I. Conventional varieties and classification of plastics In daily life, most of the plastics we can directly contact or perceive are conventional general plastics, mainly including PE, PP, ABS, PVC and PS. These five types of plastics account for the vast majority of plastic raw materials, and the rest can basically be classified as special plastic varieties, such as PPS, PPO, PA, PC, POM and so on. They are in daily life products. Plastics can be divided into thermoplastics and thermosetting plastics according to their plasticity. Usually, thermoplastic products can be recycled, but thermosetting plastics can't. According to the optical properties of plastics, they can be divided into transparent, translucent and opaque raw materials, such as PS, PMMA, AS and PC, which belong to transparent plastics, while other plastics are mostly opaque plastics.
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 the three, HDPE has better thermal, electrical and mechanical properties, while LDPE and LLDPE have better flexibility, impact properties and film-forming properties. LDPE and LLDPE are mainly used in packaging film, agricultural film and plastic modification. And HDPE is widely used in films, pipes, daily necessities for injection and other fields.
2. Polypropylene: Relatively speaking, polypropylene has more varieties, more complex uses and more fields. The main varieties are homopolypropylene, block polypropylene (copp) and random polypropylene (rapp). According to different uses, homopolymerization is mainly used in drawing, fiber, injection molding, BOPP film and other fields.
3.PVC: Because of its low cost and self-flame retardant characteristics, 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, such as car lampshades, daily transparent parts, transparent cups and cans.
5.ABS is a widely used engineering plastic with excellent physical, mechanical and thermal properties. Widely used in household appliances, panels, masks, components, accessories and so on. Especially in household appliances, such as washing machines, air conditioners, refrigerators, electric fans, etc. It is also widely used in plastic modification.
Third, the identification methods of commonly used plastics
1. density method: investigate the density of various plastics and the fluctuation of plastics in liquid medium, so as to roughly distinguish the types of plastics. For example, if a piece of plastic is put into 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 investigate the color of flame and the smell and smoke emitted during combustion. Generally speaking, the flame of polyolefin raw materials is mostly blue or light blue, with mild and light smell and white smoke, while most raw materials containing benzene or chlorine are prone to black smoke and strong smell after combustion. In addition, for example, PE and PP have dripping phenomenon, while PVC has no dripping phenomenon, but it has self-extinguishing phenomenon.
3. Optical method: mainly investigate the transparency of raw materials. Generally, transparent raw materials are: PS, PC, PMMA, As; Translucent raw materials include: PE, random PP, homopolymer PP, soft PVC, transparent ABS, etc. Other raw materials are basically opaque.
4. Color discrimination: Generally speaking, raw materials without additives will be slightly yellow if they contain double bonds. For example, ABS will be slightly yellow due to the polymerization of butadiene, and the polymer will still contain double bonds after polymerization. Other identification methods mostly rely on various instruments, such as infrared spectroscopy, mass spectrometry, nuclear magnetic resonance, differential thermal scanning, thermal analysis and so on.
Properties of polyvinyl chloride (PVC): PVC can be divided into soft and hard types: hard PVC has high mechanical strength, excellent electrical properties, strong acid and alkali resistance and good chemical stability; Disadvantages: low softening point. The tensile strength, bending strength, impact strength and impact toughness of soft PVC are low, but the elongation at break is high. Uses: Rigid PVC products include pipes, rods, plates, covered electrode, centrifugal pumps, ventilators, wheel pipes, valves and acid-base pump containers. Soft PVC products include storage tanks, sheets, films, wire insulation layers, window covers, acid and alkali resistant hoses, etc.
Polyethylene (PE) performance: It can be divided into three types: high pressure, medium pressure and low pressure polyethylene. High pressure polyethylene is flexible; Low-pressure polyethylene is hard and cold-resistant, and remains soft at -70℃. High chemical stability, acid and alkali resistance and organic solvent resistance. It has outstanding electrical properties and good radiation resistance. Flame spraying or electrostatic spraying on metal surface can reduce friction and prevent corrosion. Disadvantages are low mechanical strength, low thermal deformation temperature and inability to bear high load. Uses: Corrosion resistant lining of chemical equipment and storage tanks, chemically corroded pipes, valves, bushings and roller frames to replace copper and stainless steel. Insulation layer of high frequency underwater cable or ordinary cable. Transistor radio magnet antenna bracket.
