Changes in electrical and microstructural properties of microcrystalline cellulose as function of carbonization temperature

AC and DC electrical measurements were made to better understand the thermal conversion of microcrystalline cellulose to carbon. This study identifies five regions of electrical conductivity that can be directly correlated to the chemical decomposition and microstructural evolution of cellulose during carbonization. In Region I (250-350 degrees C), a decrease in overall AC conductivity occurs due to the loss of the polar oxygen-containing functional groups from cellulose molecules. In Region II (400-500 degrees C), the AC conductivity starts to increase with heat treatment temperature due to the formation and growth of conducting carbon clusters. In Region III (550-600 degrees C), a further increase of AC conductivity with increasing heat treatment temperature is observed. in addition, the AC conductivity demonstrates a non-linear frequency dependency due to electron hopping, interfacial polarization, and onset of a percolation threshold. In Region IV (610-1000 degrees C), a frequency independent conductivity (DC conductivity) is observed and continues to increase with heat treatment due to the growth and further percolation of carbon clusters. Finally in Region V (1200-2000 degrees C), the DC conductivity reaches a plateau with increasing heat treatment temperature as the system reaches a fully percolated state. (C) 2009 Elsevier Ltd. All rights reserved.