Identification of polymer matrix yield stress in the wood cell wall based on micropillar compression and micromechanical modelling

2016 ◽  
Vol 96 (32-34) ◽  
pp. 3461-3478 ◽  
Author(s):  
Jakob Schwiedrzik ◽  
Rejin Raghavan ◽  
Markus Rüggeberg ◽  
Silla Hansen ◽  
Juri Wehrs ◽  
...  
Keyword(s):  
Cell Wall ◽  
Yield Stress ◽  
Polymer Matrix ◽  
Wood Cell Wall ◽  
Micromechanical Modelling ◽  
Micropillar Compression

scholarly journals Micromechanical properties of beech cell wall measured by micropillar compression test and nanoindentation mapping

Holzforschung ◽  
2020 ◽  
Vol 74 (9) ◽  
pp. 899-904
Author(s):  
Petr Klímek ◽  
Václav Sebera ◽  
Darius Tytko ◽  
Martin Brabec ◽  
Jaroslav Lukeš
Keyword(s):  
Cell Wall ◽  
Yield Stress ◽  
Compression Test ◽  
State Of The Art ◽  
Middle Lamella ◽  
Uniaxial Stress ◽  
Wood Structure ◽  
Micropillar Compression ◽  
The Mean ◽  
Insight Into

AbstractWood exhibits very different behavior and properties at different scales. One important scale is the cell wall (CW) that is commonly tested by nanoindentation. Common nanoindentation provides important insight into the material but has limitations because it does not apply uniaxial stress and provides data from single spots. Therefore, the aim was to examine beech CW using two state-of-the-art techniques: micropillar compression (MCo) and nanoindentation mapping (NIP). The mean strength of the beech CW was found to be about 276 MPa and the mean yield stress was 183 MPa. These values were higher than those in most cited literature, which was attributed to the fact that libriform fibers from beech late wood were measured. Mean E obtained from MCo was about 7.95 GPa, which was lower than the values obtained on a macrolevel and about 61% of the value obtained from NIP. NIP also showed that E of the CW around the middle lamella (ML) was about 64% of the value at the location attributed to the S2 layer. Lower E from MCo may be caused by sinking of the micropillar into the wood structure under the load. Failure of the micropillars showed gradual collapse into themselves, with debonding at the S3 layer or the MLs.

Micromechanics of Wood Cell Wall

MRS Advances ◽  
2016 ◽  
Vol 1 (58) ◽  
pp. 3837-3845 ◽  
Author(s):  
Lik-ho Tam ◽  
Denvid Lau
Keyword(s):  
Cell Wall ◽  
Polymer Matrix ◽  
Damage Evolution ◽  
Wood Cell Wall ◽  
Research Work ◽  
Basic Unit ◽  
Plastic Yielding ◽  
Structural Failure ◽  
Macro Scale ◽  
Cellulose Fibrils

ABSTRACTThe damage evolution and structural failure in trees and other plants are mainly originated from the plastic yielding in the wood cell wall at the microstructural level, which consists of cellulose fibrils embedded in a polymer matrix of hemicellulose and either lignin or pectin. Understanding the mechanical behavior of wood cell wall at the plastic regime is critical to the investigation of the fracture characteristics of trees at macro-scale. In this research work, the wood cell wall, which consists of cellulose fibrils, hemicellulose chains and lignin macromolecules, is modeled at the mesoscale to investigate the mechanical responses under deformation. By examining the force-strain relationship, the mechanical behaviors of the wood cell wall at the plastic yielding range are obtained, which are initiated from the slippage between the fibrils and polymer matrix. The simulation results are compared with experimental measurements and theoretical predictions to provide a bottom-up description of micromechanics of the wood cell wall, and to explain the damage evolution and structural failure occurred at the larger scales. The wood cell wall investigated here can be applied to the construction of wood hierarchical structure as a basic unit and adapted to the studies of different natural materials.

