(255cp) Surface Coated Template Particles for Internally Functionalized Pores in Waterproof and Breathable Membranes

Authors: Mario Stucki, Christoph R. Kellenberger, Wendelin Stark

In recent years the public attention towards chemicals released to the environment has increased. In 2013, upon the discovery of multiple potentially dangerous and persistent chemicals in outdoor apparel^[1], the global NGO Greenpeace initiated the campaign â??Detoxâ? to convince global outdoor brands to switch to alternative materials. Replacements were only partially given at the time, i.e. a completely porous, functional membrane was not amongst them. With the template removal method, shown in 2012^[2], the optimal tool to find a new, environmentally benign way to produce fully porous, waterproof and breathable membranes, was available.

Commercial soft polyurethane was dissolved and mixed with template particles through ball milling. The resulting dispersion was spread on a flat surface and dried. Upon template removal a porous structure was obtained. With untreated template particles the requirements of the outdoor industry could not be met and additional practical problems like shrinking or collapsing of the porous network was observed. To overcome this, the template particles were coated with a single layer of stearic acid to increase hydrophobicity^[3]. Using a high particles to polymer ratio (4:1 in weight) a sufficiently porous network was created to allow complete template removal, which is not obvious regarding the use of fillers in many polymers. The significant increase in water proofing (300%) showed the hydrophobic nature of the internally coated porous network. Surprisingly, the apparent diameter of the pores repelling water did not affect the diffusive pathway of water vapor, therewith breathability was kept at a constant high level. Furthermore, less pore deformation was observed upon template removal. To prove the large scale feasibility, 5.8 m² of membrane were produced and laminated to a Nylon fabric. The final laminate was tailored into a functional rain jacket prototype.

[1] M. Santen, U. Kallee, Greenpeace, 2012.

[2] C. R. Kellenberger, N. A. Lüchinger, W. J. Stark,  WO2012097967 (A1), 2012.

[3] M. Stucki, W. J. Stark,  EP15198440.8, 2015.