Expandable microspheres shoes are thermoplastic hollow polymer microspheres composed of a thermoplastic polymer shell and a sealed liquid paraffin gas. The average diameter of these hollow polymer microspheres ranges from 10 to 50 µm, and their true density ranges from 1000 to 1300kg/m3. When heated, the gas pressure in the shell increases and the thermoplastic shell softens, which results in a significant increase in the volume of the expandable microspheres shoes. When cooled, the expanded shell of the expandable microspheres shoes hardens again and the volume will be fixed.
Expandable microspheres shoes have the following characteristics:
1. Expansiveness
The expansion process of expandable microspheres shoes is a delicate balance among the shell softening, air impermeability, external pressure and the increase of the gas pressure inside the microspheres. This balance is influenced by the polymer composition of the expandable microspheres shoes shell, the type of gas inside the expandable microspheres shoes, the chemicals the shell comes into contact with, external pressure, the type of expansion, the type of base materials and the heating rate.
2. Thermal stability
The stability of different types of expandable microspheres shoes is obviously different. Different types of expandable microspheres shoes have different thermo-mechanical properties and are suitable for different processes and applications.
3. The particle size
The physical expandable microspheres shoes are very small and the particle size before expansion is usually between 10-50 microns.
4. Solvent resistance
In practical applications, physical expandable microspheres shoes may come into contact with a variety of chemical solvents, and each kind of solvent has different effects on the expandable microspheres shoes, so specific analysis and test are required. The following conditions may occur: swelling, discoloration, foaming rate change, etc..
5. Elasticity
Most types of expandable microspheres shoes have good elasticity. The expanded microspheres tend to be compressed easily, and when the pressure is released, most of the expanded microspheres will return to their original volume. Because of the elasticity, expandable microspheres shoes are able to withstand multiple pressuring/pressure release without rupture.
6. Air impermeability
The polymer shell formulation of expandable microspheres shoes has been accurately designed and has relatively low permeability, which can effectively prevent the expandable microspheres shoes from leaking gas into the matrix. Gas leakage into the matrix can cause pinhole and density increase. Different types of expandable microspheres shoes have different air impermeability.
