Fiber Morphology and Flocculation
The local mass distribution - the formation of paper - is widely known as a quality parameter for paper.
The formation is for the most part determined by the technology of the headbox of the paper machine and by the properties of the furnish. Morphological parameters like fiber length, fiber curl or fiber flexibility influence the flocculation behaviour of a certain pulp to a great extent.
One of the core research topics at teh institute for Paper-, Pulp and Fiber Technology at Graz University of Technology in recent years was the characterisation of fiber morphology using image analysis. Methods for the measurement of Parameters like fiber length, width, curl, kink, flexibility and fibrillation are at hand, cross sectional parameters are under developement and can be determined to a certain extent. This new project will take a closer look on the interrelation between fiber morphology and flocculation of pulp fibers.
To discuss this interrelation not only do we need methods for the measurement of fiber morphology, but we also need methods for the evaluation of flocs and flocculation phenomena. This will be done using the following three methods:
high resolution beta-radiographie to determine the mass distribution in a paper sheet
determination of flocs and flocculation in flowing suspension
rheology of fiber networks
A beta radiograph (resolution 50µm at a field of view of 100x100mm) is at hand at the institute. The mass distribution of paper sheets can be measured and investigated using structure analysis methods like FFT or wavelets.
For the determination of the flocculation behaviour in flowing suspension a prototype was built unsing a plexiglas flow cell with a channel of 1m length and a width of 35mm and a heigth of 16mm. At the channel inlet a pressure drop induces high turbulence. Thereby any structures evident before the inlet are destroyed and flocculation can be monitored to a certain extent using a high speed camera in the decaying turbulence downstream. Suspension with a consistency of about 1% is pumped through the cell at a velocity of 2-3m/s. The images are evaluated automatically using image analysis and structure analysis. The following image shows the prototype and an image of flowing suspension as it is acquired in the system:
The method used for the measurement of the stability of the fiber network is based on a commercial Paar Physica Rheometer. Pulp suspension is measured in a 3mm gap using oscillating load. The shear forces induced by the fiber network under the load are directly related to the stability of the fiber network.
The goal of the project is a better understanding on the interrelation between fiber morphological parameters and flocculation of pulp fibers.
01.06.2008 - 30.05.2011
Rene Eckhart & Wolfgang Bauer
Andridtz AG, Smurfit Kappa Nettingsdorfer, Sappi Gratkorn, SCA Graphic Laakirchen