Polyethylene (PE Plastic) – Structure, Properties & Toxicity

What is PE?

Polyethylene or polythene is a type of polyolefin. It is often abbreviated as PE. The chemical formula of PE is (C₂H₄)_n. It is lightweight, durable, and one of the most commonly produced plastic. 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 PE. These plastics come with different crystalline structures.

Molecular Structure of PE

How is PE made?

Polyethylene is made from the polymerization of ethylene (or ethene) monomer. The PE chains are produced by addition or radical polymerization. The possible synthesis methods are:

Ziegler-Natta Polymerization and
Metallocene catalysis

What are the common types of PE?

Depending on its density and branching, different PE grades can have very different performance from one another.

PE grades are therefore classified as follows.

Branched Versions

Low-density polyethylene (LDPE)
Linear low-density polyethylene (LLDPE)

Linear Versions

High-density polyethylene (HDPE)
Ultra-high-molecular-weight polyethylene (UHMWPE)

Cross-linked polyethylene (PEX or XLPE)

Additionally, other types of PE are also available such as:

Medium-density polyethylene (MDPE)
Ultra low-density polyethylene (ULDPE)
High-molecular-weight polyethylene (HMWPE)
Metallocene polyethylene (mPE)
Chlorinated polyethylene (CPE)

Browse the largest online catalogue to select your PE grades

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How to compare between the main PE types?

	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 autoclave 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
Properties	See detailed property comparison: LDPE vs. LLDPE vs. HDPE
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
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 PE and see which one matches the best with your final application needs.

What is high density polyethylene (HDPE)?

High Density Polyethylene (HDPE) is a cost-effective thermoplastic with a linear structure. It has no or low degree of branching. It is flexible, translucent/waxy, and weather resistant. The chemical structure of HDPE is:

HDPE Molecular Structure

HDPE is more rigid due to high crystallinity (> 90%). This also means it is less transparent than LDPE & LLDPE versions. HDPE also displays toughness at low temperatures.

How is HDPE manufactured?

HDPE is manufactured at low temperatures (70-300°C) and pressure (10-80 bar). It is derived from:

Either modifying natural gas (a methane, ethane, propane mix)
Or the catalytic cracking of crude oil into gasoline

Two major techniques to produce HDPE: Slurry Polymerization or Gas Phase Polymerization.

What are the properties of HDPE?

HDPE Melting point: 120-140°C
Density of HDPE: 0.93 to 0.97 g/cm³
Chemical resistance of HDPE:
- 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)
Continuous temperature: -50°C to +60°C, relatively stiff material with useful temperature capabilities
Higher tensile strength compared to other forms of PE
Low-cost polymer with good processability
Good low-temperature resistance
Excellent electrical insulating properties
Very low water absorption
FDA compliant

Some grades are designed for your specific requirements like environmental stress cracking resistance (ESCR), high stiffness, low shrinkage, UV stabilized, etc. Check out HDPE grades here »

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

What are the 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.

What are the applications of HDPE?

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

HDPE in Packaging and Consumer Good Applications

Packaging Applications – HDPE 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.
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.

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.

What is low density polyethylene (LDPE)?

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

LDPE Structure

How is LDPE manufactured?

LDPE is produced at high pressure (1000-3000 bar) and temperature (80-300°C). It is derived via the free radical polymerization process.

Two basic processes to produce LDPE:

Stirred autoclave reactor
Tubular reactor

The tubular reactor has been gaining preference over the autoclave route due to its higher ethylene conversion rates.

What are the properties of LDPE?

LDPE Melting point: 105 to 115°C
Density of LDPE: 0.910–0.940 g/cm³
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
Temperature resistance up to 80°C continuously and 95°C for shorter times.
Low cost polymer with good processability
High impact strength at low temperature, good weatherability
Excellent electrical insulating properties
Very low water absorption
FDA compliant
Transparent in thin film form

What are the 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. Check out LDPE grades here »

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

What are the applications of LDPE?

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 LDPE is plastic bags.

LDPE Applications

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.
Pipes and Fittings – LDPE 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.

What is linear low-density polyethylene (LLDPE)?

The structure of linear low-density polyethylene (LLDPE) has a linear backbone with short and uniform branches (unlike longer branches of LDPE). These short branches are able slide against each other upon elongation without becoming entangled like LPDE. It is structurally similar to LDPE.

How is LLDPE manufactured?

