Small Molecule Additives in Multilayer Polymer-Clay Thin Films for Improved Heat Shielding of Steel

In an effort to improve the heat shielding ability of multilayer polymer-clay films, the influence of various small molecule additives was studied. Tris(hydroxymethyl)aminomethane (THAM), pentaerythritol (PER), and ammonium pentaborate (PB) are each utilized in flame retardant applications for the benefits they provide in reducing the propagation of fire. In the present study, these additives combined with polyethylenimine (PEI) and vermiculite (VMT) clay and the resulting growth of the coatings and the thermal resistivity were measured. THAM and PB salts contribute most to the overall growth of the layer-by-layer assembled films, generating an increase in film thickness of 50% or more, while PER has a greater impact on heat shielding. A 14-bilayer (THAM + PER + PEI)/VMT coating (~25 µm thick) on steel can achieve a temperature differential of over 125 °C due to a layering effect that occurs within the architecture of the macroscopic insulation bubble and disordered char. This improved thermal resistivity across a relatively thin film generates a heat shield that can be applied in novel applications such as a single-use protective barrier for aerospace components.