The first synthetic thermoplastic polymer was made of celluloid. ● Types and uses of plastics: Plastics can be divided into thermoplastics and thermosetting plastics. Thermoplastic is a kind of plastic that melts into liquid when heated and can be changed into another shape after cooling. Thermosetting plastics are only heated when they are manufactured, but they will not become liquid when heated for the second time, and they will also form stench and even endanger our health, so they should be separated when they are recycled. If you pay close attention to the surrounding environment, you will be surprised to find that there are many plastics and synthetic fibers in your home. For example, many plastics are used to make cars, which can reduce the weight of cars and avoid fuel consumption. Plastic water pipes have gradually replaced metal water pipes, so many toxic substances can be avoided. Many plastics are waterproof, so they are widely used as water containers or waterproof containers, among which polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP) or polystyrene (PS) are the most commonly used. ● Main characteristics of plastics: We all use plastics frequently. Have you ever thought about its advantages and disadvantages? Why do some people think it's convenient and some people think it's polluting? ◎ Advantages: Not easy to conduct electricity. Light weight and good chemical stability. Impact resistance. Transparent and wear-resistant. Easy molding and coloring, and low cost. Disadvantages: not easy to decompose. Poor heat resistance. Fragile at low temperature. Excessive load will cause deformation. 1.PET (polyethylene terephthalate) plastic recycling code 1 is PET, commonly known as Bote bottle when used in containers. Such as detergent, shampoo and mineral water packaging bottles, have been widely used. Identification: Potter bottles are usually colorless and transparent, and some are light green, light blue or brown. There is a dot below the bottom of the round PET bottle, and there is no seam in other parts of the bottle, which is the simplest identification method. 2.HDPE (high density polyethylene) PE (polyethylene) is the most widely used plastic in industry and life. Generally divided into high density polyethylene (HDPE) and low density polyethylene (LDPE). PE has excellent acid and alkali resistance. Almost all plastic bags and all kinds of translucent or opaque plastic bottles on the market are made of PE, such as detergent, shampoo, bath milk, cooking oil, LDPE and so on. Identification method: most of them are opaque and feel like wax. Plastic bags rustle when rubbing or rubbing. 3.PVC (polyvinyl chloride) PVC was invented quite early, and it is mostly used in industrial products, but it is mostly used in non-food aspects, such as water pipes, raincoats, schoolbags, building materials, plastic films and plastic boxes. Because PVC bottles are breathable, they will not be used to hold carbonated drinks. Mineral water is the largest in food containers, and some salad oil bottles also use PVC. Identification method: The bottom of round PVC bottle is a straight line, which is different from Baote bottle. White marks will appear when PVC is forcibly folded, and it will turn iron red after long-term exposure to the sun; When there is fire, there will be a blue flame on the edge, which has poor ductility, so it is its characteristic to stop burning as soon as the fire source leaves. (Note: Toxic monomer vinyl chloride may be released when burning PVC. Please test in an open and ventilated place. (LDPE) Most plastic bags and films are made of LDPE. LDPE containers, if not colored, are mostly translucent, such as milk bottles and film boxes. Identification method: LDPE plastic bags are soft and will not rustle when rubbed. The plastic film on the outer packaging is soft and easy to tear, while the PVC or PP film is brittle and hard. 5.PP bottle makers often use PE to make bottles, and the bottle caps and handles are made of PP with greater hardness and strength. Of course, there are also bottles made directly from PP, the most common ones are soybean milk and rice slurry bottles, but the larger containers such as buckets, trash cans and washing barrels are mostly made of PP, and disposable tableware made of PP, such as red plastic bowls and plastic boxes for microwave food, are all made of PP. Identification method: it is difficult to distinguish PP from PE. Generally speaking, PP has high hardness and shiny surface, while PE is like a wax maker, which has a heavy candle smell when burning. 6.PS (polystyrene) PS has low water absorption and good dimensional stability. Mainly used in toys, stationery, rollers, linings (like white linings of refrigerators) and industrial packaging cushioning materials. Unfoamed PS has bottles and cans of dairy industry on food containers, such as Yakult, yogurt, pudding boxes, cups and lids of fast food drinks, etc. Foamed flat plates are widely used in disposable tableware after vacuum forming, such as polystyrene foam disposable tableware. Identification method: For unfoamed products, white marks appear when they are lightly folded, and there is a diffusion phenomenon. Generally, they can be torn by hand. 7. OTHER plastic materials are marked with No.7 in many cases, and it is difficult to recycle them, such as toothpaste bottles.
Plastics are actually composed of many monomers, so plastics are polymers; However, different monomers constitute different polymers, and different polymer combinations lead to different plastic products. For example, polyvinyl chloride (polymer) is a polymer produced by addition polymerization of vinyl chloride (monomer), and urea-formaldehyde (polymer) is a polymer produced by polycondensation of urea (monomer) and formaldehyde (monomer). There are many kinds of monomers, and the common monomers are as follows. This is also a common plastic raw material. Polyethylene (polymer) is made of ethylene (monomer), for example, toy polyvinyl chloride (polymer) is made of vinyl chloride (monomer), for example, water pipe polystyrene (polymer) is made of styrene (monomer), for example, baby bottle plexiglass (polymer) is made of methyl 2- methacrylate (monomer). 6- diamine (monomer) and hexamethylene dichloride (monomer), such as nylon rope polyester (polymer) are composed of diacid (monomer) and diol (monomer), such as carpet urea-formaldehyde (polymer) is composed of urea (monomer) and formaldehyde (monomer), such as electric shock.