01 Definition of plastic
Plastic is a polymer organic material with resin as the main component, molded into a certain shape at a certain temperature and pressure, and capable of maintaining a predetermined shape at room temperature.
Resin refers to an organic polymer that usually has a transformation or melting range when heated, and is fluid when subjected to external force during transformation. It is solid or semi-solid or liquid at room temperature. It is the most basic and most important of plastics. ingredient. Broadly speaking, any polymer that is the basic material of plastics in the plastics industry can be called a resin.
02 Classification of plastics
There is currently no exact classification of plastics. The general classification is as follows:
According to the physical and chemical properties of plastics
thermoplastics: plastics that can be repeatedly heated to soften and cool to harden within a specific temperature range. Such as polyethylene plastic, polyvinyl chloride plastic.
Thermosetting plastics: plastics that can be cured into infusible and insoluble materials due to heat or other conditions. Such as phenolic plastics, epoxy plastics, etc.
Split according to plastic use
General-purpose plastics: generally refers to plastics with large output, wide use, good moldability, and low price. Such as polyethylene, polypropylene, polyvinyl chloride, etc.
Engineering plastics: generally refers to plastics that can withstand certain external forces, have good mechanical properties and dimensional stability, and can maintain their excellent performance at high and low temperatures, and can be used as engineering structural parts. . Such as ABS, nylon, poly alum and so on.
Special plastics: generally refers to plastics with special functions (such as heat resistance, self-lubricating, etc.) and used in special requirements. Such as fluoroplastics, organic silicon, etc.
According to the plastic molding method,
Molded plastic: resin mixture for molding. Such as general thermosetting plastics.
Laminated plastic: refers to the fiber fabric impregnated with resin, which can be laminated and hot-pressed to form a whole material.
Injection, extrusion and blow molding plastics: generally refers to the resin mixing department that can melt and flow at the temperature of the barrel and quickly harden in the mold. Such as general thermoplastics.
Cast plastic: A liquid resin mixture that can be poured into a mold and hardened into a certain shape product under the condition of no pressure or a little pressure. Such as MC nylon.
Reaction injection molding compound: generally refers to liquid raw materials, which are injected into the mold cavity under pressure to react and solidify to obtain a finished product. Such as polyurethane.
According to plastic semi-products and products.
Molding powder: also known as plastic powder, mainly obtained from thermosetting resin (such as phenolic) and fillers after fully mixing, pressing and crushing. Such as phenolic plastic powder.
Reinforced plastic: A type of plastic with reinforced materials and some mechanical properties that have been greatly improved than the original resin.
Styrofoam: Plastic with numerous micropores inside the whole body.
Film: generally refers to a flat and soft plastic product with a thickness of less than 0.25 mm.
03 Basic properties of plastic
1. Light weight and high specific strength.
Plastics are light in weight. The density of general plastics is between 0.9~2.3 g/cm3, only 1/8~1/4 of steel and 1/2 of aluminum. The density of various foamed plastics is even higher. Low, about 0.01~0.5 g/cm3. The strength calculated per unit mass is called the specific strength, and the specific strength of some reinforced plastics is close to or even higher than that of steel. For example, alloy steel has a tensile strength per unit mass of 160 MPa, while glass fiber reinforced plastic can reach 170 to 400 MPa.
2. Excellent electrical insulation properties.
Almost all plastics have excellent electrical insulation properties, such as extremely small dielectric loss and excellent arc resistance, which are comparable to ceramics.
3. Excellent chemical stability.
General plastics have good corrosion resistance to chemicals such as acids and alkalis, especially the chemical resistance of polytetrafluoroethylene is better than gold, and can even be resistant to corrosion by strong corrosive electrolytes such as "aqua regia". Known as the "Plastic King".
4. Good anti-friction and wear resistance.
Most plastics have excellent anti-friction, wear resistance and self-lubricating properties. Many anti-friction parts made of engineering plastics make use of these characteristics of plastics. When certain solid lubricants and fillers are added to wear-resistant plastics, their friction coefficient can be reduced or their wear resistance can be further improved.
