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What do the numbers on the plastic mean? What are the uses of different numbered plastics?

There are many plastic materials we use in our life. Different plastics have different numbers, and different numbered plastics have different purposes. So do you know what the number on the plastic item means? For what purpose? What plastics can be used for microwave heating? What plastics can come into direct contact with food? In this article, let's understand the meaning and use of numbers on different plastic products.

If you pay attention to the triangle on the plastic container, you can find that it is actually a sign of recycling. The number in it is the sign of entering different recycling channels. In other words, for the recycling personnel, when he sees the number 1 marked on the plastic bottle, he knows that it should be recycled through channel 1, and the size of the number is not directly related to the nature of the plastic itself. Many 'experts' on websites or TV have proposed that the plastic number represents the safety of plastic. The larger the number, the safer it is. It is even said that it can't be used below No. 5. This is a thing in vain - the number is not a rating of plastic at all. Sometimes when I see such programs, I also find that if experts are asked more by the host, they are obviously incoherent, so the untenable statement is untenable. To say more, although the technical content of this rumor is very low, it is very confusing. Many people who have read this statement will firmly remember this concept, because people will think that the size of this number will represent something, and security is obviously the most convincing. Unfortunately, it is contrary to their wishes. The content of security is quite complex, which can not be summarized by a number. We will talk about this topic in the next article.

At present, there are about 140 kinds of commercialized plastics and about 30 kinds of plastics for daily use. It can be said that mending is prosperous. Think of rubber and fiber, the relatives of plastics. Four rubber (cis-butyl rubber, isoprene rubber, styrene butadiene rubber and ethylene propylene rubber) and four fiber (polyester, acrylic, nylon and vinylon) have explained the regular members of the industry. The rest are generally marked with 'special', which is weak compared with the number of varieties of conventional plastics. However, among many plastic varieties, there are usually seven with large enough output and unified recycling direction, which is why there are only seven numbers of 1-7 in the triangle. Each number corresponds to different plastic varieties, followed by pet, HDPE, PVC, LDPE, PP, PS and PC. there is a 'p' in each abbreviation, which means' poly - 'in English.

No.1-PET

Soft and transparent bottles and cans are almost the world of pet. They are beautiful and cheap

No. 1 plastic pet, whose scientific name is polyethylene terephthalate, is also referred to as polyester plastic. It is very common in life. At present, almost all beverage bottles and edible oil bottles use this kind of plastic. If the molecular weight of pet is large enough, it can be used in the fiber industry, that is, polyester fiber, which is more commonly referred to now (shopping guides obviously know that it is too low-end to say that thousands of dollars of suits are polyester products), and the use of silk also determines the recovery method of pet. Most recycled beverage bottles have entered the plastic rope industry. Pet is characterized by high transparency, water and oil resistance, but it is not very heat-resistant. Many people should deeply understand this. When receiving the hot water from the water dispenser with the mineral water bottle, the bottle begins to deform, and the temperature is about 85 degrees. However, pet can usually carry under 80 ℃, so it is not surprising that No. 1 plastic is widely used in life. When it comes to pet, we have to add one more thing, that is, p-xylene Px, a chemical that causes trouble in many cities. It is not only an important raw material for the production of pet, but also a raw material for many other important consumer goods. Its position in modern industry is similar to that of ethylene and propylene. Some interest groups do not want China to achieve self-sufficiency in p-xylene, so we should keep strengthening all kinds of alarmist talk about px.

No.2-HDPE

Opaque hard bottles and cans are mostly HDPE, with strong tolerance, which is naturally suitable for daily chemical products

No. 2 plastic HDPE, scientific name high-density polyethylene, is the easiest to find daily chemical containers made of them in the bathroom, and many large beverage bottles will also use this plastic. What is obviously different from pet is that this plastic is highly crystalline, so it presents an opaque state in appearance (polymer materials are different from diamonds, and high crystallinity often reduces transparency), and has higher hardness, even a bit of crispness. It is precisely because of the high strength, not afraid of falling and not transparent that dairy products often prefer No. 2 plastic. This plastic has excellent water and oil resistance, so it has a wide range of adaptability. Similar to pet, No. 2 plastic is not very heat-resistant, but it is slightly stronger than pet. Generally, it is easy to deform when it is above 100 ℃. This kind of plastic is also particularly acid, alkali and corrosion resistant. If you don't invite fluoroplastics, a boss grade super corrosion resistant plastic, it can basically kill other materials, so it is also widely used in industry. Therefore, the polyethylene industry is an industry that can't be ignored in any industrial country.

