Preparation And Properties Of Nano SiO₂ Modified Waterborne Polyurea

Waterborne polyurea coatings use water as a dispersion medium,which is environmentally-friendly.However,the hydrophilic groups will decrease water resistance,heat resistance and mechanical properties of waterborne polyurea coatings,so it's necessary to modify waterborne polyurea and improve its performance.In this research,polyetheramine D2000,isophorone diisocyanate(IPDI),2,2-bismethylolpropionic acid(DMPA),and ethylenediamine(EDA)were used as main raw materials to synthesize a series of waterborne polyurea and it was modified with nano-SiO₂.The properties of modified waterborne polyurea were explored.On the basis of modified waterborne polyurea,a modified waterborne polyurea coating was prepared and its application value was studied.The rest of this paper mainly includes the following points:Firstly,two methods of synthesizing waterborne polyurea were compared,include synthesizing with aminoterminated polyether or polyaspartic acid ester.Finally,polyetheramine D2000,IPDI,DMPA and EDA were determined as the main raw materials for the synthesis of waterborne polyurea.The effects of the ratio of polyetheramine to isocyanate,the amount of DMPA and the use of catalysts on the synthesis of waterborne polyurea were investigated by experiments.The film was measured for water absorption,acid and alkali resistance,heat resistance,and various mechanical properties.When no catalyst was added,polyetheramine:isocyanate=1:5 and the amount of aqueous chain extender was 6%,the comprehensive performance of waterborne polyurea was the best.Then,the non-surface-treated hydrophilic nano-SiO₂ was used as a modifier through polyamine dispersion method.Polyamines has a large steric hindrance and nanoparticles are easily dispersed in polyamines.Nano-SiO₂ successfully connected to the polyurea molecular chain;as the content of nano-SiO₂ increased,the viscosity of the polyurea emulsion became larger,and the appearance gradually changed from light yellow and transparent to dark yellow and white.When the amount of nano-SiO₂ is 2%,the coating performance was the best(tensile strength at25.8MPa,elongation at break reach 285%,water absorption at 15.12%),and the overall thermal performance of the waterborne polyurea was improved by about 5?.The waterborne polyurea was modified by the sol-gel method.First,IPDI and D2000 were reacted,and then the aqueous chain extender DMPA,the small molecule chain extender EDA,and the silane coupling agent 3-aminopropyltriethyl Oxysilane(KH550)and TEA were added to the system for reaction.Finally,nano-SiO₂ aqueous solution was added respectively to the system.After emulsification,nano-SiO₂ modified waterborne polyurea was prepared.The effects of different amounts of nano-SiO₂ on the properties of modified waterborne polyurea were explored.When the amount of nano-SiO₂ is 2%,the comprehensive performance of waterborne polyurea was the best.The water absorption of the coating film was reduced from30.56%to 11.12%,the tensile strength first increased and then decreased to a maximum of 29.7MPa,and the elongation at break continued to decrease.According to TGA,the thermal decomposition temperature of the modified waterborne polyurea coating was increased by about 10?compared with the unmodified waterborne polyurea coating.The nano-SiO₂ modified waterborne polyurea prepared by the sol-gel method was used as the main film-forming substance.Nano-SiO₂ modified waterborne polyurea coating was prepared by compounding with pigments and fillers and common coating additives.Through comparison conditions,it was finally determined that 65%of the modified waterborne polyurea was added,titanium dioxide was selected as the pigment filler,the content was 20%,the amount of defoamer added was 0.15%,and the amount of wetting dispersant was 0.3%,the amount of water 10%?15%,the amount of other additives 1%,the comprehensive performance of coating was the best The prepared coating film has excellent appearance,excellent mechanical properties,good water resistance,acid and alkali resistance,and can be used in more scenarios,and has great application value.