Low-pressure polyethylene is one of the most widely used plastics in the world. It is an organic compound that looks like a white, wax-like mass. Secondary HDPE is obtained by processing plastic bottles, pipes and other products from the same material. In English, the substance is called High Density Polyethylene (HDPE). Marking – the numbers “02” in the triangle. Properties Low-pressure polyethylene is chemically and frost-resistant, insensitive to shock, does not stick (low adhesion), softens when heated to 80 – 120 ° C, and freezes when cooled. Does not conduct electric current. The material is resistant to water, does not react with alkalis, regardless of their concentration. Low-pressure polyethylene does not interact with acids (even concentrated sulfuric), and solutions of acidic, neutral and basic salts. At the same time, it decomposes under the influence of chlorine and fluorine in a liquid or gaseous state and due to the action of 50% nitric acid. Under the influence of high temperature it can dissolve in water heated to 180 ° C. From the point of view of the molecular structure, PND molecules are practically unbranched, this material is denser, since it contains a larger fraction of the crystalline phase. Obtaining HDPE Low-pressure polyethylene under industrial conditions is obtained by polymerization of ethylene with an organic solvent. This occurs under the following conditions: pressure below 0.1 – 2 MPa; temperature 120-150 ° C; Zitler-Natta catalysts. The three main technologies for the production of PND are gas phase polymerization, a reaction in suspension or in solution. After processing, the same products can be made from it as before recycling. The use of low-pressure polyethylene HDPE is resistant to a large number of factors and is widely used in the production of: parts and accessories for swimming pools; filaments of 3 D printers; washers; bottle caps; chemical resistant pipes; insulation for electrical cables; food containers; fuel tanks; anticorrosion coating for steel pipes; plastic chairs and tables; protective helmets; plastic gymnastic hoops; shoe pads; gas pipes; plastic bags; plastic bottles; clamps and other parts for medical purposes; paper substitute; water pipes for home and garden. Low-pressure polyethylene is used by manufacturers of pyrotechnics and in the agricultural sector.
Obtaining secondary HDPE
HDPE waste is processed by extrusion, casting and blowing methods. The process takes place in several stages: sorting of raw materials. It is divided by type, color, quality and level of pollution. In small enterprises, done manually; the next stage is crushing: with the help of special machines, the material is crushed to particles of the same size; then follows the washing and cleaning of dust and other non-polyethylene impurities in a special device; agglomeration – the stage following the washing of recyclables. In the working chamber of the machine, the raw material enters the rotating rotor, where it heats up due to friction and turns into a porridge-like mass; after the whole portion is melted, water is added to the machine. Due to sudden cooling, the substance turns into small balls of irregular shape. The material obtained at this stage goes to the extruder. The essence of the next process – the molten mass of the processed plastic is pressed through the forming hole. In the extruder, the mass is again melted and pressed further, creating the so-called filaments. They are cooled by “passing” through a water sleeve. After which there is the last stage – the threads are cut into small pieces, and the secondary HDPE granule is obtained at the output. What happened is a semi-finished product, material for the manufacture of pipes, bottles and other things. Granules are sorted, packed in bags and sent to plants. There are few specialized enterprises for the processing of low-pressure polyethylene nationwide. Most willingly accept boxes, pipes, bottles. Parts and building materials made of their granules of processed HDPE, subject to the technical process, are not inferior in quality to the “new” ones. Moreover, they are cheaper.