The earliest plastic appeared in the 19th century. People put camphor and a small amount of alcohol into natural cellulose to make artificial plastic. This material has plasticity and can be molded into various products under hot pressing. It was named celluloid. From then on The history of human use of plastics began, and polymer synthetic plastics began to appear in the 20th century.
Plastic is a kind of polymer in terms of molecular structure, which makes plastic very easy to shape. It can also be understood literally as a material that can be shaped, especially under high temperature and pressure. Most plastics are made from fossils. Derived from fuels, oil and natural gas are the main raw materials, making them perfect materials for plastics.
In daily life, more than 70% of daily necessities are plastic products. The main plastic materials include PP, PS, PA, PC, PE, ABS, and PVC. If you want to distinguish them, you need to know their characteristics. Characteristics and differences. Before understanding them, you must first understand what thermosetting plastics and thermoplastics are.
Thermosetting plastics are plastics that need to be heated to solidify during processing. That is, two different plastics are mixed and injected into the mold at the same time. After heating to cause a reaction, the single molecules become a network three-dimensional structure, that is, after heating, they will The advantage of hardened plastic is that it has high heat resistance, but the disadvantage is that it is not easy to recycle. Thermosetting plastics include FRP bathtubs, tableware, etc.
Thermoplastics are plastics that melt after heating. Solid plastic particles are heated, and then injected into the mold after the plastic melts. After the finished product cools and solidifies, the product is completed. The advantage is that the product can be recycled, but the disadvantage is that it cannot be recycled. Heat-resistant, thermoplastic plastics include PE, PP, PS, PVC, ABS, PA, PC, etc.
购买一个塑料产品后,如果你看起来carefully, you will see a serial number on the casing of the product. This is a plastic identification code developed to distinguish the type of plastic. This identification code is universal all over the world. It is made of A triangle composed of three clockwise rotating arrows, with a number representing each material marked in the middle. There are currently 7 identification codes. In addition to allowing us to understand plastic materials through coding, these identification codes most importantly assist recycling and can subdivide types and Reuse.
PET (polyester) code 1, also called polyester resin, the raw material is milky white or light yellow, has good transparency, non-toxic, high density, high hardness, wear resistance, but not resistant to hot water immersion, alkali resistance, etc. Features: The operating temperature is
HDPE (High Density Polyethylene) code number 2, also called low-pressure ethylene, is white in color, non-toxic and tasteless, has low density, good toughness, acid and alkali resistance, but poor anti-aging properties. It is difficult to clean and should not be recycled. Mainly Used for washing product packaging bottles, wire and cable sheathing, etc.
PVC (polyvinyl chloride) code 3, also called adhesive film, the raw material is yellow and translucent, has good transparency, has high strength, good flexibility, and is not easy to be brittle. PVC can be divided into soft and hard. The difference between them depends on Whether a softener is added, PVC itself is not toxic. If plasticizers, antioxidants, etc. are added, it will be toxic. So soft PVC is not toxic, while hard PVC is toxic. It is mainly used in packaging materials and pipes in the building materials industry. , doors and windows, etc.
LDPE (low density polyethylene) code 4, also called high-pressure polyethylene, the raw material is milky white, odorless and non-toxic, has good transparency, good softness, alkali resistance, but poor heat resistance, the density is the highest among all polyethylene Ethylene is the lowest among them. It will melt and release toxic substances when it exceeds
PP (polypropylene) code number 5, also called 100% glue, has a low density, the appearance of the raw material is transparent and light, non-toxic and tasteless, has high strength and elasticity, is resistant to chemicals, collisions, and high temperatures of 100~120 degrees Celsius, and can be discharged Heat it in a microwave oven, but it is prohibited to use recycled products to hold food. Products commonly used in plastic lunch boxes, water cups, food packaging boxes, etc. are made of PP materials. Due to these characteristics of PP, Australian currency is made of this plastic. .
PS (polystyrene) code 6, also called hard glue, has a higher hardness than PP. The raw material has high transmittance, is colorless and odorless, and is easy to dye, but has poor toughness and is easily brittle. It will release harmful substances when the temperature exceeds
PA (polyamide) is also called nylon. It has no code name. The raw material is non-toxic and odorless. It has good toughness, wear resistance, heat resistance and chemical resistance. There are many types of PA plastics, especially now that they are mixed with various fiber materials. The various properties of plastics have been significantly improved, and they have replaced some metals. They are widely used in auto parts, household appliance casings, protective equipment and other fields.
ABS plastic has no code. It is a composite of three substances: acrylonitrile (A), butadiene (B), and styrene (C). It is also called ABS resin, so ABS also has the common properties of these three substances. Impact resistance, heat resistance, low temperature resistance, good overall performance, cheap price, wide range of uses, ABS plastic is non-toxic, odorless, translucent or transparent particles in appearance, many parts in cars are made of ABS plastic, and in household appliances , the parts on office machines are also made of ABS.
Other categories, code number 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 temperatures, and cannot be exposed to direct sunlight, because this may release bisphenol A, which may cause harm to the human body. wait.
In fact, the development of plastics up to now is far more than the above. The various synthetic plastics make people instantly confused. You may have heard of them, PBT (collectively called thermoplastic polyester together with PET), HIPS (impact-resistant polystyrene). Ethylene, often referred to as engineering plastics), POM (polyoxymethylene thermoplastic crystalline polymer), EVA (copolymer of ethylene and acetic acid), etc.
The buoyancy test is to identify the material of plastic based on its density. The density of common plastics currently on the market will be between 0.9~
Combustion test, if you want to distinguish various plastic materials more clearly, you can identify them by burning them. The combustion test is to burn various plastics, observe the characteristics and changes that occur during the process, and then judge the quality of the plastics. Materials, several states to observe are, the state of leaving the fire source, burning smell, flame color, state after burning, flammability degree, the combustion test is entirely based on the special effects of plastics, and cannot be used as a scientific method to identify plastics. in accordance with.
PET burns and emits black smoke and has a sour smell.
页可以继续燃烧,火焰是黄色的p and blue at the bottom, and smells like a candle. PS can also keep burning, the flame is yellow and black smoke, and there is carbon powder and pine oil smell after burning.
ABS can burn quickly and continuously after being ignited. The flame is yellow and black smoke. It softens without dripping after burning and has a strong rubber smell.
The PE flame is yellow at the top and blue at the bottom. It softens and drips after burning, and has the smell of burning paraffin; (Have you ever burned a plastic bag when you were a child? You have not forgotten the feeling of popping and dripping.
PA is not easy to burn and will extinguish as soon as it is removed from the fire source. The flame will be yellowish gray smoke, which will bubble and drip after burning. It has the smell of sheepskin and nails;
PVC is not easy to burn. It will go out when it is removed from the fire source. The flame is blue at the top and green at the bottom with smoke. It is difficult to soften after burning and has a pungent sour smell; (the harder shrink film on the packaging is PVC)