- Zhao, Hong
University of Maine Graduate School
The overall objective of this thesis was to investigate incorporation of creosote-treated wood into untreated wood furnish to produce particleboard. The investigations were conducted in three aspects: surface energy characteristics of the materials, physical and mechanical properties of the resulting composites, and VOC emissions arising during the hot-pressing process. The experimental variables examined included four furnish ratios of creosote-treated wood (0%, 4.4%, 8.8%, and 13.2% based on dry volume of furnish), two resin systems (PF and PMDI), and three resin levels (3%, 5%, and 7%, weight-based). The overall results of material characterization imply that the creosote contained in the recycled creosote-treated wood (1) does not alter the surface energy of the wood because the treated wood (sapwood) has a total surface energy similar to the untreated wood, (2)interferes with the hydroxyl number analysis, and results in a higher value of hydroxyl number than the actual hydroxyl groups contained in the wood, and (3) will probably remain in the composites during the service period under normal exposure. The results of the composite propertytesting indicate that incorporation of creosote-treatedwoodhas adetrimental effect on the mechanical properties of the particleboard, but a positive effect on dimensional stability. Creosote-treated wood had less effect on reducing the internal bond of PMDI resin bonded particleboard compared to that of PF resin bonded board. As the resin level in the particleboard is increased, the reduction in IB strength as a function of creosote level is decreased. The thickness swelling and water absorption of PMDI resin bonded particleboard were better than that of the PF resin bonded particleboard as a result of the incorporation of creosote-treated wood. The results of the VOC quantification imply that formaldehyde emission is not affected by the increased creosote-treated wood content in the PMDI boards. The results also reveal that the VOCs arising from creosote are emitted in a smaller quantity when pressing PMDI boards compared to pressing PF boards at the same level of creosote-treated wood content. Based on bonding performance and environmental considerations, PMDI might be the resin of choice for making particleboard from recycled creosote-treated wood for outdoor applications. Overall, the findings of this research suggest that it is technically feasible to recycle creosote-treated wood by incorporation at a furnish ratio of at least 13.2% for particleboard manufacturing. These positive findings offer an alternative solution to deal with the disposal of creosote-treated wood.