5. Light transmission and protection performance.
Most plastics can be used as transparent or translucent products, among which polystyrene and acrylic plastics are as transparent as glass. The chemical name of plexiglass is polymethyl methacrylate, which can be used as aviation glass material. Polyvinyl chloride, polyethylene, polypropylene and other plastic films have good light transmission and warmth retention properties, and are widely used as agricultural films. Plastic has a variety of protective properties, so it is often used as protective equipment, such as plastic films, boxes, barrels, bottles, etc.
6. Excellent shock absorption and noise reduction performance.
Some plastics are flexible and full of elasticity. When they are subjected to frequent mechanical shocks and vibrations from the outside, viscous internal friction is generated inside, which converts mechanical energy into heat energy. Therefore, they are used as shock-absorbing and sound-absorbing materials in engineering. For example, bearings and teeth made of engineering plastics can reduce noise, and various foamed plastics are widely used as excellent shock-absorbing and sound-absorbing materials.
The excellent properties of the above-mentioned plastics make it widely used in industrial and agricultural production and people’s daily life; it has become a substitute for metal, glass, ceramics, wood, fiber and other materials from the past. An indispensable material for modern life and cutting-edge industry.
However, plastics also have shortcomings. For example, heat resistance is worse than that of metals and other materials. Generally, plastics can only be used at temperatures below 100°C, and a few can be used at around 200°C. The thermal expansion coefficient of plastics is 3-10 times larger than that of metals, and they are easily affected by temperature changes and affect dimensional stability Under the action of load, plastic will slowly produce viscous flow or deformation, that is, creep phenomenon; in addition, plastic will age under the action of atmosphere, sunlight, long-term pressure or certain properties, which will deteriorate its performance. These shortcomings of plastic more or less affect or limit its application. However, with the development of the plastic industry and the deepening of research on plastic materials, these shortcomings are gradually being overcome, and novel plastics with excellent performance and various plastic composite materials are constantly emerging.
04 Uses of plastics
Plastics have been widely used in various fields such as agriculture, industry, construction, packaging, defense cutting-edge industries, and people’s daily lives.
Agriculture: A large amount of plastic is used to make mulching film, seedling raising film, greenhouse film, irrigation and drainage pipes, fishing nets, and floating floats.
Industry: In the electrical and electrical industries, plastics are widely used to make insulating materials and packaging materials; in the mechanical industry, plastics are used to make transmission gears, bearings, bushings, and
components instead of metal products: In the industry, plastics are used as pipes, various containers and other anticorrosive materials; in the construction industry, they are used as doors and windows, stair rails, floor tiles, ceilings, heat and sound insulation panels, wallpapers, downpipes and pit pipes, decorative panels and sanitary ware.
In the defense industry and cutting-edge technology, whether it is conventional weapons, aircraft, ships, rockets, missiles, satellites, spacecraft, and atomic energy industries, plastics are indispensable materials. In people's daily life, plastics are more widely used, such as plastic sandals, slippers, raincoats, handbags, children's toys, toothbrushes, soap boxes, thermos shells, etc. on the market. At present, it has also been widely used in various household appliances, such as televisions, radios, electric fans, washing machines, refrigerators, etc.
As a new type of packaging material, plastic has been widely used in the packaging field, such as various hollow containers, injection-molded containers (turnover boxes, containers, barrels, etc.), packaging films, woven bags, corrugated boxes, foam plastics , Strapping rope and packing belt, etc.
04 Development history and current situation of the plastic industry
As early as the 19th century, people had already used natural resins such as asphalt, rosin, amber, and shellac. In 1868, natural cellulose was nitrified and camphor was used as a plasticizer to make the world's first plastic variety called celluloid. Since then, the history of human use of plastics has begun. Since then began the history of human use of plastics. In 1909, the first synthetic plastic, phenolic plastic, appeared. In 1920, another synthetic plastic-amino plastic (aniline formaldehyde plastic) was born. These two plastics played an active role in promoting the development of the electrical industry and instrument manufacturing industry at that time.
In the 1920s and 1930s, plastics such as alkyd resin, polyvinyl chloride, acrylic, polystyrene and polyamide appeared one after another. From the 1940s to the present, with the development of science, technology and industry, and the extensive development and utilization of petroleum resources, the plastics industry has developed rapidly. Polyethylene, polypropylene, unsaturated polyester, fluoroplastics, epoxy resin, polyoxymethylene, polycarbonate, polyimide, etc. appeared in the variety.