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

TL;DR

This paper explores the nitration of cellulose nanofibrils to create materials with potential advantages over traditional cellulose-based products for energetic applications.

Contribution

The study develops a methodology for nitration of cellulose nanofibrils while preserving their nanoscale properties.

Findings

Dehydration via vacuum filtration is the only suitable method for preparing CNF for nitration.

Nitrated CNF products were successfully obtained, though their degree of substitution is not yet suitable for energetic applications.

Structural and thermal properties of nitrated CNF compare favorably with those of linter cellulose and microcrystalline cellulose.

Abstract

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.

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