What are general properties of plastics
Compared to ceramic or metallic materials, plastics are characterized by a number of unusual properties:
Density and strength
The density of most plastics is between 800 and 2200 kg / m3. This makes them considerably lighter than metals or ceramic materials.
In terms of mechanical properties, plastics are often inferior to other classes of materials. Their strength and rigidity usually do not match that of metals or ceramics. Due to the low density, however, this can be partially compensated for with structural means (higher wall thicknesses) or the use of fiber-reinforced plastics. One example is the use of Kevlar in aircraft wings.
Although the strengths are comparatively low, plastic parts break less easily than ceramics or glass, for example. They mostly have good toughness. Therefore, everyday objects for children and toys are often made of plastic.
In contrast to metals, plastics are resistant to inorganic media due to their organic nature. This includes mineral acids, alkalis and aqueous salt solutions. For this reason, plastic materials are preferred for the production of easy-care household and electrical appliances, vehicle equipment, toys, etc.
In contrast to metals, however, they are sensitive to organic solvents such as alcohol, acetone and petrol. Nevertheless, it was also possible to develop durable plastics in this area. One example is the polyethylene car tank in the VW Polo. It is extremely resistant to corrosion and yet insensitive to petrol.
Low processing temperatures
The usual processing temperatures for plastics are in the range from 250 to 300 ° C. While metals have to be cast at high temperatures and there are restrictions with regard to the casting molds, thermoplastics can also be used to manufacture more complex molded parts with comparatively little effort. At the same time, additional additives such as color pigments or fibers can be incorporated into the material in one processing step, which would decompose at the high temperatures of metal casting or sintering of ceramics.
The thermal conductivity of plastics is significantly lower than that of metals. Therefore, many plastics, especially foams, are used as insulating materials.
The electrical conductivity of plastics is 15 orders of magnitude lower than that of metals, so many plastics are used to insulate electrical lines and cables.
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