Valorising wood ash as an effective green alternative pulping agent for achieving a high yield of banana micro-lignocellulose fibres of enhanced crystallinity

This study aims to explore the use of wood ash, a common waste, as an alternative and eco-friendly pulping agent. The first and most important singularity of the study is that wood ash solution, though mild in nature, has proven to be an effective pulping agent (in comparison with the common pulping solution, sodium hydroxide): comparable lignin (45%) and hemicellulose (50%) removal, high crystallinity (72–77%) and high pulp yield (70%) were obtained. Another particularity of this study is that the reported advanced aspects of pulped banana fibres, notably the chemical functionality, crystallinity and crystallite size have been correlated with the chemical composition of the wood ash used: calcium pectinate was formed on the pulped fibre surface. It apparently played a role in enhancing the fibre crystallinity. Moreover, another specialness of this study is that non-conventional factors, which would have significant bearing during industrial scale processing, such as liquor ratio, fibre input size and duration have been investigated—the latter has shown that to attain maximum delignification, small fibre input size at a high liquor ratio of 40 for an extended period of 2 h are necessary. Finally, the pulped banana fibres (which were intended to be used for membrane fabrication for use in water purification system) have depicted their applicability in the fabrication of ultrafiltration membranes by virtue of their aspect ratio, semi-hydrophilicity (due to presence of residual lignin) and projected high mechanical strength (due to high crystallinity and low crystallite size). Graphical Abstract: Graphical abstract showing outcomes when pulping with wood ash solution.