Have you mastered all the commonly used plastics?

Jan 04, 2023

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Plastics can be pure resin or a mixture with various additives. The resin acts as a binder. The additives are used to improve the physical and mechanical properties of pure resin, improve the processing performance or save resin.

Therefore, the most basic physical and chemical properties of plastics are determined by the properties of resins. Resin can be divided into natural resin and artificial resin, the latter is also called synthetic resin.

Resins are polymers, which have unique internal and external molecular structures. The internal structure of polymer determines the most basic physical and chemical properties of polymer; The external structure of polymer determines the processability and physical and mechanical properties of polymer.

Polymers can be divided into non crystalline (amorphous), semi crystalline and crystalline according to the structure and morphology between chains after solidification. Therefore, there are also amorphous and crystalline plastics.

During solidification of crystalline plastics, there is a process from crystal nucleus to crystal grain, forming a certain body state. For example, PE, PP, PA, POM, etc. are crystalline.

When amorphous plastics solidify, the growth process without crystal nucleus and grains is just the “freezing” of free macromolecular chains, such as PS, PVC, PMMA, PC, etc.

According to the reflection of its plastics on thermal action, it can be divided into thermoplastic and thermosetting plastics. Thermoplastic plastics are characterized by softening when heated and returning to solid when cooled. This reversible process can be repeated many times. Such as PS, PVC, PA, PP, POM, etc; The thermosetting plastic is characterized by being able to transform into a plastic melt at a certain temperature. However, if the temperature continues to increase, the internal polymer will be cured due to cross-linking if the heating time is prolonged. It can no longer be softened to the original state by heating, and can not be processed repeatedly. Such as epoxy, furan, amino, phenolic, etc.

Common filler

Common fillers for injection molding materials include general fillers, metal fillers, organic fillers, short fiber fillers and long fiber fillers. Adding these fillers can reduce the cost of injection molding products, and improve the physical and mechanical properties, chemical properties and photoelectric properties by increasing economic benefits; It can improve processing property, rheological property, reduce viscosity and improve dispersion.

Common fillers include limestone, calcium carbonate, talc, calcium silicate, mica, aluminum hydroxide, calcium sulfate, and agricultural and sideline products.

Organic fillers are the main fillers in plastic products at present, including natural materials and synthetic materials, including wood, wood flour, husk of Hu Nu, cotton plant cellulose, etc; Synthetic materials include recycled cellulose, including: man-made fabric, polyacrylonitrile fiber, nylon fiber, polyester fiber, etc.

Some fillers added to injection molding materials need to be treated with surface modifiers. The treatment process follows the interface chemistry theory, the wetting theory of filler and polymer surface, the acid-base interaction theory, and the mixing theory, which endow materials with some excellent properties.

At present, the commonly used surface modifiers include silane coupling agent, titanate coupling agent, organic silicon treatment agent, etc. When these surface modifiers are added, the filler efficiency can be further improved.