Recycled Textile Pulp Ozone Bleaching With Two-Step pH Control
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Solution Overview
Problem
Existing methods for ozone bleaching pulp from recycled textile material face challenges in achieving sufficient brightness and maintaining pulp viscosity due to the oxidative properties of ozone, which degrades cellulose fibers.
Innovation Solution
A method involving two ozone bleaching steps with a charge of at least 12 kg/odt, combined with pretreatment using acids and additives like chelating agents and radical scavengers, followed by additional bleaching steps such as peroxide and chlorine dioxide, to enhance brightness and maintain pulp viscosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If ozone bleaching is applied to pulp from recycled textile material, then brightness is improved, but cellulose degradation occurs and viscosity is reduced
Solution Approach 1:
The ozone bleaching process is divided into two distinct steps with different pH conditions. The first step at high pH (10-12) performs initial brightness enhancement with reduced cellulose attack. The second step at low pH (2-3) completes the bleaching while the protective additives prevent excessive cellulose degradation. This segmentation allows each step to optimize for its specific function.
Solution Approach 2:
Protective additives (radical scavengers and chelating agents) are introduced before ozone bleaching begins. These additives pre-establish protection against oxidative damage by scavenging free radicals and chelating metal ions that would catalyze cellulose degradation, thereby preventing viscosity loss before it occurs.
Solution Approach 3:
The process utilizes significant pH parameter changes between the two bleaching steps. The transition from high pH (10-12) in the first step to low pH (2-3) in the second step creates different chemical environments that optimize both brightness achievement and cellulose protection. This parameter change is central to resolving the contradiction between bleaching effectiveness and fiber preservation.
2Illumination intensity
If higher ozone charges are used to improve brightness, then brightness is enhanced, but cellulose degradation increases and viscosity decreases
Solution Approach 1:
The total ozone charge is segmented into two steps with different effectiveness profiles. The first step at high pH uses a portion of the total ozone charge for initial brightness improvement with minimal cellulose attack. The second step at low pH uses the remaining ozone charge to achieve final brightness while protective additives prevent excessive cellulose degradation. This segmentation allows higher total ozone charge without proportional increase in cellulose loss.
Solution Approach 2:
Protective additives are added before ozone bleaching to pre-establish a protective shield against oxidative damage. Radical scavengers consume harmful free radicals before they can attack cellulose, and chelating agents bind metal ions that would catalyze degradation. This preliminary protection enables the use of higher ozone charges without proportional increase in cellulose degradation.
3Device complexity
If conventional ozone bleaching methods are used, then the process is simple, but sufficient brightness cannot be achieved
Solution Approach 1:
The bleaching process is segmented into two distinct steps with different pH conditions and additive formulations. This segmentation enables the process to achieve superior brightness (up to 90% ISO brightness) compared to conventional single-step methods, while the added complexity is managed through systematic protocol development.
Solution Approach 2:
The method employs composite chemical systems combining ozone with specific additive packages in each step. The first step uses ozone with high-pH buffers and initial protective additives. The second step uses ozone with low-pH conditions and enhanced protective additives. This composite approach synergistically combines multiple chemical functions to achieve both high brightness and cellulose preservation.
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
The method achieves a brightness of about 80% in two ozone bleaching steps and up to 90% with supplementary bleaching, while minimizing cellulose degradation and maintaining pulp viscosity.
Implementation Method 1
ozone reacts with and de-composes lignin originating from the wood material
Implementation Method 2
ozone bleaching of cellulose pulp from wood material is well known in the art, where ozone reacts with and de-composes lignin
Implementation Method 3
Chelating agents provide the effect that selectivity in the ozone bleaching step is improved by reducing the content of metal ions in the pulp
Implementation Method 4
Radical scavengers have a similar effect by scavenging the metal ions
Data Source
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AI summary
The invention relates to a method for bleaching pulp formed from recycled textile material comprising cellulose, said method comprising ozone bleaching (3; 13a, 13b) of said pulp by means of adding ozone at a charge of at least 12 kg/odt, wherein said ozone bleaching (13a, 13b) is performed as two subsequent steps, each comprising adding ozone at a charge such that the overall charge is at least 12 kg/odt.