UV-cured fouling release acrylic coatings and protective coatings for clay bricks

The topic of this thesis is the protection of surface through UV cured polymeric coatings. In the first part coatings are designed to inhibit the adhesion of microorganisms on different substrate, while in the last chapter the coatings are developed to protect clay bricks from water. Degradation of surfaces caused by biofouling is a common issue in a variety of application, such as naval equipment, food industry and biomedical implants. In clay bricks, in addiction to biodegradation, the water causes other aesthetical and functional degradation phenomena, such as delamination, cracking, efflorescence, patina, black crusts. In this thesis was studied the growth of yeast in presence of different polymeric coatings prepared by UV curing. The approach followed was mainly based on the interfacial interactions between the surfaces and the microorganism. The experimental methods have been designed in order to control the physicochemical and mechanical properties of the surfaces. Interface interactions are governed by a variety of parameters, depending on the characteristic of both the substrate and the microorganism. Surface tension, hydration, wettability, roughness, topographies and elastic modulus and glass transition temperature are influent factors for polymeric materials. The microrganism selected for this works was a yeast isolated from garden soil and identified as Rhodotorula mucillaginosa. Rhodotorula species are ubiquitous, filmogenic, pigment yeasts. They are often called “pink yeast” because of the peculiar pink to orange coloration of the colonies. R. mucillaginosa and its adhesion properties are interesting in different application field. Selective and controlled proliferation of R. mucillaginosa could be useful in soil and wastewater bioremediation and industrial production of carotenoids. On the contrary, in biomedical application the biofilm formation in not desirable. Despite R. mucillaginosa generally is not harmful for human health, it is known as an emergent opportunistic pathogen able to infect immunosuppressed adults and newborns. Another important risk factor in infected patients is the presence of foreign bodies. Despite this, the Biosafety level of R. mucillaginosa is 1, this means that its manipulation in laboratory does not required special precautions. Coatings were prepared by UV-induced crosslinking processes. The UV curing or photopolymerization technique consists in the fast transformation of a liquid mixture of precursors into a solid crosslinked polymeric film. Low energy requirements, room temperature operation and solvent-free systems make UV curing an ecofriendly technology suitable for coatings industries. Monomers selected for the UV-curing process were characterized by acrylic end groups assuring fast and complete polymerization. For the protection of substrate against fouling, different monomers were selected in order to obtain coatings with different surface properties: 1. Hydrophobic monomers, i.e. perfluoropolyether diacrylates 2. Hydrophilic monomers, i.e. polyethilenglycol diacrylates. Hydrophobic coatings were based on perfuoropolyether (PFPE) diacrylic oligomer. It was studied the effect of surface tension, topography and elastic modulus on R. mucillagionosa adhesion and release. In Hydrophilic coatings were compared the effect of alkyl and poly(ethylene oxide) chain. The attention was focused on the effect of different chemical compositions, and thus different surface tension, on the induced morphology of R. mucillaginosa. Properties of acrylic coating have been checked by water absorption, contact angle measurement, profilometry and dynamic mechanical thermal analysis (DMTA). The interaction between the coatings and the yeast cells were examined through a simple in vitro test and correlated to the material properties of the polymers. The yeast test was designed to monitor the growth of R. mucillaginosa and the potential biofilm formation in presence of acrylic coatings. Biofilm release by a gentle washing was also evaluated. During the test, cell density was measure by UV visible spectroscopy. The growth morphology of the yeast on the coatings surface was observed by optical microscopy and FESEM. In addition, the effect of uncured monomers and the photoinitiator on the microorganism growth was studied. The coatings under investigation showed a different fouling behavior. The interaction between yeast cells and the coating surface appreciably change, mainly driven from the surface tension and the hydration of the materials. Different yeast morphologies were found. In the second part of the thesis are presented two hybrid coating as protective coating for clay bricks: a waterborne polyurethane coating and a perfluorinated (PFPE) coating. Masonry is susceptible from aesthetic and functional deterioration due to atmospheric agents, pollution and microorganism. The most diffuse degradations of facing bricks are lacunas, pulverization, delamination, cracking, presence of efflorescence, patina, black crusts and dissolution and leaching of mortar between brick courses. Water is known as an important factor of degradation; thus, hydrophobic coatings is an effective way to preserve bricks. The main characteristic required to this coating are hinder the liquid water absorption but maintain the water vapor transmission in the substrate. Protective coating for building porous materials are divided in two main categories: film formers and penetrants. The first coating presented in this thesis is a polyurethane based film formers coatings. It was prepared by combining two ecofriendly process: UV-curing of a waterborne diacrylic polyurethane and sol-gel reaction of a Tetraethoxysilane (TEOS). The perfluorinated coating is penetrants and was obtained by a sol-gel reaction of an α–ω-terminated triethoxysilane PFPE. Hybrid PFPE was obtaind using the sol-gel process in the presence of TEOS. Coated and uncoated facing bricks were compared by scanning electron microscopy, surface profilometry, water wettability and capillary rise tests. The hybrid coating acts as a moderate water repellent: interestingly no appreciable alteration of the aesthetical properties of the brick was observed, in particular no gloss and color change appeared after the treatment. Both the proposed coating could be applied on brick in the manufacturing process, or on existing brickwork.