PET bottle recycling
The main motivations have been either cost reduction (when oil prices spike) or recycle content of retail goods (driven by regulations or public opinion).
An increasing amount is recycled back into bottles, the rest goes into fibres, film, thermoformed packaging and strapping.
[1] After sorting, cleaning and grinding, 'bottle flake' is obtained, which is then processed by either: In either case, the resulting feedstock is known as "r-PET" or "RPET".
PET bottles are closed with polyolefin screw closure with antitamper ring, and have a label which may be printed on paper or plastic and may be glued on.
[11] The bales consisting mostly of PET mostly of a single colour are delivered to plants where the bottles may be treated by a variety of processes to convert them into usable feedstocks.
A typical system will consist of a steel housing with the filtration medium contained in moveable pistons or slide plates that enable the processor to remove the screens from the extruder flow without stopping production.
The success of any recycling concept is hidden in the efficiency of purification and decontamination at the right place during processing and to the necessary or desired extent.
The high plasticization temperature of PET in the range of 280 °C (536 °F) is the reason why almost all common organic impurities such as PVC,[19] PLA, polyolefin, chemical wood-pulp and paper fibers, polyvinyl acetate, melt adhesive, coloring agents, sugar, and protein residues are transformed into colored degradation products that, in their turn, might release in addition reactive degradation products.
Besides efficient sorting, the removal of visible impurity particles by melt filtration processes plays a particular part in this case.
Depending on composition and impurity level of input material, the general following process steps are applied.
As far as recycled PET bottles are concerned, the defects mentioned can be sorted in the following groups: Taking into consideration the above-mentioned chemical defects and impurities, there is an ongoing modification of the following polymer characteristics during each recycling cycle, which are detectable by chemical and physical laboratory analysis.
In particular: The recycling of PET bottles is meanwhile an industrial standard process that is offered by a wide variety of engineering companies.
Some exceptions like BOPET-film of low thickness, special applications like optical film or yarns through FDY-spinning at > 6000 m/min, microfilaments, and micro-fibers are produced from virgin polyester only.
Product is an amorphous re-granulate of an intrinsic viscosity in the range of 0.55–0.7, depending on how complete pre-drying of PET flakes has been done.
The fact that some machine manufacturers and line builders in Europe and the United States make efforts to offer independent recycling processes, e.g. the so-called bottle-to-bottle (B-2-B) process, such as Next Generation Recycling (NGR), BePET, Starlinger, URRC or BÜHLER, aims at generally furnishing proof of the "existence" of the required extraction residues and of the removal of model contaminants according to FDA applying the so-called challenge test, which is necessary for the application of the treated polyester in the food sector.
[citation needed] With regard to the consumption of PET bottle flakes, the main portion of about 70% is converted to fibers and filaments.
For the time-being, the amount of POY made of 100% recycling polyester is rather low because this process requires high purity of spinning melt.
[citation needed] One field of increasing interest where recycled materials are used is the manufacture of high-tenacity packaging stripes, and monofilaments.
[citation needed] PET polymer is very sensitive to hydrolytic degradation, resulting in severe reduction in its molecular weight, thereby adversely affecting its subsequent melt processability.
Therefore, it is essential to dry the PET flakes or granules to a very low moisture level prior to melt extrusion.
If the air dew point is not good, then some moisture remains in the chips and cause IV loss during processing.
Polyethylene terephthalate can be depolymerized partially or completely to yield the constituent oligomers or the monomers, MEG and PTA or DMT.
[24] Partial glycolysis (transesterification with ethylene glycol) converts the rigid polymer into short-chained oligomers that can be melt-filtered at low temperature.
The destruction of the hydro peroxide groups is, with other processes, already carried out during the last step of flake treatment for instance by adding H3PO3.
The reaction involved is as follows:[23] This recycling route has been executed on an industrial scale in Japan as experimental production.
[citation needed] converts the polyester to dimethyl terephthalate(DMT), which can be filtered and vacuum distilled:[23] Even though polyester production based on dimethyl terephthalate(DMT) is limited to legacy plants,[26] investments were announced in 2021 and 2022 into methanolysis plants.
In April 2020, a French university in collaboration with Carbios announced the discovery of a highly efficient, optimized enzyme claimed to outperform all PET hydrolases reported so far.
[36] In Europe, the EU Waste Framework Directive mandates that by 2020 there should be 50% recycling or reuse of plastics from household streams.
PET is useful for this purpose because many other materials (including window glass) that are transparent to visible light are opaque to ultraviolet radiation.
Studies have shown that mechanical recycle has a lower environmental impact than incineration, due to avoided new raw material production.
