What is polyethylene terephthalate (PET) or PET?

What is polyethylene terephthalate (PET) or PET?

Polyethylene terephthalate (PET) is a thermoplastic polymer from the polyester family, which is produced by a one-step polymerization method of the reaction between pure terephthalic acid (PTA) and monoethylene glycol (MEG). The glass transition temperature of this polymer is about Cº It is 80.

تنوع زیادی در ویژگی های این پلیمر، بسته به کاربرد و نحوه جهت یافتگی زنجیرهای پلیمری مشاهده می شود.این پلیمر در دمای حدود Cº255 ذوب می شود و در صورتیکه سریع سرد شود تقریبا به صورت کاملا آمورف در آمده و چگالی آن در حدود gr/cm31.33 خواهد بود .به دلیل حرکت های آهسته ملکولی ، بلورینگی در حدود دمای Cº80 آغاز می شود و در دمای Cº 130 چگالی آن به مقدار gr/cm3 1.37 افزایش می یابد . با جهت یافتگی مناسب و اعمال گرما چگالی تا gr/cm3 1.40 نیز افزایش می‌یابد .

Polyethylene terephthalate is a polymer that is used in most countries to produce polyester fibers (70 percent), bottle resin (22 percent), film (6 percent) and engineering polyester resins (2 percent), but in Iran this polymer is more It is used to make all kinds of drinking bottles. Due to the high resistance of these bottles against breakage, temperature and gas penetration, 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 consequently causes the entry of disposable PET bottles into the municipal waste stream. The high volume of these bottles compared to their weight, which take up a lot of space during transportation and burial, and the very long decomposition in nature (about 300 years), has caused the problem Recycle These bottles have attracted everyone’s attention, especially in recent years.

Properties of PET:

The order in the polymer chain structure increases the crystallinity, which is important for determining the mechanical properties. The phenyl group in the main chain adds rigidity to the skeleton and is responsible for the high Tg and melting temperature. Its chemical resistance is like nylon (polyamide), which makes it have very good waterproof properties.
PET can exist in both crystalline and amorphous states, and its degree of crystallization is determined by the thermal history of the material. PET fibers and thin films are prepared by extrusion and cooling at ambient temperature. Considering that the highest crystallization rate occurs at a temperature of about 170°C, the degree of crystallization can also be between the melting temperature (mT) and the glass transition temperature (Tg) by annealing. 290 occurs.
The most volatile products are: terephthalic acid, acetaldehyde and carbon monoxide. At a temperature of 900°C, a large number of hydrocarbons are produced along with carbon dioxide, carbon monoxide and methane, which are the main volatile substances, and there is a possibility of oxidation during the process. A wide range of antioxidants can be used to prevent oxidation of PET during the process.

Physical characteristics:

انواعPET :

معمولا PET در چهار نوع زیر موجود است:

• بطری: This type of PET is used to produce bottles, which determines the type of bottle used
• الیاف : This type of PET is also used in clothes and all kinds of PET films.
• Film: This type of PET is used in the preparation of various packaging sheets.
• آمورف: از این نوع PET شکل هندسی خاصی نداشه و مبنای نامگذاری آن نیز بر این اساس است .( آمورف : بی شکل)

کاربری ها :

به دلیل گستره وسیع خواص PETمانند توانایی کنترل میزان کریستالی شدن͵PET کاربردهای بسیاری پیدا کرده است. کاربرد اصلی آن در بطری های نوشیدنی های گازدار است که دلیل آن خاصیت نفوذناپذیری بالا در برابر گازها در PET می باشد.برای این منظورPET آمورف در دمای بالای Tgو به صورت جهت دار میکشند تا خاصیت کریستالی پیدا کند. یک مشکلی که PET از خود نشان میدهد این است که بعد از مدتی تمایل به حالت کریستالی پیدا میکند که این باعث تغییر در خواص می گرددو می تواند منجر به تغییرات ابعادی شود (جمع شدگی و یا تاب برداشتن).

Applications :

Of course, PET is also recyclable, and the first use of recycled PET in the world and Iran is fibers, sheets and belts, and injection or blowing products.

موارد ایمنی:

PET is biologically neutral, dermally safe to handle. اگر بلعیده و یا استنشاق شود خطرناک نمی باشد. No evidence of toxicity was found in animal feeding studies. Negative results from Ames tests and studies on synthetic DNA (non-programmable) showed that PET has no toxicity on genes. مطالعات مشابه بر روی منومرها و ترکیبات واسطه PET نشان می دهد که این مواد به صورت ضروری سمی نیستند و هیچ تهدیدی برای انسان در بر ندارد. One of the special substances used on a large scale is antimony trioxide, which causes cancer. However, thorough animal feeding studies have shown that there is no risk from the use of antimony in PET production. Studies on diets containing 20 g/kg of antimony trioxide had no detectable toxic effects on animals, and genotoxin tests were mostly negative.
غدد درون ریز بدن انسان که کنترل فرایندهای حیاتی انسان نظیر تولید مثل ، تنظیم متابولیسم و دیگر جنبه های توسعه قبل از تولد را به عهده دارد .مواد شیمیایی مصنوعی ساخت بشر ، در صورت جذب در بدن باعث از هم پاشیدن هورمون استروژن اختلال در چرخه غدد درون ریز ، اختلال در تولید مثل و کاهش در تعداد اسپرم میگردد.پس این نکته مهم است که ترکیبات استفاده شده در PET هیچ مدرکی مبنی بر فعالیت استروژنیک نداشته باشند.یک مدرک مهم وجود دارد که نشان میدهد که این مواد غیر سرطانی و نسبتا ایمن اند.

Studies on diets containing 20 g/kg of antimony trioxide had no detectable toxic effects on animals, and genotoxin tests were mostly negative.

The advantage of using PET bottles is that the bottle cap is easy to remove and can be closed again, and they are also light and cheap. PET inherently has the characteristics of biodegradable plastics and within two years below More than 30 percent of the soil is destroyed, so recycling PET and turning it into consumable products is a more suitable solution. Although these materials make up a small percent by weight of the total waste of the society (about 7%), but due to their low density, they contain a high volume of about 30% of the total waste. Normally, about 800 kilograms of waste can be placed in each cubic meter of burial space, while one cubic meter of burial space can only accommodate 35 kilograms of bottles.

Production units:

Among the producers of polyethylene terephthalate (PET) in the world are Kolon, Eastman, Polyclear, Cleartuf, Honam, Sabic.

In Iran, Shahid Tendgovian Petrochemical produces all kinds of PET grades. ; The production grades of this product are as follows:

TGpet 621 TG 621 fiber grade – Shahid Tendgoyan Petrochemical.
TG641 Super Bright Pet Super Bright TG 641 fiber grade – Shahid Tendgoyan Petrochemical.
TG Pet 645 TG 645 fiber grade – Shahid Tendgoyan Petrochemical.
TG Pet 732 TG 732 fiber grade – Shahid Tendgoyan Petrochemical.
BG Pet 781 BG 781 bottle grade – Shahid Tendgoyan Petrochemical.
BG Pet 800 BG 800 bottle grade – Shahid Tendgoyan Petrochemical.
BG Pet 805 BG 805 bottle grade – Shahid Tendgoyan Petrochemical.
BG Pet 821 BG 821 bottle grade – Shahid Tendgoyan Petrochemical.
BG Pet 825 BG 825 bottle grade – Shahid Tendgoyan Petrochemical.
BG Pet 841 BG 841 bottle grade – Shahid Tendgoyan Petrochemical.
BG Pet 845 BG 845 bottle grade – Shahid Tendgoyan Petrochemical.