1. Use classification

According to the different use characteristics of various plastics, plastics are usually divided into three types: general plastics, engineering plastics and special plastics.

①General plastic

Generally refers to plastics with large output, wide application, good formability and low price. There are five types of general plastics, namely polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS) and acrylonitrile-butadiene-styrene copolymer (ABS). These five types of plastics account for the vast majority of plastic raw materials, and 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 It is used in high-end fields such as the engineering industry and national defense technology, such as automobiles, aerospace, construction, and communications. According to its plasticity classification, plastics can be divided into thermoplastics and thermosetting plastics. Under normal circumstances, thermoplastic products 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, PC, etc. which are transparent plastics , And most other plastics are opaque plastics.

Properties and uses of commonly used plastics:

1. Polyethylene:

Commonly used polyethylene can be divided into low density polyethylene (LDPE), high density polyethylene (HDPE) and linear low density polyethylene (LLDPE). Among the three, 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 packaging films, agricultural films, plastic modification, etc., while HDPE has a wide range of applications, such as films, pipes, and injection daily necessities.

2. Polypropylene:

Relatively speaking, polypropylene has more varieties, more complex uses, and a wide range of fields. The varieties mainly include homopolymer polypropylene (homopp), block copolymer polypropylene (copp) and random copolymer polypropylene (rapp). According to the application Homopolymerization is mainly used in the fields of wire drawing, fiber, injection, BOPP film, etc. Copolymer polypropylene is mainly used in household appliances injection parts, modified raw materials, daily injection products, pipes, etc., and random polypropylene is mainly used in transparent Products, high-performance products, high-performance pipes, etc.

3. Polyvinyl chloride:

Because of its low cost and self-flame retardant properties, it has a wide range of uses in the construction field, especially for sewer pipes, plastic steel doors and windows, plates, artificial leather, etc.

4. Polystyrene:

As a kind of transparent raw material, when there is a need for transparency, it has a wide range of uses, such as automobile lampshades, daily transparent parts, transparent cups, cans, etc.

5. ABS:

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 has a wide range of uses in plastic modification.

②Engineering plastics

Generally refers to plastics that can withstand a certain external force, have good mechanical properties, high and low temperature resistance, and have good dimensional stability, and can be used as engineering structures, such as polyamide and polysulfone. In engineering plastics, it is divided into two categories: general engineering plastics and special engineering plastics. Engineering plastics can meet higher requirements in terms of mechanical properties, durability, corrosion resistance, and heat resistance, and they are more convenient to process and can replace metal materials. Engineering plastics are widely used in electrical and electronic, automotive, construction, office equipment, machinery, aerospace and other industries. Substituting plastic for steel and plastic for wood has become an international trend.

General engineering plastics include: polyamide, polyoxymethylene, polycarbonate, modified polyphenylene ether, thermoplastic polyester, ultra-high molecular weight polyethylene, methylpentene polymer, vinyl alcohol copolymer, etc.

Special engineering plastics are divided into cross-linked and non-cross-linked types. Cross-linked types are: polyamino bismaleamide, polytriazine, cross-linked polyimide, heat-resistant epoxy resin and so on. Non-crosslinked types are: polysulfone, polyethersulfone, polyphenylene sulfide, polyimide, polyether ether ketone (PEEK) and so on.

③Special plastics

Generally refers to plastics that have special functions and can be used in special applications such as aviation and aerospace. For example, fluoroplastics and silicones have outstanding high temperature resistance, self-lubricating and other special functions, and reinforced plastics and foamed plastics have special properties such as high strength and high cushioning. These plastics belong to the category of special plastics.

a. Reinforced plastic:

Reinforced plastic raw materials can be divided into granular (such as calcium plastic reinforced plastic), fiber (such as glass fiber or glass cloth reinforced plastic), and flake (such as mica reinforced plastic) in appearance. According to the material, it can be divided into cloth-based reinforced plastics (such as rag reinforced or asbestos reinforced plastics), inorganic mineral filled plastics (such as quartz or mica filled plastics), and fiber reinforced plastics (such as carbon fiber reinforced plastics).

b. Foam:

Foam plastics can be divided into three types: rigid, semi-rigid and flexible foams. Rigid foam has no flexibility, and its compression hardness is very large. It will deform only when it reaches a certain stress value and cannot return to its original state after the stress is relieved. Flexible foam is flexible, with low compression hardness, and is easy to deform. Restore the original state, the residual deformation is small; the flexibility and other properties of the semi-rigid foam are between the rigid and soft foams.

