Elucidating the formation of structural defects in flax fibres through synchrotron X-ray phase-contrast microtomography

TL;DR

This study uses advanced microtomography to investigate the origin and development of kink-bands in flax fibres, revealing they form during mechanical extraction rather than growth, which impacts biobased composite material performance.

Contribution

It provides new insights into the formation of kink-bands in flax fibres, linking their presence to mechanical extraction processes rather than plant growth stages.

Findings

Kink-bands are present in fibres but not in green stems.

Kink-bands contain large pores detectable by microtomography.

Their formation is associated with mechanical extraction, not growth.

Abstract

The creation and ultrastructure of kink-bands in flax fibres are key issues for developing more and more performing biobased composite materials. Nevertheless, despite many hypotheses and structural characterization, the exact origin of kink-bands and the moment they appear remain unexplained. Here, by using cutting-edge techniques such as microtomography, a range of flax stems and fibres, from the green stem to stretched fibres, were morphologically explored. The study shows that all the extracted fibres, whether scutched, combed or stretched, contain significant amounts of kink-bands, which can be identified by the large pores they contain. On the other hand, at the scale of the green or retted stems, tomographic analysis does not reveal any kink-bands. These original observations suggest that the stress undergone by the plants during their growth is not sufficient, without major growth or lodging accidents, to generate these structural defects; the latter are only revealed after mechanical extraction of the fibres. Hypotheses regarding the kink-band appearance deformation levels are also given to complete the observations.