Case Study of Product Safety in PET Recycling (II)

Special case: Food contact
The methods described above are also suitable for the evaluation of recycled PET applied in applications involving direct food contact. Because the analysis is based on a small sample taken from an inhomogeneous material fluid with typical components of the recycled material, an extremely conservative worst-case setting is applied when evaluating the ultra-clean recovery process, exaggerating the impurity content. In reality, this is a common thing. For example, forced challenge experiments used extremely high concentrations of chemicals to simulate the improper use of PET bottles. However, because the recycling process is evaluated under unreal conditions, this method is problematic and can create artifacts.

To solve this problem effectively, IVV has developed an online process monitoring system. Because almost 100% of the recovered stream and highly contaminated samples can be detected, it is sufficient to have a much lower level of contamination than the worst-case scenario and less cost is needed to determine the cleaning benefits.

The detection method uses an on-line chemical sensor and sampling device based on a quartz microbalance. This sensor has excellent sensitivity to impurities that may affect quality like lemon olein. On the other hand, it is less sensitive to substances like ethanol and water. Moreover, impurities can also be quantified because, unlike metal oxide sensors, quartz microbalance sensors are qualitatively selective.

Because the long-term stability of the quartz microbalance sensor has been verified experimentally, when it is carefully calibrated, it meets the need for a fast, simple and robust, yet inexpensive, quality assurance method. Correspondingly, it is possible for this system to continuously monitor, on an industrial scale, migrating impurities in recycled products. This type of sensor has been integrated into PET recycling equipment by Erema, Austria.

To optimize materials and processes
The new and well-developed analytical methods presented here create effective tools for the evaluation of PET product quality. They are also suitable for optimizing PET materials, PET processing and recycling methods. Most importantly, gas chromatography can be used as a screening tool for evaluating the quality of PET used in various market applications, identifying and quantifying individual impurities that affect quality. Finally, the possible cleaning benefits of impurities and recycling processes can be quantified.

Because additive mixtures and recycled streams have always become more and more complex, the method designed in this project has laid a foundation for effective monitoring of feed quality. They help recyclers and recyclers achieve the assurance they need for product reliability.

Food applications are the most sensitive to PET recycling. Powerful analytical methods help ensure high standards of purity.

Sources of information "plastics business" 2005, 10

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