What are the different methods for preparing polyethylene wax?

Polyethylene wax is a type of polyolefin synthetic wax, generally referring to homopolymer polyethylene with a relative molecular weight of less than 10000. In a broad sense, ethylene polymers with poor strength and toughness that cannot be processed as a single material can be called polyethylene wax. Polyethylene wax has a high softening point, low melt viscosity, good chemical stability, and 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 and appearance of the finished products.

Preparation methods of polyethylene wax: There are three main methods for synthesizing polyethylene wax. First, the polyethylene pyrolysis method, which pyrolyzes polyethylene resin into low-molecular-weight polyethylene wax at high temperatures. Second, the refined byproduct method, which collects and purifies the low-molecular-weight byproducts produced during ethylene polymerization to obtain polyethylene wax. Third, the ethylene synthesis method, which directly synthesizes polyethylene wax using ethylene as a raw material. According to its polymerization mechanism and the type of catalyst used, it can be divided into free radical polymerization, Ziegler -Natta (Z-N) catalytic polymerization and metallocene catalytic polymerization.

1. Pyrolysis preparation of polyethylene wax: Pyrolysis is the pyrolysis of high-molecular-weight pure polyethylene or waste polyethylene plastic into polyethylene wax at high temperatures. This is the main method for producing polyethylene wax in China. The quality and performance of the product are greatly affected by the source of the pyrolysis raw materials. The pyrolysis process is simple, the raw materials are abundant, and the operating cost is low. It can realize the recycling of waste polyethylene and has good economic benefits. However, the pyrolysis 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, which are quite popular in low-end applications such as color masterbatches. 2. Synthesis method for preparing polyethylene wax: Polyethylene wax directly synthesized from ethylene has high purity, narrow melting range, small molecular weight distribution, controllable product performance, and stable quality, and is used to produce high-quality and diversified polyethylene wax. According to the polymerization mechanism and the type of catalyst used, the ethylene synthesis method can be divided into Ziegler-Natta (Z-N) catalytic polymerization, free radical polymerization, and metallocene catalytic polymerization. 3. Free radical polymerization: Free radical polymerization is the polymerization of ethylene initiated by free radicals at high temperature and high pressure to obtain polyethylene wax. The molecular weight of polyethylene wax prepared by free radical polymerization is generally between 1000 and 6000 degrees, and the relative molecular weight distribution is between 2 and 5. It usually contains branches and double bonds.

Polyethylene wax has a wide range of uses, but due to limitations in China's production technology level, the product quality still has a large gap compared with foreign countries. In contrast, the quality requirements of end consumers are getting higher and higher, and high-quality polyethylene wax is in short supply. In the future, China should focus on developing the synthesis method for preparing polyethylene wax technology, improving product quality and performance indicators, strengthening modification technology, developing more functional polyethylene wax new varieties, expanding its application fields, and enhancing the brand competitiveness of China's polyethylene wax.