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Recently, molecular level stabilization of the material using nanostructured chemicals has also been considered. Acetaldehyde is a colorless, volatile substance with a fruity smell. Although it forms naturally in some fruit, it can cause an off-taste in bottled water. Acetaldehyde forms by degradation of PET through the mishandling of the material. When acetaldehyde is produced, some of it remains dissolved in the walls of a container and then diffuses into the product stored inside, altering the taste and aroma.
This is not such a problem for non-consumables such as shampoo , for fruit juices which already contain acetaldehyde , or for strong-tasting drinks like soft drinks. For bottled water, however, low acetaldehyde content is quite important, because, if nothing masks the aroma, even extremely low concentrations 10—20 parts per billion in the water of acetaldehyde can produce an off-taste.
Antimony Sb is a metalloid element that is used as a catalyst in the form of compounds such as antimony trioxide Sb 2 O 3 or antimony triacetate in the production of PET. After manufacturing, a detectable amount of antimony can be found on the surface of the product.
This residue can be removed with washing. Antimony also remains in the material itself and can, thus, migrate out into food and drinks. The Swiss Federal Office of Public Health investigated the amount of antimony migration, comparing waters bottled in PET and glass: The antimony concentrations of the water in PET bottles were higher, but still well below the allowed maximum concentration.
A later but more widely publicized study found similar amounts of antimony in water in PET bottles. Fruit juice concentrates for which no guidelines are established , however, that were produced and bottled in PET in the UK were found to contain up to At least one species of bacterium in the genus Nocardia can degrade PET with an esterase enzyme. Japanese scientists have isolated a bacterium Ideonella sakaiensis that possesses two enzymes which can break down the PET into smaller pieces that the bacterium can digest.
A colony of I. In April , a French university announced the discovery of a highly efficient, optimized enzyme that outperforms all PET hydrolases reported so far. Commentary published in Environmental Health Perspectives in April suggested that PET might yield endocrine disruptors under conditions of common use and recommended research on this topic.
There are two basic molding methods for PET bottles, one-step and two-step. In two-step molding, two separate machines are used. The first machine injection molds the preform, which resembles a test tube, with the bottle-cap threads already molded into place.
The body of the tube is significantly thicker, as it will be inflated into its final shape in the second step using stretch blow molding. In the second step, the preforms are heated rapidly and then inflated against a two-part mold to form them into the final shape of the bottle. Preforms uninflated bottles are now also used as robust and unique containers themselves; besides novelty candy, some Red Cross chapters distribute them as part of the Vial of Life program to homeowners to store medical history for emergency responders.
In one-step machines, the entire process from raw material to finished container is conducted within one machine, making it especially suitable for molding non-standard shapes custom molding , including jars, flat oval, flask shapes, etc. Its greatest merit is the reduction in space, product handling and energy, and far higher visual quality than can be achieved by the two-step system.
In , it was estimated that 56 million tons of PET are produced each year. PET has a resin identification code of 1. Because of the recyclability of PET and the relative abundance of post-consumer waste in the form of bottles, PET is rapidly gaining market share as a carpet fiber. Since that time, more than 17 billion bottles have been recycled into carpet fiber. PET, like many plastics, is also an excellent candidate for thermal disposal incineration , as it is composed of carbon, hydrogen, and oxygen, with only trace amounts of catalyst elements but no sulfur.
PET has the energy content of soft coal. When recycling polyethylene terephthalate or PET or polyester, in general three ways have to be differentiated:. Such lines could only be seen, if at all, within the production sites of very large polyester producers. Several attempts of industrial magnitude to establish such chemical recycling plants have been made in the past but without resounding success. Even the promising chemical recycling in Japan has not become an industrial breakthrough so far.
The two reasons for this are: at first, the difficulty of consistent and continuous waste bottles sourcing in such a huge amount at one single site, and, at second, the steadily increased prices and price volatility of collected bottles. Mechanical recycling or direct circulation of PET in the polymeric state is operated in most diverse variants today.
