Preparation And Cavitation Resistance Of Polyurethane Elastomer Coatings

Cavitation is a special form of wear and corrosion that usually occurs on the surface of hydraulic components and it has become one of the focuses of research all over the world.The polyurethane elastomer coated on the surface of the substrate can absorb and buffer the impact force and shock wave which caused by the bubble burst.This process can improve the cavitation resistance and realize the protection of the substrate.In this thesis,the polyurethane elastomer was used as the matrix resin and the organic segment and inorganic filler were introduced to modify it.The structure and morphology of the modified coating were tested by ATR-FTIR,XRD,EDS,SEM,three-dimensional profiler,etc.Contact angle and water absorption rate were used to test the water resistance of the coating,the drawing instrument,DMA and universal tensile machine were used to characterize the mechanical properties of the coating.The electrochemical workstation and the intelligent temperature-controlled ultrasonic material testing machine were respectively used to test the cavitation resistance and corrosion resistance of the coating.Polyurethane prepolymers with different structures were prepared by bulk polymerization with toluene diisocyanate as hard segment and polyether polyol（PTMG or PPG）as soft segments.A series of polyurethane elastomer coatings were prepared by curing with TEOA/BDO mixed crosslinker.The effects of different molecular structures and molar ratio of crosslinker hydroxyl of TEOA/BDO on the water resistance,thermal stability,mechanical properties,corrosion resistance and cavitation resistance of the coatings were compared.The cavitation resistance test showed that the PTMG type polyurethane coating（PUa0.4）with a molar ratio of TEOA and BDO of 0.4:0.6 had a minimum mass loss of 1.8mg after cavitation erosion for 10 h and the weight loss rate was 0.18 mg/h.Electrochemical impedance test showed that the PUa0.4 coating had large low-frequency impedance modulus after soaked for 20 days,indicating the coating had good corrosion resistance property.Hydroxypropyl polydimethylsiloxane（H-PDMS）was used to replace part of polyether polyol（PTMG）.And the silicone segment was introduced into the main chain of polyurethane by bulk polymerization to prepare different H-PDMS.It was found that the introduction of H-PDMS segment significantly improved the water resistance of the coating by the contact angle and water absorption test.The tensile strength of the coating was improved by tensile test.DMA test confirmed the glass transition temperature of modified coating decreased.The cavitation performance test found that the cumulative cavitation mass loss of Si-PU12.5coating at cavitation for 80 h was only 2.96 mg and the weight loss rate was 0.037 mg/h.And the adhesion was 5.12 MPa,which indicated that the coating has excellent cavitation resistance property.After immersed in NaCl solution for 360 hours,the impedance modulus of the Si-PU12.5 coating was above 8.8×10⁶Ω·cm²,indicating that the coating had excellent corrosion resistance.The coating can be used in underwater overcurrent component coating protection system.The GO@SiO₂ composite particles were successfully prepared by electrostatic self-assembly method and introduced into Si-PU12.5 polyurethane resin by in-situ polymerization.And a series of GO@SiO2 modified polyurethane coatings were prepared.Tensile properties test showed that the tensile strength and elongation of GO@SiO2 0.6 were 5.86 MPa and398.05%respectively.The adhesion of GO@SiO₂0.6 coating was 4.2 MPa.The cavitation performance test showed that the surface of the GO@SiO₂0.6 coating was not significantly damaged after 95 h of cavitation erosion.The cumulative loss of cavitation was only 3.5 mg and the cumulative weight loss rate was 0.036 mg/h.The coating has long-lasting resistance to air and good corrosion resistance performance.After immersed in NaCl solution for 360hours,the impedance modulus of the GO@SiO₂0.6 coating was above 1.65×10⁷Ω·cm²,indicating that the coating had excellent corrosion resistance property.