Unveiling Plastic No. 1—How Much Do You Really Know About PET?

2024-08-12

PET or PETE (Polyethylene Terephthalate), labeled as Plastic No. 1, is ubiquitous in daily life—from beverage bottles to storage containers and even coffee cups. You can easily spot the number 1 at the bottom of bottled water containers. In 2023, PET accounted for 20% to 25% of the global plastics market, with a market size reaching $48.43 billion. Despite its widespread use, PET is often referred to simply as “plastic bottles,” with its actual chemical name remaining unfamiliar to many.

It's time to dive deeper into plastic No. 1—PET! Here’s what you should know:

1. What is PET Resin or PET Plastic?

PET, short for Polyethylene Terephthalate, has the chemical formula (C10H8O4)n. Firstly synthesized in the 1940s, it was initially used for fiber production and later evolved in the 1970s as a substitute for glass bottles. It is called "polyester" in textiles and "PET" or "PET resin" in packaging.

2. What Are PET’s Applications?

PET is primarily used in textiles and packaging: 81.2% in polyester fibers, 11.7% in bottle grade PET, and 7.1% in films.

In textiles, PET is known for their durability, strength, and wrinkle resistance, making them widely used in clothing and home textiles. In packaging, PET's excellent barrier properties, chemical stability, non-toxicity, and lightweight nature make it a preferred alternative to glass and metal. It is categorized into water bottle grade, oil bottle grade, hot-fill grade, and carbonated bottle grade, and is widely used in flexible packaging for food, pharmaceuticals, and sterile products.

PET performs well across a wide temperature range, up to 120°C, and offers good electrical insulation. Its versatility extends to use in audio and video tapes, film, computer disks, and various electronic and automotive components, where it is valued for its durability and coating properties.

3. Why is PET Widely Used in Packaging?

PET is the most common plastic for beverage and food packaging, with about 85% (approximately 23 million tons) of the 27 million tons of PET used globally going into bottles.

Its high clarity, chemical stability, mechanical strength, and impact resistance make PET ideal for diverse packaging needs. Compared to other packaging materials, PET is lighter than glass, reducing shipping costs and minimizing breakage risk. It offers similar transparency to glass but at lower production and processing costs, and its recyclability makes it an efficient, eco-friendly packaging option.

4. How is PET Plastic Produced?

As a downstream product of the petrochemical industry, PET is produced by reacting purified terephthalic acid (PTA) with ethylene glycol (EG) through esterification and polymerization. PTA is derived from naphtha, which is processed into paraxylene (PX) and then into PTA through oxidation, crystallization, separation, and drying. MEG is produced from coal, oil, or natural gas using methods like ethylene oxidation, ethanol hydration, or petrochemical processes.

5. What Are the Considerations for Processing PET?

PET has good rheological properties when molten, with pressure affecting viscosity more than temperature. To alter melt flow, adjustments are primarily made through pressure.

Due to PET’s hydrophilic nature from its ester groups, it is sensitive to moisture at high temperatures. Excess moisture can reduce molecular weight, causing color and brittleness in the final product. Therefore, PET must be dried before processing, typically at 150°C for over 4 hours or 170°C for 3-4 hours. The effectiveness of drying can be checked using an air-blowing test.

6. How to Identify PET?

Smell: PET has a distinctive, pleasant smell when burned, unlike other plastics which may emit unpleasant odors. For example, bottles containing SEBS may be unsuitable due to their odor.

Burn Test: PET burns with minimal charring or dripping. Excessive blackening or rapid oil dripping indicates abnormal melting points, common in PET films.

String Test: When burned, PET can be drawn into a string. A longer string indicates a higher melting point. If the string curls into small rings, the melting point is higher.

7. Is PET Safe?

PET is certified as safe by the FDA, Health Canada, the European Food Safety Authority, and most global health agencies. It has been used in food and beverage containers for decades with no known adverse effects. Extensive research confirms PET’s safety.

8. Can PET Containers Be Recycled?

PET bottles are highly recyclable, with a 100% recycling rate. According to the UNEP, 88% of beverage sector packaging is recyclable, significantly higher than other sectors. China leads with a 94% PET bottle recycling rate, benefiting from an efficient, economically-driven recycling system.

9. How Does PET Compare to Other Plastics?

Versus PE: PET offers superior transparency, resembling glass in clarity and gloss, while PE, especially high-density polyethylene (HDPE) (No. 2), is typically opaque or semi-transparent. Low-density polyethylene (LDPE) (No. 4) has some transparency but is not as clear as PET. PET also excels over PE in rigidity, strength, heat resistance, and barrier properties.

Versus PVC: PVC (No.3) is usually opaque or semi-transparent and can be difficult to recycle, especially flexible PVC with plasticizers. PVC’s plasticizers (e.g., phthalates) may be harmful, limiting its use in food applications. PET is considered safe for food and drink packaging.

Versus PP: PP (No.5) is semi-transparent to opaque with moderate rigidity and strength, slightly less than PET but with better flexibility and fatigue resistance. Both are considered safe for food packaging. PP has better heat resistance and can be used in microwave applications.

Versus PS: PS (No.6) offers high transparency and is used in clear or foam materials but has lower heat resistance (melting point around 100°C) and poorer oxygen and moisture barriers.

Conclusion

PET (Plastic No. 1) is more than just a common plastic; it's a versatile material with exceptional qualities. From its crystal-clear transparency to its superior strength and safety, PET outshines many other plastics in various applications.