Investigation On The Response Characteristics In Marine Environment Of Polyurethane Antifouling Coatings

The traditional antifouling paint prevent biofouling on ship’s hull by releasing toxic substance into seawater, it will destroy the marine environment. The antifouling coatings containing organic tin and other toxic antifoulants have been banned or restricted to use in ship industry, hence development of new environmentally friendly antifouling coatings has become inevitable. Marine biofouling begin first from the protein adsorption on the surface of the materials to form condition membrane, it is the basis of macro biofouling. Therefore, designing and controlling the organizational structure of the coating, inhibiting the formation of condition membrane can delay biofouling from the source, it plays an important role. Because of the thermodynamic incompatibility between hard and soft segments, polyurethane has a microphase separation structure. In recent years, the research results on biomedical materials showed that the microphase separation structure of polyurethane can inhibit the adsorption of protein. Therefore, we design different polyurethanes by controlling the structure and content of hard segments and soft segments to prepare different microphase separation polyurethane materials, and use the synthesized polyurethane prepolymers as binder to prepare carbon nanotube composite polyurethane coatings, micro-nano powder in situ synthesis of polyurethane coatings, and then study the influence of chemical structure and the microphase separation of materials on mechanical properties, surface properties and antifouling properties of polyurethane materials and coatings, especially on their response characteristics to marine environment. The main results are as followings:First, a series of PPG-TDI-BDO polyurethane materials with different content of polyether polyols (PPG) as the soft segments and 2,4-toluene diisocyanate (TDI) and 1,4-butanediol (BDO) as hard segment was synthesized by two-step solution polymerization process. Results showed that with the increase of hard segment content, the tensile strength and elastic modulus of PPG-TDI-BDO type polyurethane increased while break elongation decreased, polyurethane changed from a soft elastomer to hard plastic, that is because the increasing hard segment content increases the effect of hydrogen bonding in polyurethane, which increase the cross-linking degree in polyurethanes and limit the movement of chain segment. The surface free energy of polyurethane increases with the increasing hard segment. The microphase separation degree of the polyurethane is positive correlated with surface roughness. With the increase of the hard segment content, the microphase separation degree and roughness increases, when hard segment content is 40 wt%, reached the maximum, hard segment content continues to increase, the microphase separation degree and roughness then decreased. The hard segment content of 40 wt% of the polyurethane sample H40 had the best antifouling performance. In addition, the study found when the hard segment content of 20-40 wt%, polyurethane materials have intrinsic self-healing characteristic at room temperature, namely the tensile fractured specimen could self-heal when reconnected. In situ FTIR analysis showed that the self-healing ability of PPG-TDI-BDO polyurethane is determined by the hydrogen bond content and the mobility of the segment.Fixed the hard segment as 40wt%, then designed and synthesized different kinds of polyurethane materials with different structures of isocyanate (TDI, MDI and IPDI) and different structure of soft segment (polyethylene glycol (PEG), poly dimethyl siloxane (PDMS), and fluorinated acrylate binary and quaternary copolymer (BFPA QFPA)). The results showed that the polar groups in isocyanate increased the interaction in the chain segments. The worse compatibility between the hard and soft segments was more likely to produce microphase separation structure. Seawater immersion reduce the degree of microphase separation of the polyurethane, the longer soaking period, the lower the degree of microphase separation of the polyurethane. Due to the low interaction force between the chain segments in the IPDI type polyurethane, it is more likely to be decomposed, and its adhesion to the substrate is significantly lower than that of the TDI and MDI type polyurethanes. The organic fluorine and silicone segment was introduced into the polyurethane could significantly reduce the surface free energy and fracture toughness and increased their degree of microphase separation. Because of the low surface characteristics of silicone and organic fluorine segment, they are enriched on the sample surface during film formation, which significantly improved the water resistance and stability of the polyurethane. On the contrary, because of the hydrophilicity of PEG, water is easier to enter into the polyurethane and react with the polarity segments, reduce the water resistance of the polyurethane. By in situ observation of diiodomethane contact angle changes between polyurethane and seawater interface, the chain migration and molecular reconstruction phenomenon in the process of immersion was investigated. It was found that diiodomethane contact angle increases and tends to be stable with the increase of immersion period in seawater, the hydrophilicity of the polyurethane is increasing, which showed that the polar hard segment in the initial immersion stage can gradually migrating to the interface between the specimen and seawater, as to reduce the total energy of the system. And the introduction of fluoropolymer, silicone polyurethane and micro/nano powders could delay this migration process, the test results of 7 months for static panels immersed in shallow sea showed that all kinds of polyurethane coatings mixed carbon nanotube showed good anti foul ing performance.In order to eliminate the problems by mixing traditionally nanopowder into paint, such as, uneven distribution, easy agglomeration, to further improve the performance of polyurethane antifouling coating composited micro/nano powder, in-situ polymerization process was used to prepare the polyurethane prepolymers in which carbon nanotube, tourmaline and nano-titanium dioxide were dispersed in advance. Then the mechanical properties, surface properties, marine fouling resistance and seawater environmental response characteristics were studied. The results showed that the nanopowder dispersed in polyurethane in-situ polymerization process could increase the degree of crosslinking of polyurethane, improve the stability of the samples in sea water, and slowed down the velocity of the polar segment moving to the interface. Because the powders themselves have certain bactericidal performance, compared with pure polyurethanes, the adhesion resistant to benthic diatom of polyurethanes have improved. After 7 months of panel immersion, all coatings prepared by in situ polymerization polyurethane have no obvious biological attachment, and show excellent antifouling performance.