PVC in PET Bottle Recycling

The term “PVC” or polyvinyl chloride (plastic identification code #3) strikes fear in the realm of PET recycling. This is due to the fact that even minuscule amounts of PVC contamination can cause significant disruptions during the processing or remanufacturing of post-consumer PET resin into new products. To provide some perspective, the negative effects of PVC contamination can arise at concentrations as low as 50 parts per million (ppm). A mere 50 ppm equates to only 0.05 kg of PVC plastic per 1,000 kg of PET flakes, which, in percentage terms, represents just 0.005%. Despite this seemingly insignificant quantity, PVC can produce acids that degrade PET resin both physically and chemically, causing the PET to become brittle and acquire a yellowish hue—two critical characteristics that diminish the quality of PET, particularly in terms of clarity and impact strength. Additionally, chlorine vapors may be emitted, posing a further hazard when recycling PVC.

Sources of PVC Contamination in PET Recycling

In most PET washing recycling facilities, controlling the concentration of PVC in the processed PET flakes is crucial. The level of acceptable PVC concentration is ultimately determined by the intended application of the end product. While some applications may tolerate higher PVC concentrations, premium applications, such as the production of top-tier polyester fibers, demand PVC levels well below 50 ppm. To meet these stringent requirements and command higher market prices, PET recyclers must exert extra effort to remove PVC from the PET flakes they produce. This process begins with identifying how PVC infiltrates the PET recycling stream.

There are generally four primary sources of PVC contamination in PET recycling:

1. PVC bottles that mimic PET bottles, leaving a white “crease” mark when flattened. These can be identified and removed by trained sorters.
2. PVC safety seals on PET bottles, such as those found on mouthwash containers, which need to be removed prior to granulation.
3. PVC liners within bottle caps and closures. While this practice is no longer common in the United States, PVC-lined bottles occasionally still appear.
4. PVC labels wrapped around PET bottles.

PVC Removal in PET Recycling

While machinery plays a key role in filtering PVC from PET streams, manual sorting remains one of the most effective methods for PVC removal. As previously noted, experienced sorters can visually identify PVC bottles. However, technological advancements have enhanced the efficiency of manual sorting.

For instance, the addition of UV lighting to a PET bottle stream has been tested to significantly improve sorting accuracy, with trained professionals achieving efficiencies of up to 99%. When PET bottles pass through UV light, they absorb the rays and emit a blue fluorescent glow in return. In contrast, although PVC itself does not fluoresce, the additives within PVC often cause PVC bottles to emit a green or yellow fluorescence. This distinction allows sorters to easily identify PVC bottles and remove them. To mitigate the harmful effects of prolonged UV exposure, sorters should work in shifts of no more than two hours.

In addition to manual sorting, automated systems are becoming increasingly popular due to the rising cost of manual labor. Fully automated sorting systems can be classified into three types: optical sorting systems, transmission technology systems, and surface scanning systems. Each system uses detection signals to differentiate plastic bottles based on their chemical or physical properties, with sensors analyzing the data. Air jets are then employed to separate the unwanted bottles from the PET stream. Among these technologies, x-ray detection has proven to be the most reliable for identifying the presence of chlorine in PVC bottles, as chlorine is absent from PET bottles.

Since neither manual nor automated sorting systems are flawless, a 2-3 pass routine is often employed to ensure minimal PVC contamination.

Another widely used method for removing PVC from PET flakes is thermal separation. At approximately 200°C, PVC softens and becomes sticky, while PET plastic remains unaffected at 260°C. This temperature gap allows for thermal separation: a PET/PVC flake mixture is passed over a rotating, heated conveyor belt set to around 180-200°C. As the plastic mixture moves along the belt, PVC sticks to it, while PET plastic remains unaffected, rolling off into a collection bin. A stationary blade beneath the conveyor scrapes off the PVC. Although automatic sorting equipment requires substantial investment, thermal separation is a relatively low-cost alternative.

Another cost-effective method is electrostatic separation. In this process, a mixture of PVC and PET plastics is exposed to a charging chamber, which induces a static charge on the plastic surfaces. Due to the differing physical and chemical properties of the plastics, PVC becomes negatively charged, while PET becomes positively charged. The mixture is then exposed to charged poles, which attract the oppositely charged plastics, separating them. Success in electrostatic separation hinges on applying the right amount of energy to charge the plastics without causing them to attract to each other.

Conclusion

This article aims to provide a deeper understanding of PVC’s role in PET recycling. As buyers of PET flakes are always concerned about PVC contamination, it is essential to take every precautionary step to minimize PVC in the final product. Routine testing for PVC content should be carried out to ensure that the PET flakes you offer meet the highest quality standards. Even small amounts of PVC can render an entire batch of PET flakes unusable.

As a general guideline, strive for PVC levels below 50 ppm, and ideally below 30 ppm. Several methods for PVC removal have been outlined, but it is ultimately up to the operator of the PET washing plant to establish a system that best suits the types of PET bottle bales they handle.

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