As a new kind of blowing agent, thermoexpandable microspheres are widely used in industry nowadays. They are tiny, milky-white, spherical plastic particles with a diameter of 10-30 microns. Despite their size, these microspheres can expand significantly when heated. When came to a certain temperature, the outer shell softens, and the gas expands inside. Its volume can rapidly grow to dozens of times its own, thus achieving the effect of foaming without destroying the structure of the core and shell.
Here we will introduce its structure, expansion principle, and applications (brief) in detail.
Construction
Thermoexpandable microspheres are spherical plastic particles with a core-shell structure. They consist of thermoplastic acrylic polymer outer shells and alkane gas inner cores. Usually 10-30 microns in diameter, the outer shell has a thickness of 2-15 microns, which is flexible to withstand high pressures and ensure that the blowing agent does not rupture when expanded. When heated to a specific temperature, the shell softens while the liquid inside the particles vaporizes and expands, increasing the volume of the microspheres tens of times.
Expansion principle
The working principle of thermoexpandable microspheres is based on the thermal expansion effect. When the temperature is above the glass transition temperature(Tg), the outer shell begins to soften. As the temperature continues to rise, the low-boiling liquid begins to vaporize. And the resulting gas increases the pressure inside, which causes the shell to expand. Ultimately, the volume of the microspheres can expand to 20-50 times their original volume in a short period.
After foaming, the outer shell does not separate and remains completely sealed. Moreover, because of their high resilience, they can return to their original volume after the pressure is released.
This process has two characteristics:
Reversibility
Under certain conditions, the expansion is reversible, which means that it can return to its original volume after cooling.
Controllability
By adjusting the nature of the shell and internal core, we can precisely control the expansion temperature and multiplicity to suit different production needs.
Application(brief)
Thermoexpandable microspheres are simple to use. You just add it to the formula and mix well, no need to adjust the original process. The amount of addition is generally 1-3% depending on the industry and the effect achieved.
They are widely used in many fields:
Lightweight materials
In plastics, rubber, and coatings, expandable microsphere can significantly reduce the density of the material thus the weight of the product. For example, in the automotive industry, lightweight materials can help improve fuel efficiency.
Thermal and sound insulation
Microsphere expansion agent can be used in building materials, home appliances, and other fields to provide thermal and sound insulation.
Foaming agents
Like blowing agent AC/ADC, microsphere expansion agent can be used to generate foam materials with uniform structure and low density. These materials are commonly used in the packaging, construction, and furniture fields.
Printing & Coatings
In paints and inks, thermoexpandable microspheres can add thickness and texture to coatings while reducing its weight, which has led to a wide range of applications for printing effects and wall coatings.
Overall, the application of expandable microsphere in the elastomer industry is mainly lightweight materials. The injection molding process is relatively simple, while the extrusion process requires more optimizations.
Conclusion
The applications of thermoexpandable microspheres are still expanding with the advancement of our technology. In the future, researchers will further enhance the performance and application value of them. At the same time, with a deeper understanding of the expansion principle, the potential of microspheres for applications in biomedical, electronic materials, and other high-tech fields will gradually emerge.