Novel Recycling, Defibrillation, and Delignification Methods for Isolating α-Cellulose from Different Lignocellulosic Precursors for the Eco-Friendly Fiber Industry

Abstract

Alpha-cellulose, a unique, natural, and essential polymer for the fiber industry, was isolated in an ecofriendly manner using eleven novel systems comprising recycling, defibrillation, and delignification of prosenchyma cells (vessels and fibers) of ten lignocellulosic resources. Seven hardwood species were selected, namely Conocorpus erectus, Leucaena leucocephala, Simmondsia chinensis, Azadirachta indica, Moringa perigrina, Calotropis procera, and Ceiba pentandra. Moreover, three recycled cellulosic wastes were chosen due to their high levels of accumulation annually in the fibrous wastes of Saudi Arabia, namely recycled writing papers (RWPs), recycled newspapers (RNPs), and recycled cardboard (RC). Each of the parent samples and the resultant alpha-cellulose was characterized physically, chemically, and anatomically. The properties examined differed significantly among the ten resources studied, and their mean values lies within the cited ranges. Among the seven tree species, L. leucocephala was the best cellulosic precursor due to its higher fiber yield (55.46%) and holocellulose content (70.82%) with the lowest content of Klasson lignin (18.86%). Moreover, RWP was the best α-cellulose precursor, exhibiting the highest holocellulose (87%) and the lowest lignin (2%) content. Despite the high content of ash and other additives accompanied with the three lignocellulosic wastes that were added upon fabrication to enhance their quality (10%, 11%, and 14.52% for RWP, RNP, and RC, respectively), they can be considered as an inexhaustible treasure source for cellulose production due to the ease and efficiency of discarding their ash minerals using the novel CaCO3-elimination process along with the other innovative techniques. Besides its main role for adjusting the pH of the delignification process, citric acid serves as an effective and environmentally friendly additive enhancing lignin breakdown while preserving cellulose integrity. Comparing the thermal behavior of the ten cellulosic resources, C. procera and C. pentandra exhibited the highest moisture content and void volume as well as having the lowest specific gravity, crystallinity index, and holocellulose content and were found to yield the highest mass loss during their thermal degradation based on thermogravimetric and differential thermal analysis in an inert atmosphere. However, the other resources used were found to yield lower mass losses. The obtained results indicate that using the innovative procedures of recycling, defibrillation, and delignification did not alter or distort either the yield or structure of the isolated α-cellulose. This is a clear indicator of their high efficiency for isolating cellulose from lignocellulosic precursors.