| The nanoscale silica hydrosol were prepared by sol-gel process,through the hydrolysis and condensation reactions of tertraethyl orthosilicate(TEOS),and then modified its surface by Vinyltriethoxysilane(A-151),used acrylic acid and methyl methacrylate to enwrap,finally,the steady and functional nanoscale silica hydrosol were obtained.Through the research of synthetic technique,the best parameter of reaction was determined.The volume ratio of TEOS and water was 1/20;added A-151 after 12 hours at room temperature for forming single layer,the reaction time was 24 hours.The sodium dodecyl sulfate(SDS)used as emulsifier and the dosage was 3-4 percent of whole system. The manner of adding acrylic acid(AA)and methyl methacrylate(MMA)was hunger and half-continue,the grafting ratio and the enwrapping degree of nano silica were excellent when the ratio of monomer and A- 151 was one.Via characterized nano silica particle by fourier transform infrared(FT-IR),thermo gravimetric analysis(TGA),X-ray diffraction(XRD)and transmission electron microscopy(TEM),conformed the particle of silica existed as amorphous,the behavior that modified its surface did not change the inner structure;the average size of silica was 18nm and mono-dispersed.About 5.42 percent A-151 was grafted and 30.59 percent macromolecule was enwrapped the surface of nano silica.Based on preparing silica sol successfully,silica-polyurethane/polyacrylate composites were prepared via in-situ polymerization and blend.The dosage of silica,the reaction method and the performance of PUA were investigated.The SPUA prepared was 30%solid content;pH value 6.5-7.5.It can be stored more than 6 months under room temperature.The viscosity of SPUA emulsion with thixotropy was slowly increase and then decrease with the increase of SiO2,no matter which method used,increase rapidly when the dosage of SiO2 over 1.5%.The viscosity of SPUA emulsion prepared by in-situ polymerization was higher than blend at the time of adding the same dosage of SiO2.FT-IR confirmed that the functional groups of PUA changed by adding nano silica. Through the TG analysis,we knew,because of silica,the temperature of thermolysis increased evidently,enhanced the heat-resistant of PUA.The glass transition temperature of SPUA was measured by differential scanning calorimetry(DSC).No matter which method used,the Tg of soft segment in PU did not changed,but the Tg of PA(Tg2)and the Tg of hard segment in PU(Tg3)were affected.As for in-situ polymerization,the highest Tg2 appeared at adding 1%SiO2,it increased 12.8℃than pure PUA,while it appeared at 1.5%for blend,increased 30.8℃;the Tg3 appeared at 1%and 3% respectively,increased 21.6℃and 32.4℃than pure PUA respectively.The water absorption of film that produced by in-situ polymerization was decrease and then increase,the best water resistance appearance at adding 1%nano SiO2 Nevertheless,in the method of blend,the water resistance did not modified better,but worse.The film of SiO2-PUA nanocomposites has better mechanical performance than pure PUA,just as hardness,tensile strength,elongation and so on. |
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