Polyethylene (PE) is one of the most popular plastics in the world. PE is widely used in various industries due to its unique physical and chemical properties. In this article you will learn what polyethylene is, its basic properties, applications, types and production methods.
Polyethylene what is it?
Polyethylene, also known as Pe, is a high molecular weight plastic with a wide range of applications. It belongs to the group of polyolefins, which are polymers composed solely of carbon and hydrogen. Pe is flexible, transparent and thermoplastic. Polyethylene has many of the basic physical and chemical properties that make it so popular in various industries.
Its density is about 0.96 g/cm3 for high-density polyethylene (LDPE) and 0.945 g/cm3 for low-density polyethylene (HDPE). Polyethylene exhibits excellent sliding and welding properties and ease of processing. It is resistant to abrasion, has high dimensional stability and excellent electrical insulating properties. Its melting point is about 122-124 degrees Celsius for HDPE. Polyethylene is also resistant to acid, alkali and salt solutions and has low toxicity.
Pe material – how is it formed?
The polyethylene production process is based on the use of two main methods: high-pressure and low-pressure synthesis. Both of these processes have their own distinctive features and differ from each other in many respects.
The high-pressure synthesis method involves producing ethylene by pyrolyzing saturated hydrocarbons in pyrolysis furnaces to produce pyrolytic gas. This gas is then subjected to a polymerization reaction under high pressure (1,000-3,000 kg/cm2), resulting in the formation of high-density polyethylene (LDPE) pellets. This type of polyethylene has a lower specific density of about 0.96 g/cm3.
The low-pressure synthesis method, on the other hand, involves polymerizing ethylene at a pressure of 1-5 kg/cm2. This process produces low-density polyethylene (HDPE) with a density of about 0.945 g/cm3. This type of polyethylene is characterized by longer polymer chains.
The difference between the two methods of producing polyethylene lies mainly in the pressure under which the polymerization process takes place. The high-pressure method requires much higher pressure than the low-pressure method. In addition, high-density polyethylene (LDPE) obtained from the high-pressure method has a lower specific density than low-density polyethylene (HDPE) obtained from the low-pressure method.
Types of polyethylene
Polyethylene LDPE
LDPE, or low-density polyethylene, is distinguished by its specific structure, which makes the material more flexible and softer compared to high-density polyethylene (HDPE). Its low density affects its greater flexibility and formability, making it an ideal choice for the production of a wide range of products that do not require high mechanical strength.
Thanks to its flexibility, LDPE is widely used in the packaging industry, where it is used to make lightweight films and garbage bags. In addition, this type of polyethylene is used to manufacture a variety of everyday items, such as home furnishings and toys. Manufactured from LDPE, bottles and containers are characterized by lower load resistance, but they are perfect for less demanding applications.
Low-density polyethylene is also known for its amorphous structure, meaning that it does not have an ordered, crystalline structure, which further enhances its flexibility. These unique characteristics make LDPE versatile in many industries where flexibility and the ability to easily form products are required.
LDPE properties
| Property | LDPE |
| Density, 230oC, g/cm3 | =<0,920 |
| Melt rate (190oC/ 2.16 kg), g/10min | 25-0,5 |
| Melting point of the crystalline phase, oC | 105-110 |
| Tensile strength at yield point, MPa | – |
| Elongation at break, % | – |
| Notched impact strength according to Charpiy, kJ/m2 | does not crack |
| Thermal stability with no change in mechanical properties, oC, in the short term | 80-90 |
| Thermal stability with no change in mechanical properties, oC, over a long period of time | 60-75 |
| Softening point according to Vicat (met. B), oC | 40 |
| Cross resistivity, ohm cm | >1016 |
| Puncture resistance, kV/cm | >700 |
| Surface resistivity, ohms | 1013 |
| Water absorption (24h), % | – |
LDPE Properties, source [1].
HDPE polyethylene
High-density polyethylene (HDPE) is distinguished from other varieties of polyethylene by its higher density, which translates into its exceptional mechanical properties. HDPE has excellent strength and rigidity, making it an extremely resistant material to damage and external influences. These characteristics make it ideal for the manufacture of products that require high durability, such as liquid bottles, food packaging and pressure pipes.
HDPE properties
| Property | HDPE | ||
| Density, 230oC, g/cm3 | =<0,954 | ||
| Melt rate (190oC/ 2.16 kg), g/10min | 17-0,35 | ||
| Melting point of the crystalline phase, oC | 130-135 | ||
| Tensile strength at yield point, MPa | – | ||
| Elongation at break, % | – | ||
| Notched impact strength according to Charpiy, kJ/m2 | 6 | ||
| Thermal stability with no change in mechanical properties, oC, in the short term | 90-120 | ||
| Thermal stability with no change in mechanical properties, oC, over a long period of time | 70-80 | ||
| Softening point according to Vicat (met. B), oC | 60-65 | ||
| Cross resistivity, ohm cm | >1016 | ||
| Puncture resistance, kV/cm | >700 | ||
| Surface resistivity, ohms | 1013 | ||
| Water absorption (24h), % | – |
HDPE Properties, source [1].
Polyethylene LLDPE
LLDPE is a type of linear, low-density polyethylene that ranks between LDPE and HDPE. Thanks to its specific structure, LLDPE combines the advantages of both materials – offering the flexibility characteristic of LDPE and the higher mechanical strength typical of HDPE. This makes it a versatile plastic that is ideal for many applications where both flexibility and durability are required.