Acetyl Group Distribution in Acetylated Wood Investigated by Microautoradiography

Holzforschung ◽  
2001 ◽  
Vol 55 (3) ◽  
pp. 270-275 ◽  
Author(s):  
Marie Rosenqvist
Keyword(s):  
Cell Wall ◽  
Weight Gain ◽  
Acetic Anhydride ◽  
Wood Cell Wall ◽  
Environmental Scanning Electron Microscopy ◽  
Environmental Scanning ◽  
Accurate Information ◽  
Concentration Gradients ◽  
Good Opportunity ◽  
Acetyl Group

Summary Sapwood of Scots pine (Pinus silvestris L.) was acetylated with 14C- and 3H-labelled acetic anhydride. The distribution of acetyl groups was investigated with microautoradiography and microautoradiographs were evaluated with ESEM, Environmental Scanning Electron Microscopy. The investigation showed that the impregnation of wood with radioisotope-labelled substances provides a good opportunity to investigate the location of substances covalently bonded to the wood material. Introduced 14C-labelled acetyl groups show an even distribution in the wood cell wall, with no discernible concentration gradients at acetylation levels of about 5, 15 and 20% weight gain. 3H-labelled acetyl groups show an even distribution in the wood cell wall at 15 and 20% weight gain, with no discernible concentration gradients. At the 5% weight gain level, however, an uneven distribution of 3H-labelled acetyl groups over the cell wall is observed. Nevertheless, the unevenness is random and no concentration gradient is discernible at this level. 3H with a relatively high resolution, 0.5–1 μm, compared to 14C with a resolution of 2–5 μm, gives more accurate information about where exactly the acetyl groups are situated in the wood cell wall. Acetic anhydride was evenly distributed when a full impregnation procedure was used. The chemical and physical properties of acetic anhydride allow a uniform penetration into the pine cell wall and a complete acetylation takes place when the specimens are heated.

scholarly journals Enhancement of the physical and mechanical properties of wood using a novel organo-montmorillonite/hyperbranched polyacrylate emulsion

Holzforschung ◽  
2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Jianfeng Xu ◽  
Xiaoyan Li ◽  
Ling Long ◽  
Ru Liu
Keyword(s):  
Mechanical Properties ◽  
Cell Wall ◽  
Pinus Radiata ◽  
Wood Sample ◽  
Wood Cell Wall ◽  
Physical And Mechanical Properties ◽  
Radiata Pine ◽  
Compact Structure ◽  
Populus Cathayana ◽  
Modified Wood

AbstractIn this work, a novel waterborne hyperbranched polyacrylate (HBPA) dispersed organo-montmorillonite (OMMT) emulsion was synthesized and used for the treatment of wood in a vacuum environment in order to enhance the physical and mechanical properties of the wood. The sapwood of Cathay poplar (Populus cathayana Rehd.) and Radiata pine (Pinus radiata D.Don) were used as the samples for experimentation. The results showed that the physical and mechanical properties of the wood improved significantly due to the successful penetration of the OMMT and HBPA into the wood cell wall. From it was also observed that OMET completely exfoliated from the HBPA matrix and formed a hydrophobic film covering on the inside walls of the cell lumen. Further, it was observed that the poplar sample displayed better mechanical properties than the pine sample because the pine has a more compact structure when compared to poplar and contains rosin. Furthermore, it was also observed that the mechanical properties of the modified wood sample gradually improved with an increase in the concentration of the emulsion. However, excessive concentration (>4 wt%) did not lead to further improvement.

scholarly journals Microstructure of thermally modified radiata pine wood

BioResources ◽  
2020 ◽  
Vol 16 (1) ◽  
pp. 1523-1533
Author(s):  
José Luis Cabezas-Romero ◽  
Linette Salvo-Sepúlveda ◽  
Helga Contreras-Moraga ◽  
Natalia Pérez-Peña ◽  
Víctor Sepúlveda-Villarroel ◽  
...  
Keyword(s):  
Cell Wall ◽  
Wood Cell Wall ◽  
Morphological Changes ◽  
Untreated Wood ◽  
Radiata Pine ◽  
Treatment Temperature ◽  
Thermal Modification ◽  
Modification Process ◽  
Potential Alternative ◽  
Two Temperatures

The thermal modification of wood is a potential alternative method for improving wood dimensional stability and increasing the resistance of wood to decay. However, during thermal modification, morphological changes occur within the microstructure of the cell, and these confer different properties to the wood. This study investigated the effects of the thermal modification process on the microstructure of radiata pine juvenile wood. Therefore, anatomical measurements were performed via optical microscopy in selected earlywood and latewood samples after each treatment, and the results were compared to untreated wood samples. In this study, two temperatures (190 °C and 210 °C) were considered for the thermal modification process. The results showed that the level of temperature of modification affected to microstructure of cell wall. The cell wall thickness decreased as treatment temperature increased, whereas the average lumen diameter increased slightly as temperature increased. Thermally modified radiata pine showed signs of damage (cracks, broken cells and deformations in the wood cell wall). The proportion of destroyed area increased as temperature increased, and significant differences were evident for the thermal treatment at 210 °C.

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