Abstracts Category : Other

Photoactive Properties of Nanostructured Titania Modified Polyurethanes

by Chao Chen

In order to enhance both the photoactivity and physical/mechanical properties of titania/polyurethane (PU) nanocomposites, in-situ polymerization and film casting were investigated. Both self-degrading PU foams and self-cleaning PU coatings were prepared. Functional monomers were prepared usingDMPA (2,2-dimethylolpropionic acid) functionalized anatse TiO2 and P25 for integration into polyurethane foam with a "grafting-from" synthetic method. This technique was found to successfully reduce the agglomeration effect of titania nanoparticles inside the foams. In addition, the photodegradation rate was enhanced by > 120% over unmodified foam at an optimized loading of 3wt% DMPA functionalized anatase TiO2. The presence of DMPA functionalized P25 nanoparticles produced an increase in the degradation rate of 66% over the unmodified foam at an optimized 1wt% loading.SiO2 encapsulated anatase and rutile TiO2 nanoparticles were successfully synthesized via a modified Stber process, and integrated into polyurethane coatings. The SiO2 encapsulation enhanced the anatase TiO2 nanoparticle distribution as well as the photocatalytic activity of the polyurethane nanocomposites when the loading weight of SiO2 was lower than 3.25wt%. By increasing the SiO2 amount on the titania surface, the contact angle of the coatings increased from 75 to 87 for anatase phase and 70 to 78 for rutile phase. The Young's Modulus was also increased from 1.06GPa to 2.77GMPa for anatase phase and 1.06GPa to 2.17GPa for rutile phase, attributed to the silica layer giving better integration. The thermal conductivity of the polyurethane coatings was also successfully decreased by encapsulating SiO2 on the titania surface, which has applications for next generation high performance coatings.In addition to nanospheres, TiO2 nanofibers were synthesized via an environmental friendly supercritical CO2 method and nanotubes were prepared via a hydrothermal reaction. They were encapsulated with silica via the modified Stber process, then integrated into polyurethane coatings. With more of SiO2 coated on the nanofibers surface, the photocatalytic activity, UV absorbance, and hydroxyl radical formation decreased due to the shielding effect of the SiO2 layers. In contrast, with more SiO2 coated on the nanotubes surface, the formed material was more photoactive at first and then became less active later. These effects in part are attributed to the surface area changes. With these modified nanofibers and nanotubes, the polyurethane coatings were found to exhibit similar photoactivity trend. The mechanical strength was enhanced and the hydrophobicity of coatings was maintained upon exposure to UV irradiation.Nanofiber shaped TiO2 xerogel was synthesized via environmental friendly approach with supercritical CO2 (ScCO2), which when mixed within polyurethane coatings through film casting method and the coatings remain transparent. The coordination between Ti and the carboxylic acid group was investigated showing a bidentate coordination. The TiO2 xerogel nanofibers