The detailed procedure for preparing the CNF
suspension has been described in our previous publication [26].
Colloidal SiO2 nanoparticles (average particle size w 100 nm, Nissan)
dispersed in water were then added into the CNF suspension,
wherein the SiO2 content was controlled at 0, 1, 5, and 10 wt.%
relative to the CNF weights