No.3-PVC

Clear PVC transparent Backpack

Everyone doesn't like PVC for food. In fact, the most valuable use of PVC is not in the food industry. Although PVC artificial leather is airtight, it is cheap

No. 3 plastic PVC, scientific name PVC, is also the only plastic not recommended to contact food among the seven plastics, because it contains chlorine. However, in fact, under general service conditions, the chlorine in the material is not easy to free out. Nevertheless, No. 3 plastic is rarely seen in food containers. PVC is also the only one of the seven plastics that must use plasticizer, which makes its state change from soft and elastic to hard and brittle. Plasticizer is the 'plasticizer' reported in the media. It is a criticized material in the food industry, but we will explain the facts in the future. Since PVC can present a soft and elastic side, it can also simulate some uses of rubber or leather, such as artificial leather, disposable inspection gloves, floor, tablecloth and plastic shoes, which are widely used in the interior of Japanese cars, because the price of PVC is much lower than that of natural rubber and polyurethane artificial leather. However, acetylene is usually used in PVC industry, so as a high energy consuming industry, it still faces many crises, which means that we may have to face Wumart's cheap PVC in the future.

No.4-LDPE

LDPE is not strong in fresh-keeping ability, but it is still one of the most ideal materials for fresh-keeping film

No. 4 plastic, LDPE, and No. 2 plastic are brothers, with the scientific name of low-density polyethylene. However, in essence, the structures of No. 2 and No. 4 are different, except that ethylene is used as monomer. No. 4 Plastic rarely appears in containers because it is very soft and sticky. At the same time, due to its low crystallinity and high transparency of LDPE, we can see it mainly in fresh-keeping films and plastic bags in our daily life. However, the oil resistance of this plastic is relatively low, and there are many such examples in life. For example, wearing PE gloves when eating sheep and scorpions, although the gloves have no pores, they still feel greasy; Or buy red oil pig ears, put them in plastic bags, throw them into bed and start playing with the computer. A few hours later, I found that the sheets should be changed. Therefore, the application of this plastic in food is relatively limited. However, No. 4 plastic is still very powerful in industry. It is a well deserved overlord in the membrane industry.

No.5-PP

PP is a very nice plastic. Its combination with microwave oven can solve the dietary problems of otaku men and women by means of non instant noodles and ham sausage.

No. 5 plastic PP is our star plastic polypropylene, and the most common is Le buckle. At present, the vast majority of special plastic containers for microwave ovens in the market are PP plastics because of its heat resistance and high chemical stability. This kind of plastic is actually very close to No. 2 plastic in essence. Its crystallinity is slightly lower than that of No. 2, so it generally presents a translucent state, and its hardness is not much different from that of No. 2. No. 5 plastic is more used in food than any other plastic. In addition to containers, there is BOPP film in flexible packaging. The outermost film of cigarette box is this kind of plastic. In addition, PPR pipes, which are also polypropylene materials, are recommended or mandatory for domestic water pipes commonly used in newly-built communities. In addition to safety considerations, it is also easy to process because of its hot-melt characteristics. Polypropylene industry is also the standard to measure the industrial level of a country.

No.6-PS

Don't think PS lunch boxes are very low. At least they can keep some small restaurants serving the bottom alive

No. 6 plastic PS, scientific name polystyrene, is a legendary plastic. Once upon a time, No. 6 plastic was all over the world, especially on both sides of China's railway, but nearly 20 years later, many people forgot the 'white pollution' at that time. Today, the important use of plastic 6 is plastic foam. Polystyrene board in home decoration refers to this plastic, but it has only a lot of reduction in the food status. It is widely used in instant noodles and family barrels. The foam lunch boxes are of course still available, but many people refuse to use them. It should be noted that No. 6 plastic itself is transparent. If you are bored to study disposable beverage cups on the plane, you can find that most of them use No. 6 plastic. Of course, if you drink coffee or tea, you will only observe paper cups or No. 5 plastic.

No.7-PC

PC is a very beautiful plastic, and very strong. Mom doesn't have to worry about breaking the cup

No. 7 plastic PC does not refer to personal computers, but polycarbonate, but it is related to personal computers. Many computer shells are made of PC plastic. Some places say that No. 7 stands for 'other plastics', which is actually true, but due to the wide use of PC, No. 7 plastic is basically equivalent to polycarbonate plastic. Different from those plastics above, PC comes from 'noble'. It is not a general-purpose plastic, but an engineering plastic. You can know from the name that this guy has excellent physical properties. In terms of electrical shell, PC and another engineering plastic ABS occupy the mainstream market, while in the food industry, the most common are space cup, water dispenser bucket and milk bottle. It is characterized by high strength, not to mention falling, and a better PC shell can't be trampled down. The famous walnut shell opener brand Nokia should have felt it for a long time, and the emergence of iphone5c makes this plastic show its face again.