A systematic study on the fabrication of transparent nanopaper based on controlled cellulose nanostructure from oil palm empty fruit bunch

Cellulose nanopaper (CNP) is a new potential candidate for flexible biopolymer substrate made of nanocellulose (NC). We systematically studied the effect of NC production from oil palm empty fruit bunch using the different types of acid hydrolysis based on sulphuric acid (NCs) as well as phosphoric acid (NCp) at varied temperatures regarding their morphology and crystallinity on the final properties of CNP. Both CNP from NCs (CNPs) and NCp (CNPp) exhibited higher optical transparency than conventional micropaper. In terms of mechanical properties, CNPs possessed an exceptional improvement of up to 200% compared to micropaper. CNPp specifically produced higher mechanical properties compared to CNPs. The stronger tensile strength of CNPp was attributed to a higher aspect ratio and thus a more flexible one compared to NCs. The greater transparency of CNPs than CNPp was postulated due to the formation of the densely packed order of intra-inter hydrogen bonds found in CNPs, which allowed more light to transmit through the film and reduce the light to scatter. In addition, the higher crystallinity with a smaller aspect ratio could also promote the higher transparency of CNPs to give the combination of influencing factors in explaining the level of transparency of CNP.