Sofia Martinez
Polyethylene (PE) is the most common plastic in the world, with over 100 million tonnes of polyethylene resins produced annually. It is made from the polymerization of ethylene and can be low-density or high-density. Low-density polyethylene (LDPE) is defined by a density range of 0.910-0.940 g/cm3. It is a transparent, flexible, tough, and naturally stain-resistant plastic with a low melting point, making it suitable for injection moulding. LDPE is commonly used for plastic bags, containers, and packaging.
| Characteristics | Values |
|---|---|
| Full Form | LDPE (Low-density polyethylene) |
| Production | Produced by the high-pressure process by radical polymerization |
| Density | 917-930 kg/m3 |
| Melting Point | 105-115 °C |
| Tensile Strength | Lower than HDPE |
| Resilience | Higher than HDPE |
| Transparency | Translucent or opaque |
| Flexibility | Quite flexible and tough |
| Temperature Resistance | 80 °C continuously and 95 °C for a short time |
| Chemical Resistance | Good resistance to aldehydes, ketones, and vegetable oils |
| Electrical Properties | Good electrical insulation |
| Stain Resistance | Stain-resistant |
| Waterproof | Yes |
| Recyclability | Recyclable symbol but not commonly recycled |
| Applications | Plastic bags, containers, bottles, tubing, plastic parts, medical devices, orthotics, prosthetics, etc. |
| Disadvantages | Prone to stress cracking, highly flammable, highly permeable to gases |
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What You'll Learn
LDPE's density range
Polyethylene (PE) is the most commonly produced plastic. It is a polymer primarily used for packaging (plastic bags, plastic films, geomembranes, and containers). Many kinds of polyethylene are known, and it can be low-density or high-density.
Low-density polyethylene (LDPE) is a thermoplastic polymer made from the monomer ethylene. It was the first grade of polyethylene, produced in 1933 by John C. Swallow and M.W. Perrin, who were working for Imperial Chemical Industries (ICI). LDPE is defined by a density range of 917–930 kg/m3 or 0.910–0.940 g/cm3. LDPE has a high degree of short- and long-chain branching, which means that the chains do not pack into the crystal structure as well. This results in less strong intermolecular forces and lower tensile strength. LDPE is created by free-radical polymerization. The high degree of branching with long chains gives molten LDPE unique and desirable flow properties. LDPE is used for both rigid containers and plastic film applications such as plastic bags and film wrap. LDPE is also used in the production of cling film for preserving food, as it can withstand a wide temperature range without decomposing.
LDPE is widely used for manufacturing various containers, dispensing bottles, wash bottles, tubing, plastic parts for computer components, and various moulded laboratory equipment. Its most common use is in plastic bags. Other products made from LDPE include:
- Juice and milk cartons made of liquid packaging board, a laminate of paperboard and LDPE (as the waterproof inner and outer layer)
- Battery casings
- Automotive parts
- Electrical components
- Packaging
- Insulation
- Medical devices
LDPE is popular due to its flexibility, low crystallinity, moisture resistance, and corrosion resistance. The melting point of LDPE falls in the range of 105 to 115°C, giving it a low density and high flexibility. LDPE is thermally stable in the temperature range of -50 to 85°C and, in the absence of oxygen, up to a degree of 290°C. It can withstand temperatures of 65 °C (149 °F) continuously and 90 °C (194 °F) for a short time.
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LDPE's advantages
Polyethylene (PE) is a polymer primarily used for packaging (plastic bags, plastic films, geomembranes, and containers, including bottles, cups, and jars). It can be low-density or high-density polyethylene, with most types having the chemical formula (C2H4)n. Low-density polyethylene (LDPE) is a thermoplastic made from the monomer ethylene. It was the first grade of polyethylene, produced in 1933 by John C. Swallow and M.W. Perrin, who were working for Imperial Chemical Industries (ICI). LDPE has numerous advantages, including:
Flexibility and Stretchiness
LDPE is flexible and stretchy, making it suitable for various applications, such as grocery bags, plastic films, and containers. This flexibility is due to its high degree of short- and long-chain branching, which also contributes to its unique flow properties during manufacturing.
Durability and Resilience
LDPE is highly durable and resilient, able to withstand continuous temperatures of up to 80°C and short-term temperatures of up to 95°C. Its resilience is due to its lower tensile strength, which also makes it less brittle than other plastics.
Chemical Resistance
LDPE exhibits excellent chemical resistance, meaning it is not attacked by strong acids or bases and is resistant to gentle oxidants, reducing agents, aldehydes, ketones, and vegetable oils. This makes it suitable for packaging and containers that come into contact with various chemicals.
Moisture Resistance
LDPE effectively deflects moisture and water, making it suitable for waterproof applications such as liquid packaging and outdoor use.
Low Cost
LDPE is inexpensive to produce, making it a cost-effective choice for manufacturers, particularly for single-use or disposable products.
While LDPE has these advantages, it is important to note that it has environmental concerns due to its decomposition resistance and the production of greenhouse gases when exposed to consistent sunlight.
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LDPE's disadvantages
Polyethylene (PE) can be low-density or high-density. Low-density polyethylene (LDPE) is a thermoplastic made from the monomer ethylene. It was the first grade of polyethylene, produced in 1933. LDPE is defined by a density range of 0.910–0.940 g/cm3, or 917–930 kg/m3.
