The raw materials for the production of synthetic resins are abundant. In the early days, coal tar products and calcium carbide calcium carbide were the main products. Most of them are mainly oil and natural gas products such as ethylene, propylene, benzene, formaldehyde and urea. The production method of the synthetic resin employs bulk polymerization, suspension polymerization, emulsion polymerization, solution polymerization, melt polymerization, and interfacial polycondensation.

Synthetic resin

Synthetic resin is a polymer compound produced by combining low molecular weight raw materials such as ethylene (such as ethylene, propylene, vinyl chloride, etc.) into macromolecules by polymerization. Polymerization methods commonly used in the industry include bulk polymerization, suspension polymerization, emulsion polymerization, and solution polymerization.

Bulk polymerization

Bulk polymerization is a polymerization process in which a monomer is carried out without the addition of other media under the action of an initiator or heat, light or radiation. The product is characterized by pure product, no complicated separation and purification, simple operation and high utilization rate of production equipment. It can directly produce pipes, plates and other quality products, so it is also called block polymerization. The disadvantage is that the viscosity of the material increases with the progress of the polymerization reaction, mixing and heat transfer are difficult, and the reactor temperature is not easy to control. Bulk polymerization is commonly used in the production of polyethyl acrylate (commonly known as plexiglass), polystyrene, low density polyethylene, polypropylene, polyester and polyamide.

Suspension polymerization

Suspension polymerization refers to the polymerization process in which the monomer is dispersed into droplets under the action of mechanical stirring or shaking and dispersing agent, and is usually suspended in water, so it is also called bead polymerization. The utility model has the following features: a large amount of water in the reactor, low viscosity of the material, easy heat transfer and control; only simple separation, washing, drying and the like after the polymerization, the resin product can be directly used for molding processing; the product is pure Even. The disadvantage is that the reactor production capacity and product purity are not as good as the bulk polymerization method, and continuous production cannot be carried out. Suspension polymerization is widely used in industry. 75% of the polyvinyl chloride resin is suspension polymerization, and polystyrene is mainly produced by suspension polymerization. The reactor is also gradually enlarged.

Emulsion polymerization

Emulsion polymerization refers to the polymerization of monomer by forming an emulsion in water under the action of emulsifier. The emulsion polymerization product is latex, which can be directly applied, or the latex can be destroyed, washed, dried, etc. After the treatment, a powdery or needle-like polymer is obtained. Emulsion polymerization can obtain higher molecular weight polymers at higher reaction rates, the viscosity of the materials is low, heat transfer and mixing are easy, production is easy to control, and residual monomers are easily removed. A disadvantage of emulsion polymerization is that the emulsifier or the like added during the polymerization affects the properties of the product. In order to obtain a solid polymer, a process such as coagulation, separation, washing, etc. is consumed. The reactor has a lower production capacity than the bulk polymerization method.

Solution polymerization

Solution polymerization is a polymerization in which a monomer is dissolved in a suitable solvent. The polymer formed is sometimes dissolved in a solvent, which is a typical solution polymerization, and the product can be used as a coating or an adhesive. If the polymer is insoluble in the solvent, it is called precipitation polymerization or slurry polymerization. For example, the production of solid polymer needs to be precipitated, filtered, washed and dried to become a finished product. In solution polymerization, both the production operation and the reaction temperature are easy to control, but both require recovery of the solvent. Industrial solution polymerization can be carried out by a continuous process and a batch process, and a large-scale production often employs a continuous process such as polypropylene.

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