High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a

thermoplastic A thermoplastic, or thermosoftening plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling. Most thermoplastics have a high molecular weight. The polymer chains as ...

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

produced from the monomer ethylene. It is sometimes called "alkathene" or " polythene" when used for HDPE pipes. With a high strength-to-density ratio, HDPE is used in the production of plastic bottles, corrosion-resistant piping, geomembranes and plastic lumber. HDPE is commonly recycled, and has the number "2" as its resin identification code. In 2008, the global HDPE market reached a volume of more than 30 million tons.

Properties

HDPE is known for its high strength-to-density ratio. The density of HDPE ranges from 930 to 970 kg/m³. Although the density of HDPE is only marginally higher than that of low-density polyethylene, HDPE has little branching, giving it stronger

intermolecular force An intermolecular force (IMF; also secondary force) is the force that mediates interaction between molecules, including the electromagnetic forces of attraction or repulsion which act between atoms and other types of neighbouring particles (e.g. ...

s and

tensile strength Ultimate tensile strength (also called UTS, tensile strength, TS, ultimate strength or F_\text in notation) is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials, the ultimate ...

(38 MPa versus 21 MPa) than LDPE. The difference in strength exceeds the difference in density, giving HDPE a higher specific strength. It is also harder and more opaque and can withstand somewhat higher

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

s (120 °C/248 °F for short periods). High-density polyethylene, unlike

polypropylene Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer Propene, propylene. Polypropylene belongs to the group of polyolefin ...

, cannot withstand normally required autoclaving conditions. The lack of branching is ensured by an appropriate choice of catalyst (e.g., Ziegler–Natta catalysts) and reaction conditions. HDPE is resistant to many different

solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...

s, and is exceptionally challenging to glue; joints are typically made by welding. The physical properties of HDPE can vary depending on the molding process that is used to manufacture a specific sample; to some degree, a determining factor is the international standardized testing methods employed to identify these properties for a specific process. For example, in rotational molding, to identify the environmental stress crack resistance of a sample, the ''notched constant tensile load test'' (NCTL) is put to use. Owing to these desirable properties, pipes constructed out of HDPE are ideally applicable for drinking water and waste water (storm and sewage).

Applications

File:HDPE Construction safety net.jpg, HDPE fibers can be spun into rope File:Pulling on the hood of the Tyveck suit (5429334133).jpg, Disposable suits; nonwoven HDPE fabric File:US Navy 100824-N-0858D-272 Sailors work on a new home for Habitat for Humanity during Boise Navy Week.jpg, Housewrap File:Registered Mail Royal Mail - Great Britain-Germany 2017 - envelope front side.jpg, Plastic mailing envelopes File:Blue Striped Water Pipe.jpg, Flexible HDPE pipes File:Hdpe pipe installation.jpg, Corrugated HDPE pipe installation in storm drain project in

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

File:Plastic outdoor chair 1 2017-06-14.jpg, The monobloc chair File:Milk crate.jpg, Bottle crates File:Cubocubo.png, Toys and playground equipment File:2014. Уничтоженные гривны в Донецке 015.jpg, Clear plastic bags (shown) are made of LDPE; blown-film shopping bags with handles are now made of HDPE File:250ml HDPE pump plastic bottle.jpg, HDPE is used to make sturdy bottles that resist oils. Transparent bottles are usually made of other plastics, such as polyethylene terephthalate File:Bottle of milk.jpg, Milk jug File:Diverse Kanisterformen.png, HDPE

jerrycan A jerrycan or jerrican (also styled jerry can or jerri can) is a fuel container made from pressed steel (and more recently, high-density polyethylene, high density polyethylene). It was designed in Germany in the 1930s for military use to hol ...

s resist softening and swelling from aromatic components of fuels File:FODS Connect202 TC-1 TRACKOUT CONROL STABILIZED CONSTRUCTION ENTRANCE 2.jpg, Roller on HDPE construction entrance mat HDPE has a wide variety of applications; for applications that fall within the properties of other polymers, the choice to use HDPE is usually economic: * 3D printer filament * Arena board (puck board) * Backpacking frames * Ballistic plates * Banners * Bottle caps * Boats *

Chemical A chemical substance is a unique form of matter with constant chemical composition and characteristic properties. Chemical substances may take the form of a single element or chemical compounds. If two or more chemical substances can be combin ...

containers * Chemical-resistant piping * Coax cable inner insulator * Conduit protector for electrical or communications cables *

Corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

protection for steel pipelines * Electrical and plumbing boxes * Far-IR lenses *

Fireworks Fireworks are Explosive, low explosive Pyrotechnics, pyrotechnic devices used for aesthetic and entertainment purposes. They are most commonly used in fireworks displays (also called a fireworks show or pyrotechnics), combining a large numbe ...

