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Plastics & Elastomers
The material selection platform
Plastics & Elastomers
Polyethylene

Comprehensive Guide on Polyethylene (PE)

Polyethylene (PE) is one of the most popular thermoplastic materials. It is available in different crystalline structures, referred to as HDPE, LDPE, and LLDPE. This commodity plastic is produced by addition or radical polymerization. It is used in a large array of applications: plastic containers, bottles, bags, plastic toys, etc.

Overview

What is Polyethylene?

What is Polyethylene?

Molecular Structure of Polyethylene
Molecular Structure of Polyethylene


Polyethylene is a type of polyolefins. This is a lightweight, durable plastic that is often used for frozen food bags, bottles, cereal liners, yogurt containers, etc. Look around you, all plastics with recycling codes 2 and 4 are made of polyethylene. PE plastics comes with different crystalline structures. We will review subfamilies (HDPE, LDPE, LLDPE, etc.) in a minute.

How is PE made?

How is PE made?

PE is made from the polymerization of ethylene (or ethene) monomer. Polyethylene chemical formula is (C2H4)n.

Polyethylene chains are produced by addition or radical polymerization. Both Ziegler-Natta and Metallocene catalysts are possible synthesis methods.

Ethylene Monomer
Structure of PE Monomer
C2H4
Arrow
Ziegler-Natta Polymerization
Or Metallocene Catalysis
Structure of Polyethylene
Structure of Polyethylene
(C2H4)n


A great variety of crystalline structure can be achieved. We will review how it impacts the final performance.

Common Types of Polyethylene (PE)

Common Types of Polyethylene (PE)

Depending on its density and branching, different polyethylene grades can have very different performance from one another.
PE grades are therefore classified as follows.
(click on the polymer name to learn about them in detail)


In addition, PE is also available in other types, such as but not limited to:


At the moment, the later ones aren't discussed in this guide, but a detailed list of commercial available grades is just a click away!

Comparison Between Main Types of Polyethylene

Comparison Between Main Types of Polyethylene

  LDPE LLDPE HDPE
Polymer Full Name Low Density Polyethylene Linear Low Density Polyethylene High Density Polyethylene
Structure High Degree of short chain branching + long chain branching High Degree of short chain branching Linear (or Low degree of short chain branching)
Catalyst and process Using radical polymerization using tubular method or auto clave method Using Ziegler-Natta catalyst or metallocene catalyst Ziegler-Natta catalyst in:
- Single-stage polymerization
- Multi-stage polymerization or a Cr or Phillips-type catalyst
Density 0.910-0.925 g/cm3 0.91-0.94 g/cm3 0.941-0.965 g/cm3
Crystallinity Low crystalline and high amorphous (less than 50-60% crystalline) Semi-crytalline, level between 35 to 60% High crystalline and low amorphous (>90% crystalline)
Characteristics
  • Flexible and good transparency
  • Good moisture barrier properties
  • High impact strength at low temperature
  • Excellent resistance to acids, bases and vegetable oils
As compared to LDPE, it has:
  • higher tensile strength
  • higher impact and puncture resistance
  • Excellent Chemical Resistance
  • High tensile strength
  • Excellent moisture barrier properties
  • Hard to semi-flexible
Recycling Code LDPE recycling code LDPE recycling code HDPE recycling code
General Applications Shrink wrap, films, squeezable bottles garbage bags, extrusion moldings, and laminates High performance bags, cushioning films, tire separator films, industrial liners, elastic films, ice bags, bags for supplemental packaging and garbage bags
  • Molecular weight distribution is relatively narrow, has applications in injection moldings or flat yarns, and the latter type

  • Molecular weight distribution is wide, is used to make film products, hollow plastic products and pipes
Commercial Products LDPE Grades LLDPE Grades HDPE Grades

Now when the basic distinction is clear, find out in detail about these 3 types of polyethylene and see which one matches the best with your final application needs.


High density polyethylene (HDPE)

High density polyethylene (HDPE)

High Density Polyethylene (HDPE) is a cost-effective thermoplastic with linear structure and no or low degree of branching. It is manufactured at low temperature (70-300°C) and pressure (10-80 bar) & derived from either modifying natural gas (a methane, ethane, propane mix) or catalytic cracking of crude oil into gasoline.

