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I believe that all my friends have encountered this kind of situation. I packed a dish in the restaurant. when I got home, I found a big hole in the bottom of the packed plastic lunch box. it was estimated that the quality of the plastic lunch box was too poor and melted by the high temperature of the oil. I also joked that I estimated that this meal was half plastic and half vegetables, and I didn't know what material it was made.

This kind of packing box, which is easy to burn, is basically a foamed box, which is made of polystyrene resin as raw material. I don't know if you have found it. In recent years, this kind of box seems to be used a lot less, especially for takeout, which is a transparent box.

Xiao Bian also found an interesting situation when consulting relevant materials. Foam tableware was stipulated in 1999 to be completely eliminated by the end of 2000, which means that it is not allowed to be used or produced. White pollution is too serious. However, the ban was lifted on February 26, 2013. Therefore, although it is used less now, it is still in use all the time.

Now there are lunch boxes of various materials, some are marked with PP, some are PS, and Pvc materials, that is, I don't know what is the difference between them, and I don't know what is harmful to the human body.

Plastic is an indispensable part of our life now. It can be understood literally as a material that can be shaped. It is a kind of polymer material. Its main component is synthetic polymer compound, also known as synthetic resin. In order to increase some properties of the product, some additives will be added to change its performance. So what is plastic and how to distinguish various plastic materials.

The earliest plastic appeared in the 19th century, people put camphor and a small amount of alcohol in natural cellulose, made of artificial plastics, this material has plasticity, under hot pressure can be molded various products, named celluloid, from then on the history of human use of plastics, the 20th century began to appear polymer synthetic plastics.

From the molecular structure of plastic is a kind of polymer, which makes plastic become very easy to shape, literally can also be understood as a material that can be shaped, especially in the high temperature and high pressure state, most of the plastic is extracted from fossil fuels, oil and natural gas are the main raw materials, they become the perfect material of plastic.

Plastic Manufacturing Process

First, crude oil and natural gas are extracted, and then they are sent to refineries to extract many kinds of substances, including the main components in plastics, that is, ethane is extracted from petroleum, propane is extracted from natural gas, ethane and propane are sent to cracking plants to decompose into molecules, ethane is used to produce ethylene, propane is used to produce propylene, and then catalysts are added to combine the molecules to form resin polymers, because of this structure, plastic is easy to shape under high temperature and high pressure.

Polymerization turns ethylene into polyethylene and propylene into polypropylene. These resins are melted and cooled, and then cut into plastic raw material particles. The plastic particles are sent to the factory to be heated to make various plastic products.

Most plastic raw materials are transparent or Milky White. Various plastic products require various colors for use or design, which requires dyeing during plastic processing. The common dyeing method is to mix a certain proportion of color masterbatch or toner in the raw materials before production, and melt the raw materials with the color masterbatch or toner in the injection molding machine to produce the required product color.

Plastic products of various shapes and sizes are used in life. The main production method of these plastic products is injection molding. The three elements required in this process are plastic raw materials, molds, and injection molding machines. The injection molding process is to put the raw materials into the machine hopper. After mixing and melting in the injection molding machine, the raw materials are filled into the mold. The raw materials are rapidly cooled and formed in the mold. Finally, the mold is opened to take out the product.

Another common processing method is blow molding. All kinds of plastic bottles, jars, barrels and the like are blow molding. It is well understood that after the raw materials are melted, they are blown up in the mold.

The most intuitive difference between injection molding and blow molding is that injection molding products are solid core bodies and blow molding is hollow core bodies.

In daily life, more than 70% of daily necessities are plastic products. Among them, the main plastic materials are PP,PS,PA,PC,PE,ABS and PVC. To distinguish them, one must understand their characteristics and differences. Before one understands them, one must first understand what thermosetting plastics and thermoplastics are.

Thermosetting plastic is a plastic that needs to be heated to solidify during processing and forming. It is to mix two different plastics at the same time and inject them into a mold. After heating causes a reaction, a single molecule is turned into a mesh three-dimensional structure, that is, a plastic that will harden after heating. Its advantage is high heat resistance, but its disadvantage is that it is not easy to recycle and reuse. Thermosetting plastics include FRP bathtubs, tableware, etc.

