Low-density polyethylene

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LDPE has SPI resin ID code 4 Symbol Resin Code 4 LDPE.svg
LDPE has SPI resin ID code 4
Schematic of LDPE branching structure Branched polymer.svg
Schematic of LDPE branching structure

Low-density polyethylene (LDPE) is a thermoplastic made from the monomer ethylene. It was the first grade of polyethylene, produced in 1933 by Dr John C. Swallow and M.W Perrin who were working for Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerization. [1] Its manufacture employs the same method today. The EPA estimates 5.7% of LDPE (resin identification code 4) is recycled in the United States. [2] Despite competition from more modern polymers, LDPE continues to be an important plastic grade. In 2013 the worldwide LDPE market reached a volume of about US$33 billion. [3]

Contents

Despite its designation with the recycling symbol, it cannot be as commonly recycled as No. 1 (polyethylene terephthalate) or 2 plastics (high-density polyethylene). [4] [5]

Properties

LDPE is defined by a density range of 917–930 kg/m3. [6] At room temperature it is not reactive, except to strong oxidizers; some solvents cause it to swell. It can withstand temperatures of 65 °C (149 °F) continuously [6] and 90 °C (194 °F) for a short time. Made in translucent and opaque variations, it is quite flexible and tough.

LDPE has more branching (on about 2% of the carbon atoms) than HDPE, so its intermolecular forces (instantaneous-dipole induced-dipole attraction) are weaker, its tensile strength is lower, and its resilience is higher. The side branches mean that its molecules are less tightly packed and less crystalline, and therefore its density is lower.

When exposed to consistent sunlight, the plastic produces significant amounts of two greenhouse gases: methane and ethylene. Because of its lower density (high branching), it breaks down more easily than other plastics; as this happens, the surface area increases. Production of these trace gases from virgin plastics increases with surface area and with time, so that LDPE emits greenhouse gases at a more unsustainable rate than other plastics. In a test at the end of 212 days' incubation, emissions recorded were 5.8 nmol g-1 d-1 of methane, 14.5 nmol g−1 d−1 of ethylene, 3.9 nmol g−1 d−1 of ethane, and 9.7 nmol g−1 d−1 of propylene. When incubated in air, LDPE emits methane and ethylene at rates about 2 times and about 76 times, respectively, more than in water. [7]

Chemical resistance

Applications

A GEECO bowl, c.1950, still used in 2014 Plastic (LDPE) bowl, by GEECO, Made in England, c1950.jpg
A GEECO bowl, c.1950, still used in 2014
A piece of packaging foam made from LDPE LDPE Foam.jpg
A piece of packaging foam made from LDPE
A Ziploc bag made from LDPE A Ziploc bag made from LDPE.jpg
A Ziploc bag made from LDPE
Facial wash gel bottle made of LDPE Facial wash gel bottle made of LDPE.jpg
Facial wash gel bottle made of LDPE

Polyolefins (LDPE, HDPE, PP) are a major type of thermoplastic. [10] 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:

See also

Related Research Articles

<span class="mw-page-title-main">Resin identification code</span> Symbol to identify the type of plastic

The ASTM International Resin Identification Coding System, often abbreviated RIC, is a set of symbols appearing on plastic products that identify the plastic resin out of which the product is made. It was developed in 1988 by the Society of the Plastics Industry in the United States, but since 2008 it has been administered by ASTM International, an international standards organization.

<span class="mw-page-title-main">Polyethylene</span> Most common thermoplastic polymer

Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bottles, etc.). As of 2017, over 100 million tonnes of polyethylene resins are being produced annually, accounting for 34% of the total plastics market.

<span class="mw-page-title-main">Thermoplastic</span> Plastic that softens with heat and hardens on cooling

A thermoplastic, or thermosoftening plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.

<span class="mw-page-title-main">Polyethylene terephthalate</span> Polymer

Polyethylene terephthalate (or poly(ethylene terephthalate), PET, PETE, or the obsolete PETP or PET-P), is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foods, and thermoforming for manufacturing, and in combination with glass fibre for engineering resins.