  • Modifying natural gas (a methane, ethane, propane mix) or
  • The catalytic cracking of crude oil into gasoline 

HDPE is produced majorly using two techniques: Slurry Polymerization or Gas Phase Polymerization.

Molecular Structure of HDPE

High Density Polyethylene Molecular Structure

High density polyethylene is flexible, translucent/waxy, weather resistant, and displays toughness at very low temperatures.

Properties of High Density Polyethylene


  1. HDPE Melting point: 120-140°C
  2. Density of HDPE: 0.93 to 0.97 g/cm3
  3. High Density Polyethylene Chemical resistance:
    • Excellent resistance to most solvents
    • Very good resistance to alcohols, dilute acids and alkalis
    • Moderate resistance to oils and greases
    • Poor resistance to hydrocarbons (aliphatic, aromatic, halogenated)
  4. Continuous temperature: -50°C to +60°C, relatively stiff material with useful temperature capabilities
  5. Higher tensile strength compared to other forms of polyethylene
  6. Low cost polymer with good processability
  7. Good low temperature resistance
  8. Excellent electrical insulating properties
  9. Very low water absorption
  10. FDA compliant

Feels like HDPE is matching your needs? Check out the list of producers »

Disadvantages of HDPE


  • Susceptible to stress cracking
  • Lower stiffness than polypropylene
  • High mold shrinkage
  • Poor UV- and low heat resistance
  • High-frequency welding and joining impossible

However, some grades have been smartly upgraded and offer some improved performance profiles.

Check out grades specifically designed for environmental stress cracking resistance (ESCR), high stiffness, low shrinkage, UV stabilized…

TIP: In case you have specific requirements, try using the “key feature” facet to narrow down your search.

Applications of High Density Polyethylene (HDPE)


Excellent combination of properties makes HDPE an ideal material in diverse applications across industries. Some of the major uses of high density polyethylene include:

HDPE in Packaging and Consumer Good Applications

  1. Packaging Applications – High Density Polyethylene is used in several packaging applications including crates, trays, bottles for milk and fruit juices, caps for food packaging, jerry cans, drums, industrial bulk containers etc. In such applications HDPE provides the end product a reasonable impact strength.

    Choose HDPE Grade Suitable for Packaging »

  2. Consumer Goods – Low cost and easy processability make HDPE a material of choice in several household/ consumer goods like garbage containers, housewares, ice boxes, toys etc.

  3. Fibers and Textiles – Thanks to its high tensile strength, HDPE is widely used for agricultural applications, such as in ropes, fishing and sport nets, nets as well as industrial and decorative fabrics.

Other applications of HDPE include pipes and fittings (pipes for gas, water, sewage, drainage, sea outfalls, industrial application, cable protection, steel pipe coating, large inspection chambers and manholes for pipe sewage etc.) due to its excellent resistance to chemical and hydrolysis, automotive – fuel tanks, wiring & cables – sheeting of energy, telecommunication cables.

Overall, as compared to other variations (LDPE, LLDPE), HDPE is more rigid due to high crystallinity (> 90%) but this also means it is less transparent.


Low density polyethylene (LDPE)

Low density polyethylene (LDPE)

Low-density Polyethylene (LDPE) is a semi-rigid polymer with low crystallinity (~50-60%). Compared to HDPE, it has a higher degree of short and long side-chain branching. The LDPE is composed of 4,000-40,000 carbon atoms, with many short branches.

It is produced at high pressure (1000-3000 bar; 80-300°C) via free radical polymerization process.

Two basic processes used for the production of low-density polyethylene: stirred autoclave or tubular routes. The tubular reactor has been gaining preference over the autoclave route due to its higher ethylene conversion rates.

Low-Density Polyethylene Structure

Low-Density Polyethylene Structure


If you need more elasticity but limited strength, then look out for LDPE material. See this exhaustive list of commercial grades to find the suitable product »

Properties of Low-Density Polyethylene


  1. LDPE Melting point: 105 to 115°C
  2. Density of LDPE: 0.910–0.940 g/cm3
  3. Chemical resistance of LDPE:
    • Good resistance to alcohols, dilute alkalis and acids
    • Limited resistance to aliphatic and aromatic hydrocarbons, mineral oils, oxidizing agents and halogenated hydrocarbons
  4. Temperature resistance up to 80°C continuously and 95°C for shorter times.
  5. Low cost polymer with good processability
  6. High impact strength at low temperature, good weatherability
  7. Excellent electrical insulating properties
  8. Very low water absorption
  9. FDA compliant
  10. Transparent in thin film form

