## 3 Results and Discussion
### Interactions between the CF/CAF and Glycerol/Glycerol Triacetate  
Both CF and CAF have high affinity with typical constituents in the mainstream of tobacco smoke. To demonstrate this point, DFT analysis was conducted. Structural models of SiO\({}_{2}\), cellulose, and cellulose acetate, mimicking CFP, CF, and CAF, respectively, were constructed. Glycerol and glycerol triacetate, major additives in cigarette filters, were selected as model substances to evaluate the affinity between the mainstream components and the filter pad. The binding energies of glycerol and glycerol triacetate on SiO\({}_{2}\) were calculated to be 0.234 and 0.241 eV, respectively (Figure 3). These positive binding energies suggest that adsorption of glycerol and glycerol triacetate on SiO\({}_{2}\) is thermodynamically unfavorable. In contrast, the binding energies of glycerol and glycerol triacetate on both CAF and CF were negative, suggesting that CAF and CF have higher affinity with mainstream components than SiO\({}_{2}\). Such a high affinity is beneficial for the trapping of these components from the smoke mainstream. The binding of glycerol and glycerol triacetate with CFP, CF, and CAF was further characterized in FTIR experiments (Figure 4). The FTIR spectra of glycerol and glycerol triacetate were firstly collected and used as a reference. The FTIR spectra of glycerol showed a characteristic peak for the stretching vibration of OH- bond (3290 cm\({}^{-1}\)) [23]. Characteristic peaks assigned to stretching vibrations of -C=O (1740 cm\({}^{-1}\)) and -C-O- (1040 cm\({}^{-1}\)) were identified from the spectra of glycerol triacetate [24]. The FTIR spectra of CFP, CF and CAF was also collected. For CFP, a typical band associated with Si-O-Si asymmetric stretching vibration (1030 cm\({}^{-1}\)) was observed in the FTIR spectra [25]. The FTIR spectra of CF showed a peak for the in-plane wagging vibration of -OH. In addition, the peak assigned to the stretching vibration of -C=O (1740 cm\({}^{-1}\)) was present in the spectra. This peak could be originated from the protein and pectin in CF [26].  
Figure 1: XRD patterns of Cambridge filter pad (CFP), cotton fiber layer (CF), and cellulose acetate fiber interlayer (CAF).  
Figure 2: SEM images of (**A**) Cambridge filter pad (CFP), (**B**) top cotton fiber layer (CF), (**C**) cellulose acetate fiber interlayer (CAF), and (**D**) bottom CF layer.  
The peak for the stretching vibration of -C=O was also observed in the spectra of CAF because CAF is rich in acetyl groups [27]. The bands corresponding to the stretching vibration of the OH- bond (3290 cm\({}^{-1}\)), C-H stretching vibration (2930 cm\({}^{-1}\), 2870 cm\({}^{-1}\)), CH\({}_{2}\) symmetric bending vibration (1430 cm\({}^{-1}\)), C-O stretching of the secondary alcohol (1105 cm\({}^{-1}\)), and C-O stretching of the primary alcohol (1040 cm\({}^{-1}\)) were observed in the FTIR spectra of glycerol-loaded samples (glycerin@CFP, glycerin@CF, and glycerin@CAF) [23]. Similarly, bands from glycerol triacetate also occurred in the FTIR spectra of glycerol triacetate@CFP, glycerol triacetate@CF, and glycerol triacetate@CAF (2950 cm\({}^{-1}\) for CH\({}_{2}\) asymmetrical stretching vibration, 1740 cm\({}^{-1}\) for C=O stretching vibration, 1370, 1220 cm\({}^{-1}\) C-H deformation vibrations, and 1040 cm\({}^{-1}\) for C-O stretching vibration) [24]. These results show that CFP, CF, and CAF could adsorb glycerol and glycerol triacetate and be used as filters for these substances.