* Folding chairs and tables * Food storage containers * Fuel tanks for vehicles * Geomembrane for hydraulic applications (such as canals and bank reinforcements) * Geothermal heat transfer piping systems * Heat-resistant firework

mortars Mortar may refer to: * Mortar (weapon), an indirect-fire infantry weapon * Mortar (masonry), a material used to fill the gaps between blocks and bind them together * Mortar and pestle, a tool pair used to crush or grind * Mortar, Bihar, a village i ...

* Housewrap ( Tyvek) * Hovercraft: The material is too heavy and dense for such craft but is still used occasionally *

Ionizing radiation Ionizing (ionising) radiation, including Radioactive decay, nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionization, ionize atoms or molecules by detaching ...

shield *Laundry detergent jugs * Luggage transitioned from metal in India * Lasts for shoes * Microwave telescope windows * Milk jugs *

Natural gas Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium ...

distribution pipe systems * Piping for fluid, slurry and gas purposes * Plastic bags * Plastic bottles suitable both for recycling or re-use * Plastic surgery (skeletal and facial reconstruction) * Potable water mains * Root barrier * Shampoo bottles * Sewage mains *

Snowboard Snowboards are boards where the user places both feet, usually secured, to the same board. The board itself is wider than most skis, with the ability to glide on snow."snowboarding." Dictionary.com Unabridged (v 1.1). Random House, Inc. 17 Mar ...

rails and boxes * Stone paper * Storage sheds * Swimming pool installation * Trackout control mats * Telecom ducts * Water pipes for domestic water supply and agricultural processes *

Wood plastic composite Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin t ...

s (utilizing recycled polymers) T Joint cross section

HDPE is also used for cell liners in United States subtitle D sanitary landfills, wherein large sheets of HDPE are either extrusion welded or wedge welded to form a homogeneous chemical-resistant barrier, with the intention of preventing the

pollution Pollution is the introduction of contaminants into the natural environment that cause harm. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the component ...

soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...

and

groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit ...

by the liquid constituents of solid waste. HDPE is preferred by the

pyrotechnics Pyrotechnics is the science and craft of creating fireworks, but also includes safety matches, oxygen candles, Pyrotechnic fastener, explosive bolts (and other fasteners), parts of automotive airbags, as well as gas-pressure blasting in mining, q ...

trade for mortars over steel or PVC tubes, being more durable and safer: HDPE tends to rip or tear in a malfunction instead of shattering and becoming shrapnel like the other materials. Milk bottles, jugs, and other hollow goods manufactured through blow molding are the most important application area for HDPE, accounting for one-third of worldwide production, or more than 8 million tonnes. Above all, China, where beverage bottles made from HDPE were first imported in 2005, is a growing market for rigid HDPE packaging as a result of its improving

standard of living Standard of living is the level of income, comforts and services available to an individual, community or society. A contributing factor to an individual's quality of life, standard of living is generally concerned with objective metrics outsid ...

. In India and other highly populated, emerging nations, infrastructure expansion includes the deployment of pipes and cable insulation made from HDPE. The material has benefited from discussions about possible health and environmental problems caused by PVC and

polycarbonate Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate ester, carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, toughness, tough materials, and some grades are optically transp ...

associated

bisphenol A Bisphenol A (BPA) is a chemical compound primarily used in the manufacturing of various plastics. It is a colourless solid which is Solubility, soluble in most common organic solvents, but has very poor solubility in water. BPA is produced on a ...

(BPA), as well as its advantages over glass, metal, and cardboard.

Production

Industrial production of HDPE from ethylene happens through either Ziegler-Natta polymerization or the Phillips slurry process. The Ziegler-Natta method uses a combination of catalysts, including titanium tetrachloride, in contact with gaseous ethylene to precipitate high-density polyethylene. In a similar way, the Phillips slurry process uses silica-based catalysts in contact with a fast-moving hydrocarbon and polyethylene slurry to precipitate high density polyethylene. Processing will determine the properties of the HDPE. The method used to synthesize the HDPE is crucial because the micro structure of the HDPE will vary. The Phillips Slurry process results in HDPE with less branching and more precise molecular weights than the Ziegler process, but the Ziegler process provides greater flexibility in the type of polyethylene produced. The molecular weight of HDPE refers to the length of the polyethylene chains, and helps determine properties such as flexibility, yield strength, and melt temperature. After the precipitate is formed, the temperature, pressure, and cooling time during processing will dictate the degree of crystallinity, with a higher degree of crystallinity resulting in greater rigidity and chemical resistance. Depending on the application, the method and processing steps can be adjusted for an ideal result. Once the HDPE has been synthesized, it is ready to be used in commercial products. Industrial production methods for HDPE products include injection molding for complex shapes such as toys. Extrusion molding is used for constant-profile products such as pipes and films. Blow molding is intended for hollow products, specifically bottles and plastic bags. Rotational molding is used for large, seamless parts such as chemical drums and kayaks. The method used during processing depends on the product requirements, with each having benefits for a given application.

References

{{DEFAULTSORT:High-Density Polyethylene Plastics Polyolefins Food packaging de:Polyethylen

Properties

Applications

Production

See also

References