Flax Fibre Yarn Coated with Lignin from Renewable Sources for Composites

Abstract

The present experimental work analyses the potential of lignin as a matrix for materials made from renewable resources for composite components and the production of hybrid semi-finished products by coating a flax fibre yarn. Natural fibres, due to their low density, in combination with lignin can be a new renewable source for lightweight products. For this purpose, the extrusion process was adapted to lignin as a matrix material for bio-based composites and coating of natural fibre yarns. A commercial flax yarn is the basis for the lignin coating by extrusion. Subsequently, the coated flax yarn was characterised with regard to selected yarn properties. In order to produce composite plates, the lignin-coated flax yarn was used as warp yarn in a bidirectional fabric due to its insufficient flexibility transversely to the yarn axis. The commercial flax yarn was used as weft yarn to increase the fibre volume content. The tensile and flexural properties of the bio-based composite material were determined. There was a significant difference in the mechanical properties between the warp and weft directions. The results show that lignin can be used as matrix material for bio-based natural fibre composites and the coating of natural fibre yarns is an alternative to spun hybrid yarns.

Keywords: bio-based matrix material; bio-based thermoplastics; composite; extrusion; flax yarn; lignin; natural fibre; yarn coating.

Figure 1

(a) Picture of the sheathing nozzle; (b) functional sketch of the sheathing nozzle.

Figure 2

(a) Example of breakage in flax yarn; (b) bobbin of flax yarn (FL) without coating; (c) bobbin of flax yarn with lignin (FL-LI coated yarn); (d) close-up view of FL-LI coated yarn (the magnification is 1.6).

Figure 3

Weaving with FL-LI coated yarn (warp) and FL commercial yarn (weft).

Figure 4

(a) Broken weft yarn; (b) broken lignin coating of the warp yarns; (c) broken Warp yarn; (d) in-homogeneous lignin coating of the warp yarn.

Figure 5

Hot pressing cycle of FL-LI composite plates.

Figure 6

(a) Consolidated FL-LI composite plate with aluminium press frame; (b) warp (90°) and weft (0°) direction of composite plate.

Figure 7

(a) Fineness-related tensile strength of yarns; (b) tensile strength of yarns (c) elongation at break of yarns.

Figure 8

(a) Tensile modulus of FL-LI composites; (b) tensile strength of FL-LI composites; (c) elongation of FL-LI composites.

Figure 9

(a) Cross section showing the course of warp yarn of the FL-LI composite; (b) cross section showing the course of weft yarn of the FL-LI composite.

Figure 10

Load transfer directions of the weft yarn during the tensile test with idealised yarn course. The red arrows indicate the force (F). The blue line shows the weft yarn in the matrix background.

Figure 11

Fracture zones of selected tensile test specimens (a) in 0° (weft direction, above front view and below back view); (b) in 90° (warp direction, above front view and below back view).

Figure 12

Blue coloured detailed view on the structure of the fracture zones of selected tensile test specimens:(a) tensile test in weft direction with plastic deformation along the diagonal twill weave lines; (b) tensile test in warp direction without plastic deformation.

Figure 13

(a) Flexural modulus of FL-LI composites; (b) flexural strength of FL-LI composites; (c) elongation of FL-LI composites.