Eventually we all get them on the interior plastic panels, from scuffs to deep scratches, especially in the trunk and at the bottom of the front door panels.
From a Google search I found a number of things that others have tried: from replacing the panels, taking the panels out and spraying them, to using Vaseline/petroleum jelly, toothpaste, Magic Erasers, Sharpies, crayons, 303 Aerospace Protectant, Armor All, Novus Scratch Remover, PlastX, Mother’s Back to Black, heat guns, vinyl dye or plastic paint.
What method will work is dependent on how deep the scratch is.
Our 2008 Nissan HB had an assortment of scratches on the black plastic panels in the cargo area that I wanted to fix before I traded it in.
I'm pretty certain that these panels are made from polypropylene, PP. The only way to be certain is to take the panel off and check the SPI code, PP is 5. I didn't want to take the panel off.
The scratches were not deep enough to fill in. I used some 400 grit sandpaper to sand them smooth. I then wiped the area with 91% isopropanol (available at Walmart) to clean any left over release agent off. Since the plastic is textured you have to be careful not to sand too much. If the scratches are deep you will need a filler like this:
http://www.jbweld.com/products/plastic-bonder-syringe
I first tried some of the methods I had come across and what I had on hand. Vaseline, Armor All, and Mother’s Back to Black do not work on scratches, maybe on very light scuff marks. Mother's Back to Black is mainly for oxidized exterior plastic and rubber.
I do not have a heat gun so I tried my wife's 1500 W hair dryer. PP has a MP of 160 - 170 C but the hair dryer at its highest heat setting didn't even soften it.
A black Sharpie was too black and had a purplish hue.
My wife who does a lot of tole painting suggested I try an acrylic paint. She uses them on plastic with no problems. I didn't want to use a spray paint or vinyl dye in the car.
The panels are a satin black. I found a small bottle of multi-surface satin black acrylic paint at Hobby Lobby for $1.69. This brand is also available at other stores.
http://www.decoart.com/multisurface/
I used one of my wife's small artist brushes to paint the scratches, let dry; then used a blending technique she uses by mixing the paint 1:1 with water and a 1" artist's brush to blend the color into the rest of the panel. For fine scratches just painting them with a thin artist's brush should be sufficient.
Not perfect but good enough to trade in.
After sanding and wiping with isopropanol. The panel is black but photographed gray since the car was out in the sun.
Attachment 109482
After painting
Attachment 109484