Combining Low-Emissivity Thin Coating and 3D-Printed Original Designs for Superior Fire-Protective Performance.

Three-dimensional (3D) printing is a very flexible process to design various objects of original shapes. Previous works highlighted the preparation of new multimaterials composed of an original sandwich structure made of the ethylene vinyl acetate copolymer containing 30 wt % of aluminum trihydroxide in which a hydrogel phase made of agar and vermiculite was incorporated. This original material revealed an extremely low heat release rate (HRR) (with a reduction of 86 and 64% with regard to the peak of the HRR and total heat release, respectively, when compared to the same sample without hydrogel filling) during its heat exposure at 50 kW/m2 according to the mass loss cone calorimetry test. However, the time to ignition (TTI) of this material was not improved. This work consequently focuses on delaying the time to ignition of this hydrogel sandwich 3D-printed multimaterial. Solution consists in depositing by pulsed DC magnetron sputtering a low-emissivity thin coating on the exposed skin surface. This coating reflects most of the infrared rays responsible for heat absorption and thus delays the ignition of the underlying material. The thermal resistance performances of this coated sandwich 3D-printed multimaterial were evaluated, and a mechanism of action was proposed to explain the dramatic enhancement of the properties.

Extreme Heat Shielding of Clay/Chitosan Nanobrick Wall on Flexible Foam.

Flexible polyurethane foam (PUF) is widely used in bedding, transportation, and furniture, despite being highly flammable. In an effort to decrease the flammability of the polymer, an environmentally friendly flame retardant coating was deposited on polyurethane foam (PUF) via layer-by-layer assembly. Treated foam was subjected to three different fire scenarios, 10 s torch test, cone calorimetry, and a 900 s burn-through test, to evaluate the thermal shielding behavior of an eight bilayer chitosan/vermiculite clay nanocoating. In each fire scenario, the nanocoating acts as a thermal shield from the flames by successfully protecting the backside of the PUF, whereas the side directly exposed to the flame results in a hollowed nanocoating that maintains the complex three-dimensional porous structure of the foam. Cone calorimetry reveals that the coating reduces the peak heat release rate and total smoke release by 53 and 63%, respectively, whereas a temperature gradient greater than 200 °C is observed across a 2.5 cm thick coated foam sample during the rigorous burn-through fire test. The thermal shielding behavior of this polymer/clay nanocoating makes this system very attractive in improving the fire safety of polyurethane foam used for insulating applications.