Image analysis for the quantification of dislocations in hemp fibres

When a natural fibre is subjected to compression stress in the longitudinal direction, local misalignments of cellulose microfibrils, so-called dislocations, may form in the cell wall. For most uses, dislocations have a negative influence on the performance of fibre-based products, and a means of characterising fibre resources with regard to dislocations would be valuable.

In the present study, we have developed a procedure for semi-automatic quantification of the amount of dislocations in elementary hemp fibres. The procedure is based on polarised light microscopy and simple image analysis tools. Results from a similar approach have been published earlier by others, but no details of the method used were reported.

In the present study, the relative dislocation area is determined from two digital images captured using polarised light microscopy. One image is optimised for the detection of the fibre edge, the other is optimised for the detection of dislocations. The area of the dislocations (obtained from the second image) relative to the total fibre area (obtained from the first image) gives a figure that expresses the relative dislocation area.

The method is sensitive to the light intensity of the microscope and to the angle between the longitudinal direction of the fibre and the vibration direction of the polariser. It follows from this that strict standardisation is important if results from different fibres are to be compared.