A fundamental investigation of the microarchitecture and mechanical properties of tempo-oxidized nanofibrillated cellulose (NFC)-based aerogels

Freeze-dried nanofibrillated cellulose based-aerogels were produced from cellulosic pulps extracted from Eucalyptus urograndis. Nanofibers were isolated under high pressure and modified with TEMPO-mediated oxidation and/or hydroxyapatite (HAp) to observe potential changes in mechanical properties. Two degrees of oxidation (DO), 0.1 and 0.2, were achieved as measured by conductimetric titration. Oxidized and non-oxidized samples were modified with HAp at a ratio of HAp:cellulose of 0.2:1. Morphology (FE-SEM), pore size, surface area, and mechanical properties were obtained to characterize the produced aerogels. The results clearly demonstrate a homogeneous morphology for aerogels fabricated with oxidized cellulose nanofibers. The nature of water present in the material was measured using time domain-nuclear magnetic resonance spectroscopy (TD-NMR) and demonstrated that it played a key role in the development of the porous and uniform micro-architecture. TEMPO-mediated oxidation and the addition of HAp resulted in aerogels with high mechanical strength as demonstrated from an increase from approximately 75-200 kPa in compressive strength when reduced to 50 % of their original height. However, the contribution of oxidation to the mechanical properties was more pronounced than the addition of HAp. In general, the density of the aerogels varied from 0.008 to 0.011 g/cm(3) in which slightly lightweight aerogels were produced by increasing the degree of oxidation, whereas the incorporation of HAp as a modifying agent for potential bio-based tissue scaffolding matrices did not significantly contribute to higher densities.