PET comes from British polyethylene? Terephthalate, Chinese translation for polyethylene terephthalate plastic. This is the name of a plastic category, including polyethylene terephthalate, polybutylene terephthalate and polyethylene terephthalate. It is a kind of heat shrinkable polyester and saturated polyester, which is formed by polycondensation of terephthalic acid and ethylene glycol.
PET plastic is a kind of plastic with high molecular structure and good crystal orientation ability. Due to these two characteristics, PET plastic has good film-forming property. Not only that, good optical properties and weather resistance are also two iconic characteristics of PET. Moreover, PET is plastic and a good insulating material. Its various characteristics determine that it is a good material for making plastic bottles. PET plastic bottles are light in weight, non-toxic and strong in structure.
Structure:
The molecular structure of PET plastic is highly symmetrical, and it has certain crystal orientation ability, so it has high film-forming and moldability. PET plastic has good optical properties and weather resistance, and amorphous PET plastic has good optical transparency. In addition, PET plastic has excellent wear resistance, friction resistance, dimensional stability and electrical insulation. PET bottles are widely used because of their high strength, good transparency, non-toxicity, permeability resistance, light weight and high production efficiency. The molecular chain structure of PBT is similar to that of PET, and most of its properties are the same, but the molecular backbone has changed from two methylene groups to four, so the molecules are more flexible and have better processability.
PET is a kind of high crystalline polymer with milky white or light yellow, and its surface is smooth and shiny. Good creep resistance, fatigue resistance, friction resistance, small wear and high hardness, with the greatest toughness in thermoplastics; Good electrical insulation, little influence by temperature, but poor corona resistance. Non-toxic, weather-resistant, chemical-resistant, high hygroscopicity, drying before molding is necessary. Resistant to weak acids and organic solvents, but not to hot water immersion and alkali.
PET resin has high glass transition temperature, slow crystallization speed, long molding cycle, large molding shrinkage, poor dimensional stability, brittle crystallization and low heat resistance.
By improving nucleating agent, crystallizing agent and glass fiber reinforcing agent, PET has the following characteristics besides PBT:
1.？ Thermal deformation temperature and long-term service temperature are the highest among thermoplastic general engineering plastics.
2.？ Due to its high heat resistance, reinforced PET can be immersed in solder bath at 250℃ for 10s, hardly deformed or discolored, and is especially suitable for welding electronic and electrical parts.
3.？ The bending strength is 200MPa, the elastic modulus is 4000MPa, the creep resistance and fatigue resistance are also good, the surface hardness is high, and the mechanical properties are similar to those of thermosetting plastics;
4.？ Because the price of ethylene glycol used to produce PET is almost half cheaper than that of butanediol used to produce PBT, PET resin and reinforced PET have the lowest price and high cost performance among engineering plastics.
5.？ Bonding of PET resin: Li Si-1706 one-component room temperature vulcanizate is an elastomer after curing, which has excellent waterproof and shockproof bonding properties and high and low temperature resistance. Because of the research on the molecular structure of resin, it is specially used for bonding engineering plastics.
Use:
Glass fiber reinforced PET is suitable for electronic appliance industry and automobile industry, and is used for various coil formers, transformers, televisions, tape recorders, automobile lamp holders, lampshades, incandescent lamp holders, relays, selenium rectifiers, etc. At present, the consumption proportion of PET engineering plastics in several application fields is: electrical appliances and electronics 26%, automobiles 22%, machinery 19%, household appliances 10%, consumer goods 10% and others 13%. At present, the total consumption of PET engineering plastics is still very small, accounting for only 1.6% of the total PET.
1. Film sheet: all kinds of food, medicine, non-toxic and aseptic packaging materials; High-grade packaging materials for textiles, precision instruments and electrical components; The base materials of audio tapes, video tapes, cinematographic films, computer floppy disks, metal coatings and photographic films; Electrical insulation materials, capacitor films, flexible printed circuit boards, film switches and other electronic and mechanical fields.
