Qualitative and Quantitative Characterization of Wood Fibers of Shrubs and Tree Species of the Tamaulipan Thorn Scrub, Northeastern Mexico and Its Possible Relation to Wood Quality and Utilization

The present study was undertaken to determine the variability in fiber cell morphology and its length among wood species of the Tamaulipan Thorn Scrub, Northeastern Mexico, used for various uses such as timber for furniture, fence, post, firewood and sources of forage. The results reveal large variability in fiber cell morphology and fiber cell dimensions. The species are classified on the basis of its fiber cell morphology and fiber cell length and recommended for their possible utilization for different purposes. Wood having fibre cells with broad lumen and thin wall could be suitable for the manufacture of paper documented in the literature viz. Acacia farnesciana, Caesalpinia mexicana, Cordia boisiieri, Diospyros palmeri, Forestieria angustifolia, Morus celtifolia, Prosopis laevigata. This technique can be used in preliminary screening of woody species for its utilization for different purposes. Further studies are needed to confirm.

Observations of Wood Cell Walls with a Scanning Probe Microscope

Scanning Probe Microscopes (SPMs) observe specimen surfaces with probes by detecting the physical amount of a material between the cantilever and the surface. SPMs have a high resolution and can measure mechanical characteristics such as stiffness, adsorptive properties, and viscoelasticity. These features make it easy to identify the surface structure of complex materials;therefore, the use of SPMs has increased in recent years. Wood cell walls are primarily composed of cellulose, hemicellulose, and lignin. It is believed that hemicellulose and lignin surround the cellulose framework;however, their detailed formation remains unknown. Therefore, we observed wood cell walls via scanning probe microscopy to try to reveal the formation of the cellulose framework. We determined that the size of the cellulose microfibril bundle and hemicellulose lignin module composite was 18.48 nm based on topography and that the size of the cellulose microfibril bundle was 15.33 nm based on phase images. In the viscoelasticity image, we found that the viscoelasticities of each cell wall of the same cell were not the same. This is because the cellulose microfibrils in each cell wall lean in different directions. The angle between the leaning of the cellulose microfibril and the cantilever affects the viscoelasticity measurement.

Effect of the suppression of BpAP1 on the expression of lignin related genes in birch

Lignin is an integral part of secondary cell walls in plants and plays important roles in maintaining the strength of stems,enhancing transport ability of stems,and providing resistance to multiple stresses.Lignin biosynthesis has become one of the hotspots in molecular forest biology research.The AP1 transcription factor plays important roles in plant fower development.However,in this study,suppression of BpAP1 altered the transcription profiles of white birch and RNA-seq was used to find that suppression of BpAP1 changed the expression of lignin pathway-related genes;C4 H/CYP73A,POD were down-regulated and HCT,CCoAOMT,REF1 and CAD were up-regulated.Cell walls of the suppressed transgenic birch were significantly thinner than the wild type of birch,and Bp AP1-repressed birch contained less lignin.In addition to regulation of foral development,BpAP1 might play a role in regulating the expression of genes in lignin biosynthesis of birch.This study could provide a new insight into the function of AP1 genes in woody species.

Multi-scale finite element simulation on large deformation behavior of wood under axial and transverse compression conditions

Multi-scale finite element method is adopted to simulate wood compression behavior under axial and transverse loading. Representative volume elements (RVE) of wood microfibril and cell are proposed to analyze orthotropic mechanical behavior. Lignin, hemicellulose and crystalline-amorphous cellulose core of spruce are concerned in spruce nanoscale model. The equivalent elastic modulus and yield strength of the microfibril are gained by the RVE simulation. The anisotropism of the crystalline-amorphous cellulose core brings the microfibril buckling deformation during compression loading. The failure mechanism of the cell-wall under axial compression is related to the distribution of amorphous cellulose and crystalline cellulose. According to the spruce cell observation by scanning electron microscope, numerical model of spruce cell is established using simplified circular hole and regular hexagon arrangement respectively. Axial and transverse compression loadings are taken into account in the numerical simulations. It indicates that the compression stress-strain curves of the numerical simulation are consistent with the experimental results. The wood microstructure arrangement has an important effect on the stress plateau during compression process. Cell-wall buckling in axial compression induces the stress value drops rapidly. The wide stress plateau duration means wood is with large energy dissipation under a low stress level. The numerical results show that loading velocity affects greatly wood microstructure failure modes in axial loading. For low velocity axial compression, shear sliding is the main failure mode. For high velocity axial compression, wood occur fold and collapse. In transverse compression, wood deformation is gradual and uniform, which brings stable stress plateau.

Characters of Fractal Ultrastructure in Wood Cell Wall

Fractal theory was introduced in order to describe the ultrastructure of wood cell wall in this paper. The cellulose chain clusters around nano-scale were viewed as a fractal object that consists of many fibrillar structural units with different scales including microfibrils. On the basis of the morphological data of wood cell wall, fractal dimensions of multi-level fibrillar structural units were calculated by fractal-geometry approach, and then the morphological and structural characteristics of fibers as well as the influences on wood properties were investigated according to the dimensions. Besides, the fractal self-nesting character of the ultrastruture was also analyzed.