Experimental and numerical analysis of mixing for adhesive barriers

This industrial Ph.D. dissertation delves into the mixing with a highly viscous, non-Newtonian polymer suspension, specifically targeting the production of adhesive barriers for stoma care products. The need of this research is amplified by persistent consumer complaints concerning adhesive effectiveness and the substantial waste generated during the manufacturing process of these barriers.

The dissertation comprises six pivotal contributions, including four papers and two technical reports that explore particular aspects of the mixing process. Initial studies successfully aligned quality metrics between industrial-scale and pilot mixers, thereby facilitating a preliminary labscale experimental investigation. The research employ indices for distributive and dispersive mixing. Distributive mixing refers to the uniform distribution of particles within the mixer, while dispersive mixing pertains to the separation of individual particles within that same volume.

A key revelation in this work is the critical role of powder purity in determining the homogeneity of the final mix. This observation finds support in both a paper and a technical report.

The research conducted during this PhD included the development of multiple numerical models to enhance the understanding of mixing a highly viscous, non-Newtonian polymer suspension. One such model focused on a pilot mixer and rigorously investigated temperature as a key parameter affecting mixing. Another numerical model simulating a change-can mixer was use to systematically screen various parameters impact on homogeneity. The final numerical model examined mixing at different fill levels in a starve-fed single-screw extruder, and showed that these had a notable impact on the dispersive mixing index.

The numerical models of both the pilot and the change-can mixer highlighted that temperature exerted a negligible influence on the mixing indices. These findings inspired an experimental investigation in the industrial mixer, which revealed that heat removal can reduce the scrap in the production of adhesive barriers. Furthermore, the detailed numerical analysis of a change-can mixer highlighted the preeminence of arm rotation as a decisive factor in the mixing process.

The thesis primarily examined one particular highly viscous, non-Newtonian polymer suspensions. However, the research has generated numerical models, methodologies, and findings that could have broader applications in the study of various suspensions and mixing processes. This broad applicability holds particular significance for Dansac and its parent organization, Hollister Inc., given the variety of mixing machines employed and the range of adhesive barrier products produced.