Properties of polystyrene (PS): It has certain mechanical strength, excellent chemical stability and electrical properties, good light transmission, good coloring and easy molding. It is characterized by almost complete water resistance, low heat resistance and high brittleness, and the product can only be used at low load and low temperature (60 ~ 75℃) due to internal stress. Uses: Various instrument shells, skeletons, instrument indicator lights, lampshades, automobile lampshades, chemical acid storage tanks, acid delivery tanks (especially hydrofluoric acid), chemical instrument parts and telecommunication parts can be used as optical instrument parts and lenses due to their good transparency.
Properties of High Impact Polystyrene (HIPS): Compared with polystyrene, HIPS has higher toughness and impact strength, while other properties are basically similar, and the molding process is good. Uses: various instruments, transistor radio housings, textile spools, TV structural parts, water tray accessories for agricultural vehicles, small plastic pipes and plates, etc. Properties of polystyrene modified plexiglass: good transparency. The mechanical strength is also high, with certain heat resistance, cold resistance, weather resistance, corrosion resistance and good insulation. The product is stable in size and easy to form. Disadvantages are fragile and soluble in organic solvents. As a light-transmitting material, the surface hardness is not enough and it is easy to scratch. As far as its comprehensive performance is concerned, it exceeds ordinary plastics such as polystyrene. Uses: Used for manufacturing parts with certain transparency and strength, such as oil labels, oil cups, optical lenses, lenses, equipment signs, transparent pipes, automobile lamps, transistor radio dials, electrical insulation parts, etc.
Properties of styrene-acrylonitrile * * * polymer (AS or SAN): Compared with polystyrene, it has higher impact strength and excellent heat resistance, oil resistance and chemical corrosion resistance. For example, it can well resist some hydrocarbons that cause stress cracking of polystyrene. The elastic modulus is one of the higher among the existing thermoplastics. Uses: It is widely used to make oil-resistant, heat-resistant and chemical-resistant industrial products, as well as instrument panels, instrument racks, housings, battery boxes, junction boxes, various switches and regulators.
Properties of Styrene-Butadiene-Acrylonitrile (ABS): ABS is a tough, hard and rigid material. It has the characteristics of high impact toughness and mechanical strength, stable size, good chemical resistance and electrical properties, and easy molding and processing. In addition, the surface can be plated with chromium, which has become a common material for plastic metallization. In addition, ABS has good adhesion with # 372 plexiglass and can be used as a two-color plastic part. Uses: Used for manufacturing cams, gears, pump impellers, bearings, motor housings, instrument boxes, battery boxes, water tank housings, handles, refrigerator linings, etc. In the mechanical industry, it is used to manufacture steering wheels, hot air conditioners, tube heaters, etc. In the automobile industry, it can also be used to make the shell of TV transistor radio.
Characteristics of polypropylene (PP): The main feature of polypropylene is its low density. Its mechanical properties are superior to those of low-pressure polyethylene, and it has outstanding rigidity and good heat resistance. Can be used above 100℃. It basically does not absorb water and has good chemical stability. Except for concentrated sulfuric acid and nitric acid, it is almost stable. Excellent high-frequency electrical properties, and is not affected by temperature, easy to shape. The disadvantage is that the wear resistance is not high enough, the molding shrinkage is large, it is fragile at low temperature and the thermal deformation temperature is low. Usage: It can be used as various mechanical parts, such as flanges, gears, joints, pump impellers, automobile parts, etc. Chemical pipeline and container equipment. It can also be used as linings, surface coatings, audio tapes, medical instruments and surgical instruments.
Performance of polycarbonate (PC): The impact strength is particularly outstanding. It is superior to ordinary thermoplastic resin. High elastic modulus, less affected by temperature. The heat-resistant temperature is 120℃. Cold resistance up to-100℃ without embrittlement. High dimensional stability. Good corrosion resistance and wear resistance. But it is sensitive to water at high temperature. Uses: Used for manufacturing gears, worms, racks, cams, spindles, bearings, washers, rivets, pump impellers, automobile carburetor parts, lampshades, flash lamp covers, throttle valves, lubricating oil pipes, various housings, containers, refrigeration and cooling device parts, electrical wiring boards, coil holders, acid battery cells and high-temperature lenses.