Category of foamed plastics
DATE：2022/5/4 9:02:49 / READ： / SOURCE：This station
Category of foamed plastics
Foamed plastic is a new type of material, which takes plastic as the basic component and contains a large number of bubbles. Therefore, foamed plastic can also be said to be a composite plastic with gas as the filler. There are many kinds of foamed plastics, but they all contain a large number of bubbles, so they have common characteristics, such as light weight, material saving, low thermal conductivity, good heat insulation performance, impact load absorption, excellent cushioning performance, sound insulation performance, high specific strength and other valuable properties. It has a wide range of uses and has developed rapidly in recent decades. Especially in some industrialized countries, the foamed plastic industry has become an important chemical industry sector. Casting film production line www.handern.com comThere are many kinds of foamed plastics, and their classification methods are also diverse. According to different foaming times, foamed plastics can be divided into high foaming and low foaming; According to the hardness and softness of the foam texture, it can be divided into rigid foam, semi-rigid foam and soft foam; According to the structure of cell, it can be divided into open cell foams and closed cell foams; According to the structure of the foam, it can be divided into free foaming plastic and structural foaming plastic. Casting film production line www.handern.com com
High foaming plastic refers to the foamed plastic with large foaming multiple, generally taking 4 times as the dividing line. The foamed plastic with more than 4 times is called high foaming plastic, and the foamed plastic with less than 4 times is called low foaming plastic. The commonly used foamed plastic mattresses, cushions, packaging linings and packaging films are mostly high foaming plastic; Foamed boards, pipes, profiles and other foamed plastics with plastic instead of wood are mostly low foaming. The foaming multiple of foamed plastics is equal to the ratio of the density of non foaming plastics to the density of the same kind of foamed plastics. The hard and soft texture of foamed plastics is a manifestation of physical properties of plastics. Skochdopole and rubeno classified foamed plastics into three categories: hard, semi-hard and soft according to their physical properties. At room temperature, the polymer in the foam is in the crystalline state, or its glass transition temperature is higher than that at room temperature. This kind of foam has a hard texture at room temperature, so it is called hard foam; The other kind of foamed plastics, the melting point of polymer crystal is lower than normal temperature, or the glass transition temperature of amorphous polymer is lower than normal temperature. This kind of foamed plastics is soft at normal temperature, so it is called soft foamed plastics; Between these two categories is called semi-rigid foam. According to this classification, phenolic foam, epoxy foam, polystyrene foam, polycarbonate foam, rigid PVC foam and most polyolefin foam belong to rigid foam; The foams of rubber, elastic polyurethane, soft PVC and some polyolefins are called soft foams. The opening and closing of the foam cell has a great influence on the mechanical properties of the foam, and is an important structural parameter of the foam. Open cell foamed plastic is shown in Figure 1-1 (1). The bubbles in the material bubble body are broken, and the bubbles are connected with each other. The gas phase and plastic in the bubble body are continuous phases. The fluid can pass through the bubble body. The difficulty of passing through is related to the performance and opening rate of the polymer material. Closed cell foamed plastic is shown in Figure 1-1 (2). The pores in the plastic foam are closed and dispersed in the foam in isolation. Only the plastic matrix is a continuous phase. In the actual liquid, the bubble is not pure open or pure closed, but with some closed holes in the opening or some openings in the closed hole. The distribution of cell in the foam also has a great influence on the properties of the foam. As shown in Figure 1-1 (3) (4), the foam body of structural foamed plastic has a non foamed or less foamed skin and a foamed core. The main difference between it and free foamed plastic is the skin, and the surface of free foamed plastic is also foamed Casting film production line www.handern.com com
After shaping, the skin layer can be flat, but it can not be as smooth as the structural foam. It is difficult to form structural foamed plastics. In order to obtain a smooth non foaming skin, there are two ways: ① the skin and the core use the same raw material formula, but when foaming, make the skin and the core use different raw material formulas under different temperature and pressure conditions. The plastic used for the skin can be the same as the core but does not contain foaming agent, or different plastics can be used without foaming agent. In order to improve the physical and mechanical properties of foamed plastics, fiber reinforcement can be added, which is difficult to form, and hollow balls can also be added. The latter kind is generally used in casting foaming and forming. There are many kinds of special foamed plastics in the construction industry. The above is only a brief introduction, and the common characteristics of foamed plastics are analyzed below, which can also be said to be the valuable properties of foamed plastics.
1. Light quality and material saving
Some of the foamed plastics are replaced by gas, so it is lighter than the non foamed plastics, several times, ten times, ten times, nearly a hundred times. It not only reduces the weight, but also saves the amount of plastic. The density of foamed plastics can be calculated by the following formula.
2. Low thermal conductivity and good thermal insulation performance
The thermal conductivity of foamed plastics is much lower than that of non foamed plastics, because the thermal conductivity of gas is nearly an order of magnitude lower than that of plastics. Casting film production line www.handern.com com
3. it has the ability to absorb impact load and has excellent cushioning performance. When the overall heat transfer foam is subjected to external impact load, the gas in the bubble hole is stagnated and compressed, so that the external action energy is consumed and dissipated. The bubble can gradually terminate the radiation heat transfer of the external gas phase and the conduction heat transfer shock load of the solid phase with a small negative acceleration. Therefore, foamed plastics have excellent cushioning capacity. Foam density
4. good sound insulation performance the heat transfer capacity of foamed plastics and the sound insulation effect of foamed plastics are mainly through the relationship between the foam density
There are two ways. One is to absorb the energy of sound wave so that it cannot be reflected or transmitted. Sound wave is a longitudinal wave, which is very similar to the shock wave. When the sound wave reaches the bubble wall, the impact energy of the bubble will consume and dissipate the energy through the compression and stagnation of the gas in the bubble, so as to achieve the purpose of absorbing sound energy. The other is to eliminate resonance and reduce noise. The volume of the foam is large, and its specific rigidity is also large. By increasing the rigidity of the foam, it can eliminate or reduce the resonance and noise caused by the impact of sound waves. Due to the above two effects, the foam has good sound insulation ability.
5. the mechanical strength of foamed plastics with high specific strength decreases with the increase of foaming multiple
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