What is polyethylene?

Polyethylene is one of the most important and widely used polymers in the world, with a fascinating and eventful history. This material is extensively used in the production of various plastics and plays a significant role in our daily lives. In the following, we will explore the history of polyethylene, from its discovery to its modern applications.

History of Polyethylene

 Accidental Discovery (1898):

The first polyethylene was accidentally produced by German chemist Hans von Pechmann in 1898 while investigating diazomethane. When his colleagues Eugen Bamberger and Friedrich Tschirner described the white, wax-like substance he had created, they realized it contained long -CH2- chains and named it polymethylene.

Discovery and Early Development:

In 1933, polyethylene was accidentally discovered by Eric Fawcett and Reginald Gibson, two British chemists working for ICI (Imperial Chemical Industries). This discovery occurred during experiments conducted under high pressure and high temperature. The material appeared as a waxy substance with a low melting point and initially seemed to have no specific industrial applications.

Development and Industrial Production (1939-1940):

In the late 1930s and early 1940s, polyethylene production processes were improved. In 1939 and 1940, ICI was able to produce polyethylene commercially. During World War II, polyethylene became a valuable material for producing insulation for radar cables. This application was of great importance in the development of wartime technologies.

 

Post-World War II Advancements

Expansion of Applications (1950-1960):

After World War II, the applications of polyethylene expanded rapidly. Due to its suitable mechanical and chemical properties, it was used in the production of bottles, plastic films, pipes, and many other products.

In the 1950s, Karl Ziegler and Giulio Natta developed new catalytic polymerization processes that led to the production of high-density polyethylene (HDPE) and low-density polyethylene (LDPE). These discoveries earned Ziegler and Natta the Nobel Prize in Chemistry in 1963.

 

Modern Developments and Current Applications

• Medium-Density and Linear Low-Density Polyethylene (1970-1980):

In the 1970s and 1980s, medium-density polyethylene (MDPE) and linear low-density polyethylene (LLDPE) were developed. Due to their specific properties, such as higher impact and tensile strength, they found new applications.

 

• Recent Developments and Advanced Technologies (1990-Present):

In recent decades, new technologies for the production and modification of polyethylene have been developed, leading to improvements in the mechanical and chemical properties of this material. These advancements have enabled the production of higher quality and more efficient products.

Polyethylene is now used in various industries such as packaging, agriculture, automotive, construction, and medical.

 

Types of Polyethylene

Polyethylene is classified based on its density and branching. Its mechanical properties depend significantly on variables such as the amount and type of branching, crystalline structure, and molecular weight. Types of polyethylene include:

• Ultra-High Molecular Weight Polyethylene (UHMWPE)
• Ultra-Low Molecular Weight Polyethylene (ULMWPE or PE-WAX)
• High Molecular Weight Polyethylene (HMWPE)
• High-Density Polyethylene (HDPE blowing)
• High-Density Cross-Linked Polyethylene (HDXLPE)
• Cross-Linked Polyethylene (PEX or XLPE)
• Medium-Density Polyethylene (MDPE)
• Linear Low-Density Polyethylene (LLDPE)
• Very Low-Density Polyethylene (VLDPE)
• Chlorinated Polyethylene (CPE)

Types of Polyethylene Based on Density

• Low-Density Polyethylene (LDPE): Low-density polyethylene is produced using very high pressures (5000-1000 atmospheres) and high temperatures (343-333 Kelvin).
• High-Density Polyethylene (HDPE): High-density polyethylene is produced using low pressure (520 atmospheres) and low temperature (333 Kelvin). PE is usually thermoplastic, but it can be modified to be thermosetting, for example, cross-linked polyethylene is a type of thermosetting PE.

High-Density Polyethylene (HDPE)

High-density polyethylene (HDPE blowing) is defined as polyethylene with a density greater than or equal to 0.941 grams per cubic centimeter. HDPE has a low number of branches. The linear molecules can pack together well, so the intermolecular forces are generally stronger than in highly branched polymers. High-density polyethylene has high tensile strength. It is used in products and packaging such as jugs, detergent bottles, butter tubs, wastebaskets, and water pipes. One-third of all toys are made from HDPE. In 2007, global consumption of HDPE reached over 30 million tons.

