Study On Controllable Degradation Of Marine Antifouling And Anticorrosive Coatings Based On Poly (Lactic-co-glycolic Acid) (PLGA)

Biofouling and corrosion are the main failure causes of marine facilities,which seriously threaten the normal use of marine working devices.Coatings are the most effective protective means,and multifunctional protective coatings have become the main research hotspot.The existing protective coatings are difficult to comprehensively apply the anti-fouling and anti-corrosion effects of the coatings at the same time.Poly（lactic-co-glycolic acid）（PLGA（75:25,MW=2000））is biodegradable,biocompatible and film-forming,and has clear application potential in the field of marine protective coatings.In this thesis,PLGA was used as the matrix material to prepare bio-controllable degradable marine antifouling and anti-corrosion coatings by regulating the chemical structure of the polymer and the content of the antifouling agent.The structure,degradation performance and anti-corrosion effect were systematically studied.In this thesis,PLGA-based polyurethane was synthesized by copolymerization of PLGA and MDI.The soft segment content of PLGA-based polyurethane（PLGA-PU）was controlled by adjusting the amount of PLGA,and its structure was verified and characterized by infrared spectroscopy and nuclear magnetic resonance hydrogen spectroscopy.Then,4,5-dichloro-N-octyl-3-isothiazolinone（DCOIT）was added to prepare PLGA-PU coatings with different components and different antifouling agents.The related tests showed that the degradation rate of PLGA-PU was larger in the early stage of immersion,and the degradation rate tended to be stable after 15 days.The release effect of the antifouling agent depends largely on the mass loss of the PLGA-PU,which in turn can change the soft segment content and the antifouling agent content to control the degradation rate of the PLGA-PU.The above results show that although the PLGA-PU coating has a good dynamic surface renewal effect,its electrochemical test shows that the corrosion resistance of the coating needs to be further improved.Secondly,in order to improve the anti-corrosion effect of the coating,4,4’-Methylenediphenyldiisocyanate（MDI）was used as a bridge to graft PLGA onto Epoxy resin（EP）to prepare PLGA-MDI-EP composite coatings with different grafting degrees,and MDI-EP with different grafting degrees was used as a control.The content of PLGA was adjusted to control the degree of grafting,and its structure was verified by infrared spectroscopy.DSC and TGA data showed that the introduction of biodegradable PLGA slightly reduced the thermal stability of the original coating.Microphase separation structure will appear in the microstructure of PLGA-MDI-EP（7.5%）composite coating,which can enhance the mechanical properties of the coating,and the impedance value of PLGA-MDI-EP（7.5%）composite coating before and after immersion can be stably maintained at 10¹¹Ω·cm²,and when the coating is damaged,the introduction of PLGA segment can effectively slow down the failure of the coating and be applied in the field of anti-corrosion.Finally,PLGA-MDI-EP（7.5%）/DCOIT composite coating was prepared by adding antifouling agent DCOIT,and the morphology,mechanical properties,corrosion resistance and other properties were tested and characterized.The test results showed that with the increase of antifouling agent content,the adhesion of the composite coating gradually decreased,and other properties such as pencil hardness had no significant effect;the immersion experiment found that the coating will continue to degrade with the increase of immersion time,resulting in mass loss.And the UV test results show that the antifouling agent will continue to seep during the degradation of the coating;electrochemical data show that PLGA-MDI-EP（7.5%）/25%DCOIT composite coating has excellent corrosion resistance,and the low frequency impedance modulus of the coating can reach 10¹¹Ω·cm²before and after immersion.