Better insight into the nano-mechanical properties of flax fibre cell walls

Abstract

International audiencePeak-Force Quantitative Nano-Mechanical property mapping (PF-QNM) was applied to explore the nano-mechanical properties of flax fibre cell walls in cross-section. After validation of the ability of PF-QNM to determine stiffness gradients in aramid fibres, measurements were performed on developing flax bast fibres. The presence of two layers with different indentation moduli implies their progressive development during thickening of the secondary cell wall. Finally, measurements were carried out on technical flax fibre cell wall; but, in this case, no significant stiffness gradient could be identified in the secondary S 2 layer

Investigation of the Mechanical Properties of Flax Cell Walls during Plant Development: The Relation between Performance and Cell Wall Structure

“…PF-QNM imaging mode with a RTESPA-525 (Bruker) probe with a spring constant of 139 N/m and a tip radius between 15 and 35 nm were used. The tip and cantilever of the probe were calibrated as detailed in Arnould et al [11]. A scan rate of 8 µm/s and a maximum load of 200 nN were used for all the measurements.…”

“…A scan rate of 8 µm/s and a maximum load of 200 nN were used for all the measurements. Nanoindentation measurements of the indentation modulus of the embedding resin and at some location in cell wall G layers of each sample were also done and serve as a control for AFM measurements [11].…”

“…At mid-stem (Figure 1b), gradients in terms of local indentation modulus are visible on fiber cell walls, with averages values from 14.0 ± 1.8 GPa for the Gn layer to 18.0 ± 1.9 GPa for the G layer [11]. The looser appearance of the Gn layer and its lower indentation modulus compared to the G layer argue for a mechanism of aggregation of cellulose microfibrils and entrapment of the matrix material, during the maturation of the cell wall from Gn to G layer.…”

“…Figure 2 shows that fibers from all stem locations exhibit thick cell walls with homogeneous indentation moduli within single fibers, but also between fibers (17.3 ± 1.7 GPa for the top, 18.4 ± 1.3 GPa for the middle, and 17.7 ± 1.4 GPa for the bottom fibers). At mid-stem (Figure 1b), gradients in terms of local indentation modulus are visible on fiber cell walls, with averages values from 14.0 ± 1.8 GPa for the Gn layer to 18.0 ± 1.9 GPa for the G layer [11]. The looser appearance of the Gn layer and its lower indentation modulus compared to the G layer argue for a mechanism of aggregation of cellulose microfibrils and entrapment of the matrix material, during the maturation of the cell wall from Gn to G layer.…”

“…Moreover, three height positions in the stem were chosen for the investigation, namely top, bottom, and middle parts of the stem. The evolution of the local indentation modulus of fiber cell wall layers was characterized by peak-force quantitative nano-mechanical property mapping (PF-QNM), a powerful tool for imaging possible gradients in stiffness of wood and other plant cell walls [10,11]. Mechanical properties of extracted single fibers over plant growth were also estimated by tensile tests, a reliable method to evaluate the average apparent tensile properties of flax fibers [3].…”