Textile Recycling Viscosity Control via Selective Oxidation
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Solution Overview
Problem
The recycling of mixtures of textiles comprising both natural cellulose fibers like cotton and man-made cellulose fibers like viscose and lyocell poses a challenge, as the viscosity of natural cellulose fibers needs to be decreased while maintaining the viscosity of man-made fibers, which is not efficiently achieved in existing methods.
Innovation Solution
A method involving sequential steps: mechanical disintegration, swelling of cellulose fibers in an aqueous solution under reducing conditions, and oxidative bleaching, which adjusts the bleaching time and concentration to reduce the limiting viscosity number of the resulting material to a suitable range for a subsequent viscose process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional bleaching methods are used to decrease viscosity of natural cellulose fibers, then the viscosity of natural fibers is reduced, but the man-made cellulose fibers are also degraded and their viscosity is reduced
Solution Approach 1:
The patent applies different chemical treatments to different types of cellulose fibers within the same textile mixture. Natural cellulose fibers (cotton) are treated with oxidizing agents to reduce viscosity, while man-made cellulose fibers (viscose, lyocell) are protected from degradation through selective chemical resistance or protective agents, achieving localized quality control for each fiber type
Solution Approach 2:
The patent modifies chemical parameters such as pH, temperature, and oxidizing agent concentration to create conditions where natural cellulose fibers are degraded to desired viscosity levels while man-made fibers remain stable. By controlling these parameters, the process selectively affects different fiber types based on their chemical composition and structure
2Productivity
If strong oxidizing agents are used to reduce viscosity, then the viscosity reduction is more effective, but the damage to fiber structure and quality increases
Solution Approach 1:
The patent optimizes the concentration, temperature, and exposure time of oxidizing agents to achieve effective viscosity reduction while minimizing fiber damage. By carefully controlling these parameters, the process maintains fiber strength and quality while achieving the desired viscosity levels for subsequent viscose production
Solution Approach 2:
The patent implements monitoring and control mechanisms to track viscosity changes and fiber quality during the bleaching process. Based on this feedback, the oxidation conditions are adjusted in real-time to prevent over-oxidation and maintain optimal fiber quality while achieving productivity goals
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 method effectively degrades natural cellulose fibers like cotton while preserving man-made fibers like viscose, resulting in a material with a suitable limiting viscosity number for use in a subsequent viscose process, thereby improving the recycling efficiency and reducing the need for hazardous chemicals.
Implementation Method 1
Some pretreatments swell the cellulose fiber and thus breaking some of the hydrogen bonds that are linking the cellulose chains together
Implementation Method 2
performing at least one oxidative bleach, wherein the time for the at least one oxidative bleach in step d) and a concentration of at least one bleaching substance in step d) are adjusted so that the limiting viscosity number
Data Source
AI summary
There is provided a method for recycling a mixture of textiles comprising natural cellulose fibers and man-made cellulose fibers. After a mechanical disintegration the material is swelled under reducing conditions and thereafter bleached with at least one oxidative bleach. The bleaching is adjusted so that the limiting viscosity number as determined by ISO 5351:2010 for the resulting material after step d) is reduced to a value in the interval 200-1200 ml/g, or not higher than the initial limiting viscosity number. The reactivity of the material is improved, in particular for repeated recycling of viscose fibers. This makes it easier to use the fibers in a subsequent viscose process where steps can be omitted or reduced.