Microwave Devulcanization of Waste Elastomers
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Solution Overview
Problem
Existing methods for devulcanizing highly vulcanized rubber waste, such as truck tire waste, face challenges with low devulcanization rates, lack of selectivity, and high energy consumption, particularly in the presence of carbon black, and do not allow for the controlled synthesis of functionalized polymers.
Innovation Solution
A process involving the use of a devulcanizing agent, such as a radical initiator of formula (1), in the presence of a solvent, heats the mixture at specific temperatures and times to break crosslinking nodes, introducing functional groups within the polymer chain, thereby achieving high devulcanization rates and selective synthesis of functionalized polymers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If mechanical devulcanization is used to process waste containing elastomers, then the processing is simple and energy-efficient, but the carbon-carbon bonds of the polymer chain are broken non-selectively resulting in low devulcanization rates
Solution Approach 1:
The patent introduces microwaves as an intermediary energy form to selectively break carbon-sulfur bonds and disulfide bridges in the vulcanized rubber network. The microwaves interact with the polar groups in the rubber matrix, generating localized heating that promotes bond cleavage without requiring high bulk temperatures, thus achieving efficient devulcanization with selective bond breaking
Solution Approach 2:
The patent changes the energy delivery parameter from conventional thermal heating to microwave irradiation. This parameter change enables selective interaction with specific bonds (carbon-sulfur and disulfide) based on their electromagnetic absorption characteristics, achieving both high devulcanization rates and selectivity that mechanical methods cannot attain
2Productivity
If microwave devulcanization is used to break carbon-sulfur bonds, then the devulcanization rate is high, but the temperature increases very significantly causing breaking of carbon-carbon bonds in the polymer chain
Solution Approach 1:
The patent employs periodic or pulsed microwave irradiation to deliver energy in controlled intervals. This periodic action allows the rubber matrix to dissipate heat between pulses, preventing excessive temperature accumulation that would lead to carbon-carbon bond breaking, while still achieving effective devulcanization during the active irradiation periods
Solution Approach 2:
The patent applies microwave energy at a level that is excessive for simple heating but selectively targets the carbon-sulfur bonds and disulfide bridges. By controlling the microwave power and exposure time, the process achieves sufficient energy input to break these specific bonds while avoiding the threshold needed to degrade the carbon-carbon polymer backbone
3Use of energy by stationary object
If chemical devulcanization by disulfide metathesis is used, then the process is relatively energy-efficient, but the balanced reaction prevents achievement of high devulcanization rates
Solution Approach 1:
The patent replaces the chemical metathesis mechanism with a physical microwave-driven bond cleavage mechanism. Instead of relying on the equilibrium-limited disulfide exchange reaction, microwaves directly break the carbon-sulfur and disulfide bonds through vibrational excitation and localized heating, eliminating the thermodynamic constraints of balanced chemical reactions and achieving high devulcanization rates
4Use of energy by stationary object
If chemical devulcanization by breaking disulfide bonds with a devulcanizing agent is used, then the process is energy-efficient, but the devulcanization rates are extremely low for highly vulcanized rubber waste
Solution Approach 1:
The patent replaces the slow chemical reaction mechanism of devulcanizing agents with direct microwave energy input. The microwaves provide sufficient energy to break the strongly bonded carbon-sulfur and disulfide linkages in highly vulcanized rubber without requiring prolonged exposure to chemical agents, achieving both energy efficiency and high devulcanization rates
Solution Approach 2:
The patent changes the energy delivery parameter from gradual chemical reaction to intense but controlled microwave irradiation. This parameter change enables the system to overcome the kinetic barriers present in chemical devulcanization of highly crosslinked rubber, achieving rapid bond cleavage with lower overall energy input
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 achieves high devulcanization rates and selective synthesis of functionalized polymers, overcoming the limitations of existing methods by providing efficient and controlled polymer production from highly vulcanized rubber waste.
Implementation Method 1
the devulcanizing agent is capable of forming radicals by homolysis
Implementation Method 2
heating the mixture obtained in step a) at a temperature between 20°C and 250°C for a period of between 15 minutes and 24 hours
Data Source
AI summary
The invention relates to a method for synthesising polymers through devulcanisation from waste containing elastomers, said method comprising: - a) contacting said waste containing elastomers with a solvent in the presence of a devulcanisation agent, - b) heating the mixture produced in step a), at a temperature of between 20°C and 250°C for a period of between 15 minutes and 24 hours in the presence of a devulcanisation agent, the concentration of devulcanisation agent being such that the ratio between said concentration of devulcanisation agent, expressed as parts per hundred of elastomer (phr) and a volume of solvent, expressed in ml, is: - greater than 0.3 phr/ml of solvent or less than 0.2 phr/ml of solvent when the method is carried out in air, - greater than 0.06 phr/ml of solvent when the method is carried out in an inert atmosphere.