Influence of drying on the mechanical behaviour of flax fibres and their unidirectional composites

• Published in: Composites. Part A, Applied science and manufacturing Vol. 43; no. 8; pp. 1226 - 1233
• Main Authors: Baley, C., Le Duigou, A., Bourmaud, A., Davies, P.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.08.2012; Elsevier
• Subjects: A. Flax fibres; Applied sciences; B. Water absorption; C. Mechanical properties; cell walls; cellulose; Composites; drying; epoxides; Exact sciences and technology; flax; Forms of application and semi-finished materials; Laminates; microstructure; Polymer industry, paints, wood; room temperature; shear strength; Technology of polymers; testing; A. Flax fibres; C. Mechanical properties; B. Water absorption; Laminate; Stress strain relation; Unidirectional fiber material; Cellulose; Epoxy resin; Plant fiber; Mechanical properties; Shear strength; Polymer; Secondary cell; Tensile property; Composite material; Flax fiber; Natural fiber; Water absorption; Flax
• ISSN: 1359-835X; 1878-5840
• DOI: 10.1016/j.compositesa.2012.03.005

The microstructure of flax fibres can be considered as a laminate with layers reinforced by cellulose fibrils. During a single fibre tensile test the S2 layer is subjected to shear. At room temperature, natural fibres contain water absorbed in the cell-walls. This paper examines the influence of this water at two scales: on the tensile behaviour of the flax fibres and on unidirectional plies of flax reinforced epoxy. Drying (24h at 105°C) is shown to reduce both failure stress and failure strain significantly. Analysis of normal stresses at the accomodation threshold provides an estimation of the shear strength of secondary cell walls as 45MPa for fibres containing 6.4% by weight of water and only 9MPa for dried fibres. Results from tensile tests on unidirectional flax/epoxy composites, reinforced by as-received and dried fibres, confirm the influence of drying on strength properties.