Pierre Ouagne

Analysis of the Film-stacking Processing Parameters for PLLA/Flax Fiber Biocomposites

Nowadays, the market demand for environmentally friendly materials is rapidly increasing. Biodegradable fibers and biodegradable polymers, mainly extracted from renewable resources, are expected to be a major contribution to the production of new industrial high performance biodegradable composites, partially solving the problem of waste management. At the end of its lifetime, a structural biodegradable composite can be crushed and recycled through a controlled industrial composting process. Bodros et al. [1] showed that biodegradable L-polylactide acid (PLLA)/flax fibers mat composites exhibiting specific tensile properties equivalent to glass fiber polyester composites can be manufactured by an un-optimized film-stacking process. In our study, the process has been investigated more extensively. Indeed, the compaction of flax mats requires a higher load than for glass mats of similar areal weight. The transverse permeability of flax mats has also been shown to be lower than for glass mats. In both cases, this is due to a higher degree of entanglement of the flax fibers within the mat. However, the range of permeability and compressibility values of the flax mats are well within the values that allow a good through-the-thickness impregnation. Flax fibers cannot sustain long exposures at the impregnation temperature of the mats by PLLA resin. Through-the-thickness impregnation of flax mats processes such as film stacking are more suitable than in-plane impregnation processes such as resin transfer molding because the flow of resin is limited on short distances and allows short times of impregnation.

Industrial Hemp Transformation for Composite Applications: Influence of Processing Parameters on the Fibre Properties

The main objective of this collaborative work is to characterize the influence of the processing stages of industrial hemp on the fibre properties. Transformation processes well suited for composite reinforcing textiles are considered. The work focuses on the different stages along the transformation chain of hemp, from the straw retting to the preform manufacturing. The main highlight is the predominant influence of retting on the tensile properties of individual fibres after their mechanical extraction from the stalks. Regarding the secondary processing, different technologies such as spinning, and use of natural binder systems are also proposed to produce yarns and woven fabrics. The effect on these secondary processing technologies and their parameters on the fibre properties are also characterised. The results show that the first steps of processing (retting and decortication) have the greatest impact on the tensile strength of hemp fibres.

From fibre extraction to the composite manufacturing processes: Which path to adopt to maximise the mechanical properties of natural fibre based composites?

This work proposes to analyse the different aspects that should be taken into account from the fibre extraction from plants to the forming process to achieve correct part forming. The study will focus in a first extent on the impact of the textile operations leading to the yarn manufacturing. The properties of the flax fabric will then be associated to its behaviour during experimental forming and related to the possible appearance of defects such as tow buckling and solutions to prevent its appearance is widely discussed.

Influence of the Textile Parameters on the Complex Shape Forming Properties of Flax Based Fabrics

This study examines the ability to develop composite parts with complex geometries without defect. An experimental approach is used to identify and quantify the defects such as buckling caused by the bending of rovings during forming. Solutions are developed to obtain a complex shape such as a tetrahedron without any defect by using specially designed flax based reinforcement architecture. However, this solution may not be sufficient for other types of shapes and that is why the optimisation of the process parameters to prevent occurrence of buckles from commercial fabrics was also investigated.

Influence de la dépose sur l'injection lors du procédé RTM de tubes gainés

This work concerns the manufacturing of a tube using a RTM process. The influence of the first step on the injection step is analyzed, by the prediction of the deformability of the braided reinforcement used and by the estimation of the yarn volume fraction. These parameters have a significant impact on the permeability component and consequently on the properties of the final piece. Some analytical models are developed based on the analysis of plane shear evolution of the reinforcement. Results are compared to experimental values obtained by tomography for the volume fraction and by the measurement of the shear angle.