Disadvantages of LDPE


The presence of more branching in polymer chain brings certain drawbacks to LDPE performance. Such as:

  • Susceptible to stress cracking
  • Low strength, stiffness and maximum service temperature. This limits its usage in applications requiring extreme temperatures.
  • High gas permeability, particularly carbon dioxide
  • Poor UV resistance
  • Highly flammable
  • High-frequency welding and joining impossible

To overcome these challenges, several LDPE grades have been developed with improved properties such as UV stabilized, high strength, antiblocking, etc.

Tip: Do not forget to use “Key Features” filter to explore other optimized grades of LDPE

Applications of Low-Density Polyethylene (LDPE)


Low-Density Polyethylene (LDPE) uses majorly revolve around manufacturing containers, dispensing bottles, wash bottles, tubing, plastic bags for computer components, and various molded laboratory equipments. The most popular application of low-density polyethylene is plastic bags.

LDPE Applications
LDPE Applications

  1. Packaging – Thanks to its low cost and good flexibility, LDPE is used in packaging industry for pharmaceutical and squeeze bottles, caps and closures, tamper evident, liners, trash bags, films for food packaging (frozen, dry goods, etc.), laminations etc.
  2. Pipes and Fittings – Low-Density Polyethylene is used to manufacture water pipes and hoses for the pipes and fittings industry due to Its plasticity and low water absorption.

Other applications include consumer goods - housewares, flexible toys, agricultural films, wiring & cables - sub-conductor insulators, cable jacketing.

Exploring LDPE grade options for food, medical or cosmetics packaging? We have exhaustive list for you here »


Linear low density polyethylene (LLDPE)

Linear low density polyethylene (LLDPE)

LLDPE is produced by polymerization of ethylene (or ethane monomer) with 1-butene and smaller amounts of 1-hexene and 1-octene, using Ziegler-Natta or metallocene catalysts. It is structurally similar to LDPE.

The structure of LLDPE has a linear backbone with short, uniform branches (unlike longer branches of LDPE). These short branches are able slide against each other upon elongation without becoming entangled like LPDE.

In the present-day scenario, linear low-density polyethylene (LLDPE) has been quite successful in replacing Low Density Polyethylene thanks to below mentioned properties.

Properties of LLDPE


  • Very flexible with high impact strength
  • Translucent and natural milky color
  • Excellent for mild and strong buffers, good chemical resistance
  • Good water vapor and alcohol barrier properties
  • Good stress crack and impact resistance

Applications of LLDPE: Suitable for a variety of film application such as general-purpose film, stretch film, garment packaging, agricultural film, etc.

While LLDPE can compete HDPE and LDPE in variety of applications, the below mentioned table can be useful to ease down your selection process among three PE types.

Property LDPE HDPE LLDPE Relative to LDPE LLDPE Relative to HDPE
Tensile Strength (MN/m2) 6.9-15.9 21.4-38 Higher Lower
Elongation (%) 90-650 50-800 Higher Higher
Impact strength (J/12.7mm) No break 1.02-8.15 Better Similar
Environmental stress cracking resistance - - Better Same
Heat distortion temperature (°C) 40-50 60-82 15°C higher Lower
Stiffness (4.5MN/m2) 1.18-2.42 5.53-10.4 Higher Lower
Warpage - - Less Similar
Processability Excellent Good - Easier
Haze (%) 40 - Worse Better
Gloss (45° %) 83 - Worse Better
Clarity Near transparent to opaque Translucent to opaque Worse Better
Melt strength - - Lower Lower
Softening point range (°C) Permeability (ml cm-2 g-1 mil-1 cm) Hg-1 at 25°C X 10-8
  • H2O vapor
  • CO2
85-87



420
60
120-130



55
13
Narrower



Better
Better
Narrower



Worse
Worse
Source: Mukherjee, A. K. et al., Popular Plastics: 15 October, 1985.

Ultrahigh-Molecular-Weight Polyethylene (UHMWPE)

Ultrahigh-Molecular-Weight Polyethylene (UHMWPE)

Ultrahigh-molecular-weight polyethylene or UHMWPE has a molecular weight about 10 times higher (usually between 3.5 and 7.5 million amu) than High Density Polyethylene (HDPE) resins.

