The chemical formula of polyethylene terephthalate is -[OCH2-CH2OCOC6H4CO]- English name: polyethylene terephtalate, abbreviated as PET, which is a high polymer obtained by dehydration and condensation of ethylene terephthalate. Ethylene terephthalate is obtained by esterification of terephthalic acid and ethylene glycol. PET is a kind of high crystalline polymer with milky white or light yellow, and its surface is smooth and shiny. It has excellent physical and mechanical properties in a wide temperature range, the long-term use temperature can reach 65438 0 20℃, and the electrical insulation performance is excellent. Even at high temperature and high frequency, its electrical properties are still good, but its corona resistance is poor, and its creep resistance, fatigue resistance, friction resistance and dimensional stability are good.
Advantages of PET as packaging material;
① Good mechanical properties, impact strength 3~5 times that of other films, and good folding resistance.
② Oil resistance, grease resistance, dilute acid resistance, dilute alkali resistance and resistance to most solvents.
③ It has excellent high and low temperature resistance, can be used for a long time in the temperature range of 120℃, and has little influence on its mechanical properties in the temperature range of 150℃ and -70℃ for a short time.
④ The permeability of gas and water vapor is low, and it has excellent gas, water, oil and odor resistance.
⑤ High transparency, blocking ultraviolet rays and good gloss. ⑥ Non-toxic, tasteless, good hygiene and safety, and can be directly used for food packaging.
Hazards of pets:
A 12-year-old girl in UAE got cancer because she used the same mineral water bottle for 16 months. Studies have found that plastic bottles contain a substance called PET, which is safe to use once, but if they are reused for thrift or convenience, they will be threatened by cancer.
There is a triangle with an arrow at the bottom of the plastic bottle, and there is a number in the triangle. The following numbers in the triangle at the bottom of plastic bottles refer to the ingredients contained in the bottles and their effects on human health-
1-PET polyethylene terephthalate is commonly found in mineral water bottles and carbonated beverage bottles. When the temperature reaches 70℃, it is easy to deform and some substances harmful to human body melt. Plastic product 1 may release carcinogen DEHP after using 10 months. This kind of bottle can't be put in the sun in the car, and it can't contain alcohol, oil and other substances.
2-HDPE high-density polyethylene is commonly found in white medicine bottles, cleaning products and bath products. Don't use it as a cup, and don't use it as a storage container to hold other things.
3-PVC PVC is commonly found in raincoats, building materials, plastic films and plastic boxes. Excellent plasticity, low price, so it is widely used, heat resistance reaches its peak at 865438 0℃, and harmful substances are easily produced at high temperature, so it is rarely used in food packaging. It is difficult to clean, easy to remain and cannot be recycled.
4-PE polyethylene is commonly found in plastic packaging and plastic film. Harmful substances will be produced at high temperature, and toxic substances may cause diseases such as breast cancer and birth defects of newborns after entering the human body with food.
5-PP polypropylene is commonly found in soybean milk bottles, sour milk bottles and microwave lunch boxes. Its melting point is as high as 167℃. It is the only plastic product that can be put into the microwave oven and reused after careful cleaning. It should be noted that some microwave lunch boxes are made of No.5 PP, but the cover is made of 1 PET. Because PET is not resistant to high temperature, it can't be put in the microwave with the box.
6-PS polystyrene is commonly used in instant noodle boxes and fast food boxes in bowls. Can not be placed in the microwave oven, so as not to release harmful chemicals at high temperature. Avoid packing hot food in fast food boxes, and don't cook bowls with instant noodles in the microwave oven.
7 —— Other types of PC are common in kettles, space cups and milk bottles. Department stores often use these cups as gifts. However, the glass made of this material can easily release the toxic substance bisphenol A, which is harmful to human body. In addition, when using this cup, don't heat it or bask in the sun.
1. 1 pet history
194 1 year, which was first developed by J.tt.Whinfield and J.T.Dickon in Britain. PET has been used as fiber material for 53 years. British Imperial Chemical Company (1. C.I) Teleron fiber was put into production at 1946, and then Dupent Company of America put into production at 1948 with polyester fiber. PET is divided into fiber grade polyester chips and non-fiber grade polyester chips. ① Fiber-grade polyester is used to manufacture polyester staple fibers and polyester filaments, and it is the raw material for processing fibers and related products in polyester fiber enterprises. Polyester is the largest variety of chemical fiber. ② Non-fiber grade polyester is also used in bottles, films and other fields, and is widely used in packaging industry, electronic appliances, medical and health care, construction, automobiles and other fields, among which packaging is the largest non-fiber application market for polyester and the fastest developing field for PET.
Classification and application of 1.2 PET
Polyethylene glycol (EG) and terephthalic acid (PTA), the main raw materials of PET, are widely used as fibers, which can be divided into two categories: non-engineering plastic grade and engineering plastic grade. PET has excellent properties (heat resistance, chemical resistance. Toughness, electrical insulation, safety, etc. ), the price is cheap, so it is widely used as fiber, film, engineering plastics, polyester bottles and so on. The industrialized products of polyester thermoplastics in the world include the following six aspects (industrialized products are available). (1) liquid crystal polymer
(2) Poly (butylene terephthalate)
(3) polyethylene naphthalate
(4) Polyethylene terephthalate engineering grade PET
(5) polyethylene terephthalate standard grade PET
(6) Polyethylene terephthalate recycled PET (including * * * mixture and 100% recycled materials) is mainly used for fibers, beverage bottles, films, sheets and baking-resistant food containers. Engineering plastic grade PET has good resistance to organic solvents and weatherability. The disadvantages are slow crystallization speed, difficult molding, high molding temperature, long production cycle and poor impact performance. Generally, the processability and physical properties of resin are improved by reinforcement, filling and * * * mixing. Glass fiber has obvious reinforcement effect, which improves the rigidity, heat resistance, drug resistance, electrical properties and weather resistance of the resin. By adding nucleating agent and crystallization promoter, the disadvantage of slow crystallization speed is improved. Adding flame retardant and anti-dripping agent can improve the flame retardancy and self-extinguishing property of PET. In addition, in order to improve the properties of PET, PET can be alloyed with PC, elastomer, PBT, PS, ABS and PA.
PET (reinforced PET) is mainly processed by injection molding, and other methods include secondary processing methods such as extrusion, blow molding, coating and welding, sealing, machining and vacuum coating. It must be fully dried before molding. The main applications of electronic appliances include: electrical sockets, electronic connectors, rice cooker handles, TV deflection coils, wiring boards, circuit breaker housings, switches, motor fan housings, instrument and mechanical parts, money counter parts, electric irons and induction cooker accessories; Flow control valve, carburetor cover, window controller, pedal transmission and switchboard cover in automobile industry; Gears, blades, pulleys, pump parts in mechanical industry, in addition to wheelchair body and wheels, lampshade shell, illuminator shell, drain pipe connector, zipper, clock parts and so on.