Effect of pyrolysis conditions on the properties of carbonaceous nanofibers obtained from freeze-dried cellulose nanofibers

Carbonaceous nanofibers (CsNFs) were produced by pyrolysis of cellulose nanofibers synthesised from wood pulp using a top-down approach. The effects of heat treatment conditions on the thermal, morphological, crystal and chemical properties of the CsNFs were investigated using TGA, SEM, XRD and FT-IR, respectively. The results showed that heat treatment conditions around the thermal decomposition temperature of cellulose greatly influence the morphology of resulting materials. Slow heating rates (1 °C/min) between 240 and 400 °C as well as prolonged isothermal heat treatment (17 h) at 240 °C were necessary to avoid destruction of the original fibrous morphology in carbonized nanofibers. On the other hand, such heat treatment had little effect on micron sized fibers. The optimized heat treatment conditions led to the release of oxygen and hydrogen from cellulose before thermal breakdown of glycosidic rings, which in turn prevented depolymerization and tar formation, resulting in the preservation of the fibrous morphology.