Alain Bourmaud

Flax stems: from a specific architecture to an instructive model for bioinspired composite structures

The present paper proposes to carefully study and describe the reinforcement mechanisms within a flax stem, which is an exceptional natural model of composite structure. Thanks to accurate microscopic investigations, with both optical and SEM method, we finely depicted the flax stem architecture, which can be view as a composite structure with an outer protection, a unidirectional ply on the periphery and a porous core; each component has a specific function, such as mechanical reinforcement for the unidirectional ply and the porous core. The significant mechanical role of fibres was underlined, as well as their local organisation in cohesive bundles, obtained because of an intrusive growth and evidenced in this work through nanomechanical AFM measurement and 3D reconstruction. Following a biomimetic approach, these data provide a source of inspiration for the composite materials of tomorrow.

Number of processing cycle effect on the properties of the composites based on alfa fiber

The objective of the investigation described in this work was to study the reprocessing effects on the alfa fiber reinforced polyvinylchloride composites with and without maleic anhydride-grafted polyvinyl chloride used as compatibilizer. The material was characterized after each extrusion using tensile tests, scanning electron microscopy (SEM), dynamic mechanical, and thermal analysis. Results indicated that generally after four cycles, the recycled composites had considerably higher modulus as compared with the original composites, which were attributed to changes in physical and chemical properties of the composites induced by the recycling process. This effect was enhanced for the compatibilized samples. Increase of the modulus strength of the poly(vinyl chloride) (PVC) matrix is detected due to the molecular chain cross-linking resulting from degradation. In addition, it was found that the reprocessing cycles increase in glass transition temperature of PVC and PVC/alfa composites.

Tensile properties of flax fibers

Abstract Flax is a dicotyledon of the Linacea family, and the plant Linum usitatissimum L. is the most widely grown. It is an annual plant, it is resown annually, and it provides fibers and seeds rich in oil. Flax fibers find uses both in textiles but also for polymer reinforcement. These uses are understandable because they are available in Europe, know-how exists, the single fibers are long compared to many fibers obtained from plants and they have good mechanical properties. The aim of this chapter is to present the properties of flax fibers generally. In the first part, the plant will be presented, then the fibers and their mechanical properties. Finally, the chapter will be completed with remarks on the use of these fibers as polymer reinforcements.

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

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.

Influence of loading rates on morpholgy and mechanical properties of PLA/clay nanocomposites

This paper reports some experimental results on the influence of loading rates on morphology and mechanical properties of clay nanocomposites based on polylactide (PLA). The dispersed phase was organically modified montmorillonite commercially known as Cloisite 30B and introduced at various loading rates: 1, 3 and 5 wt.%. The nanocomposites were prepared by melt intercalation in a Brabender Plasticorder mixer. Wide angle X–ray scattering showed that the clay was finely distributed in the PLA matrix and the nanocomposite morphology can be considered as intercalated/exfoliated structure, whatever the filler content. The effect of clay loadings on the mechanical properties of PLA/organoclay was investigated by nanoindentation and tensile measurements. Nanoindentation results showed a significant improvement in modulus and hardness with increase of the clay contents. This is consistent with the large increase in Youngs modulus obtained by tensile tests indicating a good correlation of mechanical properties at the macrometric and nanometric scales.