. 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 0.30 dℓ/g by adding small quantities of ethylene glycol and by subjecting the low-viscosity melt stream to an efficient filtration directly after plasticization. The established polyester recycling industry consists of three major sections: Intermediate product from the first section is baled bottle waste with a PET content greater than 90%.  These processes allow the conversion of undried PET flakes without substantial viscosity decrease caused by hydrolysis. Partial glycolysis (transesterification with ethylene glycol) converts the rigid polymer into short-chained oligomers that can be melt-filtered at low temperature.  This discovery may prove to be an important step towards the concept of a circular PET economy. PET is one of the most recycled thermoplastic, and has the number "1" as its recycling symbol. Terylene (a trademark formed by inversion of (polyeth)ylene ter(ephthalate)) is also spliced into bell rope tops to help prevent wear on the ropes as they pass through the ceiling. The low softening temperature of PET—approximately 70 °C (160 °F)—prevents it from being used as a container for hot foods. 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. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica.  While most thermoplastics can, in principle, be recycled, PET bottle recycling is more practical than many other plastic applications because of the high value of the resin and the almost exclusive use of PET for widely used water and carbonated soft drink bottling. Product is an amorphous re-granulate of an intrinsic viscosity in the range of 0.55–0.7 dℓ/g, depending on how complete pre-drying of PET flakes has been done. PET was patented in 1941 by John Rex Whinfield, James Tennant Dickson and their employer the Calico Printers' Association of Manchester, England. Polyethylene terephthalate can be depolymerized to yield the constituent monomers. Such lines could only be seen, if at all, within the production sites of very large polyester producers. Water is also produced as a by-product. formation of vinyl ester end groups through dehydration or decarboxylation of terephthalate acid, reaction of the OH- or COOH- end groups with mono-functional degradation products like mono-carbonic acids or alcohols. These kinds of processes are typical of small and medium-size industry. The monomer bis(2-hydroxyethyl) terephthalate can be synthesized by the esterification reaction between terephthalic acid and ethylene glycol with water as a byproduct (this is also known as a condensation reaction), or by transesterification reaction between ethylene glycol and dimethyl terephthalate (DMT) with methanol as a byproduct. Also as above, polyethylene terephthalate can be hydrolyzed to terephthalic acid and ethylene glycol under high temperature and pressure.  If crystallizable PET is used, the trays can be used for frozen dinners, since they withstand both freezing and oven baking temperatures. You can find this famous clear plastic around you as water bottle or soda bottle container. In this form, PET has become widely used in carbonated-beverage bottles and in jars for food processed at low temperatures. The treatment of polyester waste through total glycolysis to fully convert the polyester to bis(2-hydroxyethyl) terephthalate (C6H4(CO2CH2CH2OH)2). In order to protect the spinnerets, an efficient filtration of the melt is, in any case is necessary. Based on how it is processed, PET can be semi-rigid to rigid, and it is very lightweight. One of the most important characteristics of PET is referred to as intrinsic viscosity (IV).. Typically, residual moisture levels in the resin must be less than 50 parts per million (parts of water per million parts of resin, by weight) before processing. In chemical terms, ethylene glycol is a diol, an alcohol with a molecular structure that contains two hydroxyl (OH) groups, and terephthalic acid is a dicarboxylic aromatic acid, an acid with a molecular structure that contains a large six-sided carbon (or aromatic) ring and two carboxyl (CO2H) groups. PET soon became the most widely produced synthetic fibre in the world. This is causing the liberation of further degradation-supporting substances and coloring substances. One field of increasing interest where recycled materials are used is the manufacture of high-tenacity packaging stripes, and monofilaments. 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. Methanol (CH3OH) is removed by distillation to drive the reaction forward. Our editors will review what you’ve submitted and determine whether to revise the article. The resulting cool wet air is then passed through a desiccant bed. 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. 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. At a slightly higher molecular weight, PET is made into a high-strength plastic that can be shaped by all the common methods employed with other thermoplastics. The fact that some machine manufacturers and line builders in Europe and the United States make efforts to offer independent recycling processes, e.g. During this processing step, the corresponding intrinsic viscosity of 0.80–0.085 dℓ/g is rebuild again and, at the same time, the acetaldehyde content is reduced to < 1 ppm. , In the Soviet Union, PET was first manufactured in the laboratories of the Institute of High-Molecular Compounds of the USSR Academy of Sciences in 1949, and its name "Lavsan" is an acronym thereof (лаборатории Института высокомолекулярных соединений Академии наук СССР). 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. Starting from bottle flakes, the viscosity can be set via the degree of drying. Number, concentration, and variety of nonpolymer-identical organic and inorganic foreign substances are increasing. Number of polyfunctional macromolecules increases. They are often used in durable-press blends with other fibres such as rayon, wool, and cotton, reinforcing the inherent properties of those fibres while contributing to the ability of the fabric to recover from wrinkling. In dimethyl terephthalate(DMT) process, this compound and excess ethylene glycol are reacted in the melt at 150–200 °C with a basic catalyst. Several attempts of industrial magnitude to establish such chemical recycling plants have been made in the past but without resounding success. 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. It makes a good gas and fair moisture barrier, as well as a good barrier to alcohol (requires additional "barrier" treatment) and solvents. Escalator with a pile of plastic bottles at a factory for processing and recycling polyethylene terephthalate (PET). Because of wartime restrictions, patent specifications for the new material were not immediately published. Other packaging applications include rigid cosmetic jars, microwavable containers, transparent films, etc. For certain specialty bottles, such as those designated for beer containment, PET sandwiches an additional polyvinyl alcohol (PVOH) layer to further reduce its oxygen permeability. It is resealable; because it is easy to mold into any shape, it is easy to seal. The ester bonds in polyethylene terephthalate may be cleaved by hydrolysis, or by transesterification. During an ulterior treatment process, hydro peroxides are a source of oxygen radicals, which are source of oxidative degradation. E. I. DuPont de Nemours in Delaware, United States, first used the trademark Mylar in June 1951 and received registration of it in 1952. 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. With regard to the consumption of PET bottle flakes, the main portion of about 70% is converted to fibers and filaments. Commentary published in Environmental Health Perspectives in April 2010 suggested that PET might yield endocrine disruptors under conditions of common use and recommended research on this topic. Intrinsic viscosity is dependent upon the length of its polymer chains but has no units due to being extrapolated to zero concentration. Once freed of the impurities, the oligomers can be fed back into the production process for polymerization. There are two basic molding methods for PET bottles, one-step and two-step. Because of its high mechanical strength, PET film is often used in tape applications, such as the carrier for magnetic tape or backing for pressure-sensitive adhesive tapes. 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. The majority of the world's PET production is for synthetic fibres (in excess of 60%), with bottle production accounting for about 30% of global demand. 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. Thus, before the resin can be processed in a molding machine, it must be dried. In two-step molding, two separate machines are used. When recycling polyethylene terephthalate or PET or polyester, in general three ways have to be differentiated: Chemical recycling of PET will become cost-efficient only applying high capacity recycling lines of more than 50,000 tons/year. For PET bottles, the use of small amounts of isophthalic acid, CHDM, diethylene glycol (DEG) or other comonomers can be useful: if only small amounts of comonomers are used, crystallization is slowed but not prevented entirely. 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. 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. The first machine injection molds the preform, which resembles a test tube, with the bottle-cap threads already molded into place.  Although antimony trioxide is of low toxicity when taken orally, its presence is still of concern. The average chain length of a particular batch of resin can be controlled during polycondensation.
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