Contributions of Basic Chemical Components to the Mechanical Behavior of Wood Fiber Cell Walls as Evaluated by Nanoindentation

Abstract

Selective chemical extraction was applied to gradually remove classes of chemical components from wood cell walls. Nanoindentation was performed on the control and treated wood cell walls to evaluate the contributions of the chemical components to the cell walls by measuring the elastic modulus, hardness, and creep compliance. Burger's model was applied to simulate the process of nanoindentation and to gain insight into the response of visco-elastic properties to the chemical components. Wood extractives showed limited effects on the cell-wall mechanics; however, the removal of hemicelluloses and lignin resulted in reductions of 11.7% and 28.4%, respectively, in the elastic modulus and 14.8% and 30.4%, respectively, in the hardness. The extraction of hemicelluloses and lignin reduced the resistance of wood cell walls to creep. Furthermore, the extracted parameters from Burger's modeling indicated that cellulose exhibited the greatest influence on the mechanical properties of wood cell wall, while hemicelluloses exhibited the greatest contribution to cell-wall viscosity, and lignin contributed extensively to cell-wall elasticity.

Chemical Structure and Mechanical Properties of Wood Cell Walls Treated with Acid and Alkali Solution

“…The characteristic lignin band near 1600 cm −1 is due to aromatic skeletal vibrations, and the band at 1271 cm −1 is due to either the guaiacyl ring or methoxy-aromatics [24,25]. The sample without treatment is included for comparison ( Figure 2).…”

The Microstructure and Mechanical Properties of Poplar Catkin Fibers Evaluated by Atomic Force Microscope (AFM) and Nanoindentation

“…The primary wall and epidermal layer were relatively thin, the secondary wall was relatively thick, and the connection between the primary wall and epidermal layer with the secondary wall was the darkest. In the modulus image, cellulose microfibril is the bright part, and the interstitial space between the non-cellulose polysaccharide matrix and microfibril is the dark part, because this matrix is significantly less elastic and harder than the microfibril [29,[45][46][47][48]. Chen et al [17,25] concluded that from the inside of the cell wall to the outside of the cell wall, the density of cellulose microfibril aggregates was unevenly distributed.…”

Effect of Hydrophobic Modification on Mechanical Properties of Chinese Fir Wood

“…Quasi-static indentation tests were performed under environmental conditions (Zhang et al 2016) of 20 °C and 45% ± 2% RH on the cell wall of latewood. All of the samples were kept in the TriboIndenter chamber for at least 24 h before indentations were made to minimize the effects of thermal expansion or contraction during the indentation process (Wang et al 2016a). In a force-controlled mode, the indenter tip was loaded to a peak force of 200 μN at a loading rate of 10 nm•s -1 , and a 9000 nm approaching distance was used for the first segment.…”

“…To gain further understanding of the relationships between hydrophobic modification and mechanical behavior at the cell wall level, in situ experiments are usually required (Wang et al 2016a). Nanoindentation is widely used to measure the nanoscale mechanical properties of materials that are relatively isotropic in their elastic properties and to address whether the modulus measured in an indentation test represents a specific crystallographic direction (Yang et al 2015;Wang et al 2016a).…”

“…To gain further understanding of the relationships between hydrophobic modification and mechanical behavior at the cell wall level, in situ experiments are usually required (Wang et al 2016a). Nanoindentation is widely used to measure the nanoscale mechanical properties of materials that are relatively isotropic in their elastic properties and to address whether the modulus measured in an indentation test represents a specific crystallographic direction (Yang et al 2015;Wang et al 2016a). Many researchers have used this method in wood research to characterize the adhesive bond effect on cell wall properties in a defined area (Konnerth and Gindl 2006;Konnerth et al 2010) and for wood modification (StanzlTschegg et al 2009).…”