Two, physical and chemical classification

According to the different physical and chemical properties of various plastics, plastics can be divided into two types: thermosetting plastics and thermoplastic plastics.

(1) Thermoplastic

Thermoplastics (Thermo plastics): refers to plastics that will melt after heating, can flow into the mold after cooling, and then melt after heating; heating and cooling can be used to produce reversible changes (liquid ←→solid), yes The so-called physical change. General-purpose thermoplastics have continuous use temperatures below 100°C. Polyethylene, polyvinyl chloride, polypropylene, and polystyrene are also called the four general-purpose plastics. Thermoplastic plastics are divided into hydrocarbons, vinyls with polar genes, engineering, cellulose and other types. It becomes soft when heated, and becomes hard when cooled. It can be repeatedly softened and hardened and maintain a certain shape. It is soluble in certain solvents and has the property of being meltable and soluble. Thermoplastics have excellent electrical insulation, especially polytetrafluoroethylene (PTFE), polystyrene (PS), polyethylene (PE), polypropylene (PP) have extremely low dielectric constant and dielectric loss. For high frequency and high voltage insulation materials. Thermoplastics are easy to mold and process, but have low heat resistance and are easy to creep. The degree of creep varies with load, environmental temperature, solvent, and humidity. In order to overcome these weaknesses of thermoplastics and meet the needs of applications in the fields of space technology and new energy development, all countries are developing heat-resistant resins that can be melted, such as polyether ether ketone (PEEK) and polyether sulfone (PES). , Polyarylsulfone (PASU), polyphenylene sulfide (PPS), etc. Composite materials using them as matrix resins have higher mechanical properties and chemical resistance, can be thermoformed and welded, and have better interlaminar shear strength than epoxy resins. For example, using polyether ether ketone as the matrix resin and carbon fiber to make a composite material, the fatigue resistance exceeds that of epoxy/carbon fiber. It has good impact resistance, good creep resistance at room temperature, and good processability. It can be used continuously at 240-270°C. It is an ideal high-temperature insulation material. The composite material made of polyethersulfone as the matrix resin and carbon fiber has high strength and hardness at 200°C, and can maintain good impact resistance at -100°C; it is non-toxic, non-flammable, minimal smoke, and radiation resistance. Well, it is expected to be used as a key component of a spacecraft, and it can also be molded into a radome, etc.

Formaldehyde cross-linked plastics include phenolic plastics, amino plastics (such as urea-formaldehyde-melamine-formaldehyde, etc.). Other cross-linked plastics include unsaturated polyesters, epoxy resins, and phthalic diallyl resins.

(2) Thermosetting plastic

Thermosetting plastics refer to plastics that can be cured under heat or other conditions or have insoluble (melting) characteristics, such as phenolic plastics, epoxy plastics, etc. Thermosetting plastics are divided into formaldehyde cross-linked type and other cross-linked types. After thermal processing and molding, an infusible and insoluble cured product is formed, and the resin molecules are cross-linked into a network structure by a linear structure. Increased heat will decompose and destroy. Typical thermosetting plastics include phenolic, epoxy, amino, unsaturated polyester, furan, polysiloxane and other materials, as well as newer polydipropylene phthalate plastics. They have the advantages of high heat resistance and resistance to deformation when heated. The disadvantage is that the mechanical strength is generally not high, but the mechanical strength can be improved by adding fillers to make laminated materials or molded materials.

Thermosetting plastics made of phenolic resin as the main raw material, such as phenolic molded plastic (commonly known as Bakelite), are durable, dimensionally stable, and resistant to other chemical substances except strong alkalis. Various fillers and additives can be added according to different uses and requirements. For varieties that require high insulation performance, mica or glass fiber can be used as filler; for varieties that require heat resistance, asbestos or other heat-resistant fillers can be used; for varieties that require seismic resistance, various appropriate fibers or rubber can be used as fillers And some toughening agents to make high toughness materials. In addition, modified phenolic resins such as aniline, epoxy, polyvinyl chloride, polyamide, and polyvinyl acetal can also be used to meet the requirements of different applications. Phenolic resins can also be used to make phenolic laminates, which are characterized by high mechanical strength, good electrical properties, corrosion resistance, and easy processing. They are widely used in low-voltage electrical equipment.