LLDPE is produced by the polymerization of ethylene (or ethane monomer) with:

1-butene, and
smaller amounts of 1-hexene and 1-octene.

This process occurs using Ziegler-Natta or metallocene catalysts. In the present-day scenario, LLDPE has been quite successful in replacing LDPE thanks to the below-mentioned properties.

What are 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

Some grades are designed for your specific requirements like good processability, antiblocking, antioxidant, etc. Check out LLDPE grades here »

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

What are the applications of LLDPE?

LLDPE is suitable for a variety of film applications 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.

LLDPE Property	vs. LDPE Properties	vs. HDPE Properties
Tensile Strength (MN/m²)	Higher	Lower
Elongation (%)	Higher	Higher
Impact strength (J/12.7mm)	Better	Similar
Environmental stress cracking resistance	Better	Same
Heat distortion temperature (°C)	15°C higher	Lower
Stiffness (4.5MN/m²)	Higher	Lower
Warpage	Less	Similar
Processability	-	Easier
Haze (%)	Worse	Better
Gloss (45° %)	Worse	Better
Clarity	Worse	Better
Melt strength	Lower	Lower
Softening point range (°C)	Narrower	Narrower
Permeability (ml cm^-2 g^-1 mil^-1 cm) H_g^-1 at 25°C X 10^-8 H₂O vapor CO₂	Better Better	Worse Worse
Get more information about polymer properties here »

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

What is ultrahigh-molecular-weight polyethylene (UHMWPE)?

Ultrahigh-molecular-weight polyethylene has a molecular weight between 3.5 and 7.5 million amu. This is about 10 times higher than HDPE resins.

Both HDPE and UHMWPE have similar appearances. But UHMWPE is tough, abrasion-resistant, and low-cost plastic. Suitable for industrial or manufacturing applications where friction or wear may be a concern.

How is UHMWPE manufactured?

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

What are the properties of UHMWPE?

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.

Some grades are designed for your specific requirements like wear-, chemical-, and impact resistance, etc. Check out UHMWPE grades here »

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

Cross-linked Polyethylene (PEX or XLPE)

High-density crosslinked PE is a form of polyethylene with a crosslinked structure. It is abbreviated as PEX or XLPE. It is specifically designed for critical applications.

How is crosslinked PE manufactured?

XLPE is produced from polyethylene under high pressure with organic peroxides. This creates free radicals which generate the crosslinking of the polymer. This 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.

What are the properties 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

Some grades are designed for your specific requirements like environmental stress cracking resistance (ESCR), flame retarded, processability, creep resistance, etc. Check out XLPE grades here »

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

What are the features of XLPE cables?

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°C
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?

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.

HDPE 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 LDPE is extrusion (tubes, blow and cast films, cables...). LDPE can be processed by injection molding or rotomolding also.

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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 PE 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%

Which type of PE is recyclable?

Resin Identification Code for two main forms of PE are:

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

View several recycled PE grade options available today »

PE (HDPE and XLPE) is widely used for water-related applications.

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.
Cross-linked PE has become popular for potable water in recent years, but PEX requires special fittings and is not recyclable.

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Are PE resins toxic?