<span class="mw-page-title-main">Shrink wrap</span> Polymer used to bundle boxes on a pallet for transport

Shrink wrap, also shrink film, is a material made up of polymer plastic film. When heat is applied, it shrinks tightly over whatever it is covering. Heat can be applied with a handheld heat gun, or the product and film can pass through a heat tunnel on a conveyor.

<span class="mw-page-title-main">Bin bag</span> Disposable bag used to contain solid waste material

A bin bag, rubbish bag, garbage bag, bin liner, trash bag or refuse sack is a disposable bag used to contain solid waste. Such bags are useful to line the insides of waste containers to prevent the insides of the receptacle from becoming coated in waste material. Most bags today are made out of plastic, and are typically black, white, or green in color.

<span class="mw-page-title-main">High-density polyethylene</span> Class of polyethylenes

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

<span class="mw-page-title-main">Water bottle</span> Container for liquids

A water bottle is a container that is used to hold liquids, mainly water, for the purpose of transporting a drink while travelling or while otherwise away from a supply of potable water.

<span class="mw-page-title-main">Linear low-density polyethylene</span> Polymer

Linear low-density polyethylene (LLDPE) is a substantially linear polymer (polyethylene), with significant numbers of short branches, commonly made by copolymerization of ethylene with longer-chain olefins. Linear low-density polyethylene differs structurally from conventional low-density polyethylene (LDPE) because of the absence of long chain branching. The linearity of LLDPE results from the different manufacturing processes of LLDPE and LDPE. In general, LLDPE is produced at lower temperatures and pressures by copolymerization of ethylene and such higher alpha-olefins as butene, hexene, or octene. The copolymerization process produces an LLDPE polymer that has a narrower molecular weight distribution than conventional LDPE and in combination with the linear structure, significantly different rheological properties.

A polyolefin is a type of polymer with the general formula (CH2CHR)n where R is an alkyl group. They are usually derived from a small set of simple olefins (alkenes). Dominant in a commercial sense are polyethylene and polypropylene. More specialized polyolefins include polyisobutylene and polymethylpentene. They are all colorless or white oils or solids. Many copolymers are known, such as polybutene, which derives from a mixture of different butene isomers. The name of each polyolefin indicates the olefin from which it is prepared; for example, polyethylene is derived from ethylene, and polymethylpentene is derived from 4-methyl-1-pentene. Polyolefins are not olefins themselves because the double bond of each olefin monomer is opened in order to form the polymer. Monomers having more than one double bond such as butadiene and isoprene yield polymers that contain double bonds (polybutadiene and polyisoprene) and are usually not considered polyolefins. Polyolefins are the foundations of many chemical industries.

Medium-density polyethylene (MDPE) is a type of polyethylene defined by a density range of 0.926–0.940 g/cm3. It is less dense than HDPE, which is more common.

<span class="mw-page-title-main">Plastic bottle</span> Narrow-necked container

A plastic bottle is a bottle constructed from high-density or low density plastic. Plastic bottles are typically used to store liquids such as water, soft drinks, motor oil, cooking oil, medicine, shampoo, milk, and ink. The size ranges from very small bottles to large carboys. Consumer blow molded containers often have integral handles or are shaped to facilitate grasping.

Polymer engineering is generally an engineering field that designs, analyses, and modifies polymer materials. Polymer engineering covers aspects of the petrochemical industry, polymerization, structure and characterization of polymers, properties of polymers, compounding and processing of polymers and description of major polymers, structure property relations and applications.

<span class="mw-page-title-main">Commodity plastics</span> Inexpensive plastics with weak mechanical properties

Commodity plastics or commodity polymers are plastics produced in high volumes for applications where exceptional material properties are not needed. In contrast to engineering plastics, commodity plastics tend to be inexpensive to produce and exhibit relatively weak mechanical properties. Some examples of commodity plastics are polyethylene, polypropylene, polystyrene, polyvinyl chloride, and poly(methyl methacrylate) .Globally, the most widely used thermoplastics include both polypropylene and polyethylene. Products made from commodity plastics include disposable plates, disposable cups, photographic and magnetic tape, clothing, reusable bags, medical trays, and seeding trays.

Biopolyethylene is polyethylene made out of ethanol, which becomes ethylene after a dehydration process. It can be made from various feedstocks including sugar cane, sugar beet, and wheat grain.

<span class="mw-page-title-main">Plastic pipework</span> Tubular section or hollow cylinder made of plastic

Plastic pipe is a tubular section, or hollow cylinder, made of plastic. It is usually, but not necessarily, of circular cross-section, used mainly to convey substances which can flow—liquids and gases (fluids), slurries, powders and masses of small solids. It can also be used for structural applications; hollow pipes are far stiffer per unit weight than solid members.

<span class="mw-page-title-main">Twinwall plastic</span>

Twin-wall plastic, specifically twin-wall polycarbonate, is an extruded multi-wall polymer product created for applications where its strength, thermally insulative properties, and moderate cost are ideal. Polycarbonate, which is most commonly formed through the reaction of Bisphenol A and Carbonyl Chloride, is an extremely versatile material. It is significantly lighter than glass, while managing to be stronger, more flexible, and more impact resistant. Twin-wall polycarbonate is used most commonly for green houses, where it can support itself in a structurally sound configuration, limit the amount of UV light due to its nominal translucence, and can withstand the rigors of daily abuse in an outdoor environment. The stagnant air in the cellular space between sheets provides insulation, and additional cell layers can be extruded to enhance insulative properties at the cost of light transmission.

<span class="mw-page-title-main">Plastic</span> Material of a wide range of synthetic or semi-synthetic organic solids

Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptability, plus a wide range of other properties, such as being lightweight, durable, flexible, and inexpensive to produce, has led to its widespread use. Plastics typically are made through human industrial systems. Most modern plastics are derived from fossil fuel-based chemicals like natural gas or petroleum; however, recent industrial methods use variants made from renewable materials, such as corn or cotton derivatives.

Lotte Chemical Titan Holding Sdn Bhd engages in the ownership and operation of polypropylene plants, polyethylene plants, ethylene crackers, and aromatic plants. It offers high-density polyethylene (HDPE), Low-density polyethylene (LDPE), and Linear low-density polyethylene (LLDPE) for various kinds of applications, room household goods to automotives products. The company also manufactures low-density polyethylene for injection molding for cosmetic containers, bottle closures, and food containers, and is based in Pasir Gudang, Malaysia.

Biodegradable additives are additives that enhance the biodegradation of polymers by allowing microorganisms to utilize the carbon within the polymer chain as a source of energy. Biodegradable additives attract microorganisms to the polymer through quorum sensing after biofilm creation on the plastic product. Additives are generally in masterbatch formation that use carrier resins such as polyethylene (PE), polypropylene (PP), polystyrene (PS) or polyethylene terephthalate (PET).

References

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  2. "Municipal Solid Waste Generation,n word and Disposal in the United States" (PDF). EPA.gov. 15 November 2016.
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  4. Brady, Angela (28 December 2018). "How to Recycle Number 4 Plastic". San Francisco Chronicle .
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  6. 1 2 BPF. "Polyethylene (Low Density) LDPE, LLDPE". www.bpf.co.uk. Retrieved 2018-06-14.
  7. Karl, David M.; Wilson, Samuel T.; Ferrón, Sara; Royer, Sarah-Jeanne (1 August 2018). "Production of methane and ethylene from plastic in the environment". PLOS ONE. 13 (8): e0200574. Bibcode:2018PLoSO..1300574R. doi: 10.1371/journal.pone.0200574 . ISSN   1932-6203. PMC   6070199 . PMID   30067755. Creative Commons by small.svg  This article incorporates textby Royer et al available under the CC BY 4.0 license.
  8. Qiu, Xia-Wen; Pei, Jie; Wu, Chen-Chou; Song, Lin; Bao, Lian-Jun; Zeng, Eddy Y. (August 2021). "Determination of low-density polyethylene–water partition coefficients for novel halogenated flame retardants with the large volume model and co-solvent model". Chemosphere. 277: 130235. Bibcode:2021Chmsp.277m0235Q. doi:10.1016/j.chemosphere.2021.130235. PMID   33794435. S2CID   232764239.
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  12. DOW LDPE 5004I. IDES – The Plastics Web