Methods for recycling cotton and polyester fibers from waste textiles
Systems and methods are provided that involve a subcritical water reaction to recycle the cellulose and polyester components of waste cotton and cotton/polyester blend textiles that would otherwise be discarded or disposed of. Specifically, the disclosed methods provide for treatment of the waste textiles to produce advanced materials including cellulose and terephthalic acid (TPA) with a low environmental impact. The cellulose and TPA that are produced are of a high quality allowing for production of regenerated cellulose and regenerated polyethylene terephthalate (PET) suitable for fiber spinning and textile applications.
1. A method of producing one or both of cellulose and terephthalic acid (TPA) from a waste textile material comprising cotton or cotton/polyester blend material, the method comprising:
treating the waste textile material in a subcritical water reactor at a temperature of about 105° C. to 190° C., a pressure of about 40 to 300 psi, or both, wherein the treating is for a time sufficient to one or both of weaken the linkage between the cellulose fibers to produce a cellulose that comprises a degree of polymerization ranging from about 150-2500 and to produce a dissolved TPA and ethylene glycol (EG).
2. The method of claim 1 , wherein the temperature ranges from about 130° C. to 160° C.
3. The method of claim 1 , wherein the waste textile material comprises cotton/polyester blend material and the treating in the subcritical water reactor comprises adjusting the pH to a range from about 10-14.
4. The method of claim 3 , wherein the adjusting the pH comprises using 0.01-5% (v/v) organic acid, 0.5-20% (w/v) sodium hydroxide, or 0.5-20% (w/v) potassium hydroxide.
5. The method of claim 1 , wherein the waste textile material comprises cotton/polyester blend material having a cellulose content of >90.
6. The method of claim 1 , further comprising recovering the cellulose, wherein the recovered cellulose is of a purity of 94% or higher.
7. The method of claim 1 , further comprising recovering the cellulose, wherein the degree of polymerization of the recovered cellulose ranges from about 300-1700.
8. The method of claim 1 , further comprising recovering the cellulose, wherein the recovered cellulose has a degree of polymerization of at least about 1000.
9. The method of claim 1 , further comprising recovering the cellulose, wherein the recovered cellulose has a degree of polymerization of at least about 500.
10. The method of claim 1 , further comprising recovering the cellulose and subjecting the recovered cellulose to one or more steps of wash, disintegration, sour wash, activation process, dissolution dope, or wet spinning.
11. The method of claim 1 , further comprising removing color from the waste textile material before, during, or after treating with the subcritical water reactor, the removing color comprising treatment with one or more of hydrogen peroxide, sodium peroxide, sodium hypochlorite, calcium hypochlorite, dimethyl sulfoxide, lithium hypochlorite, sodium perborate, ozone, oxygen, activated carbon, biochar, sodium carbonate, peracetic acid, potassium permanganate, persulfate, sodium chloride, calcium oxychloride, chloramine, chlorine dioxide, sulfur dioxide, sodium hydrosulfite, or TAED (tetra-acetyl-ethylene-di-amine).
12. The method of claim 1 , wherein the subcritical water reactor treatment comprises one or more of methanol, ethanol, isopropanol, tetra-n-butylphosphonium bromide (TBPB), or benzyltributylammonium chloride (BTBAC), or co-polymers thereof.
13. The method of claim 1 , further comprising recovering the TPA.
14. The method of claim 13 , wherein the recovering comprises precipitating the dissolved TPA, crystallizing the precipitated TPA, and subjecting the crystallized TPA to a polymerization process to produce regenerated polyethylene terephthalate (PET).
15. The method of claim 14 , wherein the regenerated PET has an intrinsic viscosity of 0.620 dl/g.
16. The method of claim 14 , wherein the regenerated PET has a peak temperature as measured by differential scanning calorimetry and an onset temperature as measured by thermogravimetric analysis within +/−5%, or within +/−2.5%, of that of standard reference PET.
17. A recycled cellulose produced using the method of claim 1 having a purity of 94% or higher.
18. A recycled cellulose produced using the method of claim 1 having a degree of polymerization ranging from about 300-1700 and a purity of 94% or higher.
19. A recycled cellulose produced using the method of claim 1 having a degree of polymerization of at least about 1000 and a purity of 94% or higher.
20. A recycled cellulose produced using the method of claim 1 having a degree of polymerization of at least about 500 and a purity of 94% or higher.
21. The method of claim 1 , wherein the waste textile material comprises cotton/polyester blend material having a cellulose content of >50% cellulose.
22. The method of claim 1 , wherein the waste textile material comprises cotton/polyester blend material having a cellulose content of <50% cellulose.