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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 gs) were relatively similar; however, specimen densification elevated subsequent cooling-mode T gs by 5–8°C in compressive-torsion. Both modes revealed a first-heat tan δ 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 compressive-torsion; 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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The chemical structure change and rheological behaviour of heat-treated Obeche (Triplochiton scleroxylon) wood were investigated. Wood samples were treated at 160 and 200°C for 30, 60 and 120 minutes. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and dynamic mechanical analysis (DMA) were employed to characterize the chemical structure and rheological property of the heat-treated wood, respectively. Infrared data showed that there was a reduction in the number of hydroxyl groups (one of the factors normally attributed to water absorption) of heat treated wood relative to the control samples. The relative cellulose crystallinity increased slightly which may be one of the factors contributing to the stiffness of the heat-treated wood. The latter increases with increasing treatment temperature and time. The rheological properties of the wood samples were tested while submerged in N-methyl-2-pyrrolidone solvent under saturated conditions. DMA results showed that the increasing heat treatment time caused an increase in the glass transition temperature relative to the control sample, irrespective of the treatment temperature. Therefore, heat treatment at moderately high temperatures (160 and 200 °C) showed an interesting potential which could be used to reduce water absorption and improve flexural modulus of Obeche wood.

Effects of accelerated and natural weathering on the molecular weight distribution (MWD) and crystallinity of polypropylene (PP) in wood plastic composites (WPC) were investigated. The composites were produced from pine fibers (60%) and PP (40%). Prolonged weathering caused an increase in wood degradation and erosion thereby leaving cracks and ''pits'' on the surface. Pyrolysis gas chromatography-mass spectrometry (Py GC-MS) revealed that PP dominated the weathered surface due to wood degradation. For matrix analysis, PP was extracted using 1,2,4-trichlorobenzene. Crystallinity and molecular weight distribution of PP were monitored by differential scanning calorimetry (DSC) and gel permeation chromatography (GPC), respectively. PP's crystallinity increased upon longer exposure time. The weight and number average molecular weight (M w and M n ) decreased with an increase in weathering duration. An increased polydispersity (PD = M w /M n ) implies that a secondary cross-linking process occurred during weathering.