REMOVAL OF COLOR FROM THERMOPLASTICS
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.
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.