Polyethylene wax is a kind of polyolefin synthetic wax, which generally refers to homopolyethylene with relative molecular weight less than 10000. In a broad sense, ethylene polymers with poor strength and toughness and can not be processed as a single material can be called polyethylene wax. Pe waxhas high softening point, low melting viscosity, good chemical stability, good lubricity and fluidity. As a processing aid, it is widely used in PVC pipes, films, cables and other plastic and rubber products to improve the processing performance of products and improve the appearance of finished products.
Preparation method of polyethylene wax
There are three main synthetic methods of pe wax. The first is polyethylene cracking method, which breaks polyethylene resin into polyethylene wax with low molecular weight at high temperature. The second is the by-product refining method, which collects the by-products of low molecular weight components produced in the production process of ethylene polymerization and purifies them to obtain polyethylene wax. The third method is ethylene synthesis method, which directly synthesizes polyethylene wax with ethylene as raw material. Today, Sainuo will take you to learn about polyethylene wax prepared by cracking method and synthesis method.
(1) Preparation of polyethylene wax by pyrolysis
Cracking method is the main method of producing polyethylene wax in China. High molecular weight pure polyethylene or waste polyethylene plastic is cracked into polyethylene wax at high temperature. Its product quality and properties (such as hardness, melting point and apparent color) are greatly affected by the source of cracking raw materials. The cracking method has simple technology, rich source of raw materials and low operation cost. It can realize the reuse of waste polyethylene with good economic benefits. However, the cracking process is difficult to control, the molecular weight distribution of the product is wide, the quality of polyethylene wax is difficult to control, and many black spots are produced. It is popular in the middle and low-end applications such as color masterbatch.
The existing cracking processes include thermal cracking, solvent assisted cracking and catalytic cracking. Among them, thermal cracking is the simplest. Polyethylene wax products can be prepared by controlling the reaction temperature and time, but considerable energy consumption is required. People from Beijing University of chemical technology have studied the preparation of polyethylene wax by cracking PE resin at high temperature in a single screw extruder. A heater is added on the connecting pipe between the extruder and the cooling tank to heat and crack the material. The optimal cracking temperature is 420 ℃, realizing the continuous production of cracking PE resin to prepare polyethylene wax. Others have studied the preparation of polyethylene wax by cracking waste polyethylene in an autoclave with al-mcm-48 as catalyst. The reaction temperature is 360 ~ 380 ℃ and the reaction time is 4H. The use of catalyst reduces the reaction activation energy, the temperature required for pyrolysis and energy consumption. Wang Lulu and others improved the yield of polyethylene wax by solvent assisted pyrolysis of polyethylene waste plastics. The effects of different solvents and reaction conditions on the yield and properties of wax were investigated. The test shows that the yield of polyethylene wax can be improved by using aromatic solvents. When using mixed xylene as solvent, the yield is as high as 87.88%. Aromatic solvents can also improve the product quality to a certain extent and obtain light yellow polyethylene wax.
(2) Synthesis of polyethylene wax
Polyethylene wax synthesized directly from ethylene has high purity, small relative molecular weight distribution, narrow melting range, adjustable product performance and stable quality. It is used to produce high-quality and diversified polyethylene wax. According to the polymerization mechanism and the types of catalysts used, ethylene synthesis can be divided into free radical polymerization, Ziegler Natta (Z-N) catalytic polymerization, metallocene catalytic polymerization and so on.
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