Study On Preparation And Properties Of Nano-SiO₂ Modified Waterborne Phenolic Epoxy Resin

Phenolic epoxy resin(EPN)coating should be toughened and modified to meet the increasingly strict environmental standards and current requirements for high-performance composite coatings,due to the problems of high VOC emissions,hard and brittle,easy to crack,and poor toughness.In this paper,nano-SiO₂ modified waterborne phenolic epoxy resin anticorrosive coating was synthesized by the toughening modification of EPN.Not only EPN coating was made water-based,but also its properties of mechanical properties,acid and alkali resistance,toughness were greatly improved.The coating has excellent comprehensive anti-corrosion performance and can be used in anti-corrosion fields such as petrochemical industry,transportation,aerospace,construction engineering,etc.Firstly,EPN was synthesized with the phase transfer catalyst tetrabutylammonium bromide(TBAB)by adding alkali twice.The EPN was modified with diethanolamine(DEA)or sodium p-aminobenzene sulfonate through the etherification reaction and water-based phenolic epoxy resin(WEPN)was prepared.At last,it was determined that WEPN emulsion was prepared by modification of DEA.The optimized reaction conditions were as follows:n(DEA):n(epoxy)=1:3,the temperature was 65°C and the time was 2h.The results showed that the average particle size of the emulsion was about 324nm and the absolute value of the zeta potential was more than 32m V.The particles were uniformly dispersed in the system and the storage period reached more than 5 months.The section of the coating film was flat,smooth and almost no cracks,which showed obvious brittle fracture characteristics.Secondly,nano-SiO₂ was modified by?-aminopropyltriethoxysilane(APTES).The nano-SiO₂ modified water-based phenolic epoxy resin(SiO₂/WEPN)was prepared through the prepolymer method that modified nano-SiO₂ reacted with phenolic oligomer,epichlorohydrin(ECH),DEA and other main raw materials.The results showed that after APTES was hydrolyzed,it was grafted on the surface of SiO₂ in the form of Si-O-Si bonds.When the amount of APTES was 40%of the mass of nano-SiO₂,the modification effect was the best.SEM showed that the agglomeration of nano-SiO₂ was improved and the dispersion increased after modification.TEM showed that when the content of nano-SiO₂ was less than3%,it was uniformly dispersed in the emulsion.SEM showed that there were many cracks in the section of the coating film,which showed the characteristics of ductile fracture.When the content of nano-SiO₂ was 2%,the overall performance of SiO₂/WEPN composite coating film was the best.Compared with WEPN,the decomposition temperature(10%weight loss)of the coating film increased from 298.5°C to 350.1°C and the residual carbon rate increased to 29%.The mechanical properties increased by more than 15.38%.Application properties of the coating film such as acid and alkali resistance,hardness,and water resistance were improved to varying degrees.Then,the nano-SiO₂ was copolymerized with monomer phenol and formaldehyde through-OH on its surface by in-situ polymerization.SiO₂/WEPN was prepared by the way that the copolymerized reacted with epichlorohydrin(ECH),DEA and other main raw materials.The results showed that the reaction process was tracked by FT-IR,which proved that SiO₂/WEPN was successfully synthesized.When the content of nano-SiO₂ was less than2%,the absolute value of the zeta potential of the emulsion was more than 30m V and the stability of the system was good.SEM showed that with the increase of the content of nano-SiO₂,the cross-section of the coating film was flat and smooth firstly.White spots and three-dimensional gullies appeared secondly.Finally,the number of gullies gradually decreased and cracks became thicker and aggregated.It showed that the toughness increased first and decreased then.When the content of nano-SiO₂ was 1.5%,the overall performance of the coating film was the best.Compared with WEPN,the tensile strength and elongation at break of the coating film increased by 8.55%and 13.24%respectively.The water absorption rate(240h)reduced from 10.1%to 7.5%and the water contact angle increased from 89°to102°.The decomposition temperature(15%weight loss)of the coating film increased from302.2°C to 337.0°C and the thermal stability was greatly improved.Finally,SiO₂/WEPN composite anticorrosive coating was prepared by the matrix of SiO₂/WEPN emulsion and pigments,fillers,rheology additives,dispersants and other additives.And the formula design was optimized.The coating had excellent comprehensive anti-corrosion performance including smooth appearance,glossiness of 92°,pencil hardness of 3H,impact resistance of 50cm,fineness of 35?m.Compared with single EPN coating,mechanical properties and toughness of composite coating were improved.Especially acid and alkali resistance,solvent resistance and heat resistance of it were outstanding.It can be used in anti-corrosion fields such as petrochemical industry,transportation,aerospace and construction engineering.