Preparation Of CNT-Based/Organic Nanocomposite Coatings And Study Of Their Anti-corrosion Mechanism

As an important development direction for the coating industry,waterborne coatings suffer from high water absorption and unsatisfactory anti-corrosion properties.Nanotechnology provides an effective way to improve the performance of waterborne coatings.Carbon nanotubes(CNT)are functional additives with potential applications for corrosion protection due to their unique one-dimensional nanostructure and electrical properties.To address the problems of easy agglomeration of CNT,poor interfacial compatibility with polymer matrix,and unclear mechanism of corrosion protection,the thesis focuses on the following content:1.Preparation of CNT/waterborne acrylate modified epoxy nano-baked coatingsIn order to improve the interfacial bonding of CNT in aqueous coating resins,this chapter was designed to use diethylenetriamine(DETA)surface modified CNT to form a stable CNT aqueous suspension dispersion;further added in acrylate modified epoxy aqueous dispersion(EPA70)to prepare aqueous nano-baked coatings.Rheological studies showed that CNT interacted strongly with the epoxy matrix through surface-active amino groups;Young's modulus and hardness of the CNT nanocomposite coating were significantly higher compared to the EPA coating,showing a significant effect of CNT's positive influence on the mechanical and mechanical properties of the nanocomposite coating.The nanocomposite coating filled with 0.25 wt%CNT has an extended neutral salt spray resistance of 850 hours compared to 680 hours for the EPA coating,an increase of 25%.The electrochemical impedance tests results reveal that the metal corrosion protection mechanism of CNT is mainly a nano-barrier effect.2.Preparation of CNT/acrylate grafted epoxy latex composite coatingsThe corrosion protection performance of CNT nanocomposite coatings depends not only on the nano-barrier effect of CNT,but also on the cathodic inhibition effect based on the formation of CNT conductive networks.In this paper,a waterborne CNT nanopaste with stable dispersion was successfully prepared using a hyperdispersant(DC-02);it was then filled into an aqueous acrylate grafted epoxy coating(EPA30)to prepare a waterborne nano-room temperature curing coating.The hyperdispersant(DC-02)was proved to be an aqueous and efficient dispersant for CNT by TEM and rheological studies.The prepared CNT aqueous nano-paste was easily and uniformly mixed with the EPA30 coating.TEM and SEM of ultra-thin sections demonstrated the homogeneous dispersion of CNT in the coating and,as a result,the nanocomposite coating filled with 0.25 wt%CNT(CNT(0.25 wt%)/EPA30)formed a conductive network.The results of the salt spray resistance tests show that the CNT(0.25 wt%)/EPA30 nanocomposite coating has an extended salt spray resistance result of 350 hours compared to the EPA30 coating with a neutral salt spray resistance of 200 hours,an increase of 75%.The results of Tafel polarisation curves and electrochemical impedance tests reveal that the corrosion protection mechanism of CNT in the CNT(0.25 wt%)/EPA30 nano-composite coating is a synergistic effect of nano-barrier and cathodic inhibition.3.Preparation of CNT/PANI/acrylic acid amino baking coating and its anti-corrosion mechanismIn order to further improve the anticorrosive properties of waterborne nanocoatings,CNT/PANI composites with nano-fibrous PANI covering the surface of CNT were successfully prepared using aniline oxidation polymerization in CNT aqueous suspension dispersion.The thickness of PANI shell layer and interfacial interaction can be regulated by the composition ratio of aniline to CNT.This is based on the monodisperse state of CNT in aqueous solution and the formation of weak electron donor-electron acceptor interactions between CNT and aniline salts,forming a site of polymerisation with an extremely large surface compared to that in solution.The synthesised CNT/PANI nanocomposites were filled with an aqueous heat-curing resin to prepare CNT/PANI/acrylic acid amino baking coatings.Polarisation curves,electrochemical impedance tests and salt spray resistance tests show that the thickness of the shell layer PANI in nanofibre-shaped CNT/PANI has a significant effect on the coating's mechanical damage smart protection function and long-lasting corrosion resistance.The coating exhibits the best long-term corrosion protection performance when the ANI:CNT ratio is 2:1.The CNT/PANI(1:2)nanocomposite coating showed salt spray resistance results of up to 510hours,an increase of 250%,compared to the unfilled coating with a neutral salt spray resistance of 230 hours.This reveals that the metal corrosion protection mechanism of the nano-fibrous CNT/PANI composite is the easy formation of a conductive network in its organic composite coating;cathodic inhibition based on the transport of electrons from the metal surface;and anodic protection with excellent metal passivation catalysis based on the redox activity of the superior PANI.This study provides new ideas for the preparation of environmentally friendly anti-corrosion materials.