LDPE has numerous advantages, including its flexibility, low crystallinity, moisture resistance, chemical resistance, and high impact resistance. However, it also has several disadvantages. Firstly, LDPE has a lower tensile strength than HDPE due to its higher degree of branching, which also makes it less dense and more flexible. This lower tensile strength means that LDPE may crack or break when holding heavier objects.
Secondly, LDPE is not as easily recyclable as some other plastics, such as No. 1 (polyethylene terephthalate) or 2 plastics (high-density polyethylene). The EPA estimates that only 5.7% of LDPE is recycled in the United States. This is a significant issue, as polyethylene's chemical resilience makes it a long-lived and decomposition-resistant pollutant when disposed of improperly.
Thirdly, LDPE has limited resistance to certain chemicals, such as halogenated hydrocarbons, aliphatic and aromatic hydrocarbons, mineral oils, and oxidizing agents. While LDPE has good resistance to aldehydes, ketones, and vegetable oils, it is not recommended for long-term use with the aforementioned chemicals.
Finally, when exposed to consistent sunlight, LDPE produces significant amounts of the greenhouse gases methane and ethylene. This is due to its higher surface area, which increases as it breaks down more easily than other plastics. Thus, LDPE emits greenhouse gases at a more unsustainable rate than other plastics.
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LDPE's applications
Polyethylene (PE) is a polymer primarily used for packaging, including plastic bags, plastic films, geomembranes, and containers. It can be low-density or high-density, with most types having the chemical formula (C2H4)n. Low-density polyethylene (LDPE) is defined by a density range of 0.910–0.940 g/cm3, or 917–930 kg/m3. It is a versatile thermoplastic with numerous applications due to its desirable properties, such as flexibility, transparency, and moisture resistance.
LDPE is commonly used in the packaging industry, particularly for food products. It serves as plastic packaging film for both fresh and dried food items, ensuring moisture resistance and safety for food contact. LDPE is also used for industrial packaging, providing protection for clothing, electronics, and other goods. T-shirt bags, Ziplock bags, and garbage bags are commonly made from LDPE due to its lightweight and cost-saving properties.
In the agricultural sector, LDPE is valuable for irrigation systems. Farmers use LDPE plastic drip tape to effectively water their crops, optimizing growth and yield. LDPE pipes are also used for transporting potable water to livestock, offering a reliable solution for water distribution.
LDPE finds applications in the medical field as well, being used to produce various medical products and equipment. Additionally, LDPE is used in manufacturing various containers, dispensing bottles, wash bottles, tubing, and plastic parts for computer components. It is also utilized in the production of juice and milk cartons, forming the waterproof inner and outer layers of liquid packaging board.
LDPE has a unique flow property due to its high degree of branching with long chains, which is advantageous in certain applications. However, its lower tensile strength compared to HDPE is a factor to consider in specific uses. LDPE's flexibility, toughness, and ability to withstand temperatures up to 80°C continuously contribute to its versatility in various industries.
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LDPE's history
Polyethylene (PE) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes, and containers, including bottles, cups, and jars). It can be low-density or high-density and many variations thereof.
Low-density polyethylene (LDPE) is a thermoplastic made from the monomer ethylene. It was the first grade of polyethylene, produced in 1933 by John C. Swallow and M.W. Perrin, who were working for Imperial Chemical Industries (ICI). They used a high-pressure process via free radical polymerization. Its manufacture still employs the same method today.
In 1935, another ICI chemist, Michael Perrin, developed this accident into a reproducible high-pressure synthesis for polyethylene that became the basis for industrial LDPE production beginning in 1939. LDPE is defined by a density range of 0.910–0.940 g/cm3. It can withstand temperatures of 80 °C continuously and 95 °C for a short time. It is quite flexible and tough and is made in translucent or opaque variations.
LDPE is widely used for manufacturing various containers, dispensing bottles, wash bottles, tubing, plastic parts for computer components, and various molded laboratory equipment. Its most common use is in plastic bags. Other products made from it include juice and milk cartons, which are made of liquid packaging board, a laminate of paperboard and LDPE (as the waterproof inner and outer layer), and often with a layer of aluminum foil (thus becoming aseptic packaging).
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Frequently asked questions
Polyethylene, or polythene, is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes, containers, bottles, cups, jars, etc.). It is also used in industrial applications such as tanks and pipes.
LDPE is a type of polyethylene defined by a density range of 0.910-0.940 g/cm3. It is a thermoplastic made from the monomer ethylene. It has a high degree of short- and long-chain branching, which results in lower tensile strength and increased ductility. LDPE is used for both rigid containers and plastic film applications.
LDPE and HDPE are two common types of polyethylene with differing structures but similar properties. LDPE is a branched version of polyethylene, while HDPE has a linear structure. LDPE is naturally transparent, while HDPE is opaque. LDPE has a lower tensile strength and is more prone to stress cracking than HDPE. It is also less heat resistant and highly permeable to gases.
LDPE is affordable, machinable, and compatible with other materials. It has good electrical insulation properties and is impact-resistant, stain-resistant, and waterproof. LDPE is also flexible, tough, and highly malleable.
LDPE is highly flammable, which limits its use in high-temperature applications. It is also more prone to stress cracking than HDPE and is highly permeable to gases. Additionally, LDPE is not readily biodegradable, making it a long-lived pollutant when disposed of improperly.
