Modified structure of nanocellulose isolated from rice stubble and cassava bagasse for natural rubber composites fabrication

In this study, we explored the use of nanocellulose as an environmentally friendly reinforcing filler in natural rubber composites. The nanocellulose was derived from agricultural waste (rice stubble) and industrial waste (cassava bagasse), with the extraction process involving an initial alkali treatment followed by bleaching. It was found that the optimal conditions for extracting cellulose from rice stubble and cassava bagasse involved alkali treatment where rice stubble was first soaked in a NaOH solution to induce swelling, followed by treatment with a 10% (w/v) NaOH solution at 80 C for 2 hours. For cassava bagasse, alkali was treated using a 7% (w/v) NaOH solution at 80 C for 2 hours. The optimal bleaching conditions for both agricultural waste raw material utilized a mixed solution of NaOH and H202, which effectively yielded purified cellulose. Fourier transform infrared (FT-IR) spectroscopy confirmed the removal of lignin and hemicellulose. The cellulose yields were 25% for rice stubble and 30% for cassava bagasse, respectively. Nanocellulose was prepared using hydrolysis with a mixture of H2O2 and H2SO4, followed by mechanical force. The nanocellulose fibers extracted from cellulose obtained from rice stubble and cassava bagasse exhibited diameters ranging from 66 - 93 nm and 52 - 79 nm, with corresponding yields of 60% and 63%, respectively. Subsequently, the structure of the obtained nanocellulose was modified using methacrylic anhydride and 3-aminopropyl-triethoxysilane (APTES) to prepare natural rubber composites. It was found that mechanical properties of natural rubber composite was significantly increased with increasing cassava bagasse (up to 2.5 phr) as a filler. However, when 5 phr of nanocellulose was added, the mechanical properties was decreased. Additionally, nanocellulose that was structurally modified using methacrylic anhydride and 3- aminopropyl-triethoxysilane (APTES) showed notable improvements in mechanical properties compared to unmodified nanocellulose. This observation was supported by morphological studies, showing superior dispersion of the modified nanocellulose particles within the composites. The reduced hydrophilicity of the modified nanocellulose facilitated better dispersion in the hydrophobic natural rubber. Furthermore, the modification of the structure with methacrylic anhydride introduces double bonds into the nanocellulose, facilitating an efficient polymerization reaction between the nanocellulose and natural rubber. This enhancement leads to improved mechanical properties of the natural rubber composites.