Method for decolorization of a dyed polyester fiber

Abstract

A method for decolorization of a dyed polyester fiber includes: separately providing a dyed polyester fiber stained with a dye, and a solvent capable of dissolving the dye; heating the solvent to produce a fresh vapor of the solvent, the temperature of the fresh vapor ranging between the glass transition temperature and the melting point of the polyester fiber; condensing the fresh vapor to form a condensed fluid of the solvent; contacting the dyed polyester fiber with the condensed fluid of the solvent that has a temperature sufficient to dissolve the dye such that the dye is extracted from the dyed polyester fiber so as to form a dye-containing solution and a decolorized polyester fiber; and separating the dye-containing solution from the decolorized polyester fiber.

What is claimed is: 
     
         1 . A method for decolorization of a dyed polyester fiber, comprising the steps of:
 (a) separately providing a dyed polyester fiber stained with a dye, and a solvent that is capable of dissolving the dye;   (b) heating the solvent to produce a fresh vapor of the solvent, the temperature of the fresh vapor ranging between the glass transition temperature and the melting point temperature of the polyester fiber;   (c) condensing the fresh vapor to form a condensed fluid of the solvent;   (d) contacting the dyed polyester fiber with the condensed fluid of the solvent that has a temperature sufficient to dissolve the dye such that the dye is extracted from the dyed polyester fiber so as to form a dye-containing solution and a decolorized polyester fiber; and   (e) separating the dye-containing solution from the decolorized polyester fiber.   
     
     
         2 . The method as claimed in  claim 1 , wherein the solubility parameter of the solvent is from 17 to 40 (J/cm 3 ) 0.5 . 
     
     
         3 . The method as claimed in  claim 1 , wherein the solvent is selected from the group consisting of xylene, 1-hexanol, ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, ethylene carbonate, propylene carbonate, butylene carbonate, and combinations thereof. 
     
     
         4 . The method as claimed in  claim 3 , wherein xylene includes p-xylene, m-xylene, or o-xylene. 
     
     
         5 . The method as claimed in  claim 1 , wherein the temperature of the condensed fluid of the solvent in step (d) ranges between the glass transition temperature and the melting point temperature of the polyester fiber. 
     
     
         6 . The method as claimed in  claim 1 , wherein the weight ratio of the polyester fiber to the condensed fluid is from 1:1.5 to 1:4. 
     
     
         7 . The method as claimed in  claim 6 , wherein the weight ratio of the polyester fiber to the condensed fluid is from 1:1.6 to 1:2.6. 
     
     
         8 . The method as claimed in  claim 1 , wherein the dye is a disperse dye. 
     
     
         9 . The method as claimed in  claim 1 , wherein the dyed polyester fiber is separately disposed above the solvent, the fresh vapor of the solvent contacting and being condensed on the polyester fiber. 
     
     
         10 . The method as claimed in  claim 1 , wherein, in step (a), the solvent is disposed in a solvent pool, and in step (e), the dye-containing solution drops from the decolorized polyester fiber into the solvent pool by gravity. 
     
     
         11 . The method as claimed in  claim 1 , further comprising a step (f) of repeating the steps of step (a) to step (e). 
     
     
         12 . The method as claimed in  claim 11 , wherein the method is proceeded in a tank that includes a condensing device.