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.

Description

[0001] 1. Field of the Invention[0002] This invention relates to a process for removing indigo dye from denim scrap with a forced circulation kier. In particular, the process of this invention is directed to a method for removing indigo dyes from scrap textiles such as denim scrap where the vat dyes have been applied while in a reduced, soluble form and oxidized to precipitate the dye in and on the fabric in an insoluble form.[0003] 2. Background of the Invention[0004] Cotton and other cellulose scraps produced when cutting cotton fabrics in clothing manufacture are a waste product typically buried in landfills or consumed in incinerators. Garnetting to separate and recover the cotton fibers shortens the fiber length and the products had few uses. As a consequence, over 200 million pounds of denim scrap, in the U.S. alone, is destroyed as waste each year.[0005] U.S. Pat. Nos. 5,376,143 and 5,471,720 describe a process for recycling denim waste by separating the fibers, preparing a c...

AI Technical Summary

Benefits of technology

[0015] One object of this invention is a highly effective process for treating denim scrap with extraction solvents for extracting the majority of dye from denim to yield a scrap lightly tinted with indigo dye residue.

Problems solved by technology

As a consequence, over 200 million pounds of denim scrap, in the U.S. alone, is destroyed as waste each year.

This process has not been commercially implemented, perhaps because of costs of fiber separation and the limitations of the shortened fibers in the making a strong, durable fabric.

However, most of these applications require the cotton fibers be colorless and strong, and a process for recycling cotton scrap to produce cotton fibers for these applications has not been commercially feasible because of the difficulties in processing the scrap.

One principal area of difficulty is removal and / or decolorizing the vat dyes present in many cotton scraps such as denim.

If the dye molecule is contained within the cellulose substrate, the water-insoluble dye is trapped and cannot be removed by casual exposure to water and detergents.

Treatment of denim scrap by this procedure tends to produce tightly rolled up scrap pieces from which all of the dye is not extracted or to unravel the scraps, producing useless balls and tangles of yarn and fabric scraps or individual yarn pieces which foul the bath or equipment components.

However, an effective solvent extraction system for textile scraps like denim scraps has not been feasible The solvent removes size, softness, surfactants, finishes and fully oxidized dye from the fabric, producing a solution of these components.

Solvent evaporation yields a cake or solution of these components which is useless without a further, expensive purification process.

Treatment of small denim scrap in this procedure tends to unravel the scraps, producing useless balls and tangles of yarn and fabric scraps which foul the washer-extractor.

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