TOWARD THE DESIGN OF A CO-BLENDED FLAX/PLA WRAPPED YARN TO OPTIMISE BIO-COMPOSITE PERFORMANCES
Topic(s) : Special Sessions
Co-authors :
Delphine QUEREILHAC (FRANCE), Thomas CAILLAULT (FRANCE), Svetlana TEREKHINA (FRANCE), Guillaume MOREL (FRANCE), Marina FAZZINI (FRANCE), Emmanuel DE LUYCKER (FRANCE), Marwa ABIDA (FRANCE), Pierre OUAGNE (FRANCE)Abstract :
For many years, flax fibres became a great feedstock for bio-based composite industry. Their tremendous mechanical features, close to those of glass fibres, make them an ideal candidate to substitute some petro-based reinforcement. Recently, to widen the use of flax in composites, research has been focusing on additive manufacturing to obtain more complex monolithic composite structures and geometries, with micrometre resolution, without using expensive tools or moulds. The advancements of process and material development in Fused Filament Fabrication (FFF) technology have been achieved to show significant potential for different applications, varying from small scale prototype to large scale industrial applications. For the moment, however, flax is mainly commercialized in the form of short fibres with relatively low volume fraction in extruded filaments leading to modest mechanical properties. Continuous 1D structures made from aligned fibres should be promoted to maximise the potential of flax fibres. Recently, highly twisted continuous yarns were used as reinforcement to be processed using commercial and customised 3D printers, but the resin impregnation at the core of these yarns is poor and the technical fibres are misaligned compared to the yarn deposition axis.
The present study proposes to develop an optimize yarn to by-pass these issues. It is composed of a core of flax fibres and thermoplastic co-blended sliver (fig. 1a), and a wrapping multi-filament yarn of the same thermoplastic to ensure structure cohesion. PLA (polylactic acid) was chosen for this study as it is a bio-based polymer, manufactured from renewable resources and potentially biodegradable. Final volume ratio of this yarn is 50% flax/ 50% PLA (fig. 1b). A simple and customized in-nozzle impregnation method by FFF process was used to adapt the comingled flax yarns, with two separate channels, depositing the comingled yarn on the one hand, and a complementary matrix on the other, followed by mixing in the heated zone before extruding from a conic flat-head nozzle of 1 mm diameter.
The samples obtained after printing presents a flax volume ratio of 18% ± 1% before thermal compression consolidation step (fig. 1c). They will be compared to other parts manufactured using considered customized FFF process, such as a 100% flax wrapped yarn, and a conventional textile twisted yarn. Key parameters will be investigated, such as porosity content with X-ray tomography, tensile properties, and matrix impregnation with imagery. Co-blending combined to low twist of the fibre are expected to be key solutions to ensure resin penetration into the core of the reinforcement. The mechanical performance of the optimized yarn composite should also be better than that of samples produced with non-co-blended and twisted yarns.
The present study proposes to develop an optimize yarn to by-pass these issues. It is composed of a core of flax fibres and thermoplastic co-blended sliver (fig. 1a), and a wrapping multi-filament yarn of the same thermoplastic to ensure structure cohesion. PLA (polylactic acid) was chosen for this study as it is a bio-based polymer, manufactured from renewable resources and potentially biodegradable. Final volume ratio of this yarn is 50% flax/ 50% PLA (fig. 1b). A simple and customized in-nozzle impregnation method by FFF process was used to adapt the comingled flax yarns, with two separate channels, depositing the comingled yarn on the one hand, and a complementary matrix on the other, followed by mixing in the heated zone before extruding from a conic flat-head nozzle of 1 mm diameter.
The samples obtained after printing presents a flax volume ratio of 18% ± 1% before thermal compression consolidation step (fig. 1c). They will be compared to other parts manufactured using considered customized FFF process, such as a 100% flax wrapped yarn, and a conventional textile twisted yarn. Key parameters will be investigated, such as porosity content with X-ray tomography, tensile properties, and matrix impregnation with imagery. Co-blending combined to low twist of the fibre are expected to be key solutions to ensure resin penetration into the core of the reinforcement. The mechanical performance of the optimized yarn composite should also be better than that of samples produced with non-co-blended and twisted yarns.