Foreign Polymer Separation from PET Mixture via Thermal Softening
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Solution Overview
Problem
Conventional methods for separating foreign polymers from PET bottle waste are ineffective, particularly when dealing with amorphous PET flakes, as they either fail to separate PVC from PET or reduce the yield of purified PET material due to operating temperatures that also soften amorphous PET particles.
Innovation Solution
A method involving the separation of amorphous PET particles from the mixture, heating the mixture to a temperature between the softening points of foreign polymers and crystalline PET particles, and using a mechanical contact body or color sorting to effectively remove foreign polymers, ensuring high-quality PET material with minimal residual impurities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional separation methods based on density differences are used, then polymers of lower density than PET (such as PP or PE) can be separated off, but PVC can only be insufficiently separated from PET
Solution Approach 1:
The patent changes the separation parameter from density differences to softening point differences. By heating the mixture to a temperature above the softening point of foreign polymers (including PVC) but below the softening point of PET, the foreign polymers become soft and adhesive while PET remains solid, enabling effective separation of all foreign polymer types regardless of their density
Solution Approach 2:
The patent replaces the mechanical density-based separation system with a thermal field-based separation system. Instead of relying on gravitational or inertial forces for density separation, the process uses thermal energy to exploit differences in softening points, achieving superior separation effectiveness
2Manufacturing precision
If the polymer mixture is heated to a temperature above the softening point of foreign polymers to enable separation, then foreign polymers can be separated from PET, but amorphous PET flakes also adhere to the contact body, reducing the yield of purified PET material
Solution Approach 1:
The patent precisely controls the temperature parameter to fall within a specific range: above the softening point of foreign polymers (enabling their separation) but below the softening point of PET (preserving PET integrity). This parameter optimization allows selective separation without losing PET material
Solution Approach 2:
The patent creates different physical states locally within the mixture: foreign polymers become soft and adhesive while PET remains solid and non-adhesive. This local differentiation of physical properties enables selective separation based on adhesion behavior, with only foreign polymers adhering to the contact body
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 effectively separates foreign polymers, maintaining a high yield of purified PET material by avoiding the separation of amorphous PET particles and ensuring impurities are below 10 ppm, thus enhancing the recyclate's quality and process efficiency.
Implementation Method 1
heating the polymer mixture to a temperature between the softening point of the foreign polymers and that of the crystalline PET particles
Implementation Method 2
the polymer mixture is contacted with a mechanical contact body. By the mechanical adhesion of the foreign polymers to the contact body, they can be separated from the PET
Data Source
AI summary
A method of separating foreign polymers from a polymer mixture that comprises amorphous PET particles and crystalline PET particles, wherein the softening point of the foreign polymers is lower than that of the crystalline PET particles, and wherein the method includes separating the amorphous PET particles from the polymer mixture, heating the resulting polymer mixture to a temperature between the softening point of the foreign polymers and that of the crystalline PET particles, and separating the foreign polymers from the resulting polymer mixture. Also, a device for separating foreign polymers from a polymer mixture that comprises amorphous PET particles and crystalline PET particles, the device including a first separation unit for separating the amorphous PET particles from the polymer mixture, and a second separation unit for separating the foreign polymers from the resulting polymer mixture.