Exploring the defects generated by flax fibres processing from field to composite industry 4.0: an integrative approach to optimise long fibre 3D printing – FLOEME

The FLOEME project proposes an integrative approach to investigate the nature, the origin and the impact of defects, mechanically generated in flax fibres along the whole production chain. A multitude of defects may be observed throughout the production line. These defects are classified into several categories: morphological, biochemical and ultrastructural [4]. The impact of these defects on the behaviour of the materials and their processability will be assessed. One of the main originalities and contributions of FLOEME is to investigate the same batch of fibres, from the plant to the 3D printed part.

Five correlated scientific tasks are clearly identified and are complemented by a coordination action (Task 0). The FLOEME project was designed and developed to benefit from the strong complementarity between the partners, through an integrative and iterative approach.

The approach used consists of managing manage the entire transformation chain. The flax plants, from the same batch supplied by VRF, were transformed into flax reinforcement using the resources of one of the partners. The study of the interactions between the properties and structure of flax and the process parameters was conducted in close collaboration with two other partners. This study allows the development of promising initial filaments for 3D printing of long flax fibres. The second step was to optimize this filament to obtain plane composite structures with higher printing qualities. The iterative approach should make it possible to determine the microstructure of the optimum filament according to the desired use.

The combined method - multi physical and multi scale experimental characterization coupled with numerical analysis - was used to obtain deep analysis of all elements.

The major results of the FLOEME project were published in 8 scientific publications. Some others are still in progress. With the contributions of the membres involved in the project, more than 20 oral presentations at national and international conferences were done. The major results can be grouped into three categories:

1/ The interactions between process parameters and the apparition and the growth of kink-bands and their influence on mechanical properties on fibres.
2/ A better understanding of the morphology and properties of kink bands using high-resolution imaging.
3/ The development of a new long-fiber filament with long flax fibres and PLA for long-fiber 3D printing, as well as the development of a 3D printing strategy for the elaboration of composites.

The correlation between the occurrence of kink-bands, fibre extraction method and fibre mechanical properties was analysed. An extensive multi-scale statistical study was conducted on 96 elementary fibres extracted from four distinct batches processed with different scutching and combing conditions. First, kink-bands were observed and quantified through polarized light microscopy (PLM), scanning electron microscopy (SEM) and synchrotron X-ray microtomography.
The results suggest that changes in kink-bands structIn the framework of FLOEME Project, a customised commingled flax/PLA wrapped yarn was developed to overcome usual drawbacks in 3D printing filamenture are principally responsible for the flax evolutions; due to both new distribution of pores in kink-bands regions and reduction in kink-band size possibly induced by local cellulose realignment.
Deeper observation using high resolution X ray tomography on flax fibres used in FLOEME projects revealed pores in the cell wall of elementary fibres: kink-band pores and longitudinal pores, a previously unseen defect. Their morphology and organisation are examined, highlighting fibre deterioration and locally increased porosity up to 14.86 %. Under tension, cracks are thus likely to initiate at kink-band defects, may propagate through longitudinal pores to other kink-bands, and lead to fibre and composite failure as these defects are favoured zones for crack initiation and propagation.
In the framework of FLOEME Project, a customised commingled flax/PLA wrapped yarn was developed to overcome usual drawbacks in 3D printing filament, i.e. poor core impregnation and poor fibre alignment. Several compositions were developed and tested in 3D printing. The 3D printing strategy used and developed as part of the FLOEME project is promising. The impregnation of flax fibre in the composite and the alignment of the fibres make it possible to envisage composites with properties that are better than those reported in the literature.

The FLOEME project demonstrated the feasibility to elaborate a filament for 3D printing at a laboratory scale. One of the prospects and challenges will be to develop homogeneous filaments incorporating flax fibres sourced directly from industrial scutching processes. Until now, filament preparation is required prior to printing. The development of a new printing strategy that limits or even eliminates this step would be an important step towards optimising structures and enabling the printing of non-planar structures.

Loren Morgillo, Lèna Brionne, Alessia Melelli, Pierre Ouagne, Mario Scheel, et al.. Elucidating links between the mechanical performance of flax fibres and their structural defects. Industrial Crops and Products, 2023, 206, pp.117722. ?10.1016/j.indcrop.2023.117722?. ?hal-04663657?

Delphine Quereilhac, Emmanuel de Luycker, Sofiane Guessasma, Marwa Abida, Jonathan Perrin, et al.. Synchrotron X-ray microtomography and finite element modelling to uncover flax fibre defect’s role in tensile performances. Composites Part A: Applied Science and Manufacturing, 2024, 184, pp.108276. ?10.1016/j.compositesa.2024.108276?. ?hal-05049692?

Delphine Quereilhac, Lola Pinsard, Elouan Guillou, Marina Fazzini, Emmanuel de Luycker, et al.. Exploiting synchrotron X-ray tomography for a novel insight into flax-fibre defects ultrastructure. Industrial Crops and Products, 2023, 198, pp.116655. ?10.1016/j.indcrop.2023.116655?. ?hal-04125820?

Loren Morgillo, Alessia Melelli, Mario Scheel, Raymond Wightman, Timm Weitkamp, et al.. Inside the kink-bands of archaeological flax artefacts via sub-micrometer resolution micro-CT: A comprehensive microstructural analysis to better understand degradation mechanisms of fibres. Composites Part B: Engineering, 2025, 298, pp.112347. ?10.1016/j.compositesb.2025.112347?. ?hal-05049276?

At the moment of the Green Deal and climate change, the industrial use of innovative and high-performance bio-based materials, pushed by societal pressure, must accelerate. The 3D printing of structural composite parts, biobased and/or degradable, and reinforced with high-performance plant fibres is fully in line with these industrial and societal expectations. In this context, through a completed knowledge of the extraction and transformation processes of flax fibres, as well as the mechanisms of creation of defects within these fibres, the FLOEME project aims to optimise the performance of biobased composites reinforced by flax fibres. Thus, the reinforcement properties of flax fibres in the form of dedicated yarns will be maximised in order to offer new and performing solutions to 3D printing processes; long-fibre products with optimised performance will thus be designed and developed. In order to fully exploit the mechanical potential of flax fibres, we propose to study in depth the quality of fibres, all along their transformation chain, from the field to the 3D printing factory, via the extraction processes by scutching/combing and transformation (from specific spinning to the elaboration of composites). Thus, the FLOEME project proposes an integrative approach to study and identify, using advanced investigation techniques (SHG, AFM, DRX, RMN), the defects generated mechanically in flax fibres throughout their life cycle, with the major objective of limiting the appearance of these fragile areas. Thus, FLOEME aims to enhance the efficiency of the technical flax industry by developing knowledge about the link between the emergence of defects and the key stages of the first (scutching) and second transformations (specific spinning for composite reinforcement). By optimising transformation processes, FLOEME will contribute to the development of innovative and efficient solutions such as long-fibre 3D printing to develop an innovative, environmentally responsible and competitive industry 4.0.