Bottle to bottle recycling

For quite some time plastic packaging has been collected and processed into high-quality recycled materials. However, it was only in the first ten years that the closure of the circuit was actually completed. A new food package was made from packaging scrap. There are many reasons for this slow progress. First of all, there is no clear regulation on this issue. What is certain is that a European regulation has been discussed for some time, but it is unclear when it will be issued. Second, EU member states can implement their own regulations. In several countries such as Italy and Spain, recycled materials may not be used at all in packaging. Other countries, such as Germany and Switzerland, responded rapidly to the progress of recycling technology and new scientific and technological knowledge: Clear recommendations and performance specifications have opened the door for the recycling industry to become a high-growth sector.

HDPE bottles recovered clean debris

Recycling PET, Food Safety
In addition to the need for the latest recycling technology, bottle-bottle recycling also requires extensive knowledge of polymer contaminants and purification efficiency. This is the only way to ensure that no impurities are carried into the food from the package containing the recyclate. Consumer health protection depends on this security. Moreover, the recycling process must be economical. Only in this way, high investment costs will be rewarded. Although it is not always easy to combine safety with economics, looking at recycling companies will reveal that bottle-to-bottle recycling of PET has been a routine operation for a long time. This is due to the development of new or improved recycling processes and the migration of substances in PET bottles. PET is a very inactive material, that is to say it absorbs only a very small amount of post-consumer components. Contaminants attached to the outside are not a big problem in any way, because they can be removed without effort. The only risk to the consumer during the "regeneration" process is when the contamination components diffuse into the polymer and are not removed by the recycling process.

Figure 1: Large-scale separation of PET waste bottles

Figure 2: HDPE is used in bottles in the UK

The fact that PET is used for beverage bottles means that a large amount of a single resin material can be collected, so it can be used in the recovery of closed loops. Moreover, PET contains very few added components, so from this point of view it is expected that there will be no problem. In addition, PET bottles have been recycled on an industrial scale for a long time (Figure 1). From the food point of view, consumer recycled PET actually outperforms pure PET. The reason for this can be found in the accompanying decontamination or "clean" recycling process. They have an extremely high cleaning efficiency, not only removing unwanted substances from the original components of the bottle, but also removing typical polymer contaminants, such as residual monomers (ethylene glycol), oligomers, and similar aldehydes. The decomposition products. PET beverage bottles containing 30% to 50% of recycled materials are now common.

Comparison of PET and HDPE
Is it also possible to recover other inert polymers that are weaker? For example, high density polyethylene (HDPE) is used in milk bottles in the UK (Figure 2). About 90,000 tons of HDPE are processed into milk bottles every year in the UK. They are filled, sold, emptied and collected. If it turns out that it is possible to separate the parts of a single resin, the result will be an attractive raw material that can be used for closed loop recycling. So far, efforts in this direction have been hampered by a lack of knowledge about the concentration of impurities in the bottle. Because HDPE is less lazier than PET, we can estimate that these concentrations will be much higher than PET bottles. In fact, the preliminary analysis shows the opposite. Because fresh milk has a short shelf life and is stored under refrigerated conditions, the concentration of post-consumer ingredients is very similar to that of PET bottles. No evidence of improper use of HDPE bottles has been found. This is the result of an analysis of almost 30,000 used HDPE bottles. Just probed the common ingredients in food or HDPE.

The British WRAP organization decided to cooperate with a European association organization to develop a suitable industrial-grade process that would compete economically with HDPE bottle recycling methods. The raw material was a collection of mixed plastics (Figure 3) containing approximately 20% HDPE feeding bottles.

Figure 3: Collection of different bottles

Single Resin HDPE Recovery Road
First, the HDPE bottle must be separated from the packaging waste. Separation is one of the important steps because the polymer may play a negative role throughout the recycling process. Second, special attention was paid to the optimization of HDPE bottles. In particular, it is necessary to separate HDPE bottles that have been used for liquid soaps and detergents, even if they are the same color as the bottle. The process used produced a resin with a purity of approximately 98% (Figure 4), and a large number of non-food HDPE bottles were removed. This is an important and effective method because non-food HDPE bottles may contain ingredients and odors that are often found in foods and are difficult to remove from the polymer. Subsequent separation by hand substantially increases the purity to more than 99%. The sorted bottles are then crushed into thin slices (see heading figure) and subjected to a high intensity hot wash process. This cleaning process removes any contaminants that adhere to the surface, as well as labels and adhesives. Moreover, it utilizes a floatation method to separate foreign polymer moieties. Because the stream also contains colored HDPE caps in addition to the bottle, a special color sorting step was introduced into the HDPE scrap. The debris that was cleaned and colour-sorted did not contain contaminants on the exterior, and the analysis showed that their migration potential in this step was comparable to that of pure HDPE. However, the washed flakes were found to contain higher concentrations of two components: the odor component limonene and di-tert-butylphenol, which is the product of the thermal decomposition of the polymer additive. Both components are not critical from the toxicological point of view. However, their concentration in recycled materials must be kept to a minimum. For this reason, another decontamination step was introduced. The fragments are heated in a continuous reactor to a temperature just below the melting point and a high vacuum is applied to further reduce the concentration of the migratory components. The completion of this process does not decompose the additive, so there is no need to add more additives. After this decontamination step, the material is granulated.

Figure 4: Infrared Spectrum of Packaging Plastics

The final product from the recovery process is now much less likely to migrate than pure HDPE because the concentration of typical oligomers such as octane, decane, and dodecane in HDPE is reduced. This material is then made into test bottles with varying concentrations of recycled material. Test bottles containing 100% recyclables cannot be visually and visually distinguished from HDPE bottles made of pure resin. The test bottle passes all the migration tests that the clear resin bottle undergoes. Conventional mechanical testing also showed no findings. These test bottles are then used for filling tests involving fresh milk. Again, the results did not show any sensory or microbiological effects. Therefore, HDPE bottles containing recycled materials are suitable for fresh milk.

Ecological and economical
According to the results of the project, the production cost of the recycling process is calculated to be 0.41 euros per kg of HDPE. When management costs are included together, the cost of production of HDPE recyclables for food contact is 0.61 euros per kilogram. Moreover, the ecological balance calculation shows that this process is ecologically more advantageous than the landfilling method, even if the input includes only 20% HDPE. If about half of the PET bottles that are also separated as single resins in the sorting process also undergo high levels of recycling, then the ecological balance of this recycling process is better.

This project shows that polymers other than PET can be used as starting materials for high-quality bottle-to-bottle recycling. For highly diffusible components, such as polyolefins, early detection of contamination is required to outperform PET. Here, the analysis is undoubtedly indispensable. The cleaning efficiency or recycling process then has to adapt to the degree of early pollution. In the same way, the migration to food must be tested under realistic conditions.

Once all the points have been clarified, then more varieties of polymers will receive closed loop recycling. Taking into account the current high price of polymers, this can be an attractive prerequisite for many areas.

Source: International Plastics Business

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