Tuesday  |  Virtual Track 4  |  10:12 AM–10:24 AM

#11560, Investigating the Hygro-expansion of Single Pulp Fibers and Inter-fiber Bonds: a Full-field Fiber Topography Correlation Approach

Softwood and hardwood pulp fibers are the main constituent in a wide range of paper-based products used for packaging, printing and converting industries. Their extreme sensitivity to moisture content variations is one of the major concerns for most applications. As generally known, an increase in moisture content greatly affects the mechanical and geometrical properties of the material at all length scales down to the single fiber level.

To characterize the hygro-mechanical behavior of fibers in detail, a novel micromechanical characterization method is proposed which allows continuous full-field fiber surface displacement measurements during wetting and drying. A fiber specimen is tested underneath an optical profiler inside a climate chamber wherein the relative humidity is changed to capture the specimen’s dimensional change. The obtained fiber topographies are, subsequently, analyzed with an advanced Global Digital Height Correlation methodology dedicated to extract the full three-dimensional fiber surface displacement field. From this field, the longitudinal and transverse surface strain can be computed with a precision of, respectively, 1.0*10-4 and 2.0*10-4 [-] which is significantly better than existing techniques in the literature.

The proposed method is applied to multiple softwood and hardwood pulp fibers to identify significant hygroscopic fiber parameters within a single test, e.g. the longitudinal and transverse hygro-expansion coefficient ratio, major strain angle which is directly related to the fiber’s micro-fibril angle and half time at which the fiber equilibrates. Furthermore, the proposed method is extended and applied to multiple inter-fiber bonds, which allowed novel insights into the full-field inter-fiber interactions, i.e. transverse and longitudinal hygro-expansion of the freestanding fiber segments and of the bonded area.

Niels Vonk   Eindhoven University of Technology
Ron Peerlings   Eindhoven University of Technology
Marc Geers   Eindhoven University of Technology
Johan Hoefnagels   Eindhoven University of Technology