4 theses are conducted and co-financed in the framework of FLOWER project. The 4 PhD sutdents (2 with the partner INRA Nantes and 2 with University of South Brittany in Lorient) fully participate to FLOWER activities and have a privileged contact with all the project partners. Their research topics are complementary and in direct relation with the issues identified at the project setting up stage. You can find below a synthetic description of the 4 research topics and you will be able to follow their evolution and progress on a regular basis.
Exploration of the development and structure of the Flax fibres for their use as reinforcement in composite materials
Alessia Melelli – University of South Brittany
- Alain Bourmaud, Ingénieur de Recherche, HDR, IRDL Lorient
- Johnny Beaugrand, Directeur de Recherche, INRA Nantes
- Frédéric Jamme, Ingénieur de Recherche, Synchrotron SOLEIL, Gif-Sur-Yvette
The use of flax fibre has a very old origin for the creation of objects and clothing, but today there is a renewed interest in this material which has developed because of its extraordinary mechanical properties comparable to those of glass fibre. This aspect opens new frontiers for the use of flax fibre as a low-density, environmentally friendly and cost-effective material that can be used as reinforcements in composite materials, improving the mechanical properties and also the life cycle of the final product. However, flax fibre has a complex architecture and its properties may vary depending on the growing conditions of the batch, the variety, the treatments for fibre extraction and ageing. Thus, it is essential to control the performance of the plant and fibres before using them in materials for industrial purposes.
The main objectives of this thesis are to use advanced analytical tools to explore the intrinsic properties of fibres by considering different flax varieties but also different growing conditions. The complementary skills of the institutes that co-supervise this work make it possible to consider three main areas of work. Thus, the mechanical performances at the scale of elementary fibres, but also those of plant walls, will be explored by nanoindentation or AFM Peakforce.
These results will be coupled with the biochemical structuring and parietal architecture of flax that will be studied by NMR, Raman or Infrared micro spectroscopy on conventional laboratory equipment or with Synchrotron facilities. Finally, we will focus specifically on the defects (kink-bands) present in the fibres as well as the organization of cellulose and in particular its microfibrillary angle through the use of second harmonic generation imaging. The implementation of these various highly complementary tests should make it possible to propose a significant contribution to the small-scale analysis of flax cell walls.
Multi-scale study of the damage of flax fibers, structure – behavior relationship by experimental and numerical approaches
Emmanuelle RICHELY – INRAE Nantes, BIA
- Dr. Johnny Beaugrand, Directeur de Recherche INRA Nantes
- Dr. Sofiane Guessasma, Chargé de Recherche, INRA Nantes
- Dr. Davy Duriatti, Responsable R&D, Groupe Depestele, Bourguébus
This thesis topic focuses on the understanding of damage and fracture mechanisms within bundles of flax fibers. During the last decade, the sustained efforts and the resulting advances indicate that the development of composite materials reinforced with plant fibers also requires a fundamental knowledge of the intrinsic properties of fibers.
The research objectives are divided in two axes:
- Develop knowledge around the damage and rupture mechanisms in flax fiber elements.
- Determine constitutive laws through numerical modelling using finite element methodology and experimental validation.
Two architectures are studied: the bundle of fibers as well as the unitary fiber. A bundle is itself a composite consisting of unitary fibers connected by a middle lamella. The role of the latter in the individualization of unitary fibers remains to be better described and controlled.
Figure 1 : Different scales of study : from the trunc to the cell wall, adapted from 
The flax samples studied are contrasted in agreement with influential parameters of flax cultivation and processing.
The approach is multi-scale and includes the following experimental and simulation steps:
 Bourmaud, A., J. Beaugrand, D. U. Shah, V. Placet and C. Baley (2018). “Towards the design of high-performance plant fibre composites.” Progress in Materials Science 97: 347-408.
Multi-physical pretreatment combined for a flax material shaped to a composite application
Maxime Gautreau – INRAE Nantes, BIA
- Johnny Beaugrand, Directeur de Recherche, INRA, Nantes
- Alain Bourmaud, Ingénieur de Recherche, Université de Bretagne Sud, Lorient
- Fabienne Guillon, Directrice de Recherche, INRA, Nantes
The aim of the thesis is to modify the flax fiber raw materials for two main families of targeted output products, in order to improve performance according to the product specifications.
The thesis can be divided into two parts :
– The aim of the first part is to evaluate the role of the different polymers of the flax fiber on its properties. For this, a selective extraction of parietal biopolymers (pectin, hemicellulose, cellulose) by solvent affinity will be conducted. In parallel, the effect of the modifications of the chemical structure of the parietal biopolymers by biological effectors on the mechanical properties will be studied.
– The purpose of the second part is to evaluate the interest of the chemical, physical and physicochemical treatments to modify the surface of the fibers in order to improve the interface of the fibers and the matrix within the composite material. The products will be flax stems, scutched fibers and tows. In addition to modifying the surface of the fibers, another parameter will be studied : the individualization of the fibers. Finally, these treatments will be implemented on non-woven composites with polypropylene as a matrix and a mechanical characterization will be conducted.
 Zhang H, Ming R, Yang G, Li Y, Li Q, Shao H. “Influence of alkali treatment on flax fiber for use as reinforcements in polylactide stereocomplex composites.” Polymer Engineering and Science (2015)
Multi-scale characterisation of innovative flax reinforcement for composite
Delphin Pantaloni – University of South Brittany
- Alain Bourmaud, Ingénieur de Recherche, Université de Bretagne Sud, Lorient
- Christophe Baley, Professeur, Université de Bretagne Sud, Lorient
- Darshil Shah, Directeur de Recherche, Université de Cambridge, Cambridge (UK)
The aim of this thesis is to develop the use of flax fibres in composites materials. Two main axes are investigated according to two major flax characteristics.
The first one is its biodegradability and the opportunity to develop fully biodegradable biocomposite. In this way, a study will be carried out to define the most appropriate resin, keeping biodegradability of the composite and yielding a composite with acceptable mechanical properties. These composites will be composed of the new light non-woven developed by EcoTechnilin in FLOWER project. This will lead to a light composite with good mechanical properties, which could be composted to limit its negative environmental impact. Several mechanical studies will be conducted on this new material to characterise its mechanicals properties, its biodegradability and its life cycle assessments.
Flax fibres are also characterised by good mechanical properties (close to glass fibres’ ones) as well as interesting damping properties. Thus, flax fibres are relevant to be used as technical reinforcements for common thermoset composite, especially for semi-structural applications such as FLOWER’s developement. Flax fibres are assembled in yarns or strands used as feedstock to various preforms, depending on the reinforce orientation desired. The influence of the yarns architecture, as well as the fabric one, on the mechanical and structural properties of the resulting composite will be investigated. We will focus particularly on Despetele’s semi-product developed in FLOWER: a new flax fibre biaxial fabric.