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Polyethylene terephthalate

What is Polyethylene terephthalate (PET)

Polyethylene terephthalate is a polymer that is used in most countries to produce polyester fibers (70%), bottle resin (22%), film (6%) and engineering polyester resins (2%), but in Iran this polymer is mostly used for to make different types of drinking bottles. Due to the high resistance of these bottles against breakage, temperature and penetration of gases, having a low weight and cheap price compared to other packaging materials such as glass and metal, the production of plastic bottles from this resin has been widely used. Which of course causes the consumption of PET bottles to enter the municipal waste stream. The high volume of these bottles in relation to the weight, which take up a lot of space during transportation and burial, and its very long decomposition in nature (about 300 years), has caused the problem of recycling these bottles, especially in the year To attract everyone’s attention.

How to produce PET

Pure terephthalic acid (PTA) is obtained from paraxylene in a process of the same name. In the PTA unit, by oxidizing paraxylene in the presence of air and during different stages and finally washing with acetic acid, a product called pure terephthalic acid is obtained.The appearance of this product, despite the fact that its name starts with acid, is in the form of powders in the size of 40 to 200 microns. Terephthalic acid is combined with ethylene glycol in another unit during a chemical process, and finally polyethylene terephthalate or PET is obtained. The appearance of this product is similar to chips and has different grades that the bottle grade and its fiber grade is produced in the PET unit of petrochemical complexes. In fact, these chips are melted in downstream industries and converted into plastic products through chemical processes.

PET uses and properties

Today, PET is mainly obtained by combining ethylene glycol with terephthalic acid with the help of heat and catalyst, which is a linear and solvent-resistant polymer. Special physical and chemical properties of PET such as high mechanical strength, joint strength, transparency, light weight, safe Its toxicity and impermeability to CO2 have led to its widespread use in the manufacture of photographic films, beverage bottles and fibers. It is also used in the production of BCF continuous fibers and industrial yarns and POY, textile staples and garments. It is also used as food packaging due to the ineffectiveness of PET in taste and heat stability.

Advantages and disadvantages of using PET

The advantage of using PET bottles is that the bottle lid can be opened easily and can be closed again, and they are also light and cheap. PET inherently has the characteristics of biodegradable plastics and in two years more than 30% of it is destroyed underground, which is a more suitable solution to recycle PET and turn it into consumer products. Although these materials make up a small percentage of the total waste of the community (about 7%), but due to their low density, they contain a high volume of about 30% of the total waste. Typically, about 800 kg of waste is stored per cubic meter of landfill, while one cubic meter of landfill can hold only 35 kg of bottles.

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