Polyvinylpolypyrrolidone Cross-linked 25249-54-1

Pharmacopoeia Name: Crospovidone

Chemical Name: Crospovinylpyrrolidone, PVPP

INCI/CTFA Name: Insoluble PVP

CAS No.: 25249-54-1,9003-39-8

PPreparation Method:

The cross-linking process of polyethylene can be basically divided into two categories: physical method and chemical method.

2. Chemical cross-linking

There are three types of chemical cross-linking: azo compound cross-linking, peroxide cross-linking and silane cross-linking. (1) Azo compound cross-linking This method is to mix azo compounds into polyethylene and extrude it at a temperature lower than the decomposition temperature of the azo compounds. The extrudate passes through a high-temperature salt bath, and the azo compounds decompose to form free radicals, which trigger the cross-linking of polyethylene. (2) Peroxide cross-linking The peroxide mixed into the polyethylene decomposes into free radicals during the extrusion process, which triggers the polyethylene polymer chain to form active free radicals and cross-link. This technology requires high-pressure extrusion equipment to allow the cross-linking reaction to proceed in the barrel, or to form the product at a lower temperature, and then use far-infrared heating or other rapid heating methods to heat the product to produce a cross-linked product. There are three main methods for producing HDPE cross-linked pipes by peroxide method: Engel method, Pont a Mou-son method and The Daoplas method. The Engel method can be used to produce higher molecular weight polyethylene (density about 0.950g/cm3), molecular weight about 500,000, mixed with peroxide, and fed into a plunger extruder. Under high pressure of about 20 to 50 MPa, polyethylene powder agglomerates, and the agglomerates pass through a heated die. The cross-linking reaction occurs above the melting point, so the structure is quite uniform. This method has been used to produce 315 mm pipes. The Pont a Mouson method uses polyethylene with a slightly lower molecular weight (200,000 to 500,000), mixes it with peroxide, and extrude it into a pipe. The cross-linking reaction is carried out in a salt bath at a temperature exceeding 200°C. In the Daoplas method, the peroxide is not directly mixed into the polyethylene, but the extruded HDPE pipe is passed through a medium containing peroxide, and the peroxide penetrates into the pipe. Organic peroxide cross-linked polyethylene is polyethylene that uses organic peroxide as a cross-linking agent and decomposes under the action of heat to generate highly active free radicals. These free radicals generate active points on the polymer carbon chain and produce carbon-carbon cross-links to form cross-linked polyethylene. The organic peroxides used include diisopropylbenzene peroxide, di-tert-butyl peroxide, and 2,5-di-tert-butyl-2,5-dimethylhexane peroxide. Different peroxides are selected according to the type of polyethylene to be cross-linked and the cross-linking process equipment. Usually, when cross-linking low-density polyethylene, diisopropylbenzene peroxide that can react at 132°C is used; when cross-linking highly filled low-density polyethylene and high-density polyethylene, 2,5-di-tert-butyl-2,5-methyl peroxide hexane that can be processed at 144°C can be used as a cross-linking agent. Polyethylene is mixed with appropriate organic peroxides, carbon black and other inorganic fillers and other additives, and after mixing and granulation, it is processed into products using a suitable molding process. Then the product is heated for a period of time to make it cross-linked, and a cross-linked polyethylene product can be obtained. In addition, when compression molding is used, cross-linking and molding can be completed in one step

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