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

Key Properties

	Property	LDPE	LLDPE	HDPE
Chemical Resistance
Acetone @ 100%, 20°C	Limited	Limited	Limited
Ammonium hydroxide @ 30%, 20°C	Satisfying	Satisfying	Satisfying
Ammonium hydroxide @ diluted, 60°C	Satisfying	Satisfying	Satisfying
Ammonium hydroxide @ diluted, 20°C	Satisfying	Satisfying	Satisfying
Aromatic hydrocarbons @ 20°C	Non Satisfactory	Non Satisfactory	Non Satisfactory
Aromatic hydrocarbons @ hot conditions	Non Satisfactory	Non Satisfactory	Non Satisfactory
Benzene @ 100%, 20°C	Non Satisfactory	Non Satisfactory	Limited
Butylacetate @ 100%, 20°C	Limited	Limited	Satisfying
Chlorinated solvents @ 20°C	Non Satisfactory	Non Satisfactory	Non Satisfactory
Chloroform @ 20°C	Non Satisfactory	Non Satisfactory	Non Satisfactory
Glycerol @ 100%, 20°C	Satisfying	Satisfying	Satisfying
Hydrogen peroxide @ 30%, 60°C	Limited	Limited	Satisfying
Kerosene @ 20°C	Limited	Limited	Satisfying
Methanol @ 100%, 20°C	Satisfying	Satisfying	Satisfying
Methylethyl ketone @ 100%, 20°C	Limited	Limited	Satisfying
Mineral oil @ 20°C	Limited	Limited	Satisfying
Phenol @ 20°C	Satisfying	Satisfying	Satisfying
Silicone oil @ 20°C	Satisfying	Satisfying	Satisfying
Sodium hydroxide @ <40%, 60°C	Satisfying	Satisfying	Satisfying
Sodium hydroxide @ 10%, 20°C	Satisfying	Satisfying	Satisfying
Sodium hydroxide @ 10%, 60°C	-	-	Satisfying
Sodium hypochlorite @ 20%, 20°C	Satisfying	Satisfying	Satisfying
Strong acids @ concentrated, 20°C		-	Satisfying
Toluene @ 20°C	Non Satisfactory	Non Satisfactory	Limited
Toluene @ 60°C	Non Satisfactory	Non Satisfactory	-
Xylene @ 20°C	Non Satisfactory	Non Satisfactory	Limited
Dioctylphtalate @ 100%, 100°C	Non Satisfactory	Non Satisfactory	-
Dioctylphtalate @ 100%, 60°C	Non Satisfactory	Non Satisfactory	Limited
Dioctylphtalate @ 100%, 20°C	Limited	Limited	Satisfying
Ethanol @ 96%, 20°C	Limited	Limited	Satisfying
Ethyleneglycol (Ethane diol) @ 100%, 20°C	Satisfying	Satisfying	Satisfying
Ethyleneglycol (Ethane diol) @ 100%, 50°C	Satisfying	Satisfying	Satisfying
Electrical
Arc Resistance, sec	130 - 160	-	100 - 180
Dielectric Constant	2.3	2.3	2.3
Volume Resistivity x 10¹⁵, Ohm.cm	16 - 18	16 - 18	16 - 18
Dielectric Strength, kV/mm	16 - 28	-	17 - 24
Dissipation Factor x 10^-4	3 - 4	-	3 - 20
Mechanical
Hardness Shore D	40 - 50	55 - 56	60 - 70
Hardness Rockwell M	1	1	1
Strength at Break (Tensile), MPa	10 - 20	25 - 45	25 - 45
Strength at Yield (Tensile), MPa	10 - 15	10 - 30	25 - 30
Toughness at Low Temperature, J/m	240 - 694	294 - 970	-
Toughness, J/m	999	54 - 999	20 - 220
Young's Modulus, GPa	0.13 - 0.3	0.266 - 0.525	0.5 - 1.1
Elongation at Break, %	200 - 600	300 - 900	500 - 700
Elongation at Yield, %	13 - 17.5	3 - 16	15
Flexural Modulus, Gpa	0.245 - 0.335	0.28 - 0.735	0.75 - 1.575
Optical
Gloss, %	35 - 97	32 - 85	5 - 120
Haze, %	1.3 - 27.5	0.8 - 28	6
Transparency (Visible Light Transmission), %	80	-	80
Physical
Density, g/cm³	0.917 - 0.94	0.915 - 0.95	0.94 - 0.97
Gamma Radiation Resistance	-	-	Fair
Glass Transition Temperature, °C	-110	-110	-110
Shrinkage, %	2 - 4	2 - 2.5	1.5 - 4
Sterilization Resistance (Repeated)	-	-	Poor
UV Light Resistance	Fair	Fair	Poor
Water Absorption 24 hours, %	0.005 - 0.015	0.005 - 0.01	0.005 - 0.01
Service Temperature
HDT @0.46 Mpa (67 psi), °C	40 - 50	-	60 - 90
HDT @1.8 Mpa (264 psi), °C	30 - 40	-	45 - 60
Max Continuous Service Temperature, °C	80 - 100	90 - 110	100 - 120
Min Continuous Service Temperature, °C	-70	-70	-70
Ductile / Brittle Transition Temperature, °C	-70	-70	-70
Thermal
Coefficient of Linear Thermal Expansion x 10^-5, /°C	10 - 20	-	6 - 11
Thermal Insulation, W/m.K	0.32 - 0.35	0.35 - 0.45	0.45 - 0.5
Fire Resistance (LOI)	17 - 18	17 - 18	17 - 18
Flammability, UL94	HB	HB	HB

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Comprehensive Guide on Polyethylene (PE)