If the problem you're trying to address is fine cracks filled with dirt/grease, for small items like knobs a heated ultrasonic cleaner with a strong grease cutter like simple green will work as well as anything. For larger items like steering wheels, simple green and a toothbrush will help but probably won't be quite as effective. Rinse well after cleaning, as it's pretty corrosive if left to dry.
As noted above : I’d be careful there. I’ve been doing some citric acid rust removal and enjoy how it also softens paint. Have to think that it might wreak havoc on some plastics as well.
I can't think of any acid that won't affect the older plastic in some way. Toothpaste works well for cleaning plastic.
I'm not sure what you guys are thinking, but let's talk about what's the dilution of the acid? Start there then ask, what will it dissolve and what it takes to dissolve it. Heat, at what temperature? What duration of exposure? What type of plastic? Why Citric in the first place, because mol***es and vinegar are unavailable? They're also acidic? It's not hydrochloric, or sulfuric, phosphoric... it's citric, found in fruit, found in food. I'm not seeing it bubble and dissolving anything to quickly but that's just me under thinking it maybe. This from a guy who uses toilet bowl cleaner on everything and its got that hydroacid in it.
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