... the easiest way to 'whiten' a clear plastic is to paint it white or to inject/create microscopic air-bubbles in the surface.
This 'foaming' could be achieved with a laser, that heats the surface to boiling but without cracking the polymer, or it will get yellow/brownish because of carbonizing - this can be made either with ultra-short pulses with a CO2-laser or with an UV-laser with a short enough wavelength, so it won't penetrate the clear body.
Another trick could be chemistry, where a solvent reacts with the polymer to create a micro-foam in the surface region ...
Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [
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www.facebook.com]
Call for the project "garbage-free seas" - [
reprap.org]