The Surface Modification Of Nano SiO₂Sol And The Application In Polyurethane Emulsions

With the progress of era and social development, people pay more and moreattention to environmental problems. Correspondingly, environmentally friendlypaints are becoming popular. Waterborne polyurethane coatings have lots of excellentcharacteristics such as high elasticity, wear and radiation resistance. And waterbornepolyurethane paints are used in various fields. However, waterborne polyurethane alsohas many shortcomings. For example, The coatings have poor performance inwaterproof, solvent resistance and adhesion. And the gloss of coatings is very low.These defects have great influence on the application and promotion of waterbornepolyurethane coatings. Inorganic nano-materials have excellent weather resistance,high hardness, water proof and alkali resistance. Adding nano material into resin canimprove the properties of coatings. Therefore, the research in modification ofwaterborne polyurethane by nano particles has important significance.In this thesis, we used different kinds of silane coupling agent for surfacemodification in nano-SiO₂sol, and then blended modified nano-sol with polyurethaneemulsion from different application areas. The nano-composite waterbornepolyurethane emulsion with excellent performance was prepared. The main contentsinclude the following aspects:1. The methods of modifying nano-particals has been explored, we used methyltriethoxysilane （MTES）, dimethyldiethoxysilane （DMDES）, γ-methacryloxypropyltrimethoxysilane （KH570）,3-aminopropyltriethoxysilane （KH550） andγ-（2,3-glycidoxypropyl） trimethoxysilane （KH560） to modify the surface ofnano-particals respectively. The effect of types of silane coupling agent,SiO₂/coupling agent molar ratio, pH and modification time on modified nano-SiO₂sol were discussed. And the infrared spectroscopy （FTIR）was used to characterize thestructure of the nano-sol. The results showed that when the molar ratio ofSiO₂/coupling agent was6:1and pH value was about4, KH560could significantlyimprove the surface properties of the nano particles after4h of reaction. Thenanoparticles were dispersed in the aqueous emulsion uniformly. And the storage stability of modified nano-SiO₂sol was excellent.2. We added the modified nano-sol into aqueous polyurethane dispersion forABS plastic plate. The effect of the silica sol/KH560molar ratio and modifiednano-sol content on basic mechanical properties of the coating, water resistance andother performance was researched. The morphology of coatings was measured byTEM and SEM, the structure of resin was tested by FTIR. TGA was used to analysisthe thermal properties of hybrid emulsion. The results showed that when the molarratio of silica sol/KH560was6:1and the content of modified sol was5to10%, themodified waterborne polyurethane composite emulsion had excellent properties. Thependulum hardness of coating was increased by130%. The wear resistance andscratch resistance were improved significantly. The mass loss was from the initial10.3mg to7.8mg. And the film load was from1000GRMS up to1200GRMS. Thewater absorption rate was decreased from11.2%to6.5%. The hydrophobicity wasalso improved and contact angle was increased from67°to75°. Moreover, theweather ability resistance and solvent resistance were enhanced.3. We added the modified nano-sol into aqueous polyurethane for wood. Theresults indicated that when the dosage of modified sol was10～15%, the compositecoating had the best performance. The pendulum hardness was increased by37.4%;the water absorption was decreased from12.7%to10.7%; the loading of scratchresistance was risen from300GRMS up to900GRMS, the mass loss was reducedfrom50.8mg to14.3mg; the salt spray resistance ability was increased from336h to600h.