Figure 3 shows the same scale as that of Figure 2, in order to compare the effect of surface modification by solvent exchange method in CP19 up to CP22, when the inorganic particle size is just 12 nm of ASi. Firstly, ASi shows a weak band in 978 cm−1, such band is absent in NSi. A study of fly ash activation reports an intense band in 989 cm−1 related to Si–O asymmetric stretching vibration, which explains that the lower wavenumber of this band was associated with a lower degree of crosslinking of the amorphous phase of silica . The same weak band appears in the composites between 980 and 983 cm−1. The CP20 spectrum looks much more like ASi than CP19 but CP21 and CP22 spectra look much more like the cellulose matrix or like CP19, indicating that the pure cellulose composites accept the inorganic particles up to 43 wt %, while the cellulose matrix modified by solvent-exchange method, AG20, disperses up to 50 wt % even retaining the cellulose characteristic vibration bands in CP22. Such behavior has been observed in previous works of this working group . The high amounts of inorganic nanoparticles and also the particle size dispersed into the AG20 matrix will affect also the thermal stability of the composites.