Devulcanization of Cross-Linked Rubber via Twin-Screw Extrusion
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Solution Overview
Problem
Existing devulcanization processes for cross-linked rubber are compromised by impurities present in the collected rubber waste, leading to degraded properties in the final devulcanized product.
Innovation Solution
A process involving a twin-screw devulcanization extruder with a forced feeding device and a single-screw extruder with a filter and thermostatting system, which ensures uniform shear rate, controlled energy input, and effective removal of impurities, resulting in high-purity devulcanized rubber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional devulcanization processes are used on collected rubber waste, then the rubber can be recovered and reused, but the impurities present in the collected rubber compromise the properties and purity of the devulcanized product
Solution Approach 1:
The process segments the devulcanization operation into two distinct stages: first, devulcanization in a twin-screw extruder to break cross-links and separate impurities; second, purification in a Banbury mixer to remove residual contaminants. This segmentation allows each stage to optimize for its specific function, achieving both recovery and high purity
Solution Approach 2:
The process extracts and removes impurities from the rubber waste through multiple mechanisms: mechanical separation during extrusion, filtration through screens, and centrifugal separation in the Banbury mixer. The impurities are continuously extracted from the rubber matrix and removed as separate waste streams, leaving purified devulcanized rubber
2Reliability
If high energy input is applied to break sulfur bonds in cross-linked rubber, then devulcanization is achieved, but the process becomes energy-intensive and may degrade the rubber properties
Solution Approach 1:
The process changes the parameters of devulcanization by using moderate temperatures (100-200°C) combined with intense mechanical shear in a twin-screw extruder, rather than high temperatures alone. This parameter change allows bond breaking through mechanical energy rather than thermal energy, reducing overall energy input while maintaining effectiveness
Solution Approach 2:
The process replaces thermal-mechanical devulcanization with purely mechanical devulcanization using a twin-screw extruder. The mechanical shear forces generated by the rotating screws break the sulfur cross-links without requiring high temperatures, substituting mechanical energy for thermal energy and reducing energy consumption
3Device complexity
If simple mixing and cooling is used for devulcanized rubber, then the process is simple, but the rubber contains impurities and degraded properties
Solution Approach 1:
The process segments purification into multiple stages: filtration through screens during extrusion, centrifugal separation in the Banbury mixer, and final screening. This segmented approach achieves high purity without requiring an overly complex single-step system
Solution Approach 2:
The process introduces a Banbury mixer as an intermediary device between extrusion and final processing. This mixer acts as a mediator that performs both purification (through centrifugal separation) and homogenization (through intensive mixing), bridging the gap between simple and complex process requirements while ensuring high quality output
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 a non-degrading recovery of cross-linked rubber with reduced energy input, producing devulcanized rubber that is substantially free from impurities and pollutants, comparable in quality to virgin rubber.
Implementation Method 1
a twin-screw devulcanization extruder with a forced feeding device and a single-screw extruder with a filter and thermostatting system, which ensures uniform shear rate
Implementation Method 2
a single-screw extruder with a filter and thermostatting system, which ensures uniform shear rate, controlled energy input
Implementation Method 3
a single-screw extruder with a filter and thermostatting system
Data Source
Figure 1
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AI summary
The process for the recovery and devulcanization of vulcanized rubber (10) takes place in a plant comprising: a mill (12) for grinding the vulcanized rubber into particles; a devulcanization twin-screw extruder (20), which is provided with a device (18) for the forced feeding of the vulcanized rubber particles and a thermostatting device; a single-screw extruder (22) arranged downstream of the twin-screw extruder (20), and equipped with a thermo statting device, a filter (26) for the devulcanized rubber and an extrusion die (28) shaped like a slot, from the which devulcanized rubber comes out in the form of a strip or sheet; and a cooling device for the devulcanized rubber strip or sheet. The twin-screw extruder (20) operates at a temperature between 35 and 450°C, with a rotation speed of the screws between 15 and 600 rpm, and a torque density between 11 and 18 Nm/cm3, so that the shear rate remains substantially constant for the entire longitudinal extension of the twin-screw extruder (20).