When it comes to HDPE vs UHMWPE, they both have a similar appearance, but UHMWPE is an extremely tough, abrasion-resistant, low-cost plastic thus better suited for industrial or manufacturing applications where friction or wear may be a concern. Find out more about UHMWPE properties below.

UHMWPE is synthesized using metallocene catalysts and ethane units resulting is structure where ethane units are bonded together resulting in UHMWPE structure typically having 100,000 to 250,000 monomer units per molecule.

  • It has excellent mechanical properties such as high abrasion resistance, impact strength and low coefficient of friction. 
  • The material is almost totally inert, therefore it is used in the most corrosive or aggressive environments at moderate temperatures. 
  • Even at high temperatures, it is resistant to several solvents, except aromatic, halogenated hydrocarbons and strong oxidizing materials, such as nitric acid.
  • These special properties allow the product to be used in several high-performance applications.
  • UHMWPE is suitable for high wear applications such as tubes, liners, silos, containers and other equipment.

View All UHMWPE High Impact Resistance Grades »


Cross-linked Polyethylene (PEX or XLPE)

Cross-linked Polyethylene (PEX or XLPE)

High-density crosslinked polyethylene, or XLPE, is a form of polyethylene with crosslinked structure specifically designed for critical applications.

XLPE Applications Cross linked polyethylene is produced from polyethylene under high pressure with organic peroxides which creates a free radical. The free radical generates the crosslinking of the polymer which results in a resin that is specifically designed for critical applications like chemical storage pipework systems, hydronic radiant heating and cooling systems, and insulation for high voltage electrical cables.

Key Features of XLPE


  • High and low temperature
  • Hydrolysis resistance
  • High electrical and insulation properties
  • High abrasion resistance
  • Potable water approved
  • High extrusion speed on standard lines
  • Lower cost
  • Mechanically tougher 


Key Features of XLPE


XLPE cables are by far the most popular and XLPE offer unlimited benefits in several electrical applications thanks to its moisture-resistance, stress resistance and higher protection against heat deformation vs other comparable power cables. Especially when comparing XLPE vs PVC cables, XLPE power cable has:

  • Much longer service life
  • Better heat resistance, XLPE power cable can typically stand up to 260°
  • Has better tensile strength and impact resistance
  • Higher eligibility for higher rated current applications

Here is the list of all XLPE grades suited for wires and cables »


How to Process PE Plastic?

How to Process PE Plastic?

Various forms of Polyethylene can be used in processes like injection molding, blow molding, extrusion and various film creation processes such as calendaring or blown film extrusion.

  • High density polyethylene can be easily processed by injection molding, extrusion (tubes, blow and cast films, cables, etc.), blow molding and rotomolding. Being and ideal material for injection molding process, it is majorly used for batch and continuous production.

  • The most common processing technique used for Low Density Polyethylene is extrusion (tubes, blow and cast films, cables...). Low Density Polyethylene can be processed by injection molding or rotomolding also.

    Injection Molding / Extrusion: How to Avoid Plastic Quality Crashes

  • UHMWPE is processed variously by compression molding, ram extrusion, gel spinning, and sintering. It conventional methods such as injection, blow or extrusion molding, because this material does not flow even at temperatures above its melting point.

  • PE (mainly HDPE) is gradually gaining popularity as a 3D Printing material. Its strength, low density, and non-toxicity make it ideal for a wide range of 3D printed objects. Additionally, recycled polyethylene grades and bio-based PE are also used for processing by 3D Printing. The sheer availability of PE is encouraging efforts to apply this material for additive manufacturing.


HDPE LDPE
Injection Molding
  • Melt temperature: 200-300°C
  • Mold temperature: 10-80°C
  • Drying is not necessary if stored properly
  • High mold temperature will improve brilliance and appearance of the part
  • Mold shrinkage lies between 1.5 and 3%, depending on processing conditions, rheology of the polymer and thickness of the final piece
  • Melt temperature: 160-260°C
  • Post mold shrinkage lies between 1.5 and 3.5% 
  • Material Injection Pressure: Up to 150 MPa
Extrusion
  • Melt temperature: 200-300°C
  • Compression Ratio: 3:1
  • Cylinder Temperatures: 180-205°C
  • Pre-Drying: No, 3 hours at 105-110 C (221-230°F) for regrind
  • Melt temperature: 180-240°C
  • Higher melt temperatures are needed for extrusion-coating (280-310°C)
  • A three zone screw with an L/D ratio of around 25 is recommended
  • Melt temperature: 160-260°C
  • Post mold shrinkage lies between 1.5 and 3.5%


Key Applications of Polyethylene

Key Applications of Polyethylene

Polyethylene is the most common plastic produced in the world and manufactured in three different forms - HDPE, LDPE, LLDPE. So, what are the typical applications where you will find PE?.

