Polyurethane-based bionic material simulating the Vis-NIR spectrum and thermal infrared properties of vegetation

Poor stability, the toxicity of the used colorants and complex structure are the main problems for the current spectral simulation materials for vegetation. In this paper, a lightweight (0.052 g cm^-3) and environmentally friendly bionic porous spectrum simulation material (BPSSM) was developed to simulate the Vis-NIR spectra of natural leaves. The porous structure of BPSSM was used to simulate the mesophyll tissue, which endows the BPSSM with a near-infrared plateau. Moreover, the relationship between pore structure (size, open porosity and volume density) and near-infrared plateau in the spectrum was also studied. The chlorophyll of leaves was simulated by vat dyes or organic pigments, and the green apex and red edge characteristics in the visible region were further adjusted by the chlorophyllin sodium copper salt. The water absorption of BPSSM with 100-120% water contents are consistent with the natural leaves spectral curve channel. Finally, the spectral correlation coefficients (r _m) between BPSSM and different natural leaves are up to 0.984, suggesting that the BPSSM is universally applicable for the simulation of different leaves. Interestingly, the average radiant temperature difference between BPSSM and natural leaves is 0.25 °C within 24 hours, indicating it has similar thermal infrared properties to natural leaves. Moreover, the BPSSM can be combined with textiles to obtain a composite fabric, and its breaking strength and photostability were explored.