In-situ Preparation, Structure And Properties Of Polyacrylate/Nano-titanium Dioxide Composite Emulsions

In the past decades, polyacrylate emulsions have been widely used in buildings,automobile, packaging, printing, etc, which are due to non-pollution, low cost, goodperformance including film-forming ability, weather-resistance, flexibility and adherence.However, the heat-resistance and hardness of the polyacrylate latex films were poor, whichlimited the application at a certain degree. With the introduction of nano-titanium dioxide(TiO2) in polyacrylate emulsion, the polyacrylate/nano-titanlum dioxide composite emulsionscan be prepared, the heat-resistance and hardness of latex film would be improved obviously,and the application can be broadened. Nevertheless, because of the large specific surface areaand high surface energy, nano-TiO2was non-thermodynamic stable state, and the preparedcomposite emulsions had some disadvantages such as agglomeration of nanoparticles, poorstorage stability and complicated preparation technology. In this work, two technology routeswere used to prepared in-situ polyacrylate/n-TiO2composite emulsions, the important effectfactors on preparation process were discussed, the structure of nano-TiO2and compositeemulsions was characterized by Fourier transform infrared spectroscopy (FT-IR), dynamiclight scatting (DLS), X-ray diffraction (XRD) and transmission electron microscopy (TEM),the heat-resistance, mechanical properties and UV absorption property of the latex films werestudied, and the formation mechanism of the composite latex particles was discussed. Themain research contents and achievements are listed as follows:Firstly, KH-570modified nano-TiO2sol was prepared by sol-gel method with tetrabutyltitanate (TBOT) as precursor, hydrochloric acid (HCl) as catalytic agent and KH-570asmodifier, and subsequently polyacrylate/n-TiO2composite emulsions with good stability weresynthesized by in-situ emulsion polymerization method with MMA, BA and AA as reactivemonomers. The modified nano-TiO2, composite emulsion and latex film were characterizedby FT-IR, XRD, DLS and TEM. The results showed that the crystal form of modifiednano-TiO2was anatase. With the increase of HCl amount, the crystal form was unchangeable,but the crystallization degree increased. In contrast to unmodified nano-TiO2, the averagediameter of the modified nano-TiO2decreased and its distribution became narrow. When themolar ratio of