Preparation And Properties Of Composite Epoxy Powder Coatings Modified By Nanomaterials With Different Structural Dimensions

Corrosion is a common reason for failure of metallic structures,which causes great economic loss and life threat to human beings.Protective layers,electrochemical corrosion protection,and corrosion inhibitors are the methods used to achieve reduction in corrosion rate.Organic coatings are considered to be the most common used anticorrosion method because of their excellent mechanical properties,corrosion resistance and chemical stability.The anticorrosion mechanism is based on barrier protection and isolation of metal structures and corrosive environment.However,most of the traditional organic coatings are solvent-based,which will release a lot of volatile organic compounds(VOCs)and cause pollution to the environment.In recent years,epoxy resin powder coatings have been developed rapidly due to their economical features,environmental protection,high efficiency,and excellent application performance.The epoxy resin is a thermosetting polymer with a highly cross-linked structure,which has high strength,high stiffness,and brittleness.Therefore,the porosity and brittleness of the epoxy resins are the main defects that hinder their wide application.In order to solve the defects of the epoxy resin such as porosity and brittleness,nanoparticles are often added to the epoxy resin matrix as a reinforcing phase to form nanocomposite epoxy powder coating,which can improve the flexibility of the epoxy powder coating,and therefore,improve its protective performance.On the other hand,since the nanomaterials with different sizes,shapes,and types may have different effects on the properties of the epoxy powder coatings,this paper selects nanomaterials with different dimensions(zero-dimensional nano and microspheres SiO₂,one-dimensional nanotubes MWCNTs,and two-dimensional nanosheets MoS₂)for experiment and comparison.The nanomaterials with different dimensions are dispersed in the epoxy powder coating by melt mixing extruding method as a new process to explore the synergy through chemical modification and mechanical ball grinding technology.Further,the nano composite epoxy powder coating is applied on the pre-processed good carbon steel specimens by electrostatic spraying nanocomposite powder coating,followed by heat-treatment to cure the epoxy powder nano composite coating.Fourier transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS)were used to detect the modification of different nanoparticles.Transmission electron microscopy(TEM)and scanning electron microscopy(SEM)were used to evaluate the morphology and dispersion quality of the modified nanoparticles in epoxy resin.The mechanical properties of the nano composite epoxy powder coatings were evaluated by testing the adhesion,friction resistance,and impact resistance of the coatings.The thermal stability of the nanocomposite coatings with different dimensions was tested by thermogravimetric analysis(TGA)and differential scanning calorimetry(DSC).Neutral salt spray test,potentiodynamic polarization curves(Tafel),electrochemical impedance EIS,and resistance to chemical corrosion tests have been used to evaluate the influence of the nanomaterials on the barrier and anticorrosive properties of the nanocomposite coatings,and to discusses the corrosion protection mechanism of the nano composite epoxy powder coating.The main research contents and results of this paper are as follows:(1)The 0.2 wt%m-SiO₂ composite powder coating was modified by APTES as silane coupling agent.Compared with the pure epoxy powder coating,the Tg of the prepared 0.2 wt%m-SiO₂composite powder coating increased about 1.3?,the adhesion increased from 3.2 MPa to 5.8 MPa,and the impact strength increased from 33 kg·cm to 56 kg·cm.The friction coefficient decreased from 0.58 to 0.55.After soaking in 3.5 wt%Na Cl solution for 70 days,the EIS test showed that the impedance|Z|_0.01Hz value of the coating was 10^9.5cm²,which was 3.5 orders of magnitude higher than that of the pure epoxy coating.(2)Compared with pure epoxy powder coating,the prepared 0.2 wt%m-MWCNTs composite coating was modified by polyvinylpyrrolidone(PVP).The glass transition temperature(Tg)of the 0.2 wt%m-MWCNTs composite coating increased by 15.13?,and the adhesion strength increased from 3.2MPa to 4.1 MPa.The impact strength increased from 33 kg·cm to 59 kg·cm,the tensile strength increased by 53.7%,and the friction coefficient decreased from0.58 to 0.38.After soaking in 3.5 wt%Na Cl solution for 70 days,EIS test showed that EP/0.2%m-MWCNTs composite coating still maintained a relatively high impedance|Z|_0.01Hz value of 10^9.1?·cm²,which was 3.7 orders of magnitude higher than that of the pure epoxy coating.(3)Dopamine hydrochloride was successfully used to modified MoS₂.Compared with the pure epoxy powder coating,the Tg of the prepared 0.2 wt%m-MoS₂composite coating increased by 12.35?.The adhesion increased from3.2 MPa to 4.4 MPa,the impact strength increased from 33 kg·cm to 60 kg·cm,and the friction coefficient decreased from 0.58 to 0.1.The EIS tests were recorded for different coating samples after for 7 days,35 days and 70 days of soaking in 3.5 wt%Na Cl solution.The coating impedance|Z|_0.01Hz of the 0.2wt%m-MoS₂composite epoxy powder coating increased from 10^10.8?·cm² to10¹¹?·cm²,and then decreased to 10^10.2?·cm² after 70 days,which was 4.2orders of magnitude higher than that of the neat epoxy coating.Through modification,ball milling and melting mixing,nano particles are evenly dispersed in epoxy resin to form a maze effect,which extends the diffusion path of the corrosive medium and improves the barrier and anti-corrosion properties of the coating.The nanocomposite epoxy powder coating studied in this paper responds to the national requirements for green environmental protection,and provides new ideas and theoretical guidance for the industrialization process design of nanocomposite epoxy powder.