“Polyethylene (PE) is one of the most widely used plastics. Due to its unique properties, PE is used in various production processes, including blow molding. This method is particularly suitable for producing hollow products such as bottles, containers, tanks, and other similar plastic objects. In the following, we will examine the polyethylene blow molding process, its advantages, disadvantages, and applications.”

 

Introduction to HDPE Grades

“HDPE is produced in various grades, each with its specific properties and applications. Let’s examine the different HDPE grades and their applications:”

 Extrusion Grade HDPE

“This grade of HDPE is used to produce plastic products through the extrusion process.

• Features:

Suitable for producing pipes and plastic profiles: High resistance to cracking.

Suitable for producing plastic films and sheets: Thermal stability.

• Applications:

Water and gas pipes

Plastic films for packaging

Plastic sheets and profiles”

 

 Blow Molding Grade HDPE

“This grade of HDPE is used to produce hollow products through the blow molding process. This grade is usually transparent or white in color.

• Features:

Suitable for producing bottles and plastic containers: High strength.

High chemical resistance, suitable for packaging chemicals and detergents.

• Applications:

Plastic bottles and containers

Water and fuel tanks

Spray cans and similar products”

 

Pipe Grade

This HDPE grade is specifically designed for the production of plastic pipes.

• Features:

High pressure resistance: Suitable for pressurized piping systems.

Chemical and corrosion resistance: Suitable for the transfer of chemicals and industrial fluids.

• Applications:

Water and wastewater pipes

Gas pipes

Industrial pipes

Injection Molding Grade

This HDPE grade is used to produce plastic parts through the injection molding process.

• Features:

Good flexibility and impact strength: Suitable for producing impact-resistant parts.

Good surface quality: Suitable for producing parts with a smooth and attractive appearance.

• Applications:

Automotive parts

Toys

Plastic boxes and baskets

 

Film Grade

This HDPE grade is used to produce plastic films and bags.

• Features:

High transparency and flexibility: Suitable for producing thin and transparent films.

Tear resistance: Suitable for producing bags that are resistant to tearing.

• Applications:

Plastic bags

Agricultural films

Packaging films

Note:

HDPE stands for High-Density Polyethylene.

Extrusion is a process used to create continuous profiles.Injection molding is a process that injects heated plastic into a mold.

Introduction to Blow Molding and HDPE

English Translation: “High-density polyethylene (HDPE) is a widely used plastic due to its unique properties. One of the methods used to process HDPE is blow molding, which is used to produce hollow objects like bottles and plastic containers.”

Steps in HDPE blowing Molding

• Extrusion and Parison Formation: Molten HDPE is extruded into a hollow plastic tube called a parison.
• Placing in Mold: The parison is placed in a two-piece mold that determines the final shape of the product.
• Air Blowing: Compressed air is blown into the parison, causing the plastic to conform to the shape of the mold.
• Cooling and Removal: The plastic cools and once it’s sufficiently hardened, the mold is opened, and the final product is removed.

Applications of HDPE Blow Molding

• Plastic bottles and containers: For packaging food, beverages, chemicals, and personal care products.
• Industrial parts: Such as pipes and industrial containers.
• Storage: Tanks and reservoirs for water and chemicals.
• Household products: Like fuel cans, spray cans, and other similar products.

Advantages of HDPE blowing Molding

• Rapid and mass production of hollow objects
• Lightweight: HDPE is lighter than other materials, making it easier to transport and use.
• Low cost: HDPE as a raw material is relatively inexpensive, and the blow molding process itself has a low production cost.
• Chemical resistance: Products made from HDPE have high resistance to chemicals.

Disadvantages of HDPE blowing Molding

• Limitations in complex designs: Very complex designs may be difficult to produce using this method.
• Surface quality: Some products may have a lower surface quality compared to other production methods.
• Size limitations: Producing very large objects may require special and expensive equipment.

Conclusion

HDPE blowing molding is an efficient and effective method for producing hollow plastic objects. It allows for the production of strong, lightweight, and cost-effective products. Due to the unique properties of HDPE blowing and the capabilities of the blow molding process, this method is widely used in various industries. By following the principles and carefully controlling the process, it is possible to produce high-quality products that meet diverse needs.