Apart from brittle and cheap shaped polystyrene, two types of clear plastics can readily be polished and repaired. Decorative and functional items, such as jewelry boxes, ornaments, smart-phone displays and laptop cases, are usually made from acrylic due to its impressive high gloss and texture; this type of plastic isn’t hard to polish. On the other hand, tough impact-resistant things like industrial face guards, windshields and riot shields are made from polycarbonate. This type lacks the sparkle and clarity of acrylic and requires specialized polishing processes.
Acrylic Edge Scratches
Before removing scratches and noticed marks in the cut edge of sheet acrylic plastic using the flame-polishing method, make sure it is not polycarbonate by looking at the edge. Clear acrylic sheeting includes a mild gray edge, whereas polycarbonate has a different dark edge.
Unfinished sheet acrylic edges can be blended in with a flashlight that burns stabilized methylacetylene-propadiene, or MAPP, a hot, burning gasoline. Find a MAPP torch, not a lower temperature propane torch, in a hardware store. Light the torch and operate the fire fairly slowly through the cut edge. Keep the fire moving to avoid melting more. As you do that, the fire will melt the narrow surface, leaving a glistening finish with some saw marks visible.
To achieve a perfect end, cut the sheet slightly oversized with a band saw or seat saw. Then cut down the sheet to its finished size by trimming the edge with a router; this will also get rid of the unpleasant saw marks. Stand the sheet vertical and sand the cut edge smooth using a rotary power sander fitted using 320 grit sandpaper to remove the machine marks; use a sanding block if you do not have a power sander.
Flame-polish the edge as described previously. Or buff the borders on a buffing wheel fitted into a high-speed seat grinder, using moderate pressure and two or three passes to achieve a perfect end.
Polycarbonate Edge Scratches
Don’t attempt to flame-polish the cut edge on transparent polycarbonate sheeting; this substance will burn because it melts at a significantly lower temperature.
Ready the sheet as described in the prior Step 3. Because polycarbonate is softer than acrylic, sand the edge smooth using 320 grit sandpaper and a sanding block rather than using a power sander.
Buff the edge on a high-speed buffing wheel to reach the best finish possible. Use a gentle touch, as polycarbonate is relatively soft.
Wear rubber gloves and then employ acrylic cement into a fresh rag. Wipe the damp rag throughout the edge of trimmed polycarbonate sheeting to employ a shiny finish and to remove surface scratches. This method does not work on sheeting.
Use a buffing wheel mounted on a high-speed seat grinder to buff light scratches on both the acrylic and polycarbonate plastic. Utilize an extra-light touch on polycarbonate; friction from too much stress will damage the material by massaging the surface.
Polish surface scratches using a technical three-step polishing compound like Novus Plastic Polish, which is available online. Run your fingernail throughout the scratch prior to starting. If your nail catches, the scrape is too heavy to shine using this technique.
Start with coarse No. 3 compound on acrylic. Apply compound to a fresh rag and polish vigorously till the scratch disappears, leaving a slightly matte finish. Wash the surface and then use a second wash rag and less abrasive No. two compound to replace the matte finish. Finally, wash the surface and buff to a high gloss using the least abrasive No. 1 compound and a clean rag. As it is softer, begin with No. 2 compound when polishing polycarbonate.