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Synthesis and Properties of Nano-SiO2 /Fluorinated Polyacrylate Composite Emulsion

Author: MaYingZi
Tutor: XiaoXinYan
School: South China University of Technology
Course: Applied Chemistry
Keywords: seed emulsion polymerization modified nano-SiO2 fluorinated polyacrylate core-shell structure hydrophobicity
CLC: TQ320.1
Type: Master's thesis
Year: 2011
Downloads: 61
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Abstract


With the introduction of nano-SiO2 into fluorinated acrylate system, the product not only can own hardness and heat resistance of SiO2 but also can obtain excellent surface performance of fluorinated acrylate such as hydrophobicity, oleophobicity and stain resistance. In addition, the composite can obtain more excellent performance due to synergies between inorganic and organic components.Nano-SiO2 was modified byγ-（methacryloxy） propyltrimethoxy silane （KH-570） on the surface, the principle of the modification reaction between KH-570 and nano-SiO2 was studied. The influence of reaction temperature, pH value of the system, the amount of KH-570 and reaction time on the grafting ratio of nano-SiO2 was discussed. And the result of the modification was characterized by Fourier transform infrared spectroscopy （FTIR） and particle size analysis （PSA）. The results showed that, KH-570 molecules were successfully grafted on the surface of SiO2 particles via chemical bonds （Si-O-Si）. Considering the grafting ratio of nano-SiO2, the appropriate reaction temperature was 40℃, pH value of the system was 4 - 4.5, the amount of KH-570 was about 40%, reaction time was 5 h. The average particle size of modified SiO2 increased, the particle size distribution （PSD） was very narrow, which was similar to the particle size distribution of the latex and was conducive to the synthesis of emulsion with core-shell structure.The core-shell nano-SiO2/fluorinated polyacrylate emulsion containing ?uorine in the shell was successfully synthesized via semi-continuous seed emulsion polymerization in the presence of reactive anionic emulsifier and nonionic emulsifier, in which the polymerization monomers consisted of nano-SiO2 that modified by KH-570, methyl methacrylate （MMA）, butyl acrylate （BA） and acrylic acid （AA）, and dodecafluoroheptyl methacrylate （DFMA）. The mechanism of the polymerization was analysed. The influence of amount of emulsifier, initiator, modified nano-SiO2 and DFMA on the polymerization process and the comprehensive performance of latex films was investigated as well. The surface free energy of latex films was estimated through two evaluation methods. The structure and morphology of the latex particles, the surface properties and heat resistance of the latex films was characterized through particle size analysis （PSA）, transmission electron microscopy （TEM）, Fourier transform infrared spectroscopy （FT-IR）, X-ray photoelectron spectroscopy （XPS）, contact angle （CA）, differential scanning calorimetry （DSC） and thermogravimetry analysis （TG）. The results showed that nano-SiO2 grafted with double bond and fluorinated acrylate monomers are involved in the emulsion polymerization. The resultant particles had the core-shell structure obviously, the particle size of the composite latex increased comparing to polyacrylate emulsion, and the particle size distribution （PSD） showed a single peak. When the total amount of compound emulsifier （DNS-86 and OP-10） was 3%, the mass ratio of DNS-86 and OP-10 was 2: 1, the amount of initiator was 0.5%, optimal system stability and water resistance of latex films could be obtained. The water resistance of the latex films decreased when the amount of nano-SiO2 increased from 0 to 6%, and then increased slightly with the content of nano-SiO2 increased from 6% to 12%, so the appropriate amount of nano-SiO2 was about 6%. The hydrophobicity of latex films increased with the amount of DFMA increasing. When the amount of nano-SiO2 was 6% and the amount of DFMA was 15%, the contact angle of latex films with the deionized water was up to 116.8°, and the minimum surface free energy was 11.99 mN·m-1. The content of fluorine element in the latex film showed a decreasing gradient distribution from the film-air interface to the film-glass interface. The hydrophobicity and thermal stability of polyacrylate latex films could be greatly improved with the introduction of nano-SiO2 and DFMA.

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