Fig. 1. Schematic of THz-TDS experimental setup

Fig. 2. Terahertz spectra of HDPE, PP and PVC with different particle sizes. (a) Terahertz time-domain spectra of HDPE, PP, and PVC with particle size of less than 74 μm with corresponding frequency spectra shown in inset; (b) frequency-absorption coefficient correlation curves of HDPE with different particle sizes; (c) frequency-absorption coefficient correlation curves of PP with different particle sizes; (d) frequency-absorption coefficient correlation curves of PVC with different grain sizes with partial enlargement shown in inset

Fig. 3. Terahertz spectra of PVC-PP for different mass ratios. (a) Frequency-absorption coefficient spectra; (b) frequency-refractive index spectra; (c) effects of mass fraction of PVC on refractive index and absorption coefficient measured at 1.3 THz

Fig. 4. Frequency-absorption coefficient and frequency-refractive index correlation curves of HDPE, PP, and PVC mixed with different fillers

Fig. 5. Optical parameters of plastic-filler mixtures versus filler concentration at 1.3 THz. (a) Absorption coefficient of mixture versus CaCO₃ concentration; (b) refractive index of mixture versus CaCO₃ concentration; (c) absorption coefficient of mixture versus Kaolin concentration; (d) refractive index of mixture versus Kaolin concentration

Fig. 6. Frequency-absorption coefficient correlation curves of HDPE, PP, and PVC after adsorption of MO solutions for 24 h as well as those before and after oscillation of MO solutions for 24 h

Fig. 7. Terahertz spectra of original (0 h), final (24 h) MO solution and MO solution after adsorption by PVC for different time. (a) Time-domain spectra with corresponding frequency spectra shown in inset; (b) frequency-absorption coefficient spectra with time-absorption coefficient curves at 0.6 THz and 1.2 THz shown in inset

Fig. 8. Terahertz spectra of MO solutions after adsorption of 3 h by PVC with particle sizes of less than 74 μm and 2.6 μm. (a) Time-domain spectra; (b) frequency-absorption coefficient spectra