Exploiting synchrotron X-ray tomography for a novel insight into flax-fibre defects ultrastructure

Flax fibres are valuable reinforcements for tomorrow's composites. However, defects called kink-bands, which mainly appear on fibres during the extraction and transformation phases, might affect their mechanical properties. Defects induced pores, within the kink-band are investigated in this work. They were morphologically explored using synchrotron phase-contrast X-ray microtomography, a technique that displays a sharp 3D representation of the pores. The study highlights the link between kink-bands and secondary cell wall ultrastructure. Pores are organised concentrically around the lumen, and their low thickness suggest that they are located at the interface between cellulose layers within S2 (G) layer. Moreover, the pores inclination with reference to the lumen axis follows the typical microfibrillar angle changes observed in the literature in the kink-band region. The volumes of the pores were measured, and a local increase in porosity was revealed in zones where defects are most severe along the fibre.Comment: 12 pages, 6 figures. Accepted for publication in Industrial Crops and Products (ISSN 0926-6690

In-Situ Monitoring Of The Ultrastructure And Mechanical Properties Of Flax Cell Walls During Controlled Heat Treatment

International audiencePlant fibres are increasingly used as reinforcements, especially in thermoplastic composites. Understanding the impact of temperature on the properties of these fibres is an important issue for the manufacturing of high-performance materials with minimal defects. In this work, the structural evolution and mechanical behaviour of flax fibre cell walls were dynamically monitored by temperature-controlled X-ray diffraction and nanoindentation from 25 to 230°C; detailed biochemical analysis was also conducted on fibre samples after each heating step. With increasing temperature up to 230°C, a drop in the local mechanical performance of the flax cell walls was measured. This was associated with a decrease in the packing of the cellulose crystal lattice (increase in d-spacing d200), as well as significant mass losses measured by TGA and changes in the biochemical composition, i.e. non-cellulosic polysaccharides (NCPs) of the middle lamellae but also of the cell walls. This work, which proposes for the first time an in-situ investigation of the dynamic temperature evolution of the flax cell wall properties, evidences the reversible behaviour of their crystalline structure (i.e. cellulose) and local mechanical properties after cooling to room temperature, even after exposure to high temperatures

Tracking the changes into mechanical properties and ultrastructure of flax cell walls during a dynamic heating treatment

International audienceThe impact of temperature on plant fibres is key point when processing plant fibre composite with thermoplastic resin. Structural and biochemical evolution of plant cell walls with temperature may affect their final mechanical properties. These evolutions have been studied in-situ on flax fibres during a dynamic heating treatment, representative of conventional polymer processing temperatures. Originals results were observed regarding the reversibility of the indentation modulus, hardness and cellulose crystalline structure

In-situ monitoring of changes in ultrastructure and mechanical properties of flax cell walls during controlled heat treatment

Issu de : https://doi.org/10.2139/ssrn.4404621International audiencePlant fibres are increasingly used as reinforcements, especially in thermoplastic composites. Understanding the impact of temperature on the properties of these fibres is an important issue for the manufacturing of high-performance materials with minimal defects. In this work, the structural evolution and mechanical behaviour of flax fibre cell walls were dynamically monitored by temperature-controlled X-ray diffraction and nanoindentation from 25 to 230 °C; detailed biochemical analysis was also conducted on fibre samples after each heating step. With increasing temperature up to 230 °C, a decrease in the local mechanical performance of the flax cell walls, of about −72 % for the indentation modulus and −35 % for the hardness, was measured. This was associated with a decrease in the packing of the cellulose crystal lattice (increase in d-spacing d200), as well as significant mass losses measured by thermogravimetric analysis and changes in the biochemical composition, i.e. non-cellulosic polysaccharides attributed to the middle lamellae but also to the cell walls. This work, which proposes for the first time an in-situ investigation of the dynamic temperature evolution of the flax cell wall properties, highlights the reversible behaviour of their crystalline structure (i.e. cellulose) and local mechanical properties after cooling to room temperature, even after exposure to high temperatures