Date of Award
Master of Engineering Science
Chemical and Biochemical Engineering
Dr. Paul A. Charpentier
A monomer functionalization method (“grafting from” polymerization) was used for synthesizing novel polyurethane/nano TiC>2 coatings to enhance the dispersion of nTi02 particles throughout the coating. Instead of using a simple physical mixture of polyurethane coating and nTiC>2, this novel functionalization method chemically bonds the'TiOi nanoparticles to the polyurethane polymer. This was achieved by coordinating bi-functional 2,2, bis(hydroxymethyl) propionic acid (DMPA), which has 2 hydroxyl groups for reacting with the diisocyanate terminated pre-polyurethane(PU), and a carboxyl group for coordination to nTi02. This allowed the novel polyurethane coating to be prepared by directly attaching the nanoparticles to the polymer matrix.
After comparison of the Polyurethane/nTi02 coatings formed via the physical mixture
method and the “grafting from” polymerization method in terms of SEM and EDX-
Mapping images, the direct attachment method was found to provide excellent dispersion
of nTiC>2 within the polymer matrix, which enhanced the self-cleaning and anti-bacterial
properties. The anti-bacterial property of PU/nTi02 film was evaluated in terms of the
survival ratio of E. coli (Escherichia coli) as a function of UV-illumination time. Different UV light sources, i.e. a solar Simulator (AMU5), and UV fluorescent lamp were examined for comparison. Anti-bacterial behavior was analyzed by using 105 CFU/ml E. coli strains on lwt% PU/nTi02 film for various time intervals with the survival ratio of E. coli evaluated. Two control experiments were designed and conducted to prove that UV illumination and PU/nTi02 film were both necessary for the observed anti-bacterial properties. As the UV intensity was increased, faster activation and enhanced E. coli death rates were achieved. n ; :
Photocatalytic activity leading to the observed self-cleaning properties of the PU/nTi02 films was measured by monitoring the degradation of “dirt” on the polymer surface using FTIR spectroscopy. Additional DMPA and stearic acid were chosen as the model compounds for “dirt” to test the self-cleaning ability of the synthesized PUyTi02 films. iii
As the time of solar-like irradiation increased, the prominent peaks of additional DMPA and stearic acid from the FTIR spectra decreased. Therefore, excellent anti-bacterial and self-cleaning properties were achieved using the novel “grafting from” po!yurethane/nTi02 self-cleaning coatings.
A variety of characterization techniques (i.e. SEM, TGA, ATR-FTIR and EDX) were used to optimize the coordination reaction between DMPA and nTi02. Optimal conditions were achieved when lg of Ti02 (calcined at 400°C for 4h) and 4g of DMPA were reacted in 45ml anhydrous iso-propanol under N2 at 80°C for 24h.
Furthermore, as the rutile phase of Ti02 can provide UV protection, with the photocatalytic activity mainly provided from the anatase phase, the optimum anatase/rutile ratio needs to be determined to optimize the photocatalytic activity. Two convenient methods were chosen to control the anatase/rutile ratio: 1) phase transformation from anatase to rutile via calcination, and 2) hydration-dehydration treatment of physical mixtures of pure anatase and pure rutile crystal form. The characteristic results of ATR-FTIR, TGA, SEM, and EDX-mapping showed that the anatase (100% anatase) and Degussa P25 nTi02 (80%anatase and 20% rutile) when calcined at 400°C for 4h provided the best functionalization results. The formation of rutile phase was found to reduce the amount of surface-adsorbed water, OH groups, and surface area, leading to the observed decrease of the coordination activity. As the ratio of anatase/rutile decreased, the amount of the final functionalized DMPA-Ti02 decreased, and the percentage of functionalized DMPA decreased. Consequently the intensity of the characteristic FTIR peaks became weaker.
Wang, Lin, "POLYURETHANE SELF-CLEANING COATING" (2011). Digitized Theses. 3486.