PET Flake Sorting to Remove PVC in Food-Grade Recycling
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Solution Overview
Problem
Existing PET recycling methods fail to effectively remove non-PET components, particularly PVC, to a concentration below 30 ppm, which contaminates the recycled polyester and renders it unsuitable for food packaging.
Innovation Solution
A multi-step flake-sorting process combining color-sorting, screening, and polymer-sorting, including electrostatic separation, to separate and remove PVC contamination from PET flakes, producing high-purity rPET suitable for food containers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional single-step sorting is used, then device complexity is low, but PVC removal efficiency is insufficient (chlorine content remains above 30 ppm)
Solution Approach 1:
The sorting process is divided into multiple sequential steps: color sorting (d1) to separate by color, screening (d2) to separate by particle size, and polymer sorting (d3, d4) to separate by material type. This segmentation allows each step to target specific contamination sources, achieving PVC removal below 25 ppm through cumulative effect of multiple separation stages.
Solution Approach 2:
The patent combines different sorting technologies (color sorting, screening, and polymer sorting) into an integrated multi-step process. By merging these complementary methods, the system achieves comprehensive contamination removal that no single method could accomplish alone, while managing complexity through systematic integration.
2Manufacturing precision
If advanced multi-step sorting is implemented, then rPET purity increases (PVC content below 25 ppm), but processing time increases
Solution Approach 1:
Color sorting (d1) is performed as a preliminary step before polymer sorting, removing obviously colored contaminants early in the process. Screening (d2) also occurs beforehand to separate particles by size. These preliminary actions reduce the burden on subsequent polymer sorting steps, enabling high purity achievement while optimizing overall processing efficiency.
3Manufacturing precision
If thorough contamination removal is achieved, then food packaging suitability is met, but chlorine content detection precision must be extremely high
Solution Approach 1:
X-ray fluorescence analysis provides real-time feedback on chlorine content in the flake stream. This measurement feedback allows the sorting system to monitor its performance and adjust operations to maintain chlorine content below 30 ppm, ensuring food packaging suitability while providing quantitative verification of contamination removal effectiveness.
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 method achieves rPET with a PVC content below 25 ppm, meeting quality requirements for food packaging by effectively removing PVC contamination through advanced separation techniques.
Implementation Method 1
the polymer-sorting process d3, by which foreign polymers in the second screened fraction are removed, constitutes a non-optical polymer-sorting process, in particular an electrostatic polymer-sorting process
Data Source
AI summary
A method for recycling polyester containers, in particular PET containers, said method including the following method steps: sorting the containers, comminuting the containers to produce flakes, friction washing the flakes, sorting the flakes, and extruding and granulating the cleaned flakes. The flake-sorting process is used to separate flakes which have a foreign polymer that is different from the polyester, and the flake-sorting process is a combination of a color-sorting process, a screening step, and polymer-sorting process.