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Subject: Protective coatings.

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    Electrochemical and Mechanical Properties Studies of Flexible Mg-rich Primers
    (North Dakota State University, 2010) Chen, Tiantian
    The coating systems for military aircraft must protect the aluminum skin and frame, and associated fastening and joining from corrosion in a variety of aggressive environments. Excessive grinding is often needed to remove the corrosion products at the cracks formed around the seams and fasteners on the aircraft resulting from poor system flexibility of coatings, which causes high maintenance cost and damages the integrity of the aircraft's body. Thus the U.S. Air Force wants to develop an advanced performance coating system with a primer that can provide superior flexibility and good corrosion protection. Currently commercialized magnesium-rich corrosion protection primers were initially developed from some epoxy-amine coating systems, the most common polymer system for aircraft primer use. But the primers were developed under the old specification, which cannot meet the "ideal" goals of the Air Force. Thus, as a carefully selected alternate, polysulfide modified polymers, which have lowest gas permeability, outstanding oil resistance and UV resistance, and especially great flexibility, are being examined as candidate materials. In this research, a number of accelerated laboratory testing methods were applied to measure the electrochemical and mechanical properties of the modified Mg-rich primers which are based on polysulfide modified polymer as binder. Electrochemical measurement results and visual inspections show that the Mg-rich flexible primer has better or equal corrosion protection performance versus a standard epoxy-based Mg-rich primer with the same PVC. The flexibility of the newly formulated Mg-rich primer was also indicated by the results of a variety of empirical testings and instrumental characterizations. Meanwhile, the weathering impact introduced by the laboratory accelerated exposure cannot compromise the superiority of the flexible Mg-rich primers. Based on the results found, future work will be focused on creating a new formulate method or making some modification of the sulfur-containing polymer's structure to achieve a really low VOC.
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    Siloxane-Polyurethane Fouling-Release Coatings Based On PDMS Macromers
    (North Dakota State University, 2011) Sommer, Stacy Ann
    Marine biofouling is the accumulation of organisms onto surfaces immersed in sea water. Fouling of ships causes an increase in hydrodynamic drag which leads to performance issues such as increased fuel consumption and a reduced top operating speed. Fouling-release (FR) coatings are one way that paints have been used in combating biofouling by allowing for the easy removal of settled organisms. Traditional FR coatings are silicone elastomers which are soft, easily damaged, and require a tie coat for adhesion to marine primers. Siloxanepolyurethane FR coatings have shown promise as FR coatings, providing enhanced durability and toughness, better adhesion to marine primers, and comparable FR performance to commercial coatings. Preliminary studies were conducted to explore the use of PDMS macromers in the preparation of siloxane-polyurethane FR coatings. Attachment and removal of fouling organisms on the siloxane-polyurethane coatings based on PDMS macromers was comparable to commercial FR coatings. Extended water aging was also carried out to determine effects of extended water immersion on the fouling-release performance of the coatings. At up to four weeks of aging, the FR performance of the coatings was not affected. Static immersion marine field testing was performed to determine the fouling-release performance of siloxane-polyurethane coatings prepared with PDMS macromers. The performance was found to be comparable to commercial FR coatings for up to one year, including water jet removal of slimes, barnacle push-off removal, and soft sponging. The coatings showed good fouling-release performance until extremely heavy fouling was allowed to settle. Underwater hull cleaning was conducted for one siloxane-polyurethane composition identified as a top performer from static field testing. The coating was easily cleaned of fouling with rotating brushes for six months. The cleaning capability of the coating was reduced when large barnacles and other extremely heavy fouling was present. A commercial FR coating became heavily damaged with brush cleaning while the siloxane-polyurethane coating remained mostly undamaged. With more frequent cleaning, it is suspected that siloxanepolyurethane coatings would show cleaning capability for longer periods of time. Pigmentation of siloxane-polyurethane coatings based on difunctional PDMS and PDMS macromers was explored to investigate the effect on FR performance. Pigmentation with titanium dioxide caused a slight decrease in FR performance in some cases, but this was easily overcome by the addition of slightly more PDMS in the coating binder, thus illustrating the feasibility of siloxane-polyurethane coatings as effective, pigmented FR coatings. Finally, the exploration of unique PDMS polymer architectures has been explored for the development of additional, novel, fouling-release coatings. The incorporation of end-functional PDMS homopolymer molecular brushes and branched PDMS macromers into siloxane-polyurethane fouling-release coatings shows promise for the development of unique coatings where improved FR performance may be obtained.