In many branches of human activity, high pressure polyethylene (PE) is widely used today. Like PE of low pressure, it is made of the same monomer, but under completely different conditions, which gives this material absolutely different properties from HDPE. LDPE polyethylene is produced by the method of polymerization of ethylene with the participation of an initiator, which is oxygen, at a temperature of 150–200 ° C and a pressure of up to 300 MPa. The desire to reduce the cost of production often encourages manufacturers of polymer products instead of the primary use of secondary LDPE, which has a lower price and similar performance characteristics.
High-pressure polyethylene: properties, characteristics and types
LDPE polyethylene is produced in the form of granules, the structure of which consists of a large number of branched macromolecules that form in the crystal lattice. Due to weak intermolecular bonds, this material has a low density, for which it received the second name – low density polyethylene (LDPE). Its main characteristics:
molecular weight: 80,000 to 500,000;
density: 0.910 – 0.930 g / cm3;
softening temperature: +80 – + 90 ° C;
melting point: +103 – + 115 ° C;
Brinell hardness: 14 – 25 MPa.
LDPE has universal properties that allow it to be used for different purposes. Distinctive features of granules and products from this material are:
flexibility, plasticity and softness, making the product pleasant to the touch;
good resistance to exposure to chemically active media;
the possibility of obtaining products with a shiny and perfectly smooth surface, which gives the product a more attractive appearance when compared with matte products made of HDPE;
impermeability to moisture and air;
UV resistance of the sun;
complete inertness and lack of odor, including in secondary granules;
excellent dielectric ability.
In addition, LDPE is non-toxic and environmentally friendly material for humans and the environment, so it can be used for contact with food and the manufacture of toys for children.
There are different types of LDPE granules, which can be obtained by additional processing. The main modifications of this polymeric material are:
PE foamed, having a porous structure, due to the introduction of a gas mixture of hydrocarbons in PVD, which makes it plastic and at the same time strong – such material is produced in sheets, in rolls or in the form of plaits;
Cross-linked high-pressure PE with increased density and strength due to the presence of cross-links formed by a chain of hydrogen atoms between the branches of macromolecules — such a structure is achieved by introducing hydrogen peroxide into the molten raw material;
copolymers of PVD with PE of another type or various monomers
Production technology of secondary granules LDPE
To obtain a secondary LDPE, use is made of this material generated during the manufacture of various products from it, as well as the products that have served their time or become unusable. Today there are two ways to process such secondary raw materials.
The first method is mechanical, which involves grinding into a crumb or powdery mass of pre-selected, washed and dried recycled materials, followed by melting and casting. This method of processing allows you to preserve the physico-mechanical properties of used recycled materials.
The second method is a physicochemical one, which involves the sequential completion of the following stages of the technological cycle of processing LDPE:
sorting recycled materials by brand and cleaning it from impurities;
washing prepared wastes in special complexes with the addition of detergents to remove complex, persistent contaminants and their subsequent drying. At this stage, the methods of metal separation and flotation can be applied, as well as the removal of residues of solid fractions and excess moisture in the centrifuge;
crushing of raw materials and its grinding with the help of knife crushers, jet mill, rotary and hammer crushers;
agglomeration of the crushed material by heating it to the plasticization temperature with a sharp cooling of the sintered raw material, which turns it into pellets. The resulting agglomerate can already serve as a semi-finished product for the manufacture of polymer products;
pelletizing pellets, for which they are again melted and passed through an extruder: at this stage, plasticizers, bactericidal materials, antioxidants or dyes can be added to the raw materials. The yarns of the secondary PE of low density obtained at the exit from the extruder are cooled with water or air, and are also cut into granules.
Where high pressure polyethylene is used
The scope of application of secondary and primary PVD granules is quite diverse. Today they make from this material:
pipes for pressure lines or irrigation networks, as well as fittings for them;
blow moldings, such as cans and bottles;
thermal insulation, for which foamed LDPE is used;
electrical insulation sheath for cable products;
sleeves, bags, bags and films of different types, including heat shrinkable;
hot melt powder form, obtained from the crushed granules;
tile of polymer mixture and ruberoid;
component parts and components for the automotive industry;
nonwovens, threads for textile production and other products.
Our company Polimers LLC from Krivogo Rog is the country’s largest processor of polymer waste, producing, among other things, secondary high-pressure polyethylene (LDPE), which can be bought from us at the best price in Ukraine. Order secondary low density PE with the desired consumer properties and characteristics on our website!