LLDPE properties
| Property | LLDPE | |
| Density, 230oC, g/cm3 | 0,918-0,935 | |
| Melt rate (190oC/ 2.16 kg), g/10min | 23-0,5 | |
| Melting point of the crystalline phase, oC | 122-124 | |
| Tensile strength at yield point, MPa | – | |
| Elongation at break, % | – | |
| Notched impact strength according to Charpiy, kJ/m2 | does not crack | |
| Thermal stability with no change in mechanical properties, oC, in the short term | 90-115 | |
| Thermal stability with no change in mechanical properties, oC, over a long period of time | 70-95 | |
| Softening point according to Vicat (met. B), oC | 115(A) | |
| Cross resistivity, ohm cm | >1016 | |
| Puncture resistance, kV/cm | >700 | |
| Surface resistivity, ohms | 1013 | |
| Water absorption (24h), % | 0,01 |
LLDPE properties, source [1].
Applications of polyethylene
Polyethylene is used in many different industries due to its excellent physical and chemical properties. Below are some of the industries where polyethylene is used:
Petrochemical industry: Polyethylene is widely used in the petrochemical industry for pipes, tanks and other apparatus components. It is resistant to chemicals and has high dimensional stability, making it an ideal material for this industry.
Construction industry: In the construction industry, polyethylene is used for thermal and acoustic insulation, roofing membranes, sewer pipes and various structural components. Its ease of processing and weather resistance make it a popular material in this industry.
Transportation industry: Polyethylene is used in the transportation industry for automotive components such as bumpers, fenders and underbody guards. It is lightweight, strong and corrosion-resistant, making it an ideal material for this industry.
Food industry: Polyethylene is widely used in the food industry for food packaging, such as shopping bags, packaging films and milk containers. It is hygienic, easy to clean and has good chemical resistance.
In the above industries, polyethylene is also used in many other products, such as shrink hoods, packaging machine components, cardboard container liners and packaging lids. Its versatile properties make it an extremely popular and valued material in various industries.
Polyethylene properties
Polyethylene exhibits many favorable chemical properties that make it not only a versatile plastic, but also safe for health and the environment. One of the most important characteristics of polyethylene is its resistance to acid, alkali and salt solutions. This makes it suitable for use in a variety of industries where chemicals with different pH levels are present. In addition, polyethylene is low-toxic and does not emit harmful compounds or unpleasant odors, making it safe for both workers and consumers.
It is also important to emphasize that polyethylene is flammable. This means that it can burn in the presence of a fire source or high temperatures. Therefore, caution should be exercised when storing and using polyethylene products near open flames or other potentially hazardous heat sources. However, under normal use and proper storage conditions, polyethylene is safe and poses no health or environmental risk. Despite its flammability and some reactivity at high temperatures, polyethylene is widely used in many industries, from plastic manufacturing to the food industry, as evidenced by its numerous approvals, including PZH certification.
The PE material does not absorb large amounts of moisture, which ensures its stability under various conditions. PE is durable and strong, which means that it does not wear out quickly even in harsh working conditions. Pe polyethylene has excellent resistance to impact and mechanical damage.
Pe plastic has very good electrical insulation characteristics, making it an ideal choice for applications requiring protection from current flow. Pe is a lightweight material, making it easy to transport and use in a variety of products. Polyethylene can operate at temperatures from -269°C to +80°C, making it a versatile solution for many applications.
In addition, high-density polyethylene (HDPE) has a melting point of 122°C to 124°C, making it resistant to relatively high temperatures.
Is polyethylene pe toxic?
Polyethylene (PE) is one of the most widespread plastics, often used in various industries. From a human health safety perspective, polyethylene is considered a non-toxic material in its solid form. This is confirmed by numerous certificates and approvals that allow it to come into contact with food and drinking water, making it widely used in the food industry. Of course, as with any plastic, the manufacturer’s recommendations for its use must be followed, especially in production processes where it can be subjected to high temperatures.
Although polyethylene is safe for everyday use, it can pose a hazard during manufacturing processes, especially in the form of vapors or liquids. When PE is subjected to high temperatures, such as during melting, special care must be taken to avoid inhaling vapors or coming into contact with the hot material. Acting in accordance with the manufacturer’s instructions minimizes the risks associated with these processes.
One of the challenges associated with polyethylene is its negative impact on the environment, particularly in the context of polyethylene microbeads, used in some cosmetic products such as shower gels. These microbeads, entering groundwater, seas and oceans, become part of the ecosystem, often ending up in marine organisms. Although this use of PE is becoming increasingly rare, it shows the potential dangers of improper use of this material.
Plastic pe – summary
Polyethylene has great potential as a plastic with a wide range of applications. Its excellent physical and chemical properties and versatility make it indispensable in many industries. Forecasts for the growth in demand for polyethylene are very promising, especially in industry, cosmetics, chemicals and pharmaceuticals.
In industry, polyethylene is finding increasing use in the manufacture of a variety of machine components, packaging and structures. Its ease of processing, durability and chemical resistance make it an ideal material for many engineering projects. With the development of technology and the growing demand for new solutions, the prospects for the development of polyethylene as a material of the future are very promising.
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Bibliography: 1. Plastics Team, http://www.tworzywa.pwr.wroc.pl/pl/dydaktyka/polietylen accessed August 28, 2024
