Classification and application fields of plastics

The types of commonly used plastics are:

① Polyvinyl chloride (PVC)

It is the largest amount of plastic in construction. The density of rigid PVC is

1.38 ～ 1.43g / cm3, high mechanical strength, good chemical stability, the operating temperature range is generally between -15 ～ + 55 ℃, suitable for manufacturing plastic doors and windows, sewer pipes, wire grooves, etc. ② Polyethylene (PE)

Polyethylene plastic is mainly used for water supply and drainage pipes and sanitary wares in construction. ③Polypropylene (PP)

The density of polypropylene is the smallest of all plastics, about 0.90. Polypropylene is commonly used to produce pipe, sanitary ware and other building products.

④Polystyrene (PS)

Polystyrene is a colorless and transparent glass-like plastic. Polystyrene is mainly used to produce foam insulation materials, light-transmitting materials and other products in construction.

⑤ABS plastic

ABS plastic is a modified polystyrene plastic composed of three components based on acrylonitrile (A), butadiene (B) and styrene (S). ABS plastic can be used to make plastic decorative plates with patterns and so on.

Polyethylene: Performance: Good electrical insulation performance, chemical resistance, cold resistance, non-toxic Uses: can be used to make food bags, pharmaceutical packaging materials, daily necessities, pipes, insulating materials, etc., the containers made can not store cooking oil and beverages for a long time Wait. Polyvinyl chloride: performance: organic solvent resistance, chemical corrosion resistance, wear resistance, good electrical insulation performance, good water resistance, additives are toxic to the human body. Uses: can produce daily necessities, wire sheath, pipes, insulation materials

Materials, construction materials, artificial leather, etc., the film made should not be used for packaging food. Polystyrene: Performance: good electrical insulation performance, good light transmission, water resistance, chemical corrosion resistance, non-toxic. Uses: It can be used to make TV cases, automobiles, aircraft parts, toys, medical and health supplies, daily necessities, etc.

1 Conventional varieties and classification of plastics

In daily life, most of the plastics that we can directly touch or perceive are conventional general-purpose plastics, which mainly include five categories: PE, PP, ABS, PVC, and PS. These five categories of plastics account for the vast majority of plastic raw materials. , The rest can basically be classified into special plastic varieties, such as: PPS, PPO, PA, PC, POM, etc., they are used in daily life products very little, mainly used in high-end fields such as engineering industry, national defense technology, such as Automotive, aerospace, construction, communications and other fields. Plastics can be classified into thermoplastics and thermosetting plastics according to their plasticity. Under normal circumstances, thermoplastic products can be recycled, but thermosetting plastics cannot. According to the optical properties of plastics, they can be divided into transparent, translucent and opaque materials, such as PS, PMMA, AS, PC, etc. are transparent plastics , While most other plastics are opaque plastics. There are many ways to classify plastics, which are not introduced here one by one.

2 Properties and uses of commonly used plastic varieties

① Polyethylene: Polyethylene is the most productive variety in the plastics industry. Polyethylene is an opaque or translucent, light-weight crystalline plastic. It has excellent low temperature resistance (the minimum operating temperature can reach -70 ~ -100 ℃), electrical insulation, good chemical stability, energy

Resistant to most acids and alkalis, but not heat resistant. Polyethylene is suitable for processing by injection molding, blow molding, extrusion molding and other methods. Commonly used polyethylene can be divided into low-pressure polyethylene (HDPE), high-pressure polyethylene (LDPE) and linear high-pressure polyethylene (LLDPE). Among the three, HDPE has better thermal properties, electrical properties and mechanical properties, while LDPE and LLDPE have better flexibility, impact properties, film formation, etc. LDPE and LLDPE are mainly used for packaging films, agricultural films, plastic modification, etc., while HDPE is more widely used, such as films, pipes, injection daily necessities and other fields.

②Polypropylene: Polypropylene is a thermoplastic plastic obtained from the polymerization of propylene. It is usually a colorless, translucent solid, odorless and non-toxic, with a density of 0.90 ~ 0.919 g / cm3. It is the lightest general-purpose plastic and its outstanding advantages It has the characteristics of cooking resistance in water, corrosion resistance, strength, rigidity and transparency are better than polyethylene. The disadvantage is poor low temperature impact resistance and easy aging, but it can be improved by modification and addition of additives, respectively. There are three production methods of polypropylene: slurry method, liquid phase bulk method and gas phase method. Relatively speaking, there are more varieties of polypropylene, and their uses are more complicated. The fields are diverse. Polypropylene and random copolymer polypropylene, according to different uses, homopolymerization is mainly used in wire drawing, fiber, injection, BOPP film and other fields, copolymer polypropylene is mainly used in household appliances injection parts, modified materials, daily injection products, Pipes, etc., random polypropylene is mainly used for transparent products, high-performance products, high-performance pipes, etc.

③Polyvinyl chloride: Polyvinyl chloride is a plastic obtained by polymerizing vinyl chloride. By adding plasticizer, its hardness can be greatly changed. Its hard products and even soft products are widely used. The production methods of PVC include suspension polymerization method, emulsion polymerization method and this

The bulk polymerization method is mainly based on the suspension polymerization method. Because of its low cost and the product’s self-flame retardant properties, it is widely used in the construction field, especially for sewer pipes, plastic steel doors and windows, plates, and artificial leather.

④Polystyrene: General-purpose polystyrene is a polymer of styrene, which has a transparent appearance but has the disadvantage of being brittle. Therefore, impact resistance polystyrene (HTPS) can be made by adding polybutadiene. The main production methods of polystyrene are bulk polymerization, suspension polymerization and solution polymerization. As a transparent raw material, in the case of demand for transparency, it is widely used, such as car lampshades, daily transparent parts, transparent cups, cans, etc.

⑤ABS: ABS resin is the product of three monomers acrylonitrile-butadiene-styrene co-polymerization, referred to as ABS terpolymer. Due to the different proportions of components A (acrylonitrile), B (butadiene) and S (styrene) in the composition, and the manufacturing methods, the properties of this plastic also vary greatly. It is a versatile engineering plastic with outstanding 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. It is very large, and it is also widely used in plastic modification.

3 Commonly used plastic identification methods

①Density method: Check the density of various plastics, use liquid as the medium, check the sink and float of the plastic in the liquid medium, and roughly identify the major categories of plastic, such as a piece of plastic placed in water, floating on the water surface can be determined, the raw material is not PVC (Because the density of PVC> 1).

② Combustion method: Mainly examine the color of the flame and the odor and smoke emitted during combustion. Generally speaking, the burning flame of polyolefin raw materials is mostly blue or light blue, the odor is relatively mild and light, and the smoke is white, but most Raw materials with benzene or chlorine are easy to emit black smoke after burning, and the smell is strong. In addition, PE, PP have dripping ignition, while PVC, etc. have no dripping ignition, but there is self-extinguishing phenomenon.

③Optical method: Mainly check the transparency of the raw materials. 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. The raw material is basically opaque.

④Color discrimination method: Generally speaking, the raw materials without additives, if they contain double bonds, the color will be slightly yellow, such as ABS, due to butadiene copolymerization, the polymer still contains double bonds after polymerization, so Will be slightly yellow.

Most other identification methods rely on various instruments, such as infrared spectroscopy, mass spectrometry, nuclear magnetic resonance, differential thermal scanning, and thermal analysis.