Plastic is a widely used synthetic polymer material, in our daily life plastic products abound. From the use of toiletries after we wake up, tableware used for breakfast, stationery for work and study, cushions for rest, mattresses, and TV, washing machine, computer shell, and night bring us Bright all kinds of lighting fixtures ...
Plastic with its excellent performance gradually replaced many have been used for decades, hundreds of years of materials and utensils, people become an indispensable assistant in life. The flexibility of the wood, the transparency of the glass, the corrosion resistance of the ceramic, the elasticity and toughness of the rubber, so that in addition to daily necessities, plastics are more widely used in aerospace, medical equipment, oil Chemical, machinery manufacturing, defense, construction and other industries.
First, the classification of plastic
Many types of plastic, so far the world's production of plastic about three hundred kinds. Plastic classification methods are more commonly used in two:
1, according to the nature of the plastic after the heat is divided into different types of thermoplastics and thermosetting plastics
Thermoplastic molecular structure is a linear structure, in the heat when the softening or melting, plastic made into a certain shape, after cooling and harden. In the heat to a certain extent and re-softening, cooling and then hard, this process can be repeated several times. Such as polyvinyl chloride, polyethylene, polystyrene and the like. Thermoplastic molding process is relatively simple, can be continuous production, and has a very high mechanical strength, so the development of fast.
Thermosetting plastic molecular structure is the body structure, also occurs when the heat softening, can be molded into a certain shape, but heated to a certain extent or by adding a small amount of curing agent, the hardening stereotypes, and then heating will not become soft and change Shape up. Thermosetting plastics processing, the heat is no longer softened, it can not be recycled, such as phenolic plastic, amino plastic, epoxy resin and so belong to such plastic. Thermosetting plastic molding process is more complex, so continuous production has some difficulties, but its heat resistance is good, not easy to deformation, and the price is relatively low.
2, according to the use of plastic is divided into general plastic and engineering plastics
General Plastics refers to the production of large, low prices, wide range of applications of plastics, including polyolefin, polyvinyl chloride, polystyrene, phenolic plastic and amino plastic five varieties. Many of the products used in everyday life are made of these general plastics.
Engineering plastics can be used as engineering materials and metal instead of metal parts and other plastic parts. Such as polyamide, polycarbonate, polyoxymethylene, ABS resin, polytetrafluoroethylene, polyester, polysulfone, polyimide and the like. Engineering plastics with a small density, high chemical stability, good mechanical properties, excellent electrical insulation, easy processing and other characteristics, widely used in automotive, electrical, chemical, mechanical, instrumentation, instrumentation and other industries, also used in space navigation, rocket , Missiles and so on.
Second, the composition of plastic
The plastic we usually use is not a pure substance, it is made of many materials. In addition, in order to improve the performance of plastic, but also in the polymer to add a variety of auxiliary materials, such as fillers, plasticizers, lubricants, stabilizers, additives, Coloring agent, etc., can become a good performance of plastic.
1, synthetic resin
Synthetic resin is the most important component of plastic, its content in the plastic is generally 40% to 100%. Due to the large content, and the nature of the resin often determines the nature of the plastic, so people often see the plastic synonym for the plastic. For example, the polyvinyl chloride resin and PVC plastic, phenolic resin and phenolic plastic mixed with. In fact, resin and plastic are two different concepts. Resin is an unprocessed original polymer, it is not only used in the manufacture of plastic, but also paint, adhesives and synthetic fiber raw materials. The plastic in addition to a small part of the 100% resin, the vast majority of plastic, in addition to the main component of the resin, but also need to add other substances.
Fillers, also known as fillers, can improve the strength and heat resistance of plastics and reduce costs. For example, adding phenolic resin to wood powder can greatly reduce the cost of phenolic plastic to become one of the cheapest plastic, but also significantly improve the mechanical strength. Fill can be divided into two kinds of organic fillers and inorganic fillers, such as wood flour, rags, paper and a variety of fabric fibers, the latter such as glass fiber, diatomaceous earth, asbestos, carbon black and so on.
Plasticizer can increase the plasticity and flexibility of plastic, reduce the brittleness, so that the plastic easy to shape. Plasticizers are generally compatible with resin, non-toxic, odorless, light, heat stable high boiling organic compounds, the most commonly used is phthalate esters. For example, the production of PVC plastic, if you add more plasticizers can be soft PVC plastic, without or less plasticizer (dosage <10%), then the rigid polyvinyl chloride plastic The
In order to prevent the synthetic resin in the processing and use of light and heat during the decomposition and destruction of the role, to extend the service life, to join the stabilizer in the plastic. Commonly used stearate, epoxy resin and so on.
5, coloring agent
The coloring agent allows the plastic to have a variety of bright, beautiful colors. Commonly used organic dyes and inorganic pigments as colorants.
The role of the lubricant is to prevent the plastic in the molding does not stick to the metal mold, while the plastic surface can be smooth and beautiful. Commonly used lubricants are stearic acid and its calcium and magnesium salts.
In addition to the above additives, the plastic can also be added flame retardants, foaming agents, antistatic agents, etc., to meet the different requirements.
Third, the characteristics of plastic
1, plastic with plasticity
As the name implies, plastic is the material that can be shaped. The plasticity of the so-called plastic can be heated by the way to soften the solid plastic, and then turn the soft plastic in the mold, let it cool and then re-solidified into a certain shape of the solid. This property of plastic also has some shortcomings, that is easy to soften when the heat deformation, and some plastic even with a higher temperature of the water will be deformed, so the plastic products are generally not exposed to boiling water.
2, plastic with flexibility
Some plastic, like synthetic fibers, has a certain degree of elasticity. When it is stretched by external force, the curled molecules are straightened by flexibility, but once the tension is removed, it will return to the original curling state, which makes the plastic elastic, such as polyethylene and polyvinyl chloride Film products. But some plastic is not elastic.
3, plastic has a high strength
Although plastic is not as hard as metal, but with glass, ceramics, wood, etc., or have a relatively high strength and wear resistance. The plastic can be made on the machine with strong gears and bearings.
4, plastic with corrosion resistance
Plastic is not like metal in the humid air will rust, nor as wood in the wet environment will be rotten or microbial erosion, and other plastic acid corrosion. So plastics are often used as chemical plants in the water and infusion pipes, buildings, doors and windows.
5, plastic with insulation
The molecular chain of plastics is a combination of atoms covalent bonds, molecules can not ionize, can not transfer electrons in the structure, so the plastic is insulated. Plastic can be used to make the wire of the foreskin, electrical outlet, electrical appliances, and so on.