Investigation of interaction between wood constituents and variation of microfibril angle along fiber, modelling and experimentation

• Research unit: COST
• Project number: C01.0068

Key words (English)

Wood polymers; microfibril angle; wood fiber; cell wall; experiments; modelling

Research programs (English)

COST-Action E20 - Wood Fiber Cell Wall Structure

Short description (English)

See abstract

Further information (English)

Full name of research-institution/enterprise: EPF Lausanne Département des matériaux Laboratoire des matériaux de construction

Partners and International Organizations (English)

A, B, DK, FIN, F, D, GR, H, IRL, I, LV, NL, N, P, PL, S, CH, GB

Abstract (English)

One of the objectives of this project has been studying the variation of Microfiber Angle (MFA) within the wood fibers wall. In achieving this goal confocal laser scanning microscopy (CLSM) was used. The advantage of this method is possibility to measure the MFA of each layer of the wood fiber wall without degrading the main structure of the wall. This method gave us the opportunity to study the special sections like inside the border of pits or cross-filed zones (common wall area between the wood fibre and a ray cell), which had not been investigated before. Some of the results are: MFA was highly variable in the radial wall of earlywood fibers and in the vicinity of the bordered pits. On the other hand MFA of the latewood fibers and tangential wall of earlywood fibers was usually uniform. Microfibrils had a circular form of arrangement around the bordered pits of earlywood fibers with evidence of crossed microfibrils between the bordered pits. The orientation of simple pits in cross-field region had a good agreement with the mean MFA of the fiber although the measured MFAs in the small areas between the pits were not always uniform. The other objective of this project has been developing a micromechanical based model which explains the behavior of wood fiber under tensile force. To develop this model the fiber were considered cylindrical with cell wall consisting of only S2 layer. In this model, natural defects were represented as the changes in MFAs orientations. The model estimates the fiber wall stiffness through the stiffness of the constituents and considers a simple isotropic damage for the partial degradation of matrix when the tensile force cross the yield point of stress-elongation curve. Based on the model degradation of the matrix was accompanied by the reduction of MFA in damaged zone. This reduction of MFA resulted in the increasing of the reduced stiffness in the damaged zone and gave the whole fiber a macroscopic elasto-plastic behavior. This behavior (keeping the history of loading) has been confirmed by the experiments. The fibers with large mean MFA showed irreversible deformation with a ductile behavior before final rupture. The fabrication of the mini-device used in tensile test of single wood fiber was finished by mounting and calibrating a force transducer on it. The verification of the developed model is performing by following up the tensile test of single fibers. The experiments could be performed under the microscopic observation thanks to portability and small size of the mini-device.

References in databases (English)

Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. [phone] Swiss Project-Number: C01.0068