight super important? Beryllium (very brittle and can be poisonous to machine)
Composites have made tremendous inroads and can be tailored, but the initial design costs and high material cost for the really nice compounds, along with toxic outgassing cause their own problems.
The best line from "The Graduate" (1967):