17.6. Photocatalytic TiO2-based multilayer coating on polymer substrate for use in self-cleaning applications

Public examination of a doctoral dissertation in the field of chemistry

   Doctoral candidate: Licentiate in Philosophy Jussi Kasanen  

Date and venue: 17.6.2011, at 12 noon, auditorium F100, Futura, Joensuu campus  

ABSTRACT 

In the 1970s, when the research on heterogeneous semiconductor photocatalysis was just beginning, applications like self-cleaning surfaces were scarcely conceivable. Today there are numerous such applications based on inorganic surfaces but still very few on self-cleaning polymer surfaces. Polymers are a challenging matrix because of two major problems: 1) as organic materials, polymers degrade in photocatalysis, and this degradation must be controlled, and 2) polymers and inorganic semiconductors need to be combined without major loss of photocatalytic activity. The present study was undertaken to find solutions to these problems. 

A novel, reproducible multilayered photocatalytic titanium dioxide based coating was developed and prepared on two common polymer surfaces: high-density polyethylene and polyvinyl chloride. The multilayer structure consisted of a protective polyurethane layer on the polymer substrate, two layers of photocatalytic TiO2 on the protective layer, and a diluted polyurethane dispersion designed to immobilize the photocatalyst particles. Photocatalytic activity of the coating was examined in the degradation of solid palmitic acid, used as a model soiling agent. 

The adhesion between the polyethylene substrate and protective polyurethane layer was improved by applying oxygen plasma treatment to the substrate. The improved adhesion also contributed to the photocatalytic degradation of palmitic acid since the titanium dioxide was then better dispersed on the protective polyurethane layer. The UV-illumination time could be halved while photocatalytic efficiency was improved. The improved coating was also examined in aqueous environment in the degradation of methylene blue. Like that of palmitic acid, the degradation of methylene blue followed pseudo-first-order reaction kinetics. The degradation rate decreased when the pH value of the methylene blue solution was adjusted up or down from the original value, but all rates were higher than those without polyurethane binding agent. 

Since polyurethane binding plays an essential role in the coating, study was made of its UV stability. Optimization of the amount of binding agent is important if sufficient binding of titanium dioxide to the substrate and high efficiency of the photocatalysis are to be achieved in self-cleaning applications. The study indicated that titanium dioxide is successfully immobilized by application of heat-curing waterborne polyurethane dispersion. 

The doctoral dissertation of Licentiate in Philosophy Jussi Kasanen entitled “Photocatalytic TiO2-based multilayer coating on polymer substrate for use in self-cleaning applications” The opponent in the public examination is Docent Vesa-Pekka Judin, Aromtech Oy and the custos is Professor Tuula Pakkanen of the University of Eastern Finland. will be examined at the Faculty of Science and Forestry.

Photo available for download at http://www.uef.fi/vaitoskuvat

Contact: Jussi Kasanen, jussi.kasanen@uef.fi, tel.+358 40 708 1982

Publishing year: 2011

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