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Thermo-hydro-mechanical densification of western hemlock (Tsuga heterophylla)

University of British Columbia

Thermo-Hydro-Mechanical densification (THM) is a controlled wood compression at high temperatures that results in improving some of its properties. This process has not been used until now to produce a commercial product, and still, remains a laboratory-scale process. Therefore, more research is needed to explore possible applications of THM with local species. This thesis tests the hypothesis that THM will increase wood density and accordingly, improve mechanical properties such as hardness, strength, and abrasion resistance. Therefore, low-to-average density wood species could be proper candidates for densification. In addition, interactions among three important factors (pre-treatment, densification time, and temperature) on THM were examined to find the best combination of factors in process. Western hemlock (Tsuga heterophylla) as one of the most common and important local timber species was selected for THM. Because this species is used mostly in construction, thus, the development of other uses could create new markets and extra profits to the industry. Kiln-dried hemlock boards were subjected to THM process. Two different specimen pre-treatments were selected before starting the compression of wood. The independent variables considered were 12% moisture content conditioned sample surfaces with and without hydration by water spraying, three densification times (5, 10, and 15 minutes), and three temperatures (120, 160, and 200°C). Tests performed on densified and control samples by means of a hot press to evaluate density, hardness, spring-back, color change, and abrasion resistance. Data analysis shows that temperature, densification time, and moisture pre-treatment were significant factors. Compared to untreated samples, THM significantly improved density, hardness, and abrasion resistance of hemlock by 197%, 386%, and 437%, respectively. As a desired feature, this process darkened the hemlock around 200% as well. In addition, after 200 hours, spring-back reached to a steady state (less than 2% change). The optimum treatment took place for pretreated samples with water spray that were densified for15 minutes at 160°C (WS-15-160).

Text

2020-09-21

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/76119

Forestry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/