*2.3. NIR Spectral Acquisition*

The NIR spectrometer used in this study was a FOSS NIR Systems model 5000 (Foss NIRSystems Inc., Silver Spring, MD, USA). The NIR spectrometer was preheated for 30 min before the sample scanning, and the samples were only scanned when the spectra and noise tests were passed. The dried PCC powders were evenly spread in the sample round cups, respectively and compacted with the lid to ensure the sample powder was covered evenly. The spectra were scanned in the wavelength range of 400–1100 nm and 1100–2498 nm under diffuse reflection mode. Each sample was scanned three times. The scanned spectral curves were collected, and the data were processed using the Foss WinISI III calibration software throughout the whole process.
