Investigation On The Self-healing Behavior And Mechanism Of Polyurethane Elastomer

Ships and marine structures and steel structures usually need to be coated with various kinds of coating material to protect,but the protective coating during its service process,in addition to corrosion by environmental medium marine fouling,will be hit by the sea of floating debris and abrasions.In recent years,materials and coatings with self healing properties have been paid more and more attention.Many of them are self-healing materials,which rely on the microcapsule ruptured in materials or coatings to repair damaged areas.The intrinsic self-healing material,however,relies on the chemical structure and properties of the material itself to achieve the self-healing of the damage.Polyurethane materials have been proved to be an intrinsic self-healing material.In order to conform to the development of green and environmental society,the water-based protection of various protective coatings have become an inevitable choice.Therefore,it is of great scientific significance and engineering value to study the self-healing behavior of the waterborne polyurethane elastomer and its coating.PPG-BDO-TDI polyurethane emulsions with hard segment content of 25%,30%,35%,40%and 45%have been respectively designed and synthesized.The waterborne polyurethane elastomers,powder reinforcing composite coatings and protective coatings have been prepared.The structure and properties of the elastomer were characterized by infrared spectroscopy,differential thermal analysis,thermogravimetric analysis and tensile test.The effects of hard segment content,healing time,damage mode,multiple damage and loading rate on the self-healing behavior and properties of elastomers were systematically studied,and a self-healing mechanism model was proposed.The results showed that the elastomers containing different hard segment contents were successfully synthesized,and the polyurethane contained two obvious glass transition temperatures,indicating that there existed structure of soft and hard phase incompatible microphase separation in polyurethane.The thermogravimetry showed that the polyurethane elastomer has great heat resistance under 300 degrees.With the increase of the content of the hard segment,the breaking strength and modulus of the elastomer increases,but the elongation decreases.The self-healing rate decreases with the increase of the hard segment content.When the hard segment exceeds 45%,the elastomer completely loses its self-healing ability.The self-healing rate of the elastomer reaches the maximum at 48 hours,the maximum breaking strength could reach to the original 90%,and the elongation could reach to 30%.The self-healing rate of local damaged specimens are higher than that of breaking and cutting off the specimens.The self-healing ability of the specimens were repeatedly broken down in the same part,and the self-healing ability completely lost after seven breaks.With the increase of loading rate,the self-healing rate of the sample increases slightly.The self-healing rate of the powder reinforced elastomer composite decreases with the increase of the powder content.When the powder content is 3.5%,the self-healing ability of the sample loses.The self-healing rate of the mechanical shear force added to the powder is higher than that of the ultrasonic dispersion.The self-healing rate of different powder reinforced elastomer composites is from high to low to nanoscale silica>diatom>titanium dioxide>carbon nanotubes.The self-healing rate of protective coating is far lower than that of elastomer.With the increase of hard segment content,the self-healing rate decreases,and the 40%hard segment coating has lost the self-healing ability after single injury.