Investigation of the internal structure of flax fibre cell walls by transmission electron microscopy

Abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. Abstract The development of the use of flax fibre as reinforcement of eco-friendly composite materials requires a good knowledge of its hydrothermal and mechanical behaviours. To this end the fibre internal structure must be finely investigated. Transmission electron microscopy was used to analyse the morphology of the fibre cell walls in terms of the arrangement of the layers and their thickness. Thus, an alternative eco-friendly staining method, based on oolong tea extract was successfully implemented. The results reveal an arrangement at the nanoscale slightly different from the classical four layer model encountered in the literature: the inner layer includes three to four sub-layers. The cell walls comprises two outer layers of relative thickness of about 10 %, a middle layer of about 70 % and a group of thinner layers (called sub-layers) that are contiguous to the lumen with relative thickness of about 20 %.

Distribution of Lignin, Hemicellulose, and Arabinogalactan Protein in Hemp Phloem Fibers

“…Some cells showed a multilayered structure in UV microscopy and TEM observation with KMnO 4 staining (Figs. 2g, 3), as reported previously in flax (Thuault et al, 2015). This structure appeared to be similar to that observed in phloem fibers of some dicotyledonous woods (Nanko, 1979).…”

Dynamic In-Situ Observation on the Failure Mechanism of Flax Fiber through Scanning Electron Microscopy

“…It was proposed that the spiral angle, hierarchical fiber pull out, and crack bridging-all contribute to the high work of fracture of flax fiber. The fractographic approach of the failure of flax fiber reveals some of the intricate details of the structure of flax fiber such as the arrangement of mesofibrils and microfibrils, and also supports the findings of Thuault et al [13] about the presence of more than four layers in flax fibers. The strain rate sensitivity of technical flax fibers on the mechanical properties of flax fibers such as, failure strength, failure strain, elastic modulus, and failure time with three different strain rates namely, 0.01, 0.03 and 0.08 min −1 was investigated.…”

“…During this conversion process from Gn-layer to G-layer, it is possible that additional layer or strata may have created in the mature flax fiber cell wall. The transmission electron microscopy of mature flax fiber cell wall suggests that the conventional four layer model (P/S1/S2 or G-layer/S3) is not accurate enough to represent flax fiber cell wall as there are more than four layers present in the cell wall [13]. The S2 layer is analogous to a composite lamina where cellulose meso-fibrils, having a diameter of 100-200 nm, are helically arranged in an amorphous matrix of hemicellulose and pectin ( Figure 2) [3].…”

“…The secondary wall generally has three layers namely S1, S2 and S3 with a thickness of 0.5-2 µm, 5-10 µm and 0.5-1 µm respectively [2,11,12]. Among them the S2 layer is the thickest and around 70% of the Young's Modulus is mainly governed from this part of the structure [13]. The formation of these different layers occurs during the growth stage of bast fibers, more specifically, when the elongation of the cell stops and the thickening of the cell wall begins.…”

Mesoscale modelling of tensile response and damage evolution in natural fibre reinforced laminates

“…Glass where stiffness degradation tends to be constant and linear [41,42]. This difference in response is attributed to the inherent non-homogeneous nature of natural fibres: hierarchical structure [30,39,43], defects in individual fibres [44e46], and variable fibre geometry [47,48]. Depending on the matrix material used in the composite, some or all of the following distinct damage progression mechanisms have been identified through studies on NFC microstructure: (i) microfibril reorientation in the natural fibre secondary cell wall, (ii) 'intra-bundle' cracking, indicating splitting apart or separation of elementary fibres within a yarn bundle, (iii) transverse cracking in fibres, (iv) 'circum-bundle' interfacial cracks along the fibre-matrix boundary that indicate debonding or peeling, and (v) matrix shear cracks [23,49e59].…”