Basic knowledge and identification methods of the

Basic knowledge and identification methods of commonly used plastics

Plastics is a common chemical raw material, which is a high molecular organic material polymerized by one or several monomers under certain reaction conditions. Because of its light weight, low price and excellent performance, it occupies an important part of the national economy

I. conventional varieties and classification of plastics

in daily life, the plastics we can directly contact or perceive, as well as the new material industry, are mostly conventional general-purpose plastics, mainly including five categories: PE, PP, ABS, PVC, PS. these five categories of plastics account for the vast majority of plastic raw materials used, and the rest can basically be classified into special plastic varieties, such as PPS, PPO, PA, PC, POM, etc, They are rarely used in daily life products, and are mainly used in high-end fields such as engineering industry and national defense technology, such as automotive, aerospace, construction, communications and other fields. Plastics can be classified into thermoplastic and thermosetting plastics according to their plasticity. Under normal circumstances, the products of thermoplastics can be recycled, while thermosetting plastics cannot. According to the optical properties of plastics, they can be divided into transparent, translucent and opaque raw materials, such as PS, PMMA, as, P Institute of important materials: innovative rare earth applied to improve the production of nylon, C, etc. belong to transparent plastics, while most other plastics are opaque plastics. There are many ways to classify plastics, which will not be introduced one by one here

II. Properties and uses of commonly used plastics

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, electrical and mechanical properties, while LDPE and LLDPE have better flexibility, impact properties, film-forming properties, etc. LDPE and LLDPE are mainly used in the post packaging film, agricultural film and plastic modification of the provincial engineering laboratory, while HDPE is widely used in film, pipe, injection daily necessities and other fields

2. Polypropylene: relatively speaking, polypropylene has more varieties, more complex uses and a wide range of fields. The varieties mainly include homopp, block copolymerized polypropylene (copp) and random copolymerized polypropylene (Rapp). According to different uses, homopolymerization is mainly used in the fields of wire drawing, fiber, injection, BOPP film, etc. copolymerized polypropylene is mainly used in injection parts of household appliances, modified raw materials, daily injection products, pipes, etc, Random polypropylene is mainly used for transparent products, high-performance products, high-performance pipes, etc

3. PVC: because of its low cost and self flame retardant properties, it is widely used in the construction field, especially in sewer pipes, plastic steel doors and windows, plates, artificial leather and so on

4. Polystyrene: as a transparent raw material, it is widely used when there is a need for transparency, such as car lampshade, daily transparent parts, transparent cups, cans, etc

5. Abs: it is an engineering plastic with a wide range of uses. It has excellent physical, mechanical and thermal properties. It is widely used in household appliances, panels, masks, assemblies, accessories, etc., especially household appliances, such as washing machines, air conditioners, refrigerators, electric fans, etc., with a huge amount of consumption. In addition, it is also widely used in plastic modification

III. identification methods of commonly used plastics

1. Density method: examine the density of various plastics, take the liquid as the medium, and test the ups and downs of their plastics in the liquid medium, so as to roughly identify the categories of plastics. For example, if a piece of plastic is placed in water and floats on the water surface, it can be concluded that the raw material is not PVC (because the density of PVC is> 1)

2. Combustion method: mainly examine the color of the flame and the smell and smoke emitted during combustion. Generally speaking, the combustion flame of polyolefin raw materials is mostly blue or light blue, the smell is mild and light, and the smoke is white, while most raw materials with benzene or chlorine are easy to emit black smoke after combustion, and the smell is strong. In addition, for example, PE and PP have trickle burning phenomenon, while PVC has no trickle burning, but has self extinguishing phenomenon

3. Optical method: mainly examine the transparency of raw materials. Generally, the commonly used transparent raw materials are: PS, PC, PMMA, as; Translucent raw materials are PE, random copolymer PP, homopolymer PP, soft PVC, transparent ABS, etc. other raw materials basically lift the hammer away from the bottom and are opaque

4. Color discrimination method: Generally speaking, if raw materials without additives contain double bonds, the color will be slightly yellow. For example, ABS, because of butadiene copolymerization, the polymer still contains double bonds after polymerization, so it will be slightly yellow

most other identification methods rely on various instruments, such as infrared spectroscopy, mass spectrometry, nuclear magnetic resonance, differential thermal scanning, thermal analysis, etc. (end)