Preparation And Anti-Corrosion Performance Of Composite Coating From Cationic Waterborne CO₂ Based Polyurethane And Polyaniline

Chemical utilization of carbon dioxide is using CO2 as feedstock to synthesize energy chemical and organic or polymer materials,such topic is very hot both in academic and industry field,especially for sustainable carbon neutral strategy.Till now about 100 mt per year of CO2 has been utilized in the world,among which urea and metal carbonate consititute the two large commodity usages,though the value added utilization of CO2 is still far from satisfactory.In the past two decades,CO2 is used as raw material for polymer synthesis,typical examples are high molecular weight CO2 based plastics and low molecular weight CO2 based polyols,such polymers boast of 30 times increase in value compared with CO2,however,the unique performance for potential application need developing.For example,CO2 based polyols(CO2-polyols)are targeting raw materials for various kinds of polyurethanes,but which polyurethane is the very one for CO2 based polyols?In another respect,metal corrosion is a worldwide topic with worldwide annual cost due to corrosion over 3%of the world’s GDP,in fact,metal corrosion not only causes substantial economic loss,but also brings security risk.The state-of-the-art technique for metal anti-corrosion is employing Zinc-plated or Zinc rich coating,though successful in anti-corrosion performance,it is accompanied by heavy metal pollution and anxiety of sustainable supply of the exhausting Zinc resource.Polyaniline has been regarded as an emerging environmental friendly anti-corrosion material,since it displays anti-corrosion behaviour due to its unique redox behavior.However,the current polyaniline anti-corrosion coating is mainly organic solvent containing,to answer the call of waterborne metal anti-corrosion coating,though waterborne conducting polyaniline(cPANI)has been developed,the substrate resin is still unsolved,especially when high barrier performance to corrosive media like water,oxygen or chloride ion,are concerned.To enhance the anti-corrosion performance of cPANI,designing a coating containing cPANI and waterborne binder resin is a common sense strategy.Considering the cationic nature of cPANI dispersion,cationic polyurethane dispersion(CPUD)should be designed for compatibility.However,most CPUDs are acidic,which is detrimental to steel surface,let alone anti-corrosion function.In view of the above problems,near neutral or completely neutral CO2-based cationic waterborne polyurethane was designed and synthesized in this thesis,and the compatibility with cPANI was investigated,the anti-corrosion performance of the composite coating was explored,the main results were summarized as follows:1.Design and preparation of near neutral cationic waterborne polyurethane(CPUD)based on CO2-polyol.A side-chain cationic extender,1,4-butanediol di(3-diethylamino-2-hydroxypropyl alcohol)ether(BDE)was designed and synthesized.Using BDE as internal emulsifier and CO2-polyol as soft segment,a near neutral CPUD(PPC-BDE-4(0.8))was prepared with the pH value of 5.67,benefitting from the tertiary amine in BDE locating on the side chain with less steric hindrance,which was expected to be more reactive in neutralizing acid.2.Anti-corrosion performance of near neutral CPUD/cPANI composite coating.The near neutral CPUD(PPC-BDE-4(0.8))coated carbon steel(CS)plate was visually transparent without any flash rust.A good compatibility between CPUD and cPANI was proved by SEM and TEM technologies,especially when the content of cPANI was 1.0 wt%.The composite coating showed excellent stability and homogeneity.The successful incorporation of cPANI in CPUD composite coating afforded significant enhancement of barrier property and passivation behaviour evidenced by the PDP and EIS analyses.3.Preparation and anti-corrosion performance of neutral CPUD.A side-chain cationic extender,2,5,18,21-tetramethyl-9,14-dioxa-2,5,18,21-tetraazadocosane-7,16-diol(TDTD),was designed and synthesized,in which the tertiary amine faced less steric hindrance than BDE.Using TDTD as internal emulsifier and CO2-polyol as soft segment,a neutral CPUD was prepared,PPC-TDTD-4(1).Since the linear PPC-BDE-4(0.8)was unfavorable from the perspective of long-term corrosion protection,it was necessary to construct internally crosslinked dispersion for better barrier performance.Here a post-chemical modification method was taken to prepare neutral CPUD with noncovalent 3 dimensional(3D)network using commercial citric acid as crosslinker,which showed good compatibility with cPANI.The supramolecular network in the crosslinked CPUD enhanced the compactness of binder,providing a significant enhancement of barrier performance to corrosive molecules.