Surface Devulcanization of Recycled Rubber
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Solution Overview
Problem
Current rubber recycling methods face challenges in incorporating recycled sulfur-cured rubber into fresh rubber compounds due to poor bonding and increased cross-link density, leading to reduced tensile strength and durability, and require expensive processes like cryogenic grinding for small particle sizes, making large-scale recycling economically unfeasible.
Innovation Solution
The method involves surface devulcanization of recycled sulfur-cured rubber using butylthiol and a solvent to create surface-devulcanized ground rubber particles, which can be mixed with fresh rubber without the need for full devulcanization, allowing larger particle sizes and improving adhesion and tensile strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ground recycled sulfur-cured rubber particles are incorporated into fresh rubber compounds, then rubber recycling is achieved, but poor bonding between particles and fresh rubber matrix occurs leading to reduced tensile strength and durability
Solution Approach 1:
The patent applies parameter changes by modifying the surface chemistry of recycled rubber particles through devulcanization treatment. This chemical modification reduces the cross-link density at the particle surface, enabling better bonding with the fresh rubber matrix during co-vulcanization, thereby maintaining tensile strength while achieving recycling
Solution Approach 2:
The patent uses devulcanization agents as intermediaries to facilitate bonding between recycled rubber particles and fresh rubber. These agents temporarily reduce surface cross-links, acting as a mediator that enables molecular diffusion and bonding, after which the network structure is restored during co-vulcanization
2Productivity
If ground recycled sulfur-cured rubber particles are incorporated into fresh rubber compounds, then rubber recycling is achieved, but increased cross-link density occurs leading to reduced durability
Solution Approach 1:
The patent changes the cross-link density parameter selectively at the particle surface through devulcanization treatment. This temporary reduction in cross-link density allows for better matrix integration and stress distribution, improving durability while maintaining the recycled rubber's structural integrity
Solution Approach 2:
The patent applies partial devulcanization only to the surface layer of recycled rubber particles rather than complete devulcanization of the entire particle. This partial action is sufficient to improve bonding and durability while preserving the core particle's mechanical properties and avoiding over-softening
3Strength
If small particle sizes are used for ground recycled rubber, then bonding surface area is increased, but expensive processes like cryogenic grinding are required making large-scale recycling economically unfeasible
Solution Approach 1:
The patent changes the chemical state parameter of the particle surface through devulcanization, which improves bonding effectiveness without requiring reduction of particle size. This allows use of larger, more economically viable particle sizes while maintaining adequate bonding strength through chemical modification
4Ease of manufacture
If larger particle sizes are used for ground recycled rubber, then recycling costs are reduced, but poor bonding and reduced performance occur
Solution Approach 1:
The patent compensates for the reduced surface area of larger particles by changing the chemical reactivity parameter of the particle surface. Devulcanization treatment creates more reactive surface groups that form stronger chemical bonds with the matrix, offsetting the disadvantage of larger particle size and maintaining bonding strength
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 enables the use of larger recycled rubber particles with comparable or increased performance to smaller particles, increasing the recyclable rubber percentage and reducing recycling costs by eliminating the need for full devulcanization and expensive grinding processes.
Implementation Method 1
devulcanizing the surface of the ground rubber particles with a surface devulcanization agent to form surface-devulcanized ground rubber particles
Data Source
AI summary
A method, and product thereof, for modifying the surface of recycled sulfur-cured rubber via surface devulcanization that minimizes alteration of the network structure of the recycled sulfur-cured rubber, while generating strong tack between mixed recycled rubber and fresh rubber for optimal adhesion upon subsequent co-curing. In one embodiment, the surface of recycled rubber is devulcanized by treating recycled rubber with a thiol and a base dissolved in a solvent that does not effectively penetrate and only minimally swells vulcanized rubbers.