Biomorphous ceramics from lignocellulosics

Lignocellulosics represent the organic matter produced by trees. Biopolymers such as cellulose, hemicellulose and lignin are the major macromolecular constituents of ligneous cell walls which are distinguished by a hierarchical fibrilar composite micro structure. Fundamental aspects of anatomy of wood and molecular structure of wood cell wall affecting the bioorganic-inorganic conversion process are reviewed. Basic approaches to convert the native biopolymeric materials into non-oxide as well as oxide ceramic products include: (i) pyrolytic decomposition resulting in a porous carbon replica (template) which may subsequently be reacted to form carbide phases or may be infiltrated with non-reacting sols or salts which can further be processed to yield oxide reaction products. (ii) infiltration of chemically preprocessed native lignocellulosic products with gaseous or liquid organometallic and metalorganic precursors and subsequent oxidation to remove the free carbon phase. Conversion of native (wood tissue) lignocellulosics into ceramics with a microstructure pseudomorphous to the bioorganic template anatomy offers a great potential for designing novel ceramics with anisotropic cellular morphologies. These might be of interest for applications as high temperature resistant exhaust gas filters and catalyst carriers in energy, environmental and automotive industries, bioinert and corrosion resistant immobilization supports for living cells, microbes. or enzymes in biotechnology and medicine. (C) 2001 Elsevier Science Ltd. All rights reserved.