Aminoplasts include urea formaldehyde, melamine formaldehyde, urea melamine formaldehyde and so on. They have the advantages of hard texture, scratch resistance, colorless, translucent, etc. Adding color materials can be made into colorful products, commonly known as electric jade. Because it is resistant to oil and not affected by weak alkalis and organic solvents (but not acid resistant), it can be used at 70°C for a long time, and can withstand 110 to 120°C in the short term, and can be used in electrical products. Melamine-formaldehyde plastic has higher hardness than urea-formaldehyde plastic, and has better water resistance, heat resistance, and arc resistance. It can be used as an arc-resistant insulating material.

There are many types of thermosetting plastics made with epoxy resin as the main raw material, among which about 90% are based on bisphenol A epoxy resin. It has excellent adhesion, electrical insulation, heat resistance and chemical stability, low shrinkage and water absorption, and good mechanical strength.

Both unsaturated polyester and epoxy resin can be made into FRP, which has excellent mechanical strength. For example, glass fiber reinforced plastic made of unsaturated polyester has good mechanical properties and low density (only 1/5 to 1/4 of steel, 1/2 of aluminum), and is easy to process into various electrical parts. The electrical and mechanical properties of plastics made of dipropylene phthalate resin are better than those of phenolic and amino thermosetting plastics. It has low hygroscopicity, stable product size, good molding performance, acid and alkali resistance, boiling water and some organic solvents. The molding compound is suitable for manufacturing parts with complex structure, temperature resistance and high insulation. Generally, it can be used for a long time in the temperature range of -60～180℃, and the heat resistance grade can reach F to H grade, which is higher than the heat resistance of phenolic and amino plastics.

Silicone plastics in the form of polysiloxane structure are widely used in electronics and electrical technology. Silicone laminated plastics are mostly reinforced with glass cloth; silicone molded plastics are mostly filled with glass fiber and asbestos, which are used to manufacture parts that are resistant to high temperature, high frequency or submersible motors, electrical appliances, and electronic equipment. This type of plastic is characterized by its low dielectric constant and tgδ value, and is less affected by frequency. It is used in the electrical and electronic industries to resist corona and arcs. Even if the discharge causes decomposition, the product is silicon dioxide instead of conductive carbon black. . This type of material has outstanding heat resistance and can be used continuously at 250°C. The main disadvantages of polysilicone are low mechanical strength, low adhesiveness and poor oil resistance. Many modified silicone polymers have been developed, such as polyester modified silicone plastics and have been applied in electrical technology. Some plastics are both thermoplastic and thermosetting plastics. For example, polyvinyl chloride is generally a thermoplastic. Japan has developed a new type of liquid polyvinyl chloride that is thermoset and has a molding temperature of 60 to 140°C. A plastic called Lundex in the United States has both thermoplastic processing Features, and physical properties of thermosetting plastics.

① Hydrocarbon plastics.

It is a non-polar plastic, which is divided into crystalline and non-crystalline. Crystalline hydrocarbon plastics include polyethylene, polypropylene, etc., and non-crystalline hydrocarbon plastics include polystyrene, etc.

②Vinyl plastics containing polar genes.

Except for fluoroplastics, most of them are non-crystalline transparent bodies, including polyvinyl chloride, polytetrafluoroethylene, polyvinyl acetate, etc. Most vinyl monomers can be polymerized with radical catalysts.

③Thermoplastic engineering plastics.

Mainly include polyoxymethylene, polyamide, polycarbonate, ABS, polyphenylene ether, polyethylene terephthalate, polysulfone, polyethersulfone, polyimide, polyphenylene sulfide, etc. Polytetrafluoroethylene. Modified polypropylene, etc. are also included in this range.

④ Thermoplastic cellulose plastics.

It mainly includes cellulose acetate, cellulose acetate butyrate, cellophane, cellophane and so on.

We can use all the plastic materials above.
Under normal circumstances, food-grade PP and medical-grade PP are used for products similar to spoons. The pipette is made of HDPE material, and the test tube is generally made of medical grade PP or PS material. We still have many products, using different materials, because we are a mold maker, almost all plastic products can be produced