A comparison of two techniques for wood fibre isolation evaluation by tensile tests on single fibres with different microfibril angle

Fibres (tracheids) of spruce (Picea abies [L.] Karst.) were isolated by means of two isolation techniques. On the one hand, a soft chemical treatment with Jeffrey solution was used. The isolation was carried out with a reduced time of treatment (2 h), just to achieve the state where the fibres could be separated easily with tweezers. On the other hand, fibres were directly peeled out with tweezers, taking advantage of the low shear strength between them. Following this approach, a chemical treatment could be avoided completely. In order to compare the isolation techniques, single tracheids from tissue types with different microfibril angle (earlywood, latewood, juvenile wood, opposite wood, compression wood) were tested in the dry state. The microfibril angles were determined by X-ray diffraction. Single tracheids handled with both isolation techniques were strained in microtensile tests and load-strain diagrams were obtained. The chemically treated fibres were found to have much lower strength and stiffness compared to the mechanically isolated fibres, even though the influence of microfibril angle was still obvious for both kinds of treatment. The results clearly show the importance of single fibre extraction to preserve as much as possible the original properties.