Devulcanizing Scrap Rubber Using Thiol Catalysts and High Shear Mixing
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Solution Overview
Problem
Existing mechanical devulcanization processes for thermoset elastomers are inefficient and environmentally harmful due to the use of toxic chemicals, which are not regulated in all countries, limiting their widespread adoption for recycling scrap rubber from molding operations.
Innovation Solution
A high shear mixing process at temperatures below 80°C using 0.5 to 2% by weight of a non-toxic biological catalyst with a thiol terminus, such as L-cysteine, to devulcanize thermoset sulphur cross-linked elastomers, improving material properties and reducing processing time by half.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If chemical additives are used to enhance devulcanization effectiveness, then the devulcanization efficiency is improved, but toxic gases are emitted during the process
Solution Approach 1:
The invention changes the chemical parameters by using alternative catalysts (metal salts like zinc oxide, calcium stearate, or borax) instead of traditional toxic chemicals, and controls the temperature parameter (heating to 50-150°C then cooling to below 50°C) to achieve effective devulcanization without toxic emissions. This parameter substitution resolves the contradiction between efficiency and environmental harm.
Solution Approach 2:
The invention introduces intermediary substances (metal salts as catalysts and water as a medium) that facilitate the devulcanization process without producing toxic emissions. These intermediaries enable the breakdown of cross-linked structures through controlled chemical reactions that are environmentally benign, thus improving efficiency without the harmful side effects of traditional chemical methods.
2Reliability
If high shear mixing is used to un-crosslink thermoset elastomers, then material recovery is achieved, but processing time is excessive
Solution Approach 1:
The invention applies preliminary chemical action by adding catalysts (metal salts) before or during the mechanical mixing process. This preliminary chemical preparation weakens the cross-linked structures in advance, making them more susceptible to mechanical breakdown. As a result, the subsequent high shear mixing process achieves complete devulcanization in just 5-15 minutes, dramatically reducing processing time while maintaining high material recovery quality.
Solution Approach 2:
The invention merges chemical and mechanical action into a single integrated process. Instead of using mechanical mixing alone (which takes excessive time) or chemical treatment separately, the patent combines catalyst addition with high shear mixing in one operation. This synergistic combination allows the chemical catalysts to work concurrently with mechanical forces, achieving rapid and complete devulcanization that satisfies both quality and time requirements.
3Device complexity
If mechanical mixing alone is used for devulcanization, then the process is simple, but the processing time is excessive and material properties are not fully restored
Solution Approach 1:
The invention modifies the chemical composition parameter by introducing metal salt catalysts into the simple mechanical mixing process. This parameter change transforms the process from purely mechanical to a combined chemo-mechanical system, enabling complete devulcanization that fully restores material properties (tensile strength, elongation, tear resistance) while maintaining operational simplicity and reducing processing time to 5-15 minutes.
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 process effectively restores the elastomer to a pre-vulcanized state, enhancing physical properties by 12.5% and reducing processing time by 50% without generating toxic emissions, making it suitable for revulcanization into useful products.
Implementation Method 1
high shear mixing has been shown to significantly improve the properties of materials recovered and approximately halve the processing time
Implementation Method 2
addition of a suitable catalyst with a thiol terminus to the mechanical process of high shear mixing has been shown to significantly improve the properties of materials recovered
Data Source
AI summary
A thermoset cross-linked elastomer material, such as scrap tire rubber, is devulcanized by subjecting the material to a mechanical mixing process in the presence of 0.5 to 2% by wt. of an organic catalyst having a thiol terminus.