These kinds of processes are typical of small and medium-size industry. In this case, nearly all kinds of recycled-material feedback into the material circulation are possible today. These diverse recycling processes are being discussed hereafter in detail. Besides chemical contaminants and degradation products generated during first processing and usage, mechanical impurities are representing the main part of quality depreciating impurities in the recycling stream.
Recycled materials are increasingly introduced into manufacturing processes, which were originally designed for new materials only. Therefore, efficient sorting, separation and cleaning processes become most important for high quality recycled polyester. When talking about polyester recycling industry, we are concentrating mainly on recycling of PET bottles, which are meanwhile used for all kinds of liquid packaging like water, carbonated soft drinks, juices, beer, sauces, detergents, household chemicals and so on.
Bottles are easy to distinguish because of shape and consistency and separate from waste plastic streams either by automatic or by hand-sorting processes. The established polyester recycling industry consists of three major sections:. Most common trading form is the bale but also bricked or even loose, pre-cut bottles are common in the market. In the second section, the collected bottles are converted to clean PET bottle flakes.
This step can be more or less complex and complicated depending on required final flake quality. During the third step, PET bottle flakes are processed to any kind of products like film, bottles, fiber, filament, strapping or intermediates like pellets for further processing and engineering plastics. Besides this external post-consumer polyester bottle recycling, numbers of internal pre-consumer recycling processes exist, where the wasted polymer material does not exit the production site to the free market, and instead is reused in the same production circuit.
In this way, fiber waste is directly reused to produce fiber, preform waste is directly reused to produce preforms, and film waste is directly reused to produce film. 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.
In general, the following applies: The earlier in the process foreign substances are removed, and the more thoroughly this is done, the more efficient the process is. The influence of the microscopic particles, which—because they are many—increase the frequency of defects in the polymer, is relatively greater. The motto "What the eye does not see the heart cannot grieve over" is considered to be very important in many recycling processes.
Therefore, besides efficient sorting, the removal of visible impurity particles by melt filtration processes plays a particular part in this case. In general, one can say that the processes to make PET bottle flakes from collected bottles are as versatile as the different waste streams are different in their composition and quality. In view of technology there is not just one way to do it.
Meanwhile, there are many engineering companies that are offering flake production plants and components, and it is difficult to decide for one or other plant design. Nevertheless, there are processes that are sharing most of these principles. Depending on composition and impurity level of input material, the general following process steps are applied.
The number of possible impurities and material defects that accumulate in the polymeric material is increasing permanently—when processing as well as when using polymers—taking into account a growing service lifetime, growing final applications and repeated recycling.
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.
The recycling of PET bottles is meanwhile an industrial standard process that is offered by a wide variety of engineering companies. Recycling processes with polyester are almost as varied as the manufacturing processes based on primary pellets or melt.
This process consists of transforming bottle waste into flakes, by drying and crystallizing the flakes, by plasticizing and filtering, as well as by pelletizing. Product is an amorphous re-granulate of an intrinsic viscosity in the range of 0. Special feature are: Acetaldehyde and oligomers are contained in the pellets at lower level; the viscosity is reduced somehow, the pellets are amorphous and have to be crystallized and dried before further processing.
Choosing the re-pelletizing way means having an additional conversion process that is, at the one side, energy-intensive and cost-consuming, and causes thermal destruction. At the other side, the pelletizing step is providing the following advantages:. This process is, in principle, similar to the one described above; however, the pellets produced are directly continuously or discontinuously crystallized and then subjected to a solid-state polycondensation SSP in a tumbling drier or a vertical tube reactor.
During this processing step, the corresponding intrinsic viscosity of 0. The fact that some machine manufacturers and line builders in Europe and the United States make efforts to offer independent recycling processes, e. Besides this process approval it is nevertheless necessary that any user of such processes has to constantly check the FDA limits for the raw materials manufactured by themselves for their process.
