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

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 characterisation, 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.

Automated summary

This study used cutting-edge techniques to explore the morphology of flax stems and fibers and found that various extracted fibers contained significant amounts of kink-bands. However, no kink-bands were observed at the scale of green or retted stems. This suggests that the stress experienced by plants during their growth is not enough to generate these structural defects, and they are only revealed after mechanical extraction of the fibers.