Journal
HOLZFORSCHUNG
Volume 64, Issue 6, Pages 747-756Publisher
WALTER DE GRUYTER GMBH
DOI: 10.1515/HF.2010.123
Keywords
dynamic mechanical analysis; fungal degradation; hardwood; lignin glass transition; switchgrass
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Funding
- National Research Initiative of the USDA Cooperative State Research
- Education and Extension Service [2006-35504-17424]
- Wood-Based Composites Center
- Sustainable Engineered Materials Institute at Virginia Tech
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In an effort to advance the dynamic mechanical analysis (DMA) of very small biomass specimens, and/or specimens having poor mechanical integrity, the functional equivalent of pendulum-torsion (tensile-torsion) DMA was compared to parallel-plate compressive-torsion DMA. The solvent-saturated lignin glass transition in yellow-poplar (Liriodendron tulipifera) was generally similar determined by both modes; however, direct data comparisons should be avoided or carefully considered. First-heat glass transition temperatures (T(g)s) were relatively similar; however, specimen densification elevated subsequent cooling-mode Tgs by 5-8 degrees C in compressive-torsion. Both modes revealed a first-heat tan delta shoulder; it was more prominent and had grain dependency in compressive-torsion. Below fiber saturation, subambient tensile-torsion DMA was superior; compressive-torsion resulted in an anomalous response, obscuring subambient secondary relaxations. With these differences and limitations in mind, compressive-torsion offers specific advantages. Solvent-submersion studies are simplified because solvent cups are easily devised for torsional rheometers. Specimens lacking mechanical integrity are more easily analyzed. Heavily biodegraded spruce (Picea sp.) was analyzed in the solvent-submersion mode as fibrous mats and the different actions of Gloeophyllum trabeum and Postia placenta were revealed. Very small specimens are easily analyzed in compressivetorsion; tissue maturity effects were revealed in minute sections of switchgrass (Panicum virgatum) stems. Applied appropriately, parallel-plate compressive-torsion DMA will provide new research opportunities.
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