In order to save costs, an increasing number of polyester intermediate producers like spinning mills, strapping mills, or cast film mills are working on the direct use of the PET-flakes, from the treatment of used bottles, with a view to manufacturing an increasing number of polyester intermediates. For the adjustment of the necessary viscosity, besides an efficient drying of the flakes, it is possibly necessary to also reconstitute the viscosity through polycondensation in the melt phase or solid-state polycondensation of the flakes.
The latest PET flake conversion processes are applying twin screw extruders, multi-screw extruders or multi-rotation systems and coincidental vacuum degassing to remove moisture and avoid flake pre-drying. These processes allow the conversion of undried PET flakes without substantial viscosity decrease caused by hydrolysis. When using directly secondary materials such as bottle flakes in spinning processes, there are a few processing principles to obtain.
High-speed spinning processes for the manufacture of POY normally need a viscosity of 0. Starting from bottle flakes, the viscosity can be set via the degree of drying. The additional use of TiO 2 is necessary for full dull or semi dull yarn. In order to protect the spinnerets, an efficient filtration of the melt is, in any case is necessary. Most of the time, a blend of virgin and recycled pellets is used.
Staple fibers are spun in an intrinsic viscosity range that lies rather somewhat lower and that should be between 0. In this case, too, the required viscosity can be adjusted via drying or vacuum adjustment in case of vacuum extrusion. For adjusting the viscosity, however, an addition of chain length modifier like ethylene glycol or diethylene glycol can also be used.
Spinning non-woven—in the fine titer field for textile applications as well as heavy spinning non-woven as basic materials, e. The spinning viscosity is again within a range of 0. One field of increasing interest where recycled materials are used is the manufacture of high-tenacity packaging stripes, and monofilaments. In both cases, the initial raw material is a mainly recycled material of higher intrinsic viscosity. High-tenacity packaging stripes as well as monofilament are then manufactured in the melt spinning process.
Polyethylene terephthalate can be depolymerized to yield the constituent monomers. After purification, the monomers can be used to prepare new polyethylene terephthalate. The ester bonds in polyethylene terephthalate may be cleaved by hydrolysis, or by transesterification. The reactions are simply the reverse of those used in production. Partial glycolysis transesterification with ethylene glycol converts the rigid polymer into short-chained oligomers that can be melt-filtered at low temperature.
Once freed of the impurities, the oligomers can be fed back into the production process for polymerization. This aim is solved by degrading the PET bottle flakes—already during their first plasticization, which can be carried out in a single- or multi-screw extruder—to an intrinsic viscosity of about 0.
Furthermore, temperature is brought to the lowest possible limit. In addition, with this way of processing, the possibility of a chemical decomposition of the hydro peroxides is possible by adding a corresponding P-stabilizer directly when plasticizing. 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 H 3 PO 3.
This compound is purified by vacuum distillation, and is one of the intermediates used in polyester manufacture see production. The reaction involved is as follows:. This recycling route has been executed on an industrial scale in Japan as experimental production.
Similar to total glycolysis, methanolysis converts the polyester to dimethyl terephthalate DMT , which can be filtered and vacuum distilled:. Methanolysis is only rarely carried out in industry today because polyester production based on dimethyl terephthalate DMT has shrunk tremendously, and many dimethyl terephthalate DMT producers have disappeared. Also as above, polyethylene terephthalate can be hydrolyzed to terephthalic acid and ethylene glycol under high temperature and pressure.
The resultant crude terephthalic acid can be purified by recrystallization to yield material suitable for re-polymerization:. This method does not appear to have been commercialized yet. From Wikipedia, the free encyclopedia.
For other uses, see Pete disambiguation. CAS Number. Chemical formula. Solubility in water. Refractive index n D. Heat capacity C. Related Monomers. Chemical compound. A PET bottle which has been heated by a candle and has recrystallized, making it opaque. Aluminized Mylar ballons filled with helium. Добавить в корзину Перейти в корзину В лист ожидания Добавлено в Лист ожидания. Купить сейчас.
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