Comparison of the properties of scutched flax and flax tow for composite material reinforcement

• The properties of scutched flax and flax tows were studied.
• Structure and morphology of the materials were analyzed.
• Tensile properties of single fibers were not significantly different.
• Tensile properties of unidirectional composites were not different.

The industrial production of flax fibers yields two fibrous products: scutched fibers are valuable for their length, fineness and cleanness, while tows are entangled, impure and are low-priced. There is a need for technical data to compare these two kinds of fibers beyond the difference of appearance, and to assess their potential as composite material reinforcements. In this work, we have compared the properties of scutched flax and flax tows from the same batch. The morphology was first assessed by measuring the length, cleanness and fineness of fiber bundles. The tensile properties of single fibers and of unidirectionally reinforced epoxy composites were then measured. The results show that the morphology of flax tows is different from but close to the morphology of scutched flax. Tow bundles were 15% shorter than scutched flax bundles and tow bundles were 25% thicker than scutched flax bundles. The tensile properties of single fibers were in the same range. Tensile properties of the unidirectional composites show a similar evolution of properties versus fiber volume fraction. The use of scutched flax allowed volume fractions of 0.7 to be achieved while tow volume fraction was limited to 0.6. Despite the visual and morphological difference between tows and scutched flax both can be good candidates for composite reinforcement in high performance applications.