A general answer is NO.

This is qualified by asking what is the plastic and what are the strengths and temperature of the acids. Both acids are highly hazardous to handle and can violently react with some plastics.

Comeback with details of what you are specifically trying to do.

I need to clean polyurethane and PMMA, to make mirror surface on them by silver coating. The surface has to be very clean for the chemical coating procedure.
One of the steps is cleaning the surface with nitric acid.
A slight change in machanical properties due to the acid-plastic material interaction may be acceptable, as far as the materal is cleaned thoughly. Can I use nitric acid to clean the plastic materials? What are the plastic materials that I cannot clean with the acid? Are there any alternatives? Thanks.

 Peter

  Peter

kkim123,
You need to find some very detailed, Plating On Plastic (POP) instructions for your particular substrates.

The plastic is first alkaline cleaned & rinsed.

Conditioning: Some plastics are then slightly softened with chlorinated organics to make more susceptible to the acid.  

Etching:  The acid (often, hot chromic+sulfuric) attacks the plastic surface, breaking molecular bonds, converting it into a microscopically porous, wettable surface.

Neutralizing (sensitizing): A rinse containing complexing or reducing agents (for oxidizing acids such as chromic & nitric) follows.

Catalyzing (sensitizing):  A stannous chloride or dilute palladium chloride solution is used to catalyze (ativate) the surface for metal deposition.

Acceleration: Sometimes, a step using fluorides is used.

Silver can then be deposited using the Brashear Formula solution.

Caution: The procedure above follows ASTM B727, 'Standard Practice for Preparation of Plastics Materials for Electroplating,' which doesn't mention PMMA or PU.