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[Chemical Knowledge]：Production process and preparation method of polypropylene

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Polypropylene is a widely used synthetic polymer, which is widely used in plastic products and textiles because of its stable physical properties, strong chemical stability, good heat resistance, good mechanical properties and electrical insulation properties. The production process and preparation method of polypropylene are very important for its performance and quality. In this paper, the production process and preparation method of polypropylene will be introduced in detail from three aspects: the structural characteristics, production process and preparation method of polypropylene. The structural characteristics of

1. polypropylene

polypropylene is a synthetic polymer made by polymerization of propylene as monomer. Its molecular formula is (C3H6)n, and its molecular weight is generally between 80000 and 300000. The main chain of polypropylene is made up of propylene monomers through covalent bonds, and the molecular structure has two forms: linear and branched. Polypropylene has high melting point, high crystal density and orderly molecular arrangement, so it has good crystallization and mechanical properties.

2. polypropylene production process

polypropylene production process mainly includes polymerization reaction, shear separation, coagulation precipitation and other stages. The following is a specific introduction to the production process of polypropylene.

1. Polymerization stage The

polymerization stage is the first stage of the polypropylene production process. Its main process is to carry out a free radical polymerization reaction of propylene monomer under the action of a catalyst to generate a polymer. At present, the use of a wide range of catalysts are manganese-based, nickel-based, molybdenum-based and other types.

2. Shear Separation Stage

After the end of the polymerization stage, the resulting polymer is in a colloidal state. In order to separate and eliminate the dispersed particles and impurities in the colloid, shear separation is required. There are two main methods of shear separation: inertial separation and centrifugal separation. Inertial separation is through the high-speed flow of the polymer solution under the action of centrifugal force, so that the colloidal particles precipitated, to achieve the purpose of separation and purification; centrifugal separation is through the high-speed rotation of the centrifuge colloidal particles precipitated.

3, Coacervation Stage

After the shear separation stage, the resulting polymer is in a semi-solid or gel state, I .e., the polymer molecules have been crystallized. The main work in the coagulation and precipitation stage is to heat the aggregates to dissolve the polymer components. At the same time, it also needs to be filtered and dried to finally obtain the desired polypropylene product. The preparation method of

3. polypropylene The preparation method of

polypropylene mainly has three kinds of homogeneous polymerization method, heterogeneous polymerization method and gas phase polymerization method. The preparation methods of these three types of polypropylene are described below.