Of plastic raw materials and the kinds of use

Usage category:

① General plastics

Generally refers to plastic with large output, wide use, good formability and cheap price. there are five types of general plastic pellets, namely polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS) and acrylonitrile-butadiene-styrene copolymer (ABS). These five categories of plastics occupy the vast majority of the use of plastic raw materials, the rest can be classified into special plastic varieties, such as: PPS, PPO, PA, PC, POM, etc., they are very small in the amount of daily life products, mainly used in the engineering industry, national defense technology and other high-end fields, 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, while thermosetting plastics can not, according to the optical properties of plastics, can be divided into transparent, translucent and opaque raw materials, such AS PS, PMMA, AS, PC and other transparent plastics, while 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 (HD

)

Special plastics

PE) and linear Low density 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 and so on. LDPE and LLDPE are mainly used for packaging film, agricultural film, plastic modification, etc., while HDPE is widely used in many fields such as film, pipe, injection daily necessities.

2. Polypropylene: Relatively speaking, there are more varieties of polypropylene, the use is more complex, there are many fields, the main varieties are homopp (homopp), block copolymer polypropylene (copp) and random copolymer polypropylene (rapp), according to the different uses, homopP is mainly used in drawing, fiber, injection, BOPP film and other fields. Copolymer polypropylene is mainly used in household appliances injection parts, modified raw materials, daily injection products, pipes, etc. Random polypropylene is mainly used in transparent products, high-performance products, high-performance pipes and so on.

3. PVC: Due to its low cost, the product has the characteristics of self-flame retardant, so it is widely used in the construction field, especially the sewer pipe, plastic steel doors and Windows, plates, artificial leather and other most widely used.

4. Polystyrene: as a transparent raw material, it is widely used in the case of transparent demand, such as car lampshades, daily transparent parts, transparent cups, cans and so on.

5. ABS: is a widely used engineering plastic, with outstanding physical mechanical 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., the amount is very large, in addition to plastic modification, it is also widely used.

② Engineering plastics

Generally refers to the plastic that can withstand a certain external force, has good mechanical properties and resistance to high and low temperatures, has good dimensional stability, and can be used as an engineering structure, such as polyamide, polysulfone, etc. In engineering plastics, it is divided into two categories: general engineering plastics and special engineering plastics. Mechanical properties of engineering plastics

Engineering Plastics (2 photos)

Can achieve higher requirements in terms of energy, durability, corrosion resistance, heat resistance, etc., and it is more convenient to process and can replace metal materials. Engineering plastics are widely used in electronic and electrical, automotive, construction, office equipment, machinery, aerospace and other industries, to plastic instead of steel, plastic instead of wood has become an international popular trend.

General engineering plastics include: polyamide, polyformaldehyde, polycarbonate, modified polyphenylethers, thermoplastic polyester, ultra high molecular weight polyethylene, methyl pentene polymer, vinyl alcohol copolymer, etc.

Special engineering plastics also have cross-linked non-cross-linked types. The crosslinked types are: polyaminobismaleamide, polytriazine, crosslinked polyimide, heat-resistant epoxy tree finger and so on. Non-crosslinked types are: polysulfone, polyether sulfone, polyphenylene sulfide, polyimide, polyether ether ketone (PEEK) and so on.

③ Special plastics

Generally refers to plastics with special functions that can be used in special applications such as aviation and aerospace. For example, fluoroplastics and silicone have outstanding high temperature resistance, self-lubrication and other special functions, and reinforced plastics and foam have special properties such as high strength and high buffering, and these plastics belong to the category of special plastics.

a. Reinforced plastics:

Reinforced plastic raw materials in shape can be divided into granular (such as calcium-plastic reinforced plastics), fibrous (such as glass fiber or glass cloth reinforced plastics), sheet (such as mica reinforced plastics) three kinds. According to the material can be divided into cloth reinforced plastic (such as rag reinforced or asbestos reinforced plastic), inorganic mineral filled plastic (such as quartz or mica filled plastic), fiber reinforced plastic (such as carbon fiber reinforced plastic) three kinds.

b. Foam:

Foam can be divided into hard, semi-hard and soft foam three kinds. Rigid foam is not flexible, compressive hardness is very large, only to reach a certain stress value to produce deformation, stress relief can not be restored to the original state; Soft foam is flexible, small compressive hardness, easy to deform, can be restored to the original state after stress relief, residual deformation is small; The flexibility and other properties of semi-rigid foam are between hard and soft foam.