2. Application of packaging bottles: Its application has developed from carbonated drinks to beer bottles, edible oil bottles, condiment bottles, medicine bottles and cosmetic bottles.
3. Electronic appliances: manufacturing connectors, bobbins, integrated circuit housings, capacitor housings, transformer shell, TV accessories, tuners, switches, timer housings, automatic fuses, motor brackets and relays.
4. Auto parts: such as switchboard cover, ignition coil, various valves, exhaust parts, distributor cover, measuring instrument cover, small motor cover, etc. The excellent paintability, surface gloss and rigidity of PET can also be used to manufacture automobile exterior parts.
5. Machinery and equipment: manufacturing gears, cams, pump housings, pulleys, motor frames, clock parts, and can also be used as microwave oven baking trays, various ceilings, outdoor billboards, models, etc.
6.6 the molding process. PET plastics can be injected, extruded, blown, coated, bonded, machined, electroplated, vacuum metallized and printed.
Identification method:
1. Smell it first. PET tastes different from ordinary plastic. Burn it with a lighter, and it will be very fragrant and comfortable (just burn a bottle and it will smell good). If PET contains other ingredients, it will smell pungent. You can't use a bottle containing SEBS.
2. Look at the burnt part. If it is too dark or drips oil quickly, most of it is abnormal melting point, which often happens in PET films.
3, wire drawing, when lit, pull the line on the lighter to see if the line is long, and then pull the line out to see if the line is rolled into a small circle. The more coils, the higher the melting point.
However, if it is a bottle tablet, it should not be a big problem. The key point is to distinguish whether it contains PVC, which is fatal to pets. First, take more samples and put them in a sunny place. PVC is light blue in the sun. If you fold it in half, there will be a white crease. The above is naked eye recognition, and the accuracy is limited, mainly relying on experience.
A more practical and better way is to buy an oven, adjust the temperature to 250 degrees and bake there for half an hour. If the goods contain PVC, there will be a lot of yellow spots on the surface; If the melting point is not enough, it will melt quickly.
In fact, there are many varieties of PET to be made. The broken PET films, pulp blocks, rolled films, etc. produced by foreign factories have different customer groups.
The identification of these goods strongly requires oven inspection. In particular, PET reels are very scarce in the whole market. Generally, films with a length of 80 to 120 cm and a thickness of 3 to 5 filaments are expensive (white and transparent).
PET plastics are widely used in many fields. Let's have a look.
Film sheet
PET plastics are widely used in the packaging of various foods and medicines, because this kind of goods have high requirements for non-toxic and harmless plastics, and PET just meets this demand. PET plastic is also a good packaging material for precision instruments and electronic components. The use of PET plastic film for packaging can play a good protective role and prolong the service life.
Packaging bottle
We see that the industry with the most PET plastics is the packaging bottle industry. At first, PET plastic bottles were only used for carbonated beverage bottles such as Coke and Sprite. Now, PET plastic has been used to package bottles of beer, cosmetics, edible oil, medicines and other items.
mechanical equipment
PET plastics can often be seen on mechanical equipment. For example, gears, motor frames, pump housings, clocks and watches can all be made of PET plastic, and outdoor billboards and models are frequent visitors to PET plastic.
Since PET plastics have such a wide range of uses, how should we identify PET plastics?
smell
The first is the smell of pet plastic. After lighting the PET plastic with a lighter, we will smell more fragrant, and there will be no pungent smell. If there are other materials in PET plastic, it will produce a pungent smell.
roast
One of the most practical ways to identify PET plastics is baking. Because many PET plastics are doped with PVC plastics, we adjust the oven temperature to 250 degrees Celsius and bake the target plastic on it for a period of time. If there is PVC material, there will be many yellow spots on the plastic surface.
PET plastics have many advantages, and can be used as raw materials for various industrial supplies after recycling. We shouldn't throw PET plastic bottles everywhere after use, but we should recycle them in an orderly way.