Polyolefin Recyclate Purification via Sequential Washing and Sorting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current recycling processes for polyolefin plastics produce mixed-color recyclates with residual contamination and odors, limiting their use in packaging due to uneven color and foreign substances, which are not effectively removed by existing methods, making them unsuitable for consumer applications.
Innovation Solution
A process involving cold washing, hot washing with an alkaline medium, flake sorting, and temperature treatment to separate and purify polyolefin residues, removing surface impurities, adhesive residues, and migration substances, resulting in color-pure and odor-free recyclates suitable for consumer products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If polyolefins are recycled using standard recycling processes, then the recycling rate increases, but the recyclates contain residual contaminants and odors that preclude applications close to the end user
Solution Approach 1:
The recycling process is divided into multiple sequential stages: pre-treatment (shredding, washing), flotation separation, hydrocyclone classification, and extrusion. Each stage targets specific contaminants, progressively purifying the polyolefin recyclate to achieve both high recycling rates and high product quality suitable for food contact applications
Solution Approach 2:
A flotation agent is introduced as an intermediary substance to enhance the separation of contaminants from polyolefin recyclates. The flotation agent selectively binds to certain contaminants, enabling their removal through flotation separation, thereby improving product purity while maintaining high recycling rates
2Quantity of substance
If polyolefin plastics are used in mixed colors for recycling, then the processing volume increases, but the end products exhibit different shades of gray that limit their application
Solution Approach 1:
The process incorporates a color sorting stage that uses optical sensors to detect and separate polyolefin recyclates by color. This enables the production of color-uniform recyclates from mixed-color inputs, maintaining high processing volumes while achieving consistent gray shades suitable for various applications including food contact
3Adaptability or versatility
If foreign substances are absorbed in polyolefin containers during primary use, then the containers serve their function, but these substances decompose under thermal stress to create odor nuisances
Solution Approach 1:
The process includes a pre-treatment stage with washing and flotation separation that removes foreign substances and contaminants before the polyolefin recyclates undergo extrusion and thermal processing. This preliminary removal of odor-causing substances prevents their decomposition during subsequent thermal steps, eliminating odor nuisances while preserving the container's original functionality
4Reliability
If polyolefin recyclates are produced with high purity to enable end-consumer applications, then the product quality improves, but the processing complexity and costs increase
Solution Approach 1:
The process employs a multi-functional integrated treatment system where a single processing line performs washing, flotation separation, hydrocyclone classification, and extrusion operations. This universal approach achieves high-purity recyclates suitable for end-consumer applications while avoiding the need for multiple separate processing lines, thereby controlling complexity and costs
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 produces high-purity, odor-free polyolefin recyclates that can be reused in packaging, enhancing their market competitiveness and sustainability by ensuring product quality and safety.
Implementation Method 1
washing with water to remove surface contaminants
Implementation Method 2
treated with an alkaline aqueous solution at elevated temperature to remove adhesive residues and contaminants
Implementation Method 3
subjected to a thermal treatment to remove migrating substances
Data Source
Figure 1~2
AI summary
The present invention relates to a process for producing polyolefin recyclates, and in particular HDPE recyclates, in which color-mixed polyolefin-containing residues are subjected, in a predetermined sequence, to a low-temperature wash, an elevated-temperature wash in an alkaline medium, flake sorting, and an elevated-temperature treatment to remove migrating substances. The described process yields polyolefin recyclates with significantly improved purity compared to recyclates currently available on the market, which can be used to manufacture new consumer product packaging. Furthermore, the unpleasant odors associated with known polyolefin recyclates, caused by dislocation products of migrating substances formed during extrusion, are largely avoided.