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 thermoplastics.

(1) Thermoplastics

Thermoplastic (Thermo plastics) : refers to the plastic that will melt after heating, can flow to the mold to cool and form, and will melt again after heating; Heating and cooling can be used to produce reversible changes (liquid → solid), which is the so-called physical change. General thermoplastics whose continuous use temperature is below 100 ° C, polyethylene, polyvinyl chloride, polypropylene, polystyrene and known as the four general plastics. Thermoplastic plastics are divided into hydrocarbons, vinyl containing polar genes, engineering, cellulose and other types. It becomes soft when heated and hard when cooled, and can be repeatedly softened and hardened and maintain a certain shape. It can be dissolved in a certain solvent and has the property of melting and soluble. Thermoplastics have excellent electrical insulation, especially polytetrafluoroethylene (PTFE), polystyrene (PS), polyethylene (PE), polypropylene (PP) have very low dielectric constant and dielectric loss, suitable for high frequency and high voltage insulation materials. Thermoplastics are easy to form and process, but the heat resistance is low, easy to creep, and the degree of creep varies with the load, ambient temperature, solvent, and humidity. In order to overcome these weaknesses of thermoplastics and meet the needs of applications in space technology, new energy development and other fields, countries are developing heat-resistant resins that can be fused, such as polyether ether ketone (PEEK), polyether sulfone (PES), polyaromatic sulfone (PASU), polyphenylene sulfide (PPS) and so on. The composites using them as matrix resins have higher mechanical properties and chemical corrosion resistance, can be thermoformed and welded, and have better interlayer shear strength than epoxy resins. For example, polyether ether ketone is used as a matrix resin and carbon fiber composite material, fatigue resistance exceeds that of epoxy/carbon fiber. It has good impact resistance, good creep resistance at room temperature, good processability, and can be used continuously at 240 ~ 270 ° C, which is a very ideal high temperature resistant insulation material. The composite made of polyether sulfone as matrix resin and carbon fiber has higher strength and hardness at 200℃, and can maintain good impact resistance at -100℃. Non-toxic, non-combustible, least smoke, good radiation resistance, it is expected to be used as a key component of spacecraft, and can also be molded into radar radome.

Formaldehyde crosslinked plastics include phenolic plastics, amino plastics (such as urea - formaldehyde - melamine - formaldehyde, etc.).

Plastic film

Other crosslinked plastics include unsaturated polyester, epoxy resin, phthalic diallyl ester resin, etc.

(2) Thermosetting plastics

Thermosetting plastics refer to plastics that can cure or have insoluble (melting) characteristics under heat or other conditions, such as phenolic plastics, epoxy plastics, etc. Thermosetting plastics are divided into two types: formaldehyde crosslinked and other crosslinked. The resin molecules are crosslinked into a network structure by the linear structure. Additional heat will break down and destroy. Typical thermosetting plastics are phenolic, epoxy, amino, unsaturated polyester, furan, polysilether and other materials, as well as newer polyphthalate diallyl ester plastics. They have the advantages of high heat resistance, heat deformation and so on. The disadvantage is that the mechanical strength is generally not high, but the mechanical strength can be improved by adding fillers to make laminate materials or molded materials.

Thermosetting plastics made of phenolic resin as the main raw material, such as phenolic molded plastics (commonly known as bakelite), have the characteristics of durability, dimensional stability, and resistance to other chemical substances in addition to strong alkali. Various fillers and additives can be added according to different uses and requirements. For varieties requiring high insulation performance, mica or glass fiber can be used as filler; If you want heat-resistant varieties, you can use asbestos or other heat-resistant fillers; If seismic varieties are required, a variety of appropriate fibers or rubber can be used as fillers and some toughening agents to make high-toughness materials. In addition, aniline, epoxy, polyvinyl chloride, polyamide, polyvinyl acetal and other modified phenolic resins can be used to meet the requirements of different applications. Phenolic resin can also be made of phenolic laminate, which is characterized by high mechanical strength, good electrical properties, corrosion resistance, easy processing, widely used in low-voltage electrical equipment.

