Nano-silica and SiO2/CaCO3 nanocomposite prepared from semi-burned rice straw ash as modified papermaking fillers

Abstract Silica (SiO 2 ) nanoparticles and silica/calcium carbonate (SiO 2 /CaCO 3 ) core–shell nanocomposites were prepared by sol–gel technique as fillers for papermaking application. Semi-burned rice straw ash (SBRSA), as waste material, was used to prepare the targeted fillers. Preparation of SiO 2 nanoparticles and SiO 2 /CaCO 3 nanocomposites was carried out using Na 2 SiO 3 solution that was prepared from SBRSA and CaCO 3 nanoparticles of 30–70 nm. The targeted SiO 2 /CaCO 3 nanocomposites were prepared with different molar ratio of SiO 2 :CaCO 3 1:15, 1:10 and 1:5. The percentage of silica increased from 62.5% to 82.9% by thermal treatment of SBRSA at 800 °C for 2 h. The prepared SiO 2 nanoparticles and SiO 2 /CaCO 3 nanocomposites were characterized by using XRD, XRF, TEM, FT-IR and Zeta potential. The results indicate that a pure semi-crystalline SiO 2 nanoparticle and semi-crystalline shell of SiO 2 coated CaCO 3 core particles were produced. The work extended also to investigate the effect of the prepared fillers on physical, mechanical and optical properties of paper. Application of the prepared SiO 2 nanoparticles and SiO 2 /CaCO 3 nanocomposites improved the optical properties of paper (brightness, whiteness and opacity) but it slightly reduced the mechanical properties when compared to commercial precipitated CaCO 3 (PCC) filler. The results showed that the retention of SiO 2 nano-particles was highly increased. The retention of the prepared nanocomposites increased along with increasing of SiO 2 :CaCO 3 molar ratio.