Preparation And Performance Of Non-Covalent Modified Two-Dimensional Material/Waterborne Polyurethane Composite Film

Compared with solvent-based polyurethane,water-based polyurethane（WPU）,which uses water as the dispersion medium,has excellent features such as environmental friendliness and low toxicity,etc.Film-forming resins based on WPU are gradually replacing solvent-based PU as the ideal choice.However,numerous studies have shown that the inevitable shrinkage and residual hydrophilic functional groups in the film-forming process of WPU lead to limited performance,such as poor anti-corrosion properties and insufficient mechanical strength of the coating,and weak resistance to UV aging degradation,which undoubtedly limit the application and service life of WPU.To address the above issues,this paper presents a non-covalent modification（e.g.π-πinteraction,hydrogen bonding network construction）of two-dimensional material nanosheets in aqueous phase and the introduction of WPU matrix.The corrosion resistance,mechanical properties and UV aging resistance of the modified nanosheets/WPU composite film materials were further investigated to ensure the stability of the system.Compared with the covalent modification,the non-covalent modification maintains the intrinsic structure of the nanomaterials to the maximum extent and shows great superiority.The specific research of this thesis includes the following two parts:In the first part,a simple and effective method was proposed to design the emulsion system and prepare a stable composite emulsion of non-covalently modified BNNSs（BNNSs@PS）by in situ polymerization usingπ-πinteraction,construct aqueous polyurethane nanocomposite coatings（BNNSs@PS/WPU）by emulsion blending,and investigate the anti-corrosion performance of BNNSs@PS/WPU.The results showed that BNNSs@PS emulsions have good dispersion stability,uniform dispersion in WPU and good compatibility.The anti-corrosion performance of BNNSs@PS/WPU composite coatings was investigated by electrochemical impedance spectroscopy.The Bode plot shows that the composite coating（50.0BNNSs@PS/WPU）fabricated by adding 50 mg of BNNSs to the composite emulsion,and co-blended with WPU exhibited the maximum impedance value.The value of impedance|Z|_0.01Hzwas stable at 5.57×10⁸Ωcm²after 28 days of immersion,which was 4 orders of magnitude higher than that of the pure WPU coating.The inhibition efficiency（IE）of the composite coating reached 99.99%,and the corrosion rate（CR）decreased from 4.78×10^-2mm/year to 2.58×10^-6mm/year relative to the WPU coating,indicating that the corrosion protection performance of polyurethane nanocomposite coatings（BNNSs@PS/WPU）was significantly improved relative to that of pure WPU.In the second part,two-dimensional MXene（Ti₃C₂T_x）nanosheets（M）were non-covalently modified with alginate（T）and introduced into the WPU matrix to construct hydrogen bonding network-reinforced polyurethane nanocomposites T-M/WPU.The mechanical properties of the composites after accelerated ageing tests were investigated.The results showed that the two-dimensional MXene（Ti₃C₂T_x）nanosheets showed good dispersion in water before and after modification with alginate.When a certain amount of algose was added to WPU,the mechanical properties of T/WPU were better relative to WPU due to the enhanced hydrogen bonding network between the algose molecules and WPU molecules.However,an excessive amount of algose will affect the interaction between WPU molecular chains and affect the mechanical properties of the composites.At the same time,when a certain amount of MXene（Ti₃C₂T_x）nanosheets were compounded with WPU,the mechanical properties of M/WPU were also better than those of WPU to a certain extent due to the large amount of-OH and-F on the surface of MXene（Ti₃C₂T_x）and the intermolecular hydrogen bonding of WPU.The introduction of too much MXene（Ti₃C₂T_x）will affect the dispersion of the nanosheets in the WPU emulsion and the film formation of the composite film at a later stage,which will likewise lead to a decrease in the mechanical properties of the composite.By optimising the composite ratio to 1:10 T:WPU and adding 0.4 wt%of MXene（Ti₃C₂T_x）,the samples had the best mechanical properties（maximum tensile stress of 35.28 MPa,elongation at break of 756%and toughness of 35.28 MJ/m³）.After the UV accelerated ageing test,the mechanical properties of WPU decreased dramatically,with T/WPU maintaining only a small proportion of its mechanical properties,M/WPU maintaining most of its mechanical properties（70%）,and T-M/WPU remaining essentially unchanged.This indicates that the synergistic effect of the anti-UV properties of the seaweed sugar and MXene（Ti₃C₂T_x）nanosheets themselves and the enhanced hydrogen bonding network of the constructs give the WPU composite film materials excellent mechanical properties and anti-UV ageing properties.