Preparation And Properties Of Self-healing Polyurethane Anticorrosive Coating

Magnesium alloy with light weight,high specific strength and large specific stiffness is widely used in aerospace,electronic devices,new energy vehicles and other fields.However,active chemical properties make it prone to corrosion reactions with the external environment.Therefore,it is very important to improve the corrosion resistance of magnesium alloy.At present,depositing organic coating on the surface of it is the most common mean to improve the corrosion resistance.However,the protection ability of single-function coating is limited.Once the coating is damaged,the anti-corrosion performance will rapidly decline.Starting with the research idea of shape memory assisted self-healing,this paper introduces reversible quadruple hydrogen bonds with high bonding strength and physically dopes carbon nanospheres with photothermal conversion effect,and successfully prepares a polyurethane composite material with shape memory,photothermal conversion and self-healing functions.Then it is used for corrosion protection of magnesium alloy to improve the service life of the material and reduce the maintenance cost.The main research contents are as follows:（1）Shape memory polyurethane（SMPUx）matrix is prepared by solution polymerization.Reversible quadruple hydrogen bond（UPy）is introduced into SMPUx molecular chain to obtain the shape memory-hydrogen bond synergistic self-healing polyurethane material.Firstly,the effect of polyether glycol（PTMG）ratio on mechanical properties and shape memory of SMPUx is investigated.When PTMG-1000:PTMG-250=4:1,the performance of SMPU₃ is the best,the tensile strength is 3.0 MPa,and the shape recovery rate is 84.4%.Then,UPy is prepared by one-pot method.The introduction of UPy formed a new physical cross-linking point between SMPUx molecular chains,which further enhanced the microphase separation of the system.When UPy content is 30%,the tensile strength and shape recovery rate of SMPU₃-U₃₀ increase to 9.1 MPa and 90.6%respectively.The repair efficiency of SMPU₃-U₃₀increased with the temperature rised and the crack size decreased.After treatment at 80℃for2 h,the repair rate of tensile strength reaches 94.5%.The addition of UPy endows the material with intrinsic self-healing ability and higher mechanical properties.（2）Carbon nanospheres（CS）with photothermal conversion effect are prepared by high temperature calcination.CS is dispersed in SMPU₃-U₃₀ to obtain a self-healing polyurethane(SMPU₃-U₃₀@CS)composite with photothermal response.The temperature of CS suspension（0.5 wt.%）increases to 79.7℃under 4 W/cm² near infrared light（NIR）irradiation for 5 min,indicating that CS has excellent photothermal conversion performance.The SMPU₃-U₃₀@CS-0.5 with 0.5 wt.%CS has the best comprehensive performance,the tensile strength is 8.4 MPa,the elongation at break is 194.9%,and the temperature reaches 83.9℃after3 min under NIR.The shape memory effect of SMPU₃-U₃₀@CS-0.5 can be controlled remotely,stepwisely and stage by NIR.When heated at 80℃,it takes 90 min for the material to close the crack,while under NIR irradiation,the crack can be closed only 60 s.Light repair is targeted at the defective parts,and the repair process is more accurate,efficient,energy saving and environmental protection.（3）SMPU₃-U₃₀ and SMPU₃-U₃₀@CS-0.5 are spin coated on the surface of magnesium alloy.The basic properties and anti-corrosion properties of coating are studied systematically.The addition of CS increases the coating hardness from B to HB,the adhesion decreases from grade 1 to grade 2,and the contact angle magnifies from 72.1°to 80.7°.Both coatings have excellent anticorrosive effect.And the thicker the coating,the better the anticorrosive effect.The coating has maze effect and hydrophobic properties after the addition of CS,which further improves its corrosion resistance.And the corrosion potential increases from-1.38 V to-1.34 V,the impedance modulus value|Z|_1Hz risings from 10⁶ ohm·cm² to 10⁸ ohm·cm².The SMPU₃-U₃₀@CS-0.5 has excellent self-healing and anti-corrosion properties.The corrosion resistance of the coating at 300 s under NIR recovers well.The efficiency of light repair is much higher than that of simple thermal repair,indicating that it has greater application potential.