Plastic is a commonly used chemical raw material, and it is a high-molecular organic material that is formed by polymerizing one or more monomers under certain reaction conditions. Because of its characteristics of light weight, low cost, and excellent performance, it is in the national economy. Occupy an important part.
First, the conventional plastic varieties and classification
In daily life, we can directly touch or perceive plastics, most of which are conventional general-purpose plastics, mainly including five categories: PE, PP, ABS, PVC, and PS. These five types of plastic occupy the vast majority of plastic raw materials used. The rest can basically be classified as special plastic types, such as PPS, PPO, PA, PC, POM, etc., and they are used in a small amount in daily life products. They are mainly used in high-end fields such as engineering industry and national defense technology. Automotive, aerospace, construction, communications and other fields. Plastics are classified according to their plasticity and can be divided into thermoplastics and thermosetting plastics. Under normal circumstances, thermoplastic products can be recycled, but thermosetting plastics can not, according to the optical properties of plastic, can be divided into transparent, translucent and opaque materials, such as PS, PMMA, AS, PC, etc. are transparent plastic Most other plastics are opaque plastics. There are many ways to classify plastics, which are not introduced here.
Second, the performance and use of commonly used plastic varieties
1. Polyethylene: Commonly used polyethylene can be divided into low pressure polyethylene (HDPE), high pressure polyethylene (LDPE) and linear high pressure polyethylene (LLDPE). Among them, HDPE has better thermal performance, electrical properties and mechanical properties, while LDPE and LLDPE have better flexibility, impact properties, and film forming properties. LDPE and LLDPE are mainly used for packaging films, agricultural films, and plastics modification, while HDPE is widely used in various fields such as films, tubes, and daily necessities for injection.
2. Polypropylene: Relatively speaking, polypropylene is more variety and its use is also more complicated. There are many fields. The main varieties are homo polypropylene (homopp), block copolymer polypropylene (copp) and random copolymer polypropylene ( Rapp), according to the different uses, homopolymerization is mainly used in the drawing, fiber, injection, BOPP film and other fields, polypropylene copolymer is mainly used in household appliances injection, modified raw materials, daily injection products, pipe, etc., random polymerization Propylene is mainly used for transparent products, high-performance products, high-performance pipes and so on.
3, PVC: Because of its low cost, the product has the characteristics of self-inflammability, it is widely used in the construction field, especially the sewer pipe, plastic steel doors and windows, panels, artificial leather and other uses the most widely.
4. Polystyrene: As a transparent raw material, it has a wide range of uses in the case of transparent requirements, such as automotive lampshades, daily transparent parts, transparent cups, and cans.
5, ABS: is a widely used engineering plastics, with outstanding physical and thermal properties, widely used in household appliances, panels, masks, assemblies, accessories, etc., especially household appliances, such as washing machines, air conditioners, refrigerators, Fans, etc., are used in very large quantities. In addition, the use of plastics is also very versatile.
Third, the identification of commonly used plastics
1. Density method: Examine the density of various plastics, and use liquid as medium to test the ups and downs of plastics in liquid medium to roughly identify the major categories of plastics. For example, if a piece of plastic is placed in water, it can be concluded that the raw material is not PVC (due to PVC density>1).
2. Combustion method: mainly examines the color of the flame and the odor and smoke emitted when it is burned. In general, the burning flames of polyolefin materials are mostly blue or light blue, the odor is relatively mild and pale, and the smoke is white. Most raw materials with benzene or chlorine are prone to black smoke after burning, and the smell is intense. In addition, such as PE, PP drip phenomenon, and PVC, no drip, but there are self-extinguishing phenomenon.
3, optical method: mainly examine the transparency of raw materials, commonly used transparent materials: PS, PC, PMMA, AS; translucent materials: PE, random copolymer PP, homopolymer PP, soft PVC, transparent ABS, etc. The other raw materials are essentially opaque.
4, color discrimination method: In general, raw materials without additives, if they contain double bonds, the color will appear slightly yellow, such as ABS, due to butadiene copolymer, polymer still contains double bonds, So it will look yellow.
Most other methods of identification require the use of various instruments such as infrared spectroscopy, mass spectroscopy, nuclear magnetic resonance, differential scanning, thermal analysis, and the like.
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