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Zhang Y.,Nanjing Forestry University | Cai L.,665 East Mall
Drying Technology | Year: 2011

Mills experience reduced kiln productivity in drying sub-alpine fir lumber. High-temperature drying is an effective approach to accelerate the process. Thermal modification improves the dimensional stability and decay resistance. During these processes, two distinct stages, wood heating and water vaporization, were encountered. This research was aimed at developing a method to evaluate the vaporization process using an approximate analytic solution. The heating process was predicted by combining the analytic solution with numeric simulation. Using a scanning electron microscope, the impact of vaporization on wood micro-structure was examined. The vaporization process was able to open the aspirated pits and break the membranes. Laboratory drying experiments confirmed that the program could obtain satisfactory estimations of heating rates and times. The results indicated that the vaporization time is a function of the moisture content and size of the lumber, the temperature and air velocity in the kiln. © 2011 Taylor & Francis Group, LLC. Source

Janin A.,University of Toronto | Coudert L.,University of Quebec | Blais J.-F.,University of Quebec | Mercier G.,University of Quebec | And 3 more authors.
Separation and Purification Technology | Year: 2012

Increasingly stringent regulations regarding waste disposal encourage the development of options for reuse, recycling and revalorisation of waste. Metals-bearing treated wood wastes are no exception. Previous studies identified a possible treatment technology for chromated copper arsenate (CCA) preservative-treated wood waste based on sulphuric acid leaching. In this study, the scale-up of this technology was extended from 200 ml flask to 80 l working volume stirred-tank reactor. The study involved three leaching steps of 2 h each, at 75 °C with 0.2 N H 2SO 4 and 15% solids content followed by three rinsing steps. This procedure led to removal of 99.5% of the arsenic, 95.7% of the chromium and 99.6% of the copper from the wood chips on average. The effluents generated by the leaching steps were then treated by precipitation. This technology allowed 99% removal of As, Cr and Cu from the leachate, leading to effluents satisfying the regulations for effluent discharge in municipal sewers. The mass balance was assessed for the whole process (leaching, rinsing and precipitation of the leachate) and the output to input ratio was between 80% and 100%. Furthermore, the economic analysis concluded that the operating cost of the process (leaching, rinsing and precipitation of the leachate) was about 250 $/ton of treated wood (t.t.w.) with the conditions employed in this study. However, the cost could be reduced at least to 89 $/t.t.w. by using a counter current leaching process as developed in a previous study. © 2011 Elsevier B.V. All rights reserved. Source

Zhou C.,University of British Columbia | Dai C.,665 East Mall | Smith G.D.,University of British Columbia
Holzforschung | Year: 2010

To improve the fundamental understanding of wood composite consolidation, the viscoelastic behavior of aspen wood strands is experimentally investigated for a range of temperatures (20-200°C) and moisture contents (0-15%). The results show that the strand stress relaxation modulus and time follows a linear relationship in a log-log plot. The strand stress relaxation rate is highly dependent on the imposed strain levels and the environmental conditions. A model for predicting the stress relaxation of wood strands is developed and compared with the experimental results. It will be useful to further predict the stress relaxation response of strand-based wood composite mats during hot pressing. © 2010 by Walter de Gruyter Berlin New York 2010. Source

Zhao Y.,University of Toronto | Yan N.,University of Toronto | Feng M.W.,665 East Mall
ACS Sustainable Chemistry and Engineering | Year: 2013

In this study, two types of biobased bark-derived phenol formaldehyde (PF) resins, namely, liquefied bark-PF and bark extractive-PF, were synthesized from acid-catalyzed phenol-liquefied bark and bark alkaline extractives, respectively. The biobased resins were characterized for their chemical compositions and molecular structures using the liquidstate 13C nuclear magnetic resonance (NMR) technique. The results indicated that the introduction of bark components (either as liquefied bark or as bark extractives) to the phenolic resin synthesis affected resin structures and curing performance. Methylene ether bridges were found in the bark-derived PF resins. Bark components made the formation of para-ortho-methylene linkage more favorable in bark-derived PF resins than in lab PF resins. Molecular structures of the liquefied bark-PF resin differed significantly from those of the bark extractive-PF resins. The liquefied bark-PF resin showed a higher ratio of para-para/ortho-para-methylene link (-CH2-), a higher unsubstituted/substituted hydrogen (-H/-CH2OH) ratio and a higher methylol/methylene (-CH2OH/-CH2-) ratio than the bark extractive-PF resin. The tannin components of the bark extractives accelerated the curing rate of the resulting bark extractive-PF resin. The bark extractives made the ortho position of phenol react more favorably with formaldehyde than the para position. The liquefied bark with phenolated structures had more reactive sites toward formaldehyde than the bark extractives and accelerated the curing rate of the resulting liquefied bark-PF resin. © 2012 American Chemical Society. Source

Zhao Y.,University of Toronto | Yan N.,University of Toronto | Feng M.,665 East Mall
International Journal of Adhesion and Adhesives | Year: 2010

In this study, lodgepole pine (Pinus contorta Dougl.) barks with and without infestation by mountain pine beetle (MPB, Dendroctonus ponderosae Hopkins) were liquefied in phenol with sulfuric acid. The liquefied portions of the bark were used to synthesize bark-derived phenolformaldehyde (BPF) adhesive resins under alkaline conditions. In comparison to a commercial phenolformaldehyde (PF) resin and a lab PF resin, the BPF resins were found to have larger average molecular weights, higher polydispersity indices and shorter gel times. The viscosities of the BPF resins were higher than the viscosity of the lab PF resin but lower than the viscosity of the commercial PF resin. Isothermal DSC tests indicated that all resins exhibited both nth-order and autocatalytic cure mechanisms. The post-curing thermal stability of the BPF resins was similar to that of the lab PF resin at higher temperatures but differed significantly from that of the commercial PF resin. All these resins had similar dry bonding strengths; the BPF resins showed the highest wet bonding strengths. Beetle infestation was shown to have no negative effect on the bonding properties of the BPF resins. © 2010 Elsevier Ltd. Source

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