Dissertation > Excellent graduate degree dissertation topics show

Properties of Pressurized-steam-treated Wood-A Theoretical Research

Author: DingTao
Tutor: GuLianBai
School: Nanjing Forestry University
Course: Wood Science and Technology
Keywords: Heat-treated wood Atmospheric Steam Pressurized Steam Mechanical Strength Dimensional Stability Surface Roughness Tool Temperature
CLC: TS652
Type: PhD thesis
Year: 2010
Downloads: 147
Quote: 2
Read: Download Dissertation

Abstract


Research on wood heat treatment is currently active in the field of wood physical modification. By means of heating wood up to around 200℃in inert atmosphere, significant improvement on dimensional stability and biological durability can be obtained. Besides, when used, heat-treated wood will not release any toxic substance to the environment, making it an environmentally friendly product compared to chemically modified wood.In this paper, emphasis is put on the comparison of physical, mechanical and machining properties of heat-treated wood treated in atmospheric steam and pressurized steam, respectively. Chemical and instrument analysis have been performed to explore the underlying reasons for the property difference. Samples of Mongolian pine and Mongolian oak were chosen for the experiments, and results as follows were obtained:At the same treatment temperature, pressurized steam exerted more influence on properties of wood than atmospheric steam. Samples treated in pressurized steam were inferior to those treated in atmospheric steam when mechanical properties, such as Modulus of Elasticity (MOE), Modulus of Rupture (MOR), compressive strength parallel to grain, dynamic fracture toughness and hardness, are considered. However, most of these differences were not statistically significant. Pressurized-steam-treated samples performed better in experiments on hygroscopicity and dimensional stability. Lower equilibrium moisture content (EMC) and less swelling in both radial and tangential directions were found compared to atmospheric-steam-treated samples. Machining experiments showed that, when samples treated in pressurized steam were milled, temperature of the blade was lower. The roughness of the processed surface of both kinds of heat-treated samples was statistically the same. However, samples treated in pressurized steam intended to emit more fine sawdust, asking for better dust collecting system and respiratory protection device.Research on the change of wood structure was performed through chemical and instrument analysis. It was found that the main chemical components of samples treated in different pressure experienced different reaction and degradation. Hemicelluloses of samples treated in pressurized steam degraded more compared to samples treated in atmospheric steam. Meanwhile, the portion of lignin and extractives in the former was higher than in the latter. Those above were supported by the outcome of Fourier transform infrared spectroscopy (FTIR) analysis. Furthermore, the structure of lignin was found changed after heat treatment, although the exact pattern of the change needed further exploration. From the results of chemical and instrument analysis, we concluded that the lower strength of pressurized-steam-treated samples was attributed to more intense degradation of its main chemical components, especially the carbohydrates. Such degradation also decreased the number of free hydroxyl groups in the wood, making it absorb less moisture. The lower strength and hygroscopicity, in turn, were responsible for less energy consumption and finer dust emission of pressurized-steam-treated wood during machining process.Conclusions mentioned above showed that the benefit of pressurized steam heat treatment lied in better dimensional stability, less energy consumption during machining process and guaranteed surface quality of its products. Although pressurized steam made the strength of heat-treated wood even lower, in most cases, it was not statistically significant. What should be pointed out here is that, by means of thermogravimetry (TG)-FTIR analysis, we found that the degradation of wood components was limited if the treatment temperature was lower than 200℃. What’s more, factors such as less hygroscopicity of wood and higher crystallinity of cellulose made positive contribution to the strength of wood. That’s why some strength values like MOE and compressive strength parallel to grain of heat-treated samples were higher than the control ones. So, it can be concluded that pressurized-steam-treated wood has the potential of full scale application.

Related Dissertations

  1. The Influence on the Dimensional Stability and Elastic Deformation Caused by Two Types of Disinfectant Solution to Different Impression Material,R783
  2. The Effect of Different Microwave Polymerizations on Accuracy and Physical Properties of Denture Base Resin,R783.6
  3. Comparison of the Physical and Mechanical Properties Among Four Kinds of Die Stone Casts,TQ177.3
  4. Nuclear Power Plant Steel Milling Surface Integrity Study,TG54
  5. Transparent substrate surface scattering and volume scattering studies,TH74
  6. ABS -based high-speed milling of aluminum hydraulic valve Processing Research,TG54
  7. Nickel microlens array mold core micro electroforming process and surface quality,TH74
  8. Study on Properties of Vinylon-Milk Fiber and Knitted Fabrics with Size Stability,TS181
  9. Study on the Dimensional Stability of Medium Density Fiberboard Produced by Modified Urea-formaldehyde Resin,TS653
  10. Substrate Surface alloying coating microstructure and properties of hot dip galvanized sheet,TG174.44
  11. Effect of the Rubbing and Wearing Behavior of Steel Rail by Ultrasonic Peening,TG115.58
  12. Research on Key Technologies of Three-dimensional Surface Roughness Measurement,TG84
  13. The Multi-parameter Disquisition of High-speed Grinding Which Is Based on Minimum Quantity Lubrication Cooling Method,TG580.6
  14. Research on Dimensional Stability of the Submicron Al2O3P/Al Composite,TB331
  15. Influence of Surface Roughness on Gold Alloy and Ni-Gr-Ti Alloy on Adhesion Bacteria,R783
  16. Influence Research of the Different Expansion Coefficient Plaster Cast Material on Resin Denture Accuracy and Physical Properties,R783.6
  17. A Study on Hairy Pads of Drosophila Melanogaster and Its Adhesive Force on Touched Surfaces with Different Roughness,Q811
  18. Research on Speckle Suppression in Laser Micro-Projector,O436
  19. The Study on Characterization of Machined Surface Micro-Topography in High Speed Milling of SiC_p /Al Composites,TG506.1
  20. Research on the Control of Processing Quality When Cutting Nickel-Base Superalloyat High Speed,TG506.1
  21. Study on Micro/Nano Structures Evaluation and Surface Characterization Methods,TG806

CLC: > Industrial Technology > Light industry,handicrafts > Wood processing industry,furniture manufacturing industry > Processing > Lumber processing
© 2012 www.DissertationTopic.Net  Mobile