Comparing the Nitration of Nanostructured CNF and Other Cellulose Forms for Energetic Applications

This work focuses on the nitration of nanocellulose to obtain products with potential advantages over traditional ones obtained from linter cellulose (LC). The material used was a sample of cellulose nanofibrils (CNF) commercially available as an aqueous suspension with a 3% solid content. The main objective of the research was to develop the reaction conditions for nitration, including the preparatory methods for the cellulose raw material, so that the properties on the nanometric scale were maintained. The dehydration of the CNF to concentrate the fibrils in suspension was investigated using different methods: gravity and vacuum filtration, centrifugation, oven, and freeze-drying. The nitration experiments were carried out with dehydrated CNF following a protocol based on methodologies reported in the literature. For comparative purposes, commercial samples of cotton LC and microcrystalline cellulose (MCC) were also evaluated. A complete characterization of the structural and thermal properties of the cellulose materials and their nitration products was carried out using the following techniques: size-exclusion chromatography, scanning electron microscopy, infrared spectroscopy, X-ray diffraction, simultaneous thermogravimetric analysis, and elemental analysis. The results of the analysis revealed that the chemical structure of the cellulose chains is neither altered by the removal of water nor by the temperature and pressure conditions. However, the agglomeration of the fibrils is favored due to the interconversion of hydrogen bonds between cellulose-water and cellulose-cellulose, as in the heating and freezing treatments, making the redispersion of the nanofibers impossible. Only dehydration by vacuum filtration was suitable for preparing CNF for the reaction to obtain nitrocellulose. Although the resulting degree of substitution was not yet suitable for energetic applications, it was possible to obtain nitrated products from the commercial cellulosic materials under study. Comparing the structural and thermal properties of the nitrated CNF with those of LC and MCC nitration products obtained under identical conditions, the results corroborated the work in the literature and the theories developed so far. Therefore, the study demonstrated the potential viability of the synthesis methodology developed for the nitration of cellulose of different origins, dimensions, and morphological types.