Authors: Cheng Xing Siqun Wang George M Pharr
Publish Date: 2009/06/23
Volume: 43, Issue: 7-8, Pages: 615-
Abstract
The effects of thermomechanical refining pressures varying from 2 to 18 bars on the cellwall properties of refined wood fibers of a 54yearold loblolly pine Pinus taeda L with reference to both juvenile JW and mature wood MW were investigated using nanoindentation and atomic force microscopy The results of this study indicate that refining pressure plays a significant role in the physical damage sustained by refined wood fibers No obvious damage was observed in the cell walls of MW fibers refined at 2 and 4 bar Nanocracks 500 nm in width were found in fibers refined at pressures in the range of 2–12 bar for JW and 6–12 bar for MW and micro cracks 3000 nm in width were found in both MW and JW fibers subjected to a refining pressure of 14 and 18 bar The micro damage to the fibers refined at higher pressures was more severe inside the lumen than on the surface of the fibers and the lumen or S3 layer was significantly damaged The elastic modulus hardness and creep resistance of MW fibers were higher than those of the JW fibers subjected to the same refiningpressure conditions The elastic modulus and hardness decreased whereas nanoindentation creep increased with increasing refining pressure This study also suggests that lower refining pressures 4 bar and higher pressures 14 bar for MW and 12 bar for JW should be avoided in the manufacture of fiberboards and wood fiber–polymer composites because of the lower aspect ratio of the fiber bundles shorter length of the fibers and fines and severe damages to the fiber cell wallsThe authors wish to thank Dr John Dunlap and Dr SeungHwan Lee for their kind help in preparing the specimens We gratefully acknowledge Dr Les Groom at the Southern Research Station Forest Service of USDA for providing the fiber samples The National Research Initiative of the USDA Cooperative State Research Education and Extension Service grant number 200502645 the Tennessee Agricultural Experiment Station Project TEN 00MS96 and the USDA Wood Utilization Research Grant supported the project Instrumentation for the nanoindentation work was provided through the SHaRE Program at the Oak Ridge National Laboratory which was sponsored by the Division of Materials Science and Engineering US Department of Energy under contract DEAC05000R22725 with UTBattelle LLC
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