Polyethylene Terephthalate PET: Properties and Applications

Polyethylene Terephthalate (PET) - Complete Overview

What is Polyethylene Terephthalate?

Polyethylene terephthalate (PET, PETP) is a thermoplastic polymer and the most common representative of the polyester class. It is known under various trade names: Dacron, Mylar, Terylene, Lavsan. PET is a solid, colorless, transparent substance in its amorphous state and white, opaque in its crystalline state.

Polyethylene terephthalate is produced by polycondensation of terephthalic acid (or its dimethyl ester) with ethylene glycol. The molecular formula is (C₁₀H₈O₄)n. The molecular weight is 20,000-40,000.

History

Research on polyethylene terephthalate began in 1935 in Great Britain by Whinfield and Dickson. Patent applications for the synthesis of fiber-forming PET were filed in 1941 and 1943. In the USSR, the polymer was first obtained in 1949 at the Institute of High Molecular Compounds of the Academy of Sciences, giving rise to the name "LAVSAN". The PET bottle was patented in 1973.

How is PET Produced?

The main raw materials for PET production are terephthalic acid and ethylene glycol, derived from petroleum and coke chemistry products. The production process consists of two main stages:

Esterification - esterification of the acid with ethylene glycol in a molar ratio of 1:1.2 to 1:1.5 at 240-250 °C under pressure up to 0.2 MPa.

Polycondensation - the resulting mixture undergoes polycondensation in sequentially arranged units at temperatures up to 300 °C and pressure reduced to 66 Pa.

The finished PET material is produced as granules of 2-4 mm in size. All necessary dyes and additives are introduced during synthesis or into the resulting melt.

PET can exist in two states: amorphous (transparent, formed by rapid cooling) and crystalline (opaque, white). An important parameter of PET is intrinsic viscosity, determined by the polymer chain length.

Key Physical and Chemical Properties

Polyethylene terephthalate has a number of unique properties that determine its wide application.

Density - amorphous: 1.335-1.370 g/cm³, crystalline: 1.420-1.455 g/cm³. Crystallinity of unoriented PET is 40-45%, oriented - 60-65%.

Melting point - 250-265 °C. Softening temperature - 245-248 °C. Glass transition temperature: amorphous PET - 67 °C, crystalline - 81-98 °C.

Strength - tensile strength is 172 MPa, tensile modulus - 1.41×10⁴ MPa. PET is characterized by wear resistance, dimensional stability under mechanical loads, and good impact toughness. Elongation at break - 12-55%.

Dielectric properties - dielectric constant (at 23 °C, 1 kHz) is 3.25. PET is a good dielectric.

Chemical resistance - PET is insoluble in water and organic solvents, resistant to dilute acids (70% H₂SO₄, 5% HCl, 30% CH₃COOH), cold alkali solutions, and bleaching agents. Resistant to alcohols, oils, and fats. At temperatures above 100 °C, it is hydrolyzed by alkali solutions, and at 200 °C - even by water.

Water absorption - 0.3%. At 65% relative humidity, textile fiber absorbs 0.4% moisture.

Operating temperature range - retains properties from -40 to +75 °C. Cold resistance - down to -50 °C. PET does not burn and does not support combustion.

Bottle-Grade PET

Bottle-grade PET is a special polymer grade designed for the production of food and beverage containers. The key parameter for bottle-grade PET is intrinsic viscosity (IV). For water bottles, grades with IV 0.72-0.78 dL/g are used; for carbonated beverages - IV 0.80-0.84 dL/g.

Bottle production - PET granules are processed by injection molding followed by blow molding. PET is used to make plastic bottles for soft drinks and mineral water, bottles and jars for cosmetics.

Advantages of PET containers - unlike glass bottles, PET containers do not break and weigh less. PET packaging has transparency, high strength, good plasticity, and high barrier properties.

Textile PET (Polyester Fibers)

Textile PET is a polymer processed into fibers and yarns for fabric production. PET is the predominant polyester used for fiber production.

Fiber production - most PET fibers are produced by melt spinning, where the molten polymer is forced through a spinneret. There are two main types of production processes: two-stage (batch) spin-draw process.

Properties of textile PET - PET fibers do not wrinkle, are strong, absorb little water, and are breathable. Breaking strength of fibers can reach 4.2 cN/tex. PET textiles are considered hydrophobic.

Applications - polyester fibers are used for clothing (including functional sportswear), technical textiles, and nonwoven materials. PET is used for blended fabrics based on wool and cotton.

PET Recycling (rPET)

Polyethylene terephthalate is well suited for recycling. Recycling used PET bottles into fibers and new bottles is an important area of the circular economy.

Recycling technologies - there are "bottle-to-bottle" technologies allowing up to 100% recycled material for new bottles. Studies show that recycled PET fibers compete with virgin materials in tensile strength, elongation, and abrasion resistance.

Applications of recycled PET - rPET is used for clothing, technical textiles, and nonwoven materials.

Applications of PET

Thanks to its unique combination of properties, polyethylene terephthalate has found the widest application in various industries.

Packaging and containers - the largest consumption segment. Plastic bottles for beverages and mineral water, packaging films and tapes, trays and blister packaging, bottles and jars for cosmetics.

Textile industry - polyester fibers and yarns, blended fabrics based on wool and cotton.

Films - BOPET (biaxially oriented) for flexible packaging, PET-G (heat-shrinkable and printing), A-PET (amorphous high-strength) for food packaging. Films have high grease resistance, no odor, and do not react with food products.

Mechanical engineering and automotive - pipes, washer reservoirs, bumpers, fuel tanks, body parts.

Electronics - electronic components, cable products.

Medicine - packaging for pharmaceutical products.

3D printing - used in additive manufacturing.

Major PET Producing Countries

The global polyethylene terephthalate market is characterized by high production concentration. China remains the world's largest producer, accounting for about 36% of global production volume. The United States ranks second with about 13% share, Saudi Arabia - third.

Major manufacturers:

• Indorama Ventures (Thailand) - the world's largest integrated PET and rPET producer with operations in more than 30 countries.

• Alpek S.A.B. de C.V. (Mexico) - one of the largest PET suppliers in the western hemisphere.

• Reliance Industries Limited (India) - one of the largest integrated polyester producers.

• Far Eastern New Century (Taiwan).

• Lotte Chemical (South Korea).

• Sinopec (China).

• Toray Industries (Japan).

• Eastman Chemical (USA).

Production regions: The Asia-Pacific region dominates PET production. Major production facilities are also located in North America, Europe, and the Middle East.

Conclusion

Polyethylene terephthalate is one of the most versatile and in-demand polymer materials of our time. Thanks to its unique combination of transparency, strength, chemical resistance, and easy processability, it holds key positions in the production of bottles, textile fibers, packaging films, and technical products. The ability to recycle makes PET an important material for the circular economy. Understanding the specifics of production, properties, and global trends helps market participants make informed purchasing decisions for this raw material.