Hydrothermal Carbonization of Nanofibrillated Cellulose: A Pioneering Model Study Demonstrating the Effect of Size on Final Material Qualities

The morphological and physical properties of hydrochar from the hydrothermal carbonization of nanofibrillated cellulose (NFC) are herein described; it was found that the initial starting structure influences the final hydrochar structure to a great extent, as observed by a scanning electron microscope (SEM). Effects of temperature and heating time on the resulted hydrochars were also explored. For comparison purposes, fully bleached macroscopic softwood pulp fibers with a composition similar to the NFC were also converted into hydrochar and characterized. The carbonization of the NFC started at >200 degrees C although time did not affect the properties of the hydrochar when the hydrothermal carbonization (HTC) was performed at 250 degrees C. The SEM images of the NFC hydrochar revealed broad nanoscale topological features that may be characterized as nodule-filled surfaces connecting continuously, without a bulk surface as the base, where the nodule dimensions range from 2 to 400 nm. The nanostructure of the NFC did not modify the elemental composition of the resultant hydrochar relative to the hydrochar from softwood. However, the morphology of hydrochar from NFC was different from the hydrochar from the softwood fibers, indicating that there is an advantage to using nanostructured starting material. The NFC hydrochar also had much higher pore volume (0.91 cm(3)/g) and average pore size (127.1 nm) than the softwood fiber (0.01 cm(3)/g and 4.5 nm, respectively).