Electromagnetic radiation shielding by composites of conducting polymers and wood

Polyaniline or polypyrrole composites with fir or oak wood have been prepared by in situ polymerization of the corresponding monomers in an aqueous suspension of wood sawdust. The percolation threshold of compressed coated particles is located below 5 wt % of the conducting component and, above this limit, the conductivity of most composites was higher than 10(-3) S cm(-1). The conductivity of composites containing ca 30 wt % of conducting polymer was of the order of 10(-1) S cm(-1), an order of magnitude lower than that of the corresponding homopolymers, polyaniline and polypyrrole. The conductivity stability has been tested at 175degreesC. The polypyrrole-based composites generally lasted for a longer time than pyrrole homopolymers, also on account of the improved mechanical integrity of the samples provided by the presence of wood. The reverse order was found with polyaniline composites. The dielectric properties of the composites were determined in the range of 100 MHz-3 GHz, indicating that thick layers of composite material, similar to 100 mm, are needed for the screening of the electromagnetic radiation below similar to10 dB level in this frequency range. Nevertheless, considering the potential production cost of composites and their low weight, such composite materials could be of practical interest in the shielding of electromagnetic interference. (C) 2004 Wiley Periodicals, Inc.