Cellulose nanocrystals: from extraction to applications

Abstract

In this research the possibility of extracting nanocellulose from different sources, such as cotton, wastepaper and waste from agricultural production was studied. Particular attention has been paid to the characterization of the obtained products to establish the morphology, the type of polymorph and the degree of crystallinity of each sol. Some surface functionalizations of the nanocrystals were presented, with particular attention to the presence of the newly added functional groups. The ability of nanocellulose to act as a carrier for silver nanoparticles, whose biocidal activity against gram + and gram - bacteria, has been reported, have been also studied. Successively, the possibility to use nanocellulose in different fields, such as cultural heritage, environmental and building was investigated. Nanocellulose was used as coating for ligno-cellulosic materials, such as paper and painted canvas, with a promising consolidating ability. The possibility to not alter the substrate chromatically, before and after accelerated artificial ageing cycles, and the mechanical properties of the treated substrates have been also evaluated. These characteristics were compared with those relating to Aquazol 500, a commercial product still used in restoration. To develop the research in medical and environmental fields, two different matrices based on nanocellulose were proposed. For the first application, 3D printed hydrogel scaffolds made of nanocellulose and alginate, mixed with silver nanoparticles to promote antimicrobial action were studied. For the second type of application, three-dimensional hydrogel scaffolds, made of carboxymethylcellulose mixed with nanocellulose, obtained by freeze-thaw method, for the removal of heavy metals in water were presented. Finally, the research activity was focused on the study of innovative eco-compatible geopolymer mortars and plasters. The present research mainly focuses on the possibility of replacing the liquid alkaline activator. For the development of binders, mortars and plasters, parameters such as workability (consistency, plasticity and cohesion) must be considered. One-part binders were investigated: the powder precursors were varied to evaluate the product with best performance. After choosing the binder, mortars and plasters were developed. Then, for both materials, several formulations were proposed. Particular attention has also been paid to the use of various natural additives, such as starch and cellulose, due to their adhesive properties and rheological modifiers, respectively, which influence the properties of the fresh and hardened mortar: as the type and quantity of additives vary, workability, adhesion to the substrate and mechanical resistance were evaluated. Finally, mortars and plasters were applied on autoclaved aerated concrete blocks: the correction time and the adherence were evaluated. All products were fully characterized, to assess the chemical, physical and mechanical properties.