Overview of plastics
DATE：2022/6/7 8:38:41 / READ： / SOURCE：This station
Overview of plastics
1、 Basic conceptsPolymer refers to the multiple repetitions of one or more atoms or atomic groups (structural units) connected with each other, and its relative molecular weight reaches enough to make the overall performance not change significantly with the addition or removal of several structural units. Because the polymer is formed by repeated covalent bonding of structural units with the same composition and structure, its relative molecular weight is large, but its composition is not complex. Coating compound production line www.handern com
Macromolecules (macromolecules) refer to organic or inorganic molecules with high relative molecular weight. Compounds composed of many polymer chains are called polymer compounds, also known as polymers or polymers.
Polymerization refers to the process by which a monomer or a mixture of monomers is transformed into a polymer. Monomer refers to a compound composed of molecules that can provide one or more structural units. According to different reaction mechanisms, polymerization can be divided into two types: addition polymerization and polycondensation. Coating compound production line www.handern com
① Addition polymerization is a polymerization reaction carried out according to the repeated addition process. The reaction is characterized by the formation of no water or other small molecules during the repeated addition process. Coating compound production line www.handern com
② Polycondensation is a polycondensation reaction carried out according to the repeated polycondensation process. The reaction is characterized by the production of small molecules in the reaction process
Resin refers to organic substances with high relative molecular weight, which are semi-solid, solid or pseudo solid, and sometimes liquid. There is no fixed melting point, but there is softening or melting range, and it tends to flow under stress. It is non-conductive and becomes soft when heated, and gradually softens and melts. Most of them are insoluble in water and soluble in organic solvents. They are the basic materials of plastics. Polymer molecular chain is a structure composed of numerous small molecules connected with each other to form polymer macromolecules. Polymer molecular chain structure can be divided into three types: linear, branched and body type.
① The combination of chain separation ② chain polymerization ③ long chains with branched chains of three-dimensional structure polymer are formed between chains, most of which are in the shape of curly irregular clusters, such as polyethylene, polystyrene, nylon, etc.
In general, objects have three states of aggregation, namely, solid state, liquid state and gas state. The relative molecular weight of the polymer is very large. When the polymer solid is heated, it will change from solid to liquid. Because the vaporization temperature of the polymer is too high, the polymer chain has been decomposed before reaching the vaporization temperature. Coating compound production line www.handern com
Common linear polymers undergo three physical and mechanical states at different temperatures, namely glass state, high elastic state and viscous flow state.
① Glassy state. Due to the low temperature, the macromolecular chain segment is in the frozen state. At this time, the deformation of the polymer is very small after being subjected to external force, showing a physical state as hard as the glass of small molecules, so it is called the glass state
② High elastic state. With the increase of temperature, the macromolecular chain can not move at this time, only the physical properties change caused by the movement of the segments in the long chain. The high elastic properties of the polymer come from the movement of the segments. At this time, when the polymer material is stretched by an external force, the macromolecular chain can adapt to the action of the external force through the movement of the chain segment, so that the molecular chain is stretched from the curled state. After the external force is removed, the straightened molecular chain can return to the curled state, showing good elasticity, so it is called high elastic state
③ Viscous flow regime. When the temperature rises to the viscous fluidization temperature, the polymer has the energy to move the whole macromolecule. Under the action of external force, the molecular chains slide and show viscous flow. At this time, the deformation of the polymer is very large and the deformation cannot be recovered. This kind of mechanical phenomenon with large deformation and irreversible deformation is called plastic deformation. The mechanical state of polymer in viscous flow is called viscous flow state.
2、 Definition and composition of plastics
Plastic is a kind of material with resin as the basic component, which can be molded into a certain shape in the process of processing at a certain temperature and pressure, and can maintain the given shape at room temperature. Resin is the most basic and important component of plastics. Resins can be divided into natural resins and synthetic resins, such as rosin, shellac, etc; Synthetic resins such as polyethylene, polypropylene, polyvinyl chloride, etc. Additives can improve the processing and use properties of plastics, including plasticizers, stabilizers, foaming agents, lubricants, fillers, colorants, etc. Coating compound production line www.handern com
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