Endows Hard, Brittle Heat Shields with Malleability and High Char Yield
This polymer offers potent heat protection and retains its shape during use while having the ability to be molded during manufacturing, reprocessing, and recycling. Conventional heat-shielding materials consist of brittle polymers that burn down to an insulating layer of char under high temperatures. The hardness of such polymers is useful for shielding but complicates manufacturers’ ability to mold or recycle them. With the growing need for robust thermal shielding materials in aerospace, defense, and electronic applications, it is important to consider re-processability and ease of manufacturing.
Researchers at the University of Florida have developed a dynamic polymer with mutable inter-chain links that allow it to access a shapeable state during manufacture and a shielding state for heat protection. Furthermore, this material contains a remarkable amount of inorganic filler, so it can form a large, insulating char layer when burned.
Application
Heat-shielding material for extreme temperature applications that is straightforward to manufacture, mold, and recycle
Advantages
- Responds to increasing temperature by allowing the polymer’s long molecular chains to freely swap their inter-chain links so the material becomes shapeable
- Maintains its shape as it chars, extending the benefits of shapeability during processing and dimensional stability during use
- Incorporates a high weight percent of inorganic molecular cages into its chemical structure, generating char yields of up to 51 percent
- Exhibits only 5 percent mass loss at 300 °C, thereby remaining durable throughout high-temperature industrial processes
- Selectively degrades in the presence of acids, leading to efficient chemical recycling
Technology
Polymers are composed of long molecular chains that interact through a combination of physical and chemical forces, including covalent inter-chain linkages, such as crosslinks. These linkages restrict the mobility of chains relative to one another, which significantly influences the mechanical properties of the material. Crosslinking typically enhances rigidity and thermal stability, making such polymers suitable for applications like heat shielding. However, for processes such as reshaping or recycling, materials with greater malleability are desired.
This innovation introduces a dynamic polymer, classified as a vitrimer, combining the desirable traits of rigidity and malleability. Vitrimers feature dynamic covalent bonds capable of bond exchange reactions under specific conditions, enabling reprocessing or reshaping without compromising their structural integrity.
To further enhance its performance, this material is reinforced with polyhedral oligomeric silsesquioxane (POSS), a cage-like inorganic molecule. The incorporation of POSS improves thermal stability and contributes to the integrity and expansion of the insulating char layer formed during combustion. This char layer provides enhanced heat shielding and fire resistance. Researchers at UF successfully synthesized and characterized several dynamic polymer systems reinforced with POSS, demonstrating their potential for advanced applications requiring a combination of thermal stability, mechanical robustness, and recyclability.
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