From electrical insulation, household containers, packaging and films to buckets and bottles, each form of polyethylene has a wide range of applications as discussed below.

There is no doubt that the excellent combination of properties makes polyethylene an ideal material in diverse applications across industries. Further, it can be engineered according to the end use requirements.

Among more than 6800 Polyethylene grades available today in the market, you can find PE uses in the following applications.

  • Packaging bottles & films - HDPE is widely used to manufacture crates, trays, bottles caps, drums, etc. While LDPE is majorly used in films, plastic bags, trash bags, and other food packaging material.

  • Medical and healthcare - Used to create medical products such as patches, personal protective equipment, packaging films, containers, lidstock, and bag headers, etc.

  • Pipes, Hoses & Fittings - PE parts are used in gas pipes, water pipes, sewer pipes, hoses, etc. thus offering excellent resistance to chemicals and hydrolysis.

  • Household products/ Consumer Goods - Garbage containers, kitchenware, housewares, ice boxes, bowls, buckets, ketchup bottles, etc.

  • Agriculture - PE films are used widely for greenhouse, walk-in tunnel and low tunnel covers, and mulching.

  • Wiring & Cable - Crosslinked polyethylene or polyethylene copolymer resins are useful for wire and cable insulation and jacketing.

(To see several material options available today, click on application)
Polyethylene Recycling and Toxicity

Polyethylene Recycling and Toxicity

Resin Identification Code for two main forms of polyethylene are:

Polyethylene Recycling

LDPE and HDPE are non-biodegradable in nature and contribute significantly to the world’s plastic waste products. Both the forms of polyethylene are recyclable and used to produce bottles for non-food items, plastics for outdoor applications, compost bins, etc.

In solid form, Polyethylene is safe and non-toxic in nature but could be toxic if inhaled and/or absorbed as a vapor or liquid (i.e., during manufacturing processes).

View several recycled polyethylene grade options available today »

PE (HDPE and XLPE) is widely used for water-related applications. Cross-linked polyethylene has become popular for potable water in recent years, but PEX requires special fittings and is not recyclable. High-Density Polyethylene (HDPE) pipes are used for non-potable water applications. For potable water, HDPE can be used for both hot water and cold-water service applications.

Drive your R&D efforts faster and in the right direction with a clearer view on plastics recycling material advances (volume resins, upcycling additives, recyclate compounds…) and applications (packaging, consumer goods, automotive…). Take this exclusive course by Industry Expert Donald Rosato.

Plastic Recycling Innovation: Materials, Technologies, Applications Update


Is polyethylene an ideal plastic for your case?

Is polyethylene an ideal plastic for your case?


PE has a broad-application spectrum. It is used for plastic containers, bottles, bags, plastic toys, films, tubes, plastic parts, laminates, etc.

Basically, if you’re application does not call for extreme performance, PE could be a material of choice. Under certain circumstances, polyethylene can also compete with engineering plastics. As you can imagine, given its cost and wide availability, industry has found smart ways to push its performance limit.

If you’re still hesitating between PE and PP, PET, PVC… let’s review the main reason to choose PE over other types of plastics; and when it may not be the best choice.


Key Applications

Key Properties

Suppliers

Brands

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2 Comments on "Polyethylene (PE)"
GOURDON B Apr 28, 2022
Bon article de synthèse sur LES LES POLYETHYLENES. On aurait peut-être essayé de mieux différencier les structures en fonction de la catalyse ZIEGLER/ NATTA et les MELTALLOCENES et aussi face à la radicalaire. MERCI bernard.gourdon2@wanadoo.fr
macdenis e Feb 27, 2022
GOOD EVENING PLEASE, I NEED TO KNOW WHO AUTHORED THIS-Advanced Guide for A to Z Information on PE-so that I will cite it correctly and appropriately in my write-up

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