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

Alain Bourmaud; David Siniscalco; Loïc Foucat; Camille Goudenhooft; Xavier Falourd; Bruno Pontoire; Olivier Arnould; Johnny Beaugrand; Christophe Baley

doi:10.1016/j.carbpol.2018.10.065

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

Carbohydr Polym. 2019 Feb 15:206:48-56. doi: 10.1016/j.carbpol.2018.10.065. Epub 2018 Oct 28.

Authors

Alain Bourmaud¹, David Siniscalco², Loïc Foucat³, Camille Goudenhooft², Xavier Falourd³, Bruno Pontoire³, Olivier Arnould⁴, Johnny Beaugrand³, Christophe Baley²

Affiliations

¹ IRDL, Université Européenne Bretagne, CNRS, UMR 6027, Lorient, France. Electronic address: alain.bourmaud@univ-ubs.fr.
² IRDL, Université Européenne Bretagne, CNRS, UMR 6027, Lorient, France.
³ UR1268 Biopolymères Interactions Assemblages, INRA, Nantes, France.
⁴ LMGC, Université de Montpellier, CNRS, UMR 5508, Montpellier, France.

PMID: 30553348
DOI: 10.1016/j.carbpol.2018.10.065

Abstract

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 compaction 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.

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