MATERIALE PLASTICE https://revmaterialeplastice.ro https://doi.org/10.37358/Mat.Plast.1964 Mater. Plast., 58 (3), 2021, 41-50 41 https://doi.org/10.37358/MP.21.3.5502 Organic Coatings with Low IR Emission CRISTIANA EPURE 1 , VIOREL TIGANESCU 2 , TEODORA ZECHERU 1,3 , GABRIEL EPURE 1 , OVIDIU IORGA 1 *, ANDREI SCHIOPU 1 , MIHAIL MUNTEANU 1 , ALEXANDRU MARIN 1 , RALUCA GINGHINA 1 , DANIEL TURCANU 4 , CORNEL TODIRICA 3,4 1 Scientific Research Center for CBRN Defense and Ecology, 225 Sos. Oltenitei, 041309, Bucharest, Romania 2 Military Equipment and Technologies Research Agency, 16 Aeroportului Str., 077025, Clinceni, Romania 3 General Directorate for Armaments, 9-11 Drumul Taberei, 061418, Bucharest, Romania 4 Center for Test-Evaluation and Scientific Research for Armaments, 16 Aeroportului Str., 077025, Clinceni, Romania Abstract: A series of methods were employed to assess the performances of advanced coating materials based on components that can modify the spectral parameters of the surfaces on which these materials are applied in order to obtain passive military camouflage. Powder materials with high infrared (IR) reflectance were used to obtain this type of coatings, which also ingrain in their structure a significant volume of air that allow limitation of the radiative heat transfer of the coated source. The components were embedded in a polyurethane matrix, which facilitated the coating process on different surfaces. The bicomponent polyurethane-based binder used within the different composition tested is transparent to incident IR radiation, has no organic solvents, is highly flexible and possesses remarkable physical, chemical and mechanical properties: high surface adhesion, high flexibility and resistance against a number of chemical agents and external factors with destructive effect. The efficiency of these composite materials was further demonstrated by analyzing the thermal images of different objects. Keywords: passive camouflage, glass microspheres, aerogel, polyurethane 1. Introduction Polymer coatings characterized by complete or selective infrared (IR) reflectivity are employed in many research and industrial fields. E.g., paint or other architectural coatings are used to reflect the incident solar radiation or the heat radiation from inside, therefore obtaining thermal isolations that reduce energetic cost. Similarly, camouflage coatings reflect the IR radiation in the surrounding medium, thus delaying or preventing targeting and identification of strategic objectives. Military vehicles which are in operation can generate IR radiation from sources such as engines and exhaust plumes. The IR sensors of the thermal camera are capable of detecting the radiation with the wavelength between 700- 1350 nm (near IR - NIR), 3-5 μm and 8-14 μm (thermal IR - TIR). Thermal imaging cameras measure the relative temperature between the source of radiation and the surrounding environment, identifying the object by its heat or IR signature (the object emitting the radiation has a different color versus the surrounding environment). Thermal imaging cameras can detect objects by their emissivity, a parameter that characterizes the surface of the object. The emissivity of a material represents the efficiency with which the object radiates energy as thermal radiation and is the ratio of radiance from a surface sample to that of a black body surface at the same temperature; the value obtained is between 0 and 1, and the emissivity of the black body is considered equal to 1. Thus, by reducing the emissivity of a surface, the thermal signature of the object is reduced efficiently. Moreover, it was demonstrated that a surface with an emissivity between 0.4-0.6 can produce an efficient camouflage [1]. In order to reduce the emissivity, the surface can be coated with a film forming material with solid particles that present a high IR reflectivity, a property which is directly influenced by the geometry, the powder materials particles dimensions and their concentration [2-4]. The binder must protect the particles against external aggressive factors during the entire period the object is coated and also must have a low absorbance, thus allowing the incident radiation to intersect with the solid particles [5]. *email: iorga_ovidiu@yahoo.com