The laws of physics. Dissolve low boiling hydrocarbon or halogenated hydrocarbon into plastic. When heated, the plastic will soften, and the dissolved liquid will volatilize, expand and bubble. For example, polystyrene foam can be prepared by dissolving pentane in monomer during suspension polymerization of styrene, or by treating polystyrene resin which has been polymerized into beads with pentane under heating and pressure.

Then put these beads into hot water and steam for pre-foaming, and then put them into the mold to introduce steam, so that the pre-foamed particles expand for the second time and merge with each other, and after cooling, the product with the same shape as the mold cavity can be obtained.

Mechanical method. Strong stirring is carried out to introduce a large amount of air or other gases into the liquid plastic. This method is mainly used to produce urea-formaldehyde foam in industry, which can be used as thermal insulation material, and can also be used as scenery material in film and television dramas, such as artificial snowflakes.

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Characteristics of foamed plastics

Foam plastic is made of resin as the main raw material, and there are countless micropores inside. Light weight, heat insulation, sound absorption, earthquake resistance and corrosion resistance. There are soft and hard points. Widely used as heat insulation, sound insulation, packaging materials and vehicle and boat shells.

Compared with pure plastic, foamed plastic has low density, light weight and high specific strength, and its strength increases with the increase of density. It has the ability to absorb impact load, excellent cushioning and shock absorption performance, sound insulation and sound absorption performance, low thermal conductivity, good thermal insulation performance, excellent electrical insulation performance, corrosion resistance and mildew resistance. Flexible foam has excellent elasticity and other properties.