## 3 Results and Discussion  
### Characterization of Fillers  
The results show that the size of the non-activated Per and Verm fillers (Figure 1b,d) was up to 1.25 mm. The highest percentage of particles was observed at 0.2 mm. Per filler consisted of snowflake-like particles (Figure 1a). In contrast, Verm particles were larger in size and non-homogeneous in shape (Figure 1c). In addition, Figure 1f,h demonstrate Dex-activated Per and Verm fillers (PerDex and VermDex, respectively). It can be seen that the fillers' particle size distribution ranged up to 0.63 mm, with the highest accumulation of particles observed on the 0.1 mm sized sieve. The smaller particles in both PerDex and VermDex fillers were obtained through the ball-milling process, as confirmed by [PERSON] et al. [48], which alters their surface, size, and chemical reactivity. PerDex filler also  
FTIR analysis was employed to assess the presence of functional groups in the fillers before and after activation. Figure 2 presents FTIR spectra of the Per and PerDex, Verm, and VermDex fillers. For the Per filler (Figure 2a), the band located in the 1669-1577 cm\({}^{-1}\) range, with a peak at 1629 cm\({}^{-1}\), is assigned to the vibration of hydroxyl groups. A large band observed at 1038 cm\({}^{-1}\), within the range of 1280-864 cm\({}^{-1}\), corresponds to the stretching vibrations of Si-O-Si [49]. Further, the peak at 789 cm\({}^{-1}\) is assigned to the Si-O stretching vibration of Si-O-Al [50].  
After the activation of the Per with Dex, a new band is noticed at the range of 3359-3082 cm\({}^{-1}\) with a peak intensity at 3349 cm\({}^{-1}\), which is associated with the presence of water molecules in the material structure, while a less pronounced band at 2918 cm\({}^{-1}\) due to the C-H stretching of the -CH\({}_{2}\) group in the case of Dex absorbed Per. This indicates that hydroxyl groups of Dex only partially react with silanols in Per filler.  
For Verm filler (Figure 2b), the broad band between 3726 cm\({}^{-1}\) and 3016 cm\({}^{-1}\) is related to interlayer water molecules' \(-\)OH stretching vibration. The peak of 3416 cm\({}^{-1}\) is attributed to the silanol groups in Verm and VermDex [51] and \(-\)OH vibrations. The spectrum of Verm and VermDex exhibited a weak band at 1648 cm\({}^{-1}\), corresponding to Si-OH vibrations. In addition, a strong band in the range of 1210-827 cm\({}^{-1}\), with a peak at 981 cm\({}^{-1}\), is associated with the Si-O stretching vibration [52].  
Contrary to the case of Per and PerDex fillers, after activation with Dex, a hydroxyl stretching frequency, which should be visible at \(\sim\)2918 cm\({}^{-1}\) in VermDex filler, has no intensity, thus indicating that the \(-\)OH groups of Dex are fully reacted with the silanol groups of Verm. In this case, the formation of a Dex-O-Si-O-Dex linkage could be assumed. Similar observations were made in the study of [PERSON] et al. [53]. The authors researched the chitosan adsorption on vermiculite. However, they noticed only a partial reaction of chitosan with silanols in Verm filler.  
Figure 2: FTIR spectra of fillers: (**a**) Dex, Per, and PerDex (red circle indicate C-H stretching) and (**b**) Dex, Verm, and VermDex.  
The proposed Verm and Per particles activation with the Dex scheme is presented in Figure 3. The formation of O-H groups from Dex on the surface of the analyzed fillers will contribute to the reaction with N-C-O groups from isocyanate.  
As hydroxyl groups are important for the synthesis of PUR foam, Dex-activated fillers will react with N-C-O groups with isocyanate, thus assumably improving the interfacial adhesion between VermDex, PerDex fillers, and the polymeric PUR foam composites matrix.