Plastic furniture is most often found in the form of chairs and tables on patios and other places where the elements quickly wear out or ruin wooden furniture. Frequently made of polyethylene and polypropylene, plastic furniture is waterproof, lightweight, durable at a wide range of outdoor temperatures and resistant to damage from ultraviolet light in sunshine.
Unfortunately, however, both classes of plastics scratch easily, so stiff brushes of any kind, gritty cleansers or abrasive pads aren’t recommended cleaning tools. Remember, scratches increase surface area and roughness, making future cleaning increasingly difficult.
The garden hose is the best tool for removing accumulated dust and dirt. Soak the furniture well; use a sponge or soft cloth to dry, which will help prevent spotting from hard water and new deposits of dust. Folks who don’t have a garden hose may be able to substitute a shower enclosure or bathtub to clean smaller pieces, such as chairs and end tables. Once clean and dry, apply automotive wax to protect smooth plastic surfaces and make them more soil resistant.
To remove food stains or greasy spots, apply a solution of water and liquid dishwashing detergent to plastic furniture with a sponge, damp cloth or a soft-bristle nylon brush (gently); soak the spot well and allow the detergent to work for a few minutes. Re-apply more detergent and scrub gently. Rinse well with a garden hose and dry completely.
Spots and stains that remain after washing — particularly the fiendish grime that seems all but unreachable on those rough, no-skid surfaces on plastic side tables — call for stronger measures. Solvents such as alcohol and acetone can be applied to these plastics by cloth or soft brush. Wipe until all residue is gone. Both solvents are flammable and hazardous to breathe, so use them in a well-ventilated area. Wear protective gloves while working with acetone.
Reference:
Jeff Bredenberg, editor, in Clean It Fast, Clean It Right: The Ultimate Guide to Making Everything You Own Sparkle & Shine.