Amino plastics have 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 oil resistant, not affected by weak alkali and organic solvents (but not acid resistant), it can be used for a long time at 70 ° C, and can be resistant to 110 ~ 120 ° C in the short term, and can be used for electrical products. Melamine formaldehyde plastic has higher hardness than urea formaldehyde plastic, has better water resistance, heat resistance and arc resistance, and can be used as arc resistance insulation material.

There are many kinds of thermosetting plastics made of epoxy resin as the main raw material, of which bisphenol A type epoxy resin as the base material accounts for about 90%. It has excellent adhesion, electrical insulation, heat resistance and chemical stability, small shrinkage and water absorption, good mechanical strength and so on.

Unsaturated polyester and epoxy resins can be made into glass steel, with excellent mechanical strength. Such as unsaturated polyester fiberglass, its mechanical properties are good, the density is small (only 1/5 to 1/4 of steel, 1/2 of aluminum), easy to process into various electrical parts. The electrical and mechanical properties of the plastics made of diallyl phthalate resin are better than those of phenolic and amino thermosetting plastics. It has small hygroscopicity, stable product size, good molding performance, acid and alkali resistance and boiling water and some organic solvents. Molded plastics are suitable for the manufacture of parts with complex structures, both temperature resistance and high insulation. Generally can be used in the temperature range of -60 ~ 180 ° C for a long time, and the heat resistance grade can reach F to H, which is higher than the heat resistance of phenolic and amino plastics.

Silicone plastics in the form of polysilether structure are widely used in electronic and electrical technology. Silicone laminate plastics mainly use glass cloth as reinforcing material; Silicone molded plastics are mostly filled with glass fiber and asbestos, which are used to manufacture high-temperature, high-frequency or submersible motors, electrical and electronic equipment parts and so on. This type of plastic is characterized by low dielectric constant and tgδ values, low frequency impact, used in the electrical and electronics industry to resist corona and arc, even if the discharge causes decomposition, the product is silica rather than conductive carbon black. This kind of material has outstanding heat resistance and can be used continuously at 250℃. The main disadvantages of polysiloxane are low mechanical strength, small adhesion, and poor oil resistance. Many modified silicone polymers, such as polyester modified silicone plastics, have been developed and applied in electrical technology. Some plastics are both thermoplastic and thermosetting plastics. For example, polyvinyl chloride, generally thermoplastic, Japan has developed a new type of liquid polyvinyl chloride is thermosetting, molding temperature of 60 ~ 140℃; A kind of plastic called Lundex in the United States has both the characteristics of thermoplastic processing and the 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.

② Vinyl plastics containing polar genes. In addition to fluorine plastics, most of the non-crystalline transparent bodies, including polyvinyl chloride, polytetrafluoroethylene, polyvinyl acetate and so on. Most vinyl monomers can be polymerized using free base catalysts.

③ Thermoplastic engineering plastics. It mainly includes polyformaldehyde, polyamide, polycarbonate, ABS, polyphenylene ether, polyethylene terephthalate, polysulfone, polyether sulfone, polyimide, polyphenylene sulfide and so on. Polytetrafluoroethylene. Modified polypropylene, etc., is also included in this range.

④ Thermoplastic cellulose plastics. It mainly includes cellulose acetate, cellulose acetate butyrate, cellophane, cellophane, etc.

Processing method Classification:

According to the different molding methods of various plastics, it can be divided into film pressing, laminating, injection, extrusion, blow molding, casting plastic and reaction injection plastic and other types.

Film compression plastics are mostly physical properties of the processing properties and general solid plastics similar to plastics; Laminated plastic refers to the fiber fabric impregnated with resin, which is combined into a whole material by superposition and hot pressing; Injection, extrusion and blow molding are mostly plastics with physical properties and processing properties similar to general thermoplastics; Casting plastic refers to the liquid resin mixture that can be poured into the mold to harden into a certain shape product under no pressure or a little pressure, such as MC nylon, etc. Reactive injection plastic is a plastic that uses liquid raw materials and is pressurized into a film cavity to react and solidify into a certain shape product, such as polyurethane.