Thermoplastic is the plastic that will melt after heating, that is, the solid plastic particles are heated and injected into the mold after the plastic is melted. After the finished product is cooled and solidified, the product is completed. The advantage is that the product can be recycled, but the disadvantage is that it is not heat resistant. Thermoplastic includes PE,PP,PS,PVC,ABS,PA,PC, etc.

Each of us has his own ID card. It can distinguish everyone's identity. Can plastic also be distinguished? After buying plastic products, if you observe carefully, you will see that there are numbers on the shell of the product. This is to distinguish the types of plastics and develop a plastic identification code. This identification code is universal in the world. It is a triangle composed of three clockwise rotating arrows, with numbers representing each material marked in the middle. At present, there are 7 identification codes, in addition to these identification codes, we can understand plastic materials through coding, and the most important thing is to assist in recycling, which can subdivide types and reuse.

PET (polyester) code 1, also known as polyester resin, raw materials are Milky White or light yellow, good transparency, non-toxic, high density, high hardness, wear resistance, but not hot water invasion, alkali resistance and other characteristics, the use of temperature 65 ℃ ~-20 ℃, more than this temperature is easy to release harmful substances, can not be used repeatedly for a long time, mainly used in packaging materials in beverage bottles, mineral water bottles, electronic appliances in the shell and accessories.

HDPE (high density polyethylene) code 2, also known as low-pressure ethylene, raw materials are white, non-toxic and tasteless, with low density, good toughness, acid and alkali resistance, but the characteristics of poor anti-aging performance, difficult to clean do not recycle, mainly used for washing supplies packaging bottles, wire and cable sheath, etc.

PVC (polyvinyl chloride) code 3 is also called adhesive film. The raw material is yellow, translucent, transparent, high strength, good flexibility, not easy to be brittle, etc. PVC is divided into soft and hard. The difference between them depends on whether softener is added. PVC itself is not toxic. If plasticizer and antioxidant are added, it is toxic. Therefore, soft PVC is not toxic and hard PVC is toxic. It is mainly used in packaging materials, building materials industry in the pipeline, doors and windows.

LDPE (low density polyethylene) code 4, also known as high pressure polyethylene, raw materials are Milky White, tasteless and non-toxic, with good transparency, good flexibility, alkali resistance, but heat resistance is not good, the density is the lowest of all polyethylene, more than 110 ℃ will melt the release of toxic substances, mainly used for plastic film, plastic film and so on.

PP (polypropylene) code 5, also known as 100-fold glue, has low density, transparent and light raw material appearance, non-toxic and tasteless, high strength and elasticity, chemical resistance, collision resistance, high temperature resistance of 100~120 degrees celsius, and can be heated in microwave oven. however, it is forbidden to use recycled products to contain food. PP materials are commonly used in plastic lunch boxes, water cups, food packaging boxes and other products. due to these characteristics of PP, so Australia's currency is made of this plastic.

PS (polystyrene) code 6, also known as hard glue, hardness will be higher than PP, raw material transmittance is high, colorless and tasteless, easy to dye, but poor toughness, easy to brittle, temperature over 70 ℃ will release harmful substances, commonly used in disposable foam lunch boxes, packaging lining, decoration materials, etc., because it is not easy to recycle, now gradually replaced by paper materials.

PA (polyamide) is also called nylon. It has no code name. The raw materials are non-toxic and odorless, with good toughness, wear resistance, heat resistance and chemical resistance. PA plastics have a wide variety of varieties. Especially now, by mixing various fiber materials, the various properties of PA plastics have been significantly improved. It has replaced some metals and is widely used in auto parts, household appliances housings, protective articles and other fields.

ABS plastic also has no code name. It is a composite of acrylonitrile (A), butadiene (B) and styrene (C), also known as ABS resin. Therefore, ABS also has the common properties of these three substances, impact resistance, heat resistance, low temperature resistance, good comprehensive performance, low price and wide range of uses. ABS plastic is non-toxic, tasteless and translucent or transparent in appearance, many parts in automobiles are made of ABS plastic, and parts in household appliances and office machines are also made of ABS.

Other categories, code 7, include acrylic, polycarbonate, polylactic acid, etc. The characteristics of these plastics are that they cannot be heated in a microwave oven, cannot be sterilized at high temperature, and cannot be directly exposed to the sun, because this may release bisphenol A and cause harm to the human body.

In fact, the development of plastics up to now is far more than the above. All kinds of synthetic plastics make people confused in an instant. You may have heard of PBT (collectively referred to as thermoplastic polyester together with PET) ,HIPS (impact resistant polystyrene, which is commonly referred to as engineering plastics), POM (polyoxymethylene thermoplastic crystalline polymer), EVA (copolymerized with ethylene and acetic acid), etc. There are too many, so there are no examples here.

You will find that there are many plastic products are not marked with identification codes, so how can we know what plastic material they are? In addition to the use of professional instruments for analysis, there are relatively simple identification methods, of course, this method is only a reference, and can not completely determine the type of plastic.

Buoyancy test is to distinguish the material according to the density of plastic. At present, when no other components are added, the density of common plastic in the market will be between 0.9 and 2.0 g/cm, and the density of water is exactly 1 g/cm. In common plastic, only PP and PE have densities less than 1.0, so PP and PE can float on the water surface, other plastic materials will sink to the bottom because they are more dense than water.

Combustion test, if you want to more clearly distinguish a variety of plastic materials, can be identified by burning, combustion test is by burning a variety of plastic, in the process of observation of the characteristics and changes, and then determine the plastic material, observation of several states are, leaving the fire source of the state, combustion smell, flame color, the state after combustion, flammability, the combustion test is based solely on the special effects of plastics and cannot be used as a scientific basis for identifying plastics.

PET burning black smoke, sour taste

PP can burn all the time. The flame is yellow and blue. PS can burn all the time with the smell of candle. The flame is yellow and black smoke. After burning, there is carbon powder and pine oil smell.

ABS can burn quickly and continuously after ignition, the flame is yellow black smoke, soften without dripping after combustion, and the rubber smell is very heavy

PE flame is yellow on top and blue on bottom. After burning, it softens and drips, with paraffin burning smell. (Did you burn plastic bags when you were a child? Have you forgotten the feeling of poop-poop dripping? Do you remember the pain of dripping on your hands?)

PA is not easy to burn and extinguishes when leaving the fire source. The flame is yellow gray smoke, foaming and dripping after burning, with sheepskin and nail odor;

PVC is not easy to burn, leave the fire source is extinguished, the flame is blue and green with smoke, it is difficult to soften after burning, and it has a pungent sour taste. (The shrink film on the package is PCV, the harder one is PCV)

As people pay more and more attention to health, bisphenol A often appears in various reports. Bisphenol A, also known as BPA, white crystal, is mainly used in the manufacture of epoxy resin and polycarbonate, and is also widely used as a catalyst in plastic products, such as water bottles, medical devices, milk bottles and other products. The addition of bisphenol A can make plastic products colorless and transparent, improve toughness, lightness, durability and other characteristics. After research, bisphenol A is a low-toxic chemical that can cause harm to the human body, especially to the health of infants and young children, and now China and many countries in the world prohibit bisphenol A from being used in baby bottles, water bottles and other products.

Because of the increasing use of plastics, the global production of plastics is also increasing. Most of these plastics end up in garbage, especially some disposable plastic products, a large part of which are not recycled and will eventually harm animals and destroy the earth's environment.

Fortunately, now people have realized its harm and have begun to take various measures, such as reducing the use of disposable plastics, adopting reusable substitutes, using some organisms to decompose plastics, and using some microorganisms to reduce the degradation time of plastics from hundreds of years to just a few days. Plastics are almost everywhere. Only by fully understanding plastics can we make good use of plastics and reduce the pollution of plastics to the earth.