Moisture Dependent Softening Behavior of Wood

An improved understanding of material behavior during the manufacture of wood-based composites can increase the efficiency of wood utilization and provide insight into the development of new processes and products that manipulate the viscoelastic nature of wood. One specific area where additional knowledge can be of great benefit is the influence of heat and moisture on the softening behavior of wood.The thermal softening behavior of wood at four moisture levels from 0 to 20% was evaluated using dielectric thermal analysis (DETA). Coincident in situ relaxations attributed to the softening of amorphous wood components in the range of 20 to 200°C were observed and found to exhibit the characteristics of a glass transition. The moisture dependence of this transition was characterized, and differences in the observed Tg were detected between juvenile and mature wood. Time-temperature superposition was also shown to be applicable to the wood and water system

Investigations of Flakeboard Mat Consolidation Part II. Modeling Mat Consolidation Using Theories of Cellular Materials

This work tested the applicability of theories designed to predict the compressive stress-strain behavior of cellular materials for modeling the consolidation of a wood flake mat. Model mats designed to simulate narrow sections of randomly aligned and preferentially oriented flake mats were compressed at ambient temperature and moisture conditions in a specially designed apparatus fitted to a servo-hydraulic testing machine. Load and deflection data were collected in real time, and theoretical equations designed to predict the compression of cellular materials were fit to the experimental data. Wood flake mats are cellular-cellular materials, exhibiting two overlapping phases of densification and a highly nonlinear stress-strain response. No differences in the observed stress-strain responses of mats resulted from variations in flake orientation. Theoretical models developed for the stress-strain relationships of cellular foams were fairly effective in predicting the stress-strain relationships of wood flake mats at strains less than 70%. At higher strain levels, the relative density surpassed the initial flake density, causing a violation of model assumptions and forcing the predicted stress levels to increase asymptotically. Combining one cellular material model for the densification of the mat with another for the densification of the wood flakes may be an effective way to model the complex mechanical behavior occurring during consolidation of a wood flake mat

Expression proteomics of UPF1 knockdown in HeLa cells reveals autoregulation of hnRNP A2/B1 mediated by alternative splicing resulting in nonsense-mediated mRNA decay

BACKGROUND: In addition to acting as an RNA quality control pathway, nonsense-mediated mRNA decay (NMD) plays roles in regulating normal gene expression. In particular, the extent to which alternative splicing is coupled to NMD and the roles of NMD in regulating uORF containing transcripts have been a matter of debate. RESULTS: In order to achieve a greater understanding of NMD regulated gene expression we used 2D-DiGE proteomics technology to examine the changes in protein expression induced in HeLa cells by UPF1 knockdown. QPCR based validation of the corresponding mRNAs, in response to both UPF1 knockdown and cycloheximide treatment, identified 17 bona fide NMD targets. Most of these were associated with bioinformatically predicted NMD activating features, predominantly upstream open reading frames (uORFs). Strikingly, however, the majority of transcripts up-regulated by UPF1 knockdown were either insensitive to, or even down-regulated by, cycloheximide treatment. Furthermore, the mRNA abundance of several down-regulated proteins failed to change upon UPF1 knockdown, indicating that UPF1`s role in regulating mRNA and protein abundance is more complex than previously appreciated. Among the bona fide NMD targets, we identified a highly conserved AS-NMD event within the 3` UTR of the HNRNPA2B1 gene. Overexpression of GFP tagged hnRNP A2 resulted in a decrease in endogenous hnRNP A2 and B1 mRNA with a concurrent increase in the NMD sensitive isoforms. CONCLUSIONS: Despite the large number of changes in protein expression upon UPF1 knockdown, a relatively small fraction of them can be directly attributed to the action of NMD on the corresponding mRNA. From amongst these we have identified a conserved AS-NMD event within HNRNPA2B1 that appears to mediate autoregulation of HNRNPA2B1 expression levels

Equilibrium Moisture Content of Wood in High-Temperature Pressurized Environments

Experiments were conducted on the water sorption characteristics of three wood species, for both juvenile wood and mature wood, at conditions above and below 100°C. A pressurized chamber was constructed for this purpose. At 50°C, equilibrium moisture content (EMC) behavior deviated only slightly from predictions based on the published data for Sitka spruce. At 160°C, the sorption behavior was distinctly different from the 50°C data, or any extrapolation from published low-temperature data. The data suggested that a change in the sorptive properties of the wood occurred as temperature and moisture conditions exceeded the glass transition temperature for lignin. At 50°C, juvenile wood tended to equilibrate at a higher moisture content than mature wood. At 160°C, however, juvenile wood exhibited a markedly lower EMC than mature wood. Thermal degradation of wood was detected during the experiments. Reduction in the sorptive behavior as a result of thermal degradation is proposed as a possible explanation for differences in EMC behavior for juvenile and mature wood at 160°C

Investigations of Flakeboard Mat Consolidation. Part I. Characterizing The Cellular Structure

As the wood-based composites industry continues to grow larger and more advanced, there is a need for a more fundamental understanding of material behavior during the hot-pressing process. This work describes the development and implementation of a method for quantifying the cellular structure of a flakehoard mat. Cross-sectional images of narrow mat sections and 6-in, x 6-in. mats were obtained, and structural parameters were quantified using computer image analysis techniques. Mat structure was analyzed with respect to: the percent area of mat cross section occupied by voids, the size and shape of individual voids, and the distribution of void size and shape. For mats formed with flakes oriented both randomly and parallel to the image plane, there was no significant difference in the average area of individual voids between the narrow mat sections and 6-in. x 6-in. mats. However, a significant difference in average area of individual voids between the two mat types was observed in mats formed with flakes oriented perpendicular to the image plane. Void size was not significantly allected by the direction of flake orientation. Void shape was significantly affected by both the method of mat formation and the direction of flake orientation