Preparation,Modification And Study On Cavitation Erosion Properties Of Polyether Polyurethane Coatings

Cavitation erosion is a common damage form of underwater parts,which causes huge economic losses and safety risks.Therefore,how to reduce or restrain cavitation erosion damage has become one of the hot research directions at home and abroad.Due to its excellent impact resistance and underwater stability,polyurethane（PU）elastomer can effectively absorb buffer energy through its own deformation.Therefore,PU coated on the surface of parts is expected to significantly reduce the damage caused by cavitation erosion.However,the research and application of high-performance PU protective coatings are severely restricted due to the lack of systematic research and deep understanding on the cavitation erosion properties and damage mechanism of PU.Therefore,focusing on the two scientific problems of"difficult analysis of cavitation erosion damage mechanism of organic coating"and"difficult construction of polymer coating with high strength and toughness against cavitation erosion",this paper carried out research on the synthesis and preparation of polyether PU coating,physical and chemical properties analysis,cavitation erosion mechanism characterization,nano modification enhancement and organic/inorganic interface combination regulation.Based on the comprehensive test results of molecular chain structure evolution,mechanical and thermal properties of PU,the response behavior and damage mechanism of PU under cavitation erosion load and cavitation heat were deeply revealed,which guided the development of polyether PU elastomer coatings with better anti-cavitation erosion.The main research contents and results are as follows:1.Using isophorone diisocyanate as the hard segment and polybutanediol as the soft segment,the prepolymers were synthesized.Then,PU elastomers with five different crosslinking ratios were prepared by adjusting the molar ratio of hydroxyl group of the mixed chain extender.Through a series of tests on mechanical properties,water absorption and cavitation erosion resistance,it was found that PU_0.4had the best anti-cavitation erosion and the least cumulative mass loss after 30 hours of cavitation erosion,just had 10.6mg,the surface damage is slight;In addition,excessive crosslinking results in embrittleation of PU elastomer,which degrades its mechanical properties and cavitation corrosion resistance.2.Aiming at the unclear mechanism of cavitation erosion damage of PU elastomer,the surface morphology,element content,types of functional groups and molecular structure of PU coating before and after cavitation erosion were compared by SEM,XPS,infrared qualitative analysis and thermogravimetric analysis.The results showed that:under the action of cavitation heat,not only melting pits appear on the surface of PU coating,but also accelerate the hydrolysis and thermal oxidation degradation of groups such as carbamate group and ether bond,which damages the integrity and mechanical properties of the material surface.Under the action of cavitation load,the degree of microphase separation of PU elastomer is obviously intensified,which promotes the accumulation of hard segment molecular chains with low thermal decomposition temperature and poor flexibility on the surface,further deteriorates the mechanical properties and temperature resistance of the material,and finally leads to the obvious fatigue stripping damage of PU coating under the force/thermal coupling.3.By adding graphene oxide（GO）,the way to enhance the cavitation erosion resistance of PU elastomer was explored.According to the test results of dynamic thermomechanical properties,mechanical properties,heat resistance and cavitation erosion resistance of the material,it was optimized that the optimal amount of GO was 0.5 wt.%,and the cavitation erosion resistance of the prepared PU elastomer coating was nearly 7 times higher than that before modification.On this basis,in order to further enhance the interface binding between GO and the base resin,aniline oligomer（AO）was used to functionalize GO and promote the formation of chemical bonding between GO and the base resin.The final results show that compared with GO,the graphene oxide modified with aniline oligomer（AOFG）has more obvious reinforcing effect on PU elastomer,and the PU elastomer coating added with AOFG has better overall performance.