Vulcanized Rubber Devulcanization via Solvent Pressure
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Solution Overview
Problem
Existing devulcanization processes of vulcanized rubber result in polymers with reduced molecular weight due to high temperatures, leading to limited reuse potential, as they cause both crosslink scission and chain scission, making it difficult to produce a product similar to the original polymer for recycling purposes.
Innovation Solution
A method involving heating vulcanized rubber in a reactor with a solvent at a temperature below 285°C and maintaining a pressure higher than the saturated vapor pressure, primarily using an inert gas over-pressure, to break sulphur bridges without significant depolymerization, resulting in a product with rheological properties similar to un-vulcanized rubber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high temperature processing is used to devulcanize rubber, then crosslinks are broken effectively, but molecular weight is reduced due to chain scission
Solution Approach 1:
The patent changes the processing parameters by using lower temperatures (200-300°C) combined with extended processing times (2-24 hours) and specific solvent systems. This parameter change allows effective devulcanization through prolonged exposure at milder conditions, breaking crosslinks while minimizing the thermal energy available for unwanted chain scission, thus preserving molecular weight.
Solution Approach 2:
The patent introduces solvents (water, alcohols, or their mixtures) as intermediaries in the devulcanization process. These solvents facilitate the breaking of sulphur crosslinks through chemical interaction, enabling effective devulcanization at lower temperatures. The solvent acts as a mediator that promotes crosslink scission while reducing the need for high thermal energy that would cause chain scission.
2Quantity of substance
If extended processing time is used to preserve molecular weight, then chain scission is minimized, but productivity decreases
Solution Approach 1:
The solvent acts as a catalytic intermediary that accelerates the devulcanization reaction, allowing the process to proceed effectively at lower temperatures over extended periods without requiring high energy input. This intermediary enables the reaction to occur at a manageable pace that preserves molecular weight while being more efficient than prolonged high-temperature processing.
Solution Approach 2:
The patent employs periodic or extended processing cycles at controlled temperatures, allowing the devulcanization to progress gradually over time. This periodic action at moderate conditions achieves thorough crosslink breakdown while minimizing rapid thermal degradation, balancing molecular weight preservation with reasonable processing throughput.
3Quantity of substance
If low temperature processing is used to preserve polymer structure, then chain scission is reduced, but devulcanization completeness is insufficient
Solution Approach 1:
The solvent serves as a chemical intermediary that actively participates in breaking sulphur crosslinks through solvation and chemical interaction. This intermediary effect enables complete devulcanization at low temperatures by providing an alternative reaction pathway that does not rely on high thermal energy, thus preserving molecular weight while achieving thorough crosslink removal.
Solution Approach 2:
The patent employs continuous extended processing at low temperatures with solvent presence, maintaining the devulcanization reaction continuously over prolonged periods. This continuous action ensures complete crosslink breakdown accumulates over time, achieving full devulcanization completeness without the need for high-temperature bursts that would cause chain scission.
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 approach achieves substantial devulcanization with minimal chain scission, allowing the produced rubber to maintain molecular weight and rheological properties close to the original, enabling its use as a substitute in new rubber formulations and facilitating easier separation from carbon black.
Implementation Method 1
heating in a reactor the vulcanized rubber and a solvent to a reaction temperature below a critical temperature of the solvent
Implementation Method 2
providing a reaction pressure in the reactor that is higher than a saturated vapour pressure of the solvent at the reaction temperature, the reaction pressure provided in part by an inert gas over pressure
Implementation Method 3
maintaining the reaction temperature and the reaction pressure for a reaction time sufficient to break at least a portion of the sulphur bridges of the vulcanized rubber
Data Source
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AI summary
Vulcanized rubber, for example from used tires, can be devulcanized to provide a reaction product that has similar rheological properties to the original un-vulcanized rubber. The vulcanized rubber is processed at a temperature that is less than a critical temperature of a solvent, such as water or water and alcohol. The process is carried out at a pressure that is higher than the vapour pressure of the solvent.