What is Low-Density Polyethylene (LDPE)?

As a member of the polyethylene family, low-density polyethylene (LDPE) is recognized as a type of thermoplastic. It consists of long chains of ethylene molecules known as monomers.

Once formed, LDPE possesses flexible and translucent characteristics. Its high corrosion resistance, flexibility, and lower cost make it an ideal choice to be used in plastic cling wraps and containers.

Its chemical formula is (C₂H₄)n, which is the same as high-density polyethylene. While its flexibility and translucency allow the substance to be manufactured into preferred shapes, its low cost makes it accessible for most consumers.

LDPE can be identified by the number four in a triangle, which is located on the side or bottom of many products.

How Is LDPE Made?

Ethylene in gaseous form is LDPE’s main precursor. It is kept under very high temperatures (350 °C [660 °F]) and high pressures (about 350 megapascals, or 50,000 pounds per square inch).

The presence of oxide initiators during the heating means LDPE is formed quicker. Because its melting point is very generous at roughly 110 °C (230 °F), translating into LDPE being a supremely flexible material.

In order to obtain low density polyethylene, you will have to resort to the radical polymerization method. This requires a heat of up to 570 degrees Kelvin and pressure of up to 3,000 atm.

Initially, the petrofuel raw materials are first reduced to small monomeric units, afterwards, the ethylene gas is isolated and directed towards a reactor.

In the reactor, an initiator such as oxygen or organic peroxide will be used alongside with the gas, then, polymerization will begin.

Low density polyethylene has a little bit of freedom to change shape to become either pellets or granules for easier conversion in other products.

LDPE is widely used in other processes like molds from liquid plastics primary resources by Injection molding and plastic extrusion. This type of polyethylene can also be used in other processes of fabricating:

Blow molding
Thermoforming
Vacuum casting
Film making

Properties Low-Density Polyethylene (LDPE)

LDPE (low density polyethylene) is a soft, flexible, lightweight substance of plastic material. LDPE has most features rotations from its lowers flexible ability, skin toughness, and corrosion resistance.

It is not well suited for foments where rigidity, high temperature resilience, and intensive support are needed. Besides, it is common in the production of orthoses and prostheses. LDPE shows fair chemical and impact strength, is readily fabricated, and is easier to mold.

The chart below presents the functional aspects of low-density polyethylene:

Property	English	Metric
Density	0.0331-0.0347 (lb/in3)	0.915-0.960 (g/cm3)
Tensile Strength, Yield	1100-2030 (psi)	7.60-14.0 (MPa)
Tensile Strength, Ultimate	1300-7830 (psi)	8.96-54.0 (MPa)
Modulus of Elasticity	22.0-42.1 (ksi)	0.152-0.290 (GPa)
Elongation at Break	226-650 (%)	226-650 (%)
Hardness, Shore D	42.0-56.0	42.0-56.0
Melting Point	216-235 (oF)	102-113 (oC)
Processing Temperature	293-644 (oF)	145-340 (oC)
Moisture Vapor Transmission (@37.8oC/100oF)	1.04 (cc-mil/in2-24hr-atm)	0.410 (cc-mm/m2-24hr-atm)
Water Vapor Transmission	0.0167-1.55 (g/100in2/day)	0.260-24.0 (g/m2/day)

Applications Low-Density Polyethylene (LDPE)

Both LDPE and HDPE polyolefins, as well as PP, belong to the class of thermoplastic polymers. LDPE is known to be versatile in the production of several items such as containers, dispensing and wash bottles, tubing, plastic components of computer machinery, and other molded laboratory apparatus.

As noted, the most widespread application is seen in plastic bags. Other products manufactured from it include:

General-purpose containers and trays
Laminate work surfaces resistant to corrosion
Weldable and machinable parts
Flexible components
Extremely soft and flexible components like snap-on lids
Rings used for holding together six cans of beverage
Juice and milk cartons are created using liquid packaging board that combines paperboard with layers of LDPE and aluminum foil, serving as aseptic packaging.
Hard disk drives, screen cards, and optical disc drives, in addition to being used in plastic containers, are packaged.
Slides of playgrounds
Plastic wrap
Bags made out of plastic
Containers made out of plastic
Tubes
Houseware products
Cases for batteries
Components of vehicles
Parts of electrical machinery

What is LDPE plastic used for?

LDPE is utilized in the production of containers, plastic parts for computers, dispensing and squeeze bottles, caps and closures, molded laboratory equipment, tubing, and numerous caps and closures. It is strong enough to be virtually unbreakable.

Its primary use is for thin plastic bags used for food shopping as well as the dry cleaning covers that shield your freshly cleaned garments.

For commercial purposes, it LDPE is mainly utilized as a film and for plastic wrapping of various items, taking advantage of its flexible, tough, and transparent characteristics.

LDPE Plastic Recycling Process

Shredded LDPE is fed into the recycling system, where it is first chopped into smaller pieces and then melted to form pellets.

These pellets can be processed into different products, and virgin LDPE can be added to improve strength and functional reliability.

Most recycled LDPE products will have a black hue, as it is simpler to color clear plastic black. This includes products like bin liners, agricultural film, irrigation pipes, floor tiles, and furniture.

When it comes to working with plastics, processing LDPE is among the simplest. It has possible applications in injection, film, and blow molding, as well as the production of plastic materials with a range of properties, such as anti-skid, anti-static, anti-bacterial, and flame retardant capabilities.

An efficient means of cleaning and decontaminating the collected plastic packaging will be a challenge for the recycling plant.

Advantages and Disadvantages

Low-density polyethylene possesses decent resistance to various chemicals and boasts good electrical properties. However, it has relatively high thermal expansion and is prone to failure when subjected to mechanical or thermal stress.

Glass reinforcement improves low-density polyethylene’s thermal expansion and strength, as well as its rigidity and resistance to elevated temperatures.

There are good reasons to use low-density polyethylene, but depending on the type of product that you are manufacturing, there are also some disadvantages that you need to keep in mind.

Advantages.

Flexibility: LDPE features low crystallinity, allowing it to stretch, bend, and be flexible.
Moisture repellent: LDPE is more than capable of deflecting moisture and water.
Impact resistance: LDPE is able to withstand being exposed to concentrated or diluted chemicals without breaking down.
Cost effective: LDPE has a low production cost and can be recycled..

Disadvantages:

Susceptibility to cracking: When LDPE is required to hold heavier objects, it has a tendency to crack or break and lose strength.
Has a Max Temperature: Although LDPE can withstand hot temperatures, anything above 221 degrees Fahrenheit will start to melt it.
High gas permeability: Gasses such as carbon dioxde are able to pass through easily.
Poor UV resistance: UV rays make it difficult for LDPE to maintain its shape, color, and integrity.
Moderately recyclable: LDPE can be recycled, however, not every product made from LDPE can be thrown into the standard home or business recycling bins. It will have to go through sorting or special treatment at certain facilities, especially softer and more flexible cling film.

Low-Density vs High-Density Polyethylene

Both LDPE and HDPE are the two most common forms of polyethylenes, differing in structures but not in properties.

HDPE is opaque and has a linear structure, and LDPE is transparent branched polyethylene.

Both materials are strong and weldable. They have high impact and chemical resistance as well as being malleable and manufacturable.

LDPE and HDPE are both processed by injection molding and additive manufacturing, however, LDPE is more suited for injection molding than HDPE. Tight tolerances of CNC machining can be achieved with HDPE.

Conducting the necessary research to determine the optimal material for an upcoming project is the responsibility of product teams. A reliable partner for manufacturing could assist you in making these choices with greater assurance.