Comparative Preparation Method and Associated Cost of Lignin-Cellulose Nanocrystals

Lignin is a natural source of UV-shielding materials, though its recalcitrant and heterogeneous structure makes the extraction and purification processes complex. However, lignin's functionality can be directly utilised when it stays as native with cellulose and hemicellulose in plant biomass, rather than being separated. The fabrication process of this native lignin is sustainable, as it consumes less energy and chemicals compared to purified lignin; thus, it is an economic and more straightforward approach. In this study, the properties of native and purified lignin-cellulose nanocrystals (L-CNCs) sourced from hemp hurd waste were compared to explore the differences in their morphology, UV-shielding properties and chemical structure affected by their distinct fabrication process. These two kinds of L-CNCs were further added into polyvinyl alcohol (PVA) to evaluate their reinforcement characteristics. The resulting native L-CNCs/PVA film showed stronger UV-shielding ability than purified L-CNCs. Moreover, the native L-CNCs showed better compatibility with PVA, while the purified L-CNCs/PVA interfaces showed phase separation. The phase separation in purified L-CNCs/PVA films reduced the films' tensile strength and Young's modulus and increased the water vapour transmission. The laboratory-scale cost of native L-CNCs production (~AUD 80/kg) was only 10% of purified L-CNCs (~AUD 850/kg), resulting in a comparatively lower cost for preparing native L-CNCs/PVA composite films. Overall, this study shows that the proposed method of production and use of native L-CNCs can be an economic approach to deliver UV-shielding properties for potential applications, such as food packaging.