Dye removal from denim scrap with a forced circulation kier

Abstract

A recycling process for liquid treatment of denim scrap comprising placing denim scrap on a support surface to form a thickness of flat, layered denim scrap. To the top surface is applied a compression plate to form the thickness of denim scrap into a compact cake. Then treatment liquid is passed through the interior of the compact cake in a direction parallel to the surfaces of the scrap, the liquid passing between opposed surfaces of the denim pieces. The denim scrap is preferably cut into relatively uniform sizes having their largest dimension less than about 4 inches. The treatment liquid can be a solvent for oxidized indigo dye, whereby indigo dye is removed from the denim scrap by said liquid; an aqueous solution containing a desizing agent, whereby size is removed from the denim scrap pieces; an aqueous solution containing a reducing agent for indigo dye, whereby dye in the denim pieces is reduced to a soluble, leuco form, dissolves in the solution, and both size and dye are removed from the denim scrap pieces; a solution containing desizing and reducing agent, whereby size and dye is removed from the denim scrap pieces; or an aqueous solution containing a reducing agent for indigo dye, whereby dye in the denim pieces is reduced to a soluble, reduced form, dissolves in the solution, and is removed from the denim scrap pieces; or a sequences of these liquids.

The invention claimed is:  
     
         1 . A process for liquid treatment of denim scrap comprising the steps of: 
 a) placing sufficient denim scrap pieces on a support surface to form a thickness of flat, layered denim scrap comprising individual denim pieces with opposed surfaces having approximately parallel orientations, the thickness having a top surface;    b) applying a compression plate to said top surface to form the thickness of denim scrap into a compact cake; and    c) passing liquid through the interior of the compact cake in a direction parallel to the surfaces of the scrap, the liquid passing between opposed surfaces of the denim pieces.    
     
     
         2 . A process according to  claim 1  wherein the denim scrap pieces have a widest width of less than 4 inches.  
     
     
         3 . A process according to  claim 1  wherein the denim scrap pieces have a widest width of less than 2 inches and an average widest width of greater than 1 inch.  
     
     
         4 . A process according to  claim 1  wherein the liquid is solvent for the oxidized form of indigo dye, whereby indigo dye is removed from the denim scrap by said liquid.  
     
     
         5 . A process according to  claim 1  wherein liquid is an aqueous solution containing desizing agent, whereby size is removed from the denim scrap pieces.  
     
     
         6 . A process according to  claim 5  wherein the liquid is an aqueous solution containing reducing agent for indigo dye, whereby dye in the denim pieces is reduced to a soluble, reduced (leuco) form, dissolves in the solution, and both size and dye are removed from the denim scrap pieces simultaneously.  
     
     
         7 . A process according to  claim 1  wherein the liquid is an aqueous solution containing reducing agent for indigo dye, whereby dye in the denim pieces is reduced to a soluble, reduced form, dissolves in the solution, and is removed from the denim scrap pieces.  
     
     
         8 . A process according to  claim 1  wherein the liquid is an aqueous solution containing catalyzed hydrogen peroxide solution, the catalyst being a catalyzing amount of a transition metal cation or quaternary alkylamine salt which catalyzes oxidation reactions of hydrogen peroxide, whereby indigo dye in the denim scrap pieces is bleached or destroyed to remove color therefrom.  
     
     
         9 . A process of  claim 1  wherein the liquid is an aqueous solution containing an alkali metal hypochlorite.  
     
     
         10 . A process for liquid treatment of denim scrap to remove dye from the scrap and decolorize the scrap comprising the steps of: 
 a) placing sufficient denim scrap pieces on a support surface to form a thickness of flat, layered denim scrap comprising individual denim pieces with opposed surfaces, the thickness having a top surface;    b) applying a compression plate to said top surface to form the thickness of denim scrap into a compact cake;    c) passing a first aqueous solution through the interior of the compact cake in a direction parallel to the surfaces of the scrap, the first aqueous solution passing between opposed surfaces of the denim pieces, the first aqueous solution containing reducing agent for indigo dye, whereby dye in the denim pieces is reduced to a soluble, reduced form, dissolves in the solution, and is removed from the denim scrap pieces; and    d) passing a second aqueous solution through the interior of the compact cake in a direction parallel to the surfaces of the scrap, the second aqueous solution passing between opposed surfaces of the denim pieces, the second aqueous solution containing catalyzed hydrogen peroxide solution, the catalyst being an catalyzing amount of a transition metal cation or quaternaryalkylamine salt which catalyzes oxidation reactions of hydrogen peroxide, whereby indigo dye, other vat dyes, and sulfur dyes in the denim scrap pieces are bleached or destroyed to remove color therefrom.    
     
     
         11 . A process according to  claim 10  wherein the first aqueous solution contains desizing agent, whereby both size and dye are removed from the denim scrap pieces.  
     
     
         12 . A process according to  claim 10  wherein the denim scrap pieces have a widest width of less than 4 inches.  
     
     
         13 . A process according to  claim 12  wherein the denim scrap pieces have a widest width of less than 2 inches and an average widest width of greater than one inch.  
     
     
         14 . The process of  claim 10  in which a third aqueous solution is passed through the interior of the compact cake and consists of a combination of one or more dyes, chemicals or reagents used to assist in the optimization of the treated fabrics to be employed in subsequent processing or end use applications.  
     
     
         15 . The process of  claim 10  in which the third aqueous solution contains one or more of a surfactant, humectant, antibacterial agent, fiber lubricant, dyes or tints, optical brighteners, hand modifiers, or antistatic agents.  
     
     
         16 . A process for liquid treatment of denim scrap to remove dye from the scrap and decolorize the scrap comprising the steps of: 
 a) placing sufficient denim scrap pieces on a support surface to form a thickness of flat, layered denim scrap comprising individual denim pieces with opposed surfaces, the thickness having a top surface;    b) applying a compression plate to said top surface to form the thickness of denim scrap into a compact cake;    c) passing a first aqueous solution through the interior of the compact cake in a direction parallel to the surfaces of the scrap, the first aqueous solution passing between opposed surfaces of the denim pieces, the first aqueous solution containing reducing agent for indigo dye, whereby dye in the denim pieces is reduced to a soluble, reduced form, dissolves in the solution, and is removed from the denim scrap pieces; and    d) passing a second aqueous solution through the interior of the compact cake in a direction parallel to the surfaces of the scrap, the second aqueous solution passing between opposed surfaces of the denim pieces, the second aqueous solution containing an alkali metal hypochlorite whereby the indigo vat dye, other vat dyes, or sulfur dyes are bleached or destroyed.