Nanocelulosas producidas por un proceso de oxidación no convencional: interacciones y aplicaciones

ENG- The dependence on petroleum poses environmental problems and limits reserves, while the proliferation of microplastics affects health. This drives the development of renewable and biodegradable biomaterials. Cellulose, the most abundant natural polymer, offers solutions to these challenges. Cellulose micro/nanofibers (CMNF) obtained from wood and plant cell walls are of growing interest as reinforcements for various materials due to their inherent properties. Typically, CMNF are prepared by applying intense mechanical treatments, where the fibers are subjected to large shear forces that fibrillate and release microfibrils. Additionally, it is known that applying mechanical and/or chemical pre-treatments facilitates the fibrillation process, preventing blockages and reducing energy consumption. This allows for higher nanofibrillation yields and notable properties. Mechanical pre-treatments such as PFI refiners and Ultra-Turrax homogenizers are viable alternatives. On the other hand, oxidation mediated by 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) has been widely used as a chemical pre-treatment for obtaining highly fibrillated CMNF. However, the cost of the reagent is high, and although it can be reused, its disposal raises environmental concerns. In this regard, it is worthwhile to consider other alternatives, such as oxalic acid. Treatment with this reagent produces carboxylation through Fischer-Speier esterification between an oxalic acid carboxyl group and a hydroxyl group on the accessible surface of cellulose. Oxalic acid is advantageous because it is economical, recoverable, and its corrosive effects on equipment are controllable. Specifically, the effect of oxalic acid concentration, the impact of different mechanical pre-treatments, the influence of the number of steps, and the pressure applied in the pressurized homogenizer are evaluated on the key characteristics of CMNF that define their potential applications. Currently, the main application of CMNF is paper reinforcement. The most significant limitation is the need to dose the appropriate amount of retention agents to ensure CMNF adsorption on cellulose fibers and prevent excessive drainage loss during paper production. In this thesis, polyelectrolyte complexes (PEC) can be very useful for this purpose. Therefore, the ability of natural polyelectrolyte complexes based on hemicelluloses to aid in the application of different cellulose micro/nanofibers obtained via chemical pre-treatment with oxalic acid (Ox-CMNF) on paper is evaluated. Moreover, contamination caused by heavy metals or gases is a serious problem that poses a risk to food safety and public health. Thus, reducing and properly treating waste and finding innovative methods to detect and capture heavy metals and contaminant gases are essential. Membranes represent a rapid, effective, low-cost, and flexible alternative for this purpose, as different manufacturing processes yield varied functionalities and final material characteristics. The incorporation of Ox-CMNF into membrane production presents an interesting challenge. This thesis evaluates the ability of these Ox-CMNF to enhance the mechanical properties of cellulose acetate membranes and their potential for CO2 retention. Additionally, the suitability of reactive nanopapers and Ox-CMNF membranes for detecting aqueous and gaseous HgCl2 is analyzed. This thesis is presented as a compendium of 5 articles and aims to determine the scope of CMNF application produced by an unconventional oxidative process. Specifically, the published articles assess the interaction between CMNF and various agents, such as PEC or polyethyleneimine (PEI), with the goal of optimizing their technological properties for various environmental applications, from recycled paper to water treatment