The most concerning word in PET recycling is PVC. This is because even small amounts of PVC can create problems during the processing of PET resin and the production of new products. Due to this, the negative effects of PVC contamination can occur at concentrations as low as 50ppm.
50ppm is an extremely small amount—just 0.5kg of PVC plastic in 1,000kg of PET flakes, which equals 0.005%. Despite this minimal content, PVC can form acids and physically and chemically degrade PET resin, causing the PET plastic to become brittle and pale yellow (two key dimensions for judging PET flake quality are transparency and impact resistance). Additionally, chlorine may volatilize, which is a general hazard associated with recycling PVC.
Sources of PVC Contamination in PET Recycling
For most PET recycling facilities, controlling PVC content is crucial. The acceptable PVC tolerance level is ultimately determined by the end-user. Some users can accept higher proportions of PVC content, while most high-end applications require PVC content below 50ppm. Therefore, to command a good price, PET recyclers make every effort to remove PVC. First, let’s understand how PVC enters the PET recycling system.
Generally, PVC contaminants enter PET recycling through four sources:
Some PVC bottles resemble PET bottles, but when baled, PVC bottles leave distinctive creases that can be manually sorted out.
Some PET bottles have PVC seals (such as mouthwash bottles) that need to be removed before shredding.
Some PET bottle caps and stoppers have PVC liners, which are no longer used in the United States but occasionally appear.
PVC labels wrapped around bottles
PVC Removal in PET Recycling
While recycling equipment plays a significant role in removing PVC, we cannot overlook one of the most effective PVC removal methods: manual sorting. As mentioned earlier, an experienced manual sorting worker can identify PVC bottles within their visual range, after which equipment can be used to enhance sorting efficiency.
The use of ultraviolet light has been proven to increase sorting efficiency to 99%. When PET passes under ultraviolet light, the PET plastic absorbs UV rays and reflects blue fluorescence. As for PVC, although it doesn’t reflect any light itself, its additives reflect green/yellow fluorescence. When PET and PVC emit two different types of light under UV exposure, sorting workers can easily identify and separate them. Because ultraviolet light is harmful to humans, workers need to rotate in two-hour shifts.
In addition to manual sorting, fully automated sorting has become increasingly popular as labor costs rise. Fully automated sorting technologies generally fall into three categories: optical sorting systems, transmission sorting systems, and surface scanning systems. All three methods utilize detection signals, with air nozzles used to blow away unwanted bottles. Among all the technologies applied, the most reliable is using X-rays to detect chlorine within PVC bottles (PET bottles contain no chlorine).
Since neither manual nor fully automated techniques are perfect, employing 2-3 methods is advisable to ensure low PVC content.
Another method for removing PVC is heat separation. At around 200°C, PVC becomes very soft and sticky, while PET requires 260°C. This 60-degree difference makes heat separation possible. In this process, we place the PET and PVC mixture into a rotating heated belt machine (or drum) set at approximately 180-200°C. As the mixed material passes through, PVC sticks to the belt while PET rolls into a collection bin.
Another lower-cost method is electrostatic separation. When a PVC and PET mixture enters a charging chamber, it generates an electrostatic charge. Due to different physical and chemical properties, PVC becomes negatively charged while PET becomes positively charged. Once charged, the two materials repel each other. A key factor is having sufficient energy to charge the plastics; if the energy is insufficient, the materials may attract each other.
Conclusion
We believe this article has helped you better understand PVC and its role in PET recycling. Since buyers are always concerned about PVC content, it is essential to employ various methods to remove it. Testing for PVC content is necessary to ensure you provide high-quality PET flakes. As mentioned earlier, even small amounts of PVC can render an entire batch of PET flakes useless.
Generally, always strive for PVC content below 50ppm, ideally under 30ppm. We have provided numerous methods for removing PVC. However, the final decision depends on you—you can determine which system to implement based on your specific material requirements.
