Recycling process for the recovery of cotton from polyester-cotton fabrics and/or fibers
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Solution Overview
Problem
Current recycling methods for polyester-cotton blends face challenges such as degradation of cotton properties, unusable cotton, and residual polyester residues, making it difficult to recover high-quality cotton and recyclable polyester monomers.
Innovation Solution
A depolymerization process using an amine organocatalyst and/or carboxylic acid salt, combined with an alcohol solvent, to react with polyester-cotton fabrics, resulting in the recovery of polyester-free cotton, reusable catalyst, and recyclable polyester monomers like bis(2-hydroxyethyl)terephthalate (BHET).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If polyester digestion using harsh catalysts (e.g., alkali metal hydroxide base) is used to recycle polyester from polyblend fabrics, then polyester can be recovered, but the cotton component breaks down rendering the fabric unusable
Solution Approach 1:
The patent changes the chemical parameters of the digestion process by using milder catalysts (alkaline earth metal hydroxides like Ca(OH)2 or Sr(OH)2 instead of alkali metal hydroxides) and controlling reaction conditions (temperature, time, catalyst concentration) to achieve selective polyester degradation while preserving cotton integrity
Solution Approach 2:
The patent introduces a selective intermediary catalyst system that mediates between polyester and cotton, allowing the catalyst to preferentially attack polyester ester bonds while leaving cotton cellulose intact, thus enabling selective depolymerization without damaging the cotton component
2Loss of substance
If polyester dissolution is used to recycle polyester from polyblend fabrics, then polyester can be recovered, but polyester residues remain on the cotton surface rendering the fabric unacceptable for reuse
Solution Approach 1:
The patent replaces mechanical separation methods with a chemical depolymerization system that selectively breaks down polyester into soluble monomers, allowing complete separation from cotton without leaving residues, and the monomers can be fully recovered through filtration and precipitation
Solution Approach 2:
The patent changes the chemical state of polyester from undissolved or partially dissolved forms to complete depolymerization into soluble monomers, allowing thorough separation from cotton fibers and complete recovery of both cotton and polyester monomers without residual contamination
3Ease of manufacture
If mechanical recycling is used for polyester-cotton blends, then processing is simple, but contamination by dissimilar polymers and dyes causes severe degradation of properties
Solution Approach 1:
The patent introduces a chemical intermediary (selective depolymerization catalyst) that mediates the separation process, enabling chemical differentiation between polyester and cotton components based on their distinct chemical structures, thus achieving high-purity separation that mechanical methods cannot accomplish
Solution Approach 2:
The patent changes the approach from physical mechanical separation to chemical parameter-based separation, utilizing differences in chemical reactivity between polyester ester bonds and cotton cellulose bonds to achieve selective degradation and purification, resulting in high-quality recovered materials
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This process effectively recovers high-quality, polyester-free cotton and recyclable polyester monomers, maintaining the integrity and usability of the cotton fibers while enabling the reuse of catalysts and solvents.
Implementation Method 1
reacting a fabric and/or fibers comprising polyester and cotton with an amine organocatalyst and/or carboxylic acid salt of same and an alcohol solvent
Implementation Method 2
depolymerization process using an amine organocatalyst and/or carboxylic acid salt, combined with an alcohol solvent, to react with polyester-cotton fabrics
Implementation Method 3
reacting a fabric and/or fibers comprising polyester and cotton with an amine organocatalyst and/or carboxylic acid salt of same and an alcohol solvent
Data Source
AI summary
Polyester-free cotton is obtained from a fabric and/or fibers containing polyester and cotton by reacting the fabric and/or fibers with an amine organocatalyst and/or carboxylic acid salt of same and an alcohol solvent. The reaction, which may be run in batches or as a continuous flow process, recovers (i) polyester-free cotton as a solid inert by-product of the reaction, (ii) the amine organocatalyst and/or carboxylic acid salt of same for reuse, (iii) a polyester monomer product, and (iv) unreacted alcohol. The reaction works on any polyester-cotton fabric and/or fibers, including those that have at least one additional material, such as polyethers polyolefins, polyurethanes, nylon, rayon, acetate, viscose, modal, acrylic, wool, and combinations thereof.