Back when I was a youngster coming up in the trade, cleaning acrylic was the last step before back-spraying a lighted sign face with translucent paints. For cleaning, and removing static, we always used alcohol cut with water, roughly 2 to 1, just like the "rubbing alcohol" used in hospitals as a disinfectant, which is isopropyl alcohol mixed with purified water. Isopropyl alcohol (isopropanol) is the least toxic of all the alcohols except ethanol. "Denatured" alcohol, sold in hardware stores, is simply ethanol that has been mixed with something to make it poisonous, rendering it undrinkable. Often the added ingredient is methanol, a very toxic alcohol. Methanol is the simplest of the alcohols, and it is cheap, commonly used as an engine fuel in race cars, and, unlike ethanol and isopropanol, it is miscible in both oil and water, but it is highly toxic so it is commonly added in small amounts to ethanol to "denature" it, making it useless for anything except as a cleaner.
We were taught to always add water to the alcohol when wiping down acrylic—it cleans better. I never understood why till I worked as a janitor. Water is considered the "universal solvent." It dissolves and cleans more substances than any other liquid. In the early 3M technical bulletins for cleaning surfaces prior to applying vinyl, a final wipe with isopropanol/water was recommended as the final step.
But the real secret to cleaning acrylic without introducing static is to use a chamois. A rag or cloth will always add static when rubbing. A chamois does not.
Also, about flame-polishing: it introduces micro-fissures in the plastic—thousands of tiny invisible cracks. So when you hit them with a fast-evaporating solvent, the cracks can expand and become visible.
Brad in Kansas City
