Bacterial cellulose composites loaded with SiO₂ nanoparticles: Dynamic-mechanical and thermal properties

The aim of this paper was to prepare composites of bacterial cellulose (BC) filled with silica (SiO₂) nanoparticles to evaluate the influence of the SiO₂ contents (3, 5 and 7wt%) on the thermo-mechanical properties of the composites. BC hydro-gel was immersed in an aqueous solution of silanol derived from tetraethoxysilane (TEOS), the silanol was then converted into SiO₂ in the BC matrix by pressing at 120°C and 2MPa. The BC/SiO₂ translucent sheets were examined by dynamic-mechanical analysis (DMA), thermo gravimetric analysis (TGA), and scanning electron microscopy (SEM). The temperature dependence of the storage modulus, loss modulus and tan delta was determined by DMA. In general, the results revealed that the increment of storage modulus and thermal stability increased concomitantly with the augmentation of SiO₂ content. Therefore, it could be concluded that the mechanical properties of the composites were improved by using high amounts of nano silica. This would be a high aspect ratio of BC capable of connecting the BC matrix and SiO₂, thereby enhancing a large contact surface and resulting in excellent coherence. A decrease of the storage modulus was consistent with increasing temperature, resulting from softening of the composites. The storage modulus of the composites increased in the order: BC/S7>BC/S5>BC/S3, while the loss modulus and tan delta decreased. On the other hand, the thermal stabilities of all BC/SiO₂ composites were remarkably enhanced as compared to the pristine BC. TGA curves showed that the temperature of decomposition of the pure BC gradually shifted from about 260°C to about 370°C as silica content increased. SEM observations illustrated that the nano-scale SiO₂ was embedded between the voids and nano-fibrils of the BC matrix. Overall, the results indicated that the successful synthesis and superior properties of BC/SiO₂ advocate its effectiveness for various applications.