Removal of color from thermoplastics

Abstract

A process of decolorizing dyed thermoplastics are provided that includes intermixing a dyed thermoplastic with a decolorization agent solution at a temperature that maintains the crystalline structure of the thermoplastic. The processes for the first time are capable of removing substantial portions of dye from the thermoplastic providing a material that is suitable for recycling processes and use in subsequent recycled articles.

We claim: 
     
         1 . A process for forming a decolorized thermoplastic material comprising:
 mixing a colored thermoplastic material in solid form with a decolorizing agent solution comprising one or more decolorizing agents, said thermoplastic material comprising one or more dyes providing color to said thermoplastic material;   heating said colored thermoplastic material to a decolorization temperature that maintains the crystalline structure of said thermoplastic material, said step of heating for a decolorization time subsequent to or simultaneous with said step of mixing; and   decolorizing said thermoplastic material by said mixing step, and optionally by said heating step, thereby forming a decolorized thermoplastic material.   
     
     
         2 . The process of  claim 1  further comprising the step of irradiating said thermoplastic material subsequent to or simultaneous with said step of mixing. 
     
     
         3 . The process of  claim 3  wherein said oxidizing agent is a hypohalite compound. 
     
     
         4 . The process of  claim 3  wherein said oxidizing agent is an organic or inorganic peroxide. 
     
     
         5 . The process of  claim 1  wherein said decolorization agent is hydrogen peroxide. 
     
     
         6 . The process of  claim 1  wherein said decolorization agent has the structure of Formula I:
   R 1 -[O(CH 2 ) m ) n -]OR 2   (I)
 
 
       where: R 1  and R 2  are each independently H or a C 1-18  alkyl radical, benzyl radical, benzoyl radical, or phenyl radical; n is 2, 3 or 4; and m is any value from 1 to 35;
 said decolorization agent solution substantially free of a dye prior to said step of mixing. 
 
     
     
         7 . The process of  claim 6  wherein said decolorization agent includes an R 1  that is an ethyl, propyl or butyl. 
     
     
         8 . The process of  claim 6  wherein m is 2, 3 or 4. 
     
     
         9 . The process of  claim 6  wherein n is 2 or 3. 
     
     
         10 . The process of  claim 6  wherein said benzyl, benzoyl, or said phenyl is substituted in the aromatic ring by alkyl and/or halogen. 
     
     
         11 . The process of  claim 1  wherein said decolorization agent is 2-butoxyethanol. 
     
     
         12 . The process of  claim 1  wherein said thermoplastic is polyethylene terephthalate. 
     
     
         13 . The process of  claim 1  wherein said step of heating is by immersing said thermoplastic material in an aqueous solution of decolorizing agent preheated to said decolorization temperature. 
     
     
         14 . The process of  claim 1  wherein said decolorization temperature is less than 100 degrees Celsius. 
     
     
         15 . The process of  claim 1  wherein said decolorization temperature is between 81 and 91 degrees Celsius. 
     
     
         16 . The process of  claim 1  wherein said dye material penetrates said material to less than 1 millimeter. 
     
     
         17 . The process of  claim 1  wherein said dye is a thermoliable dye. 
     
     
         18 . The process of  claim 1  wherein said dye is an unstable dye. 
     
     
         19 . The process of  claim 1  wherein said dye is an azo or quinone dye. 
     
     
         20 . The process of  claim 1  wherein said dye is Disperse Red 1.