Graduation date: 2008The objective of this research project was to increase the density, strength, and stiffness of two low to medium-density diffuse-porous hardwood species. Wood used in this study was processed using a method of wood densification known as “Viscoelastic Thermal Compression” (VTC). The VTC process is a three phase treatment which incorporates saturated steam treatment, mechanical compression, and a heat treatment. The strategy of the VTC process is to increase the density, strength, and stiffness of wood through non-destructive means. The two hardwood species chosen for this study were 7-year old Eastern cottonwood (Populus deltoides) and sweetgum (Liquidambar styraciflua) from the Pensacola, Florida area. The primary justification for this research was to test the suitability of VTC processed wood for future use in a high-strength structural composite. Analysis of VTC processed Eastern cottonwood has shown increases in density, MOE, and MOR of up to 178, 254, and 156 percent, respectively. VTC processed sweetgum showed increases in density, MOE, and MOR of up to 168, 213, and 182 percent, respectively. Both species exhibited increases in MOE and MOR which were approximately proportional to increases in wood density. Data obtained from this research project was used to develop equations to estimate the potential increase in wood strength and stiffness that can be achieved with the VTC process. Eastern cottonwood control specimens showed statistical differences in wood density as a result of vertical location. The upper stem locations were of higher density than the lower sections. Controls from the upper stem were found to contain a greater percentage of branchwood and earlywood vessels. A significantly smaller lumen diameter and presence of a gelatinous layer was seen in the latewood regions of the upper stem controls. This resulted in thicker lumen cell walls in the longitudinal fibers, which may have contributed to the wood density increase seen. Sweetgum control specimens showed no statistical difference in wood density as a result of stem location. The findings from this research showed that significant gains in wood strength and stiffness could be obtained with the VTC process, without causing cell wall fractures. These results were seen in two low to medium-density, diffuse porous hardwood species. Similar results could likely be seen in other species, both hardwood and softwood, providing the same procedure is followed. VTC processed wood shows potential for use as a high-strength laminate in a composite product.