Evolution of flax cell wall ultrastructure and mechanical properties during the retting step

Alain Bourmaud (1) , David Siniscalco (1) , Loic Foucat (2) , Camille Goudenhooft (1) , Xavier Falourd (2) , Bruno Pontoire (2) , Olivier Arnould (3) , Johnny Beaugrand (2) , Christophe Baley (1)

1 IRDL - Institut de Recherche Dupuy de Lôme
2 BIA - Unité de recherche sur les Biopolymères, Interactions Assemblages
3 BOIS - Bois

Flax retting is a major bioprocess in the cultivation and extraction cycle of flax fibres. The aim of the present study is to improve the understanding of the evolution of fibre properties and ultrastructure caused by this process at the plant cell wall scale. Initially, investigations of the mechanical performances of the flax cell walls by Atomic Force Microscopy (AFM) in Peak Force mode revealed a significant increase (+33%) in the cell wall indentation modulus with retting time. Two complementary structural studies are presented here, namely using X-Ray Diffraction (XRD) and solid state Nuclear Magnetic Resonance (NMR). An estimation of the cellulose crystallinity index by XRD measurements, confirmed by NMR, shows an increase of 8% in crystallinity with retting mainly due to the disappearance of amorphous polymer. In addition, NMR investigations show a com-paction of inaccessible cell wall polymers, combined with an increase in the relaxation times of the C4 carbon. This densification provides a structural explanation for the observed improvement in mechanical performance of the secondary wall of flax fibres during the field retting process.

Mots clés: Solid-state; Nuclear magnetic resonance; Atomic force microscopy; Retting; Flax fibres; X-ray diffraction; Mechanical properties

Domaines: Mécanique des matériaux [physics.class-ph]; Polymères

Alain Bourmaud, David Siniscalco, Loic Foucat, Camille Goudenhooft, Xavier Falourd, et al.. Evolution of flax cell wall ultrastructure and mechanical properties during the retting step. Carbohydrate Polymers, 2019, 206, pp.48 - 56. ⟨10.1016/j.carbpol.2018.10.065⟩. ⟨hal-01937778⟩