Name and synonyms for LDPE:
IUPAC-Name (International Union of Pure and Applied Chemistry) for polyethylene:
poly(ethene)
Synonyms:
PE-LD, PELD, high pressure polyethylene, HPLD
(Synonyms for polyethylene: Poly(methylene), Polythene)
German: Hochdruck-Polyethylen, Polyethylen niedriger Dichte
Spanish: polietileno de baja densidad
French: Polyéthylène basse densité (PEBD)
Italian: Polietilene bassa densità (PE b.d.)
Russian: Полиэтилен низкой плотности (ПЭНП), Полиэтилен высокого давления (ПЭВД)
Arabic: البولي إثيلين منخفض الكثاف
Chinese: 低密度聚乙烯
Japanese: 低密度ポリエチレン
Basic information on LDPE:
Chemical Formula: (CH2=CH2)n (general polyethylene)
CAS-Nr.: 9002-88-4 (general polyethylene)
ESIS-entry:
-- (no EINECS or ELINCS registration)
LDPE is a semi-crystalline thermoplastic polymer, which belongs to the polyolefin group and is manufactured through the polymerization of ethene. The presence of numerous long-chain branches in its molecules (generally with more than 20 carbon atoms) gives melted LDPE unique flowing characteristics, which make processing easier with a variety of technologies. This secures LDPE as the first choice for many applications, despite competition from newer and cheaper varieties of polyethylene.
Low density polyethylene is the oldest polyethylene product and has been industrially manufactured since 1939. Soft, ductile, and pliable LDPE is used for strong, flexible articles like screw caps and lids. It has been known to be a good insulating material for quite some time. Today, the most popular applications are films, from which bags, packaging materials, and protective sheets for agriculture are manufactured. LDPE films are also used, for example, to reinforce dikes.
Information on manufacturing and processing of low density polyethylene can be found in Market Study Polyethylene - LDPE, available soon from Ceresana Research.
Important Characteristics of LDPE:
Parameter: LDPE:
Density (g/cm³) ~ 0.910 - 0.925
Melting point (°C) between 105 and 120
Service temperature (°C) 80 - 100 (maximum continuous use temperature)
Tensile strength (N/mm²) 4.71 to 37.1
Tensile strength at break (N/mm²) 8 to 30
Chemical resistance Conditional resistance; affected by strong acids; not affected by strong bases, diluted bases and diluted acids; good resistance to aldehydes, ketones, and vegetable oil; limited resistance to aliphatic and aromatic hydrocarbons, mineral oils and oxidizers; poor resistance to halogenated hydrocarbons
Polyethylene plastics have the generally advantageous characteristics of rigidity, high tensile strength, and excellent barrier characteristics against moisture. These characteristics can be specifically modified through suitable copolymerization. A particularly important characteristic of polyethylene is its ability to be easily heat-sealed when used as packaging. This is due to the plastic's relatively low melting point. However, its barrier properties are only moderate with regard to oxygen and organic substances.
Polyethylene's characteristics vary with the primary parameters of density/crystallinity, molecular weight, and molecular weight distribution. Yield strength and stiffness, for example, increase along with density; clarity on the other hand, generally improves with reduced density: While HDPE films are brittle and opaque; LDPE films are usually soft and relatively transparent. The lower the crystallinity, and accordingly the density, the more limp and flexible the material is. An LDPE product with a density of 0.918-g/cm³ has a better resistance to environmental stress corrosion, but worse barrier characteristics than a product with a density of 0.930 g/cm³. Density and flow-ability are primarily determined by the amount of pressure applied during manufacture: polyethylene obtains a low density with the use of high pressure. LDPE is more light-weight and more loosely constructed than HDPE; if one makes an indentation in the material and lets-go, it will elastically return to its original form
An overview of LDPE's most important characteristics, as well as detailed information on additives and fillers used in this plastic are provided in Market Study Polyethylene - LDPE, available soon from Ceresana Research.
Hazard Indications for LDPE:
No mandatory danger symbols (R/S statements) are required to label LDPE. The plastic is relatively inert, as well as safe and non-toxic, and is used in applications that come into contact with foods, drinking water, and medications. Health concerns and provisions for LDPE only relate to the use of pigments and other additives which can migrate from the material. LDPE is easily recyclable.
Additional information on environmental discussions on plastics, legal issues, work safety, and various recycling methods can be found in Market Study Polyethylene - LDPE, available soon from Ceresana Research.
LDPE Manufacturing Methods:
LDPE is manufactured exclusively using the high-pressure method: high pressure (81-276 MPa) and high temperatures (130-330°C) are utilized with a radical initiator, such as peroxide or oxygen. Polymerization takes place in either a tubular or stirred autoclave reactor.
Long-chain branches result in an unusual rheological behavior when sheared and stretched. The radical polymerization mechanism also allows for the copolymerization of polar comonomers - a unique peculiarity of LDPE. Presence of comonomers like vinyl acetate (EVA), methyl acrylate (EMA), ethyl acrylate (EWR), and acrylic acid (EAA) minimizes crystallinity and gives the end product more flexibility and softness. An increased amount of these comonomers offers improved adhesion to other materials. LDPE's superior adhesion to different substances, such as metal, film, cardboard, and paper cannot be achieved by other polyolefins.
An overview of LDPE production, as well as the employed stirred autoclave and tubular reactors is provided in Market Study Polyethylene - LDPE, available soon from Ceresana Research.
Application examples for LDPE:
LDPE is able to be processed using most standard methods for plastics. Common methods include blow and cast film extrusion and coextrusion, as well as extrusion coating, blow molding, injection molding, rotational molding, and wire extrusion. Due to its thermal stability and low toxicity, LDPE is utilized in a multitude of applications, such as films, coatings, moldings, and cable insulation.
Films and sheets are the largest application areas for LDPE, although LLDPE and metallocene grades are penetrating the market. Packaging applications include pallets, shrink wrap, heavy bags, and food packaging. Additional examples include waste sacks, bags and agricultural films. Products like garbage and shopping bags, stretch films, and food films, which were once made exclusively from LDPE, are now largely manufactured from LLDPE or LLDPE-rich LDPE mixtures. However, for some applications LDPE remains the material of choice because it is easy to extrude and odorless. This concerns for instance, films of high clarity.
The cleanliness of LDPE, that is to say its lack of gel and inorganic catalyst residue, is a significant advantage for wire insulation. Another benefit of LDPE is its ease of extrusion - as lines for wire coatings are run at high speeds. LDPE is accordingly desirable for wire and cable applications.
Injection molded goods, such as garbage bins, buckets, food containers, sporting goods, toys, and medical equipment, make up a large application area for LDPE. It is preferred when transparency is desired, for example in caps and fasteners. However, LLDPE has mechanical advantages over LDPE: better resistance to environmental stress cracks, reduced warping and shrinking, and better rigidity at low temperatures.
Market Study Polyethylene - LDPE, available soon from Ceresana Research, offers comprehensive information on consumption amounts within individual application areas and divides them among the different world regions.
LDPE manufacturers and trade names:
(->for more info see Market Study Polyethylene - LDPE, available soon from Ceresana Research)
Last revision: 19.01.09
