Institute of Chemical Engineering
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Characterisation of regenerated cellulosic fibres and therein contained particles by optical image analysis

In the course of time, viscose fibres have been imposed with extended demands on product quality, especially mechanical properties and the constancy of these on the overall fibre length; for instance, tyre production is currently using cords from highly stretched viscose yarns for the setting-up of the supporting connective tissue within the bearing surfaces, that are exposed to intense strain while in operation. With quality control in the manufacturing sector mainly, knowledge of characteristic distribution parameters (fibre length, fibre diameter, etc.) as well as fundamental comprehension on the mechanisms that lead to the formation of undesirable contamination are of increasing importance; it is necessary to employ analysis methods or to develop such respectively, which render possible the drawing of conclusions on nature and content as well as size distribution of contaminating entities or - for special purposes - intentionally added particles (i.e., flame retardants, particles for strengthening). In addition to repeatable methods for characterisation of fibre properties and registration and accordingly illustration of particles, on-line methods for manipulation and process monitoring for the very production processes are to be developed.

One of the main starting-points here is optical image analysis by means of light microscopy and scanning. For a first move a convenient form of preparation and presentation of the samples is chosen and physical parameters with the analysis method as resolution, contrast, etc., are adapted. Subsequently, software-assisted, images preferably presenting the properties to be studied are taken. At this point, qualitative findings can be obtained already, as well as decisions on constructive approaches for further analysis (transmitted light, phase contrast, fluorescence, usage of polarisation filters to name but a few) can be made. By purpose-made algorithms for image processing a multitude of fibre parameters, particle-concentrations and particle size distributions can be gathered even quantitatively, statistic characteristics can be compared and finally correlated to mechanical properties recorded just as well such as strength and elongation at rupture.

Sample preparation and work sequence do not reveal trivially, though. As for the task given, prior size reduction in a cutting mill can be required, for example, as well as a comparison of data derived from automated measuring procedures on fibre analysis (cf. MorFi) with data from optical image analysis. Then, when characterising regenerated cellulosic fibres one also has to take into account the considerable swelling of the cellulose in aqueous solutions as equally a good correspondence in refractive indexes of sample and dispersant needed at high resolution levels. Above all, different sample concentrations in the dispersion and sample-specific strategies for dyeing the structures to be investigated can lead to decisive improvements where interpretability and image quality are concerned.

Therefore, a wide field of properties being surveyed faces a diversity of options related to sample preparation and analysis, that are fit to the topic accordingly.


Additional information can be found here.



Privatdozent Dipl.-Ing. Dr.techn. Andreas Bartl