Preparation and performance characterization of leaf-mimetic polyurethane/Al-ZnO composite coatings with low infrared emissivity and green peak characteristics

A high performance infrared and visible light compatible stealth coating was prepared by a simple method. • The leaf-mimetic PU/Al-ZnO composite coatings with yellow-green color and green peak characteristics. • The PU/Al-ZnO composite coating exhibits a prominent green peak at 544 nm, resembling that of green vegetation. • The PU/Al-ZnO composite coating exhibits excellent infrared stealth performance and mechanical properties. With the rapid development of various reconnaissance equipment targeting land-based equipment, traditional green camouflage coatings and low infrared emissivity camouflage coatings have become inadequate to meet practical needs. Developing green-based low infrared emissivity coatings with distinct green peak characteristics is an effective approach to address the aforementioned issues. In this study, using polyurethane resin as the matrix, yellow-blue polyurethane color paste as the colorant, flaky Al powder and zinc oxide (ZnO) as low emissivity functional fillers, a systematic regulation and optimization were carried out using the variable control method for the washing and drying duration of Al powder, the content of low emissivity fillers (Al powder + ZnO), the ratio of ZnO to Al powder, and the total amount of pigment and filler based on the comprehensive performance of the coating. The results show that after washing and drying the Al powder with ethanol for 3.5 h, the prepared coating exhibits a yellow-green appearance that matches green leaves. It has a characteristic reflection peak at 544 nm similar to that of green vegetation, and the coating has the lowest emissivity. Under the optimal washing and drying duration conditions for Al powder, the emissivity of the coating can be adjusted within the range of 0.738 to 0.807 by regulating the amount of low emissivity filler, while ensuring that the coating exhibits distinct yellow-green characteristics. When the amount of low emissivity filler is 16 wt% and the ratio of ZnO to Al powder is 6:4, the infrared emissivity of the coating reaches its lowest at 0.738, while maintaining distinct green peaks and yellow-green appearance characteristics. Finally, when the total amount of pigment and filler is adjusted to 40 wt%, the emissivity of the coating is the lowest, the yellow-green characteristics are prominent, and it has excellent mechanical properties.