Organometallic Devulcanization of Sulfur-Crosslinked Tire Rubber
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Solution Overview
Problem
The recycling of end-of-life (EOL) tire rubber into a form suitable for use in new tire production is challenging due to the vulcanization process, which makes it difficult to reclaim the rubber's original properties, leading to limited success in devulcanization methods and environmental and cost inefficiencies.
Innovation Solution
A method involving the application of pressure to a mixture of sulfur-crosslinked rubber particles and copper sulfide or iron acetate, transferring sulfur from the rubber crosslinks to the copper sulfide, and using organometallic compounds to reduce sulfur content, resulting in a rubber-based elastomer with desirable properties for use in new tire manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional devulcanization methods are used on vulcanized rubber, then some sulfur bonds are broken, but the process is environmentally harmful and costly while failing to fully reclaim original rubber properties
Solution Approach 1:
The patent changes the chemical parameters of the devulcanization process by using organometallic compounds (Fe, Cu, Zn, Mn, Co, Ni) with specific molecular structures and reactivities. These compounds enable selective bond breaking at milder conditions, transforming the harsh conventional process into a controlled chemical reaction that achieves complete devulcanization without environmental harm.
Solution Approach 2:
The organometallic compounds act as intermediary catalysts between the sulfur crosslinks and the breaking mechanism. These compounds facilitate the breakdown of sulfur-sulfur and sulfur-carbon bonds through coordinated insertion and elimination reactions, mediating the transformation without requiring harsh conditions or producing harmful byproducts.
2Ease of manufacture
If sulfur crosslinks are broken to reclaim rubber properties, then the rubber can be reused, but the vulcanization structure is destroyed
Solution Approach 1:
The patent applies partial action by selectively breaking only the sulfur-sulfur and sulfur-carbon crosslink bonds while leaving the carbon-carbon backbone of the rubber polymer intact. This selective devulcanization removes the vulcanization structure just enough to enable recycling while preserving the fundamental rubber polymer structure needed for re-vulcanization and reuse.
3Productivity
If ground rubber is produced from scrap tires, then recycling volume increases, but the rubber loses its original elastic properties
Solution Approach 1:
The devulcanized rubber product is designed to serve itself by restoring the rubber's ability to be re-vulcanized. The process removes sulfur crosslinks completely, allowing the rubber to regain its pre-vulcanization state where it can form new crosslinks, enabling the material to service itself through multiple recycling cycles without permanent property loss.
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 efficiently and cost-effectively transforms EOL tire rubber into a form with properties similar to virgin rubber, addressing the environmental and economic challenges of recycling and providing up to 70% of the natural rubber gap identified in critical raw material studies.
Implementation Method 1
The process involves breaking of sulfur-sulfur and/or sulfur-carbon bonds through action of the carbon sulfide
Implementation Method 2
A method involving the application of pressure to a mixture of sulfur-crosslinked rubber particles and copper sulfide or iron acetate
Data Source
AI summary
An organometallic compound is incorporated into a vulcanized rubber matrix. A tunable, multi-phase copper sulfide lattice is compounded within an existing sulfur cross-linked morphology, as in crumb rubber obtained from recycled tires or other vulcanized rubber, whereby thermotropic properties of the rubber matrix are modulated. The process involves breaking of sulfur-sulfur and/or sulfur-carbon bonds through action of the carbon sulfide. The resulting rubber is suitable for use in applications typically utilizing virgin rubber, such as new tires, engineered rubber articles, and asphalt rubber for use in waterproofing and paving applications. In other embodiments, an organometallic compound comprising iron acetate or alkaline earth metal acetate is incorporated into the vulcanized rubber matrix.