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Some results are descibed of an innovative approach for producing net shape polymer, ceramic and carbon composites using wood and other lignocellulose precursors. Wood monoliths have been carbonized without producing cracks as typically found in charcoal materials. These porous carbon monoliths have been readily shaped using standard tools. Conversion to final material has been accomplished without any change in dimensions from the carbon stage, The net-shape materials produced include carbon/epoxy and carbon/carbon composites, silicon carbide, silicon carbide/silicon composites, titanium carbide, and aluminum nitride. Carbonized poplar has been found to be 30% stronger and a carbon/epoxy derived from poplar 250% stronger than the original poplar wood.

By using a combination of very accurately cut wood specimens and highly controlled pyrolysis conditions, we have for the first time obtained precise volumetric and linear shrinkage measurements for wood carbonization which we use to formulate a new theory of cellulose microfibril dominance. Characterization of these crack-free carbonized wood monoliths was performed by measuring density, dimensions, acoustic velocity, yield and crystallinity for heat treatment temperatures ranging from 400 to 2500 °C. Axial dimensions increased at the highest temperatures while radial and tangential dimensions continued to decrease. Acoustic velocity in the axial direction remained constant at 5 mm/μs above 1200 °C. Radial and tangential velocities went through a maximum before diminishing at the highest temperatures. Helium density of powdered carbonized monoliths was found to go through a maximum of 1.9 g/cm3 at 1000 °C before decreasing at the highest temperatures to 1.4 g/cm3, the value obtained for 400 °C char. The experimental results are used to support a model for the relationship between the cellulose molecular arrangement in the wood and the microstructure of the resulting carbon monoliths. It is proposed that cellulose microfibrils dominate the mechanism of dimensional change during pyrolysis and result in a preferred orientation of crystallites in the carbonized wood.

A unique process for conversion of monolithic wood structures to carbons that retain the cellular structure of the wood without the formation of cracks and other defects associated with charcoal materials is described. A variety of wood species are carbonized to produce the materials which are characterized using TGA, density, dimensional changes, acoustic velocity, SEM and mechanical testing. We demonstrate that through controlled pyrolysis monolithic carbonized wood can be produced without the macro-cracks normally associated with charcoal. A linear relationship is established between the bulk densities of wood and carbonized wood which spans the entire range of species. For the conditions presented, the carbonized wood had 82% of the bulk density of the precursor wood. Carbonized wood acoustic velocity ranged from 4.7 to 1.3 mm/μs for Tilia americana and Ochroma pyramidale , respectively. Carbonization resulted in decreased acoustic velocity in the axial principal direction and increases in the radial and tangential directions. Acoustic anisotropy was retained through carbonization, but reduced in magnitude. Mechanical testing showed the carbonized wood to be 28% stronger than the precursor. The cellular morphology of the porous carbonized wood is described and compared to carbon foams.