Preparation And Application Of In-situ Formed Silica Modified Waterborne Polyurethane

In this paper,silica(SiO2)sols with controlled particle size and morphology were prepared by sol-gel method.Then SiO2 was synthesized in-situ compounded into waterborne polyurethane(WPU)matrix or on the surface,and finally silica/waterborne polyurethane composites were prepared.The main research contents and experimental results are divided into the following three parts.The nano-SiO2 sol with controllable size could be obtained by regulating the hydrolysis degree of sodium silicate aqueous solution.Then the SiO2 was compounded into the waterborne polyurethane(WPU)matrix by in-situ synthesis.The effect of SiO2 content and particle size on the properties of WPU grouting materials was investigated.The experimental results show that the addition of inorganic silicon in WPU can improve the compressive strength of WPU materials.With the increase of SiO2 content,the compressive strength of composites first increased and then decreased.When the SiO2 content was 3 wt%,the compressive strength reached the maximum of 0.22 MPa.In the case of controlling the pH value of the solution in the silica sol to 4,the longer the silica sol is allowed to stand at room temperature,the larger the particle size of the nano-SiO2 prepared by the in-situ synthesis method is.Especially,the compressive strength reached the maximum of 0.302 MPa,when the nano-SiO2 loading was 3 wt%and the standing time of the silica sol was 2.5 h.The formation process of nano-SiO2 prepared was regulated by the effect of polyethylene glycol and pH on the hydrolysis of sodium silicate,and then the silica sol containing amorphous nano-silica(A-SiO2),spherical nano-silica(S-SiO2)and the layered hexagonal nano-silica(LH-SiO2)particles were obtained,respectively.Then the SiO2 was compounded into the waterborne polyurethane(WPU)matrix by in-situ synthesis.The effect of SiO2 morphology on the properties of WPU grouting materials was investigated.The experimental results show that the addition of inorganic silicon in WPU can improve the mechanical properties of WPU grouting composites.Specifically,S-SiO2 modified WPU has higher compression strength,but LH-SiO2 modified WPU possesses better toughness.However,the enhanced toughening effect of A-Si02 modified WPU was limited.By using the biomimetic mineralization technology and using the sol-gel method,a layer of silica was rapidly mineralized on the surface of WPU coatings by utilizing the condensation reaction between silanols.To achieve this goal,we first synthesized silane-terminated waterborne polyurethane(SPU)copolymer end-capped with 3-aminopropyltriethoxy silane(APTES).Then,the prepared SPU coating was soaked insilica sol,and finally a layer of silica was rapidly mineralized on the surface of SPU by utilizing the condensation reaction between silanols.The chemical structure and morphology of the obtained composite materials were studied using ATR-FTIR and SEM.The thermal stability and mechanical properties were investigated by TGA and pencil hardness test,respectively.Finally,the anticorrosion properties of coating materials were evaluated by Tafel polarization curves and salt-immersion tests.The experimental results showed that hardness,heat resistance and corrosion resistance of the WPU coatings have been improved due to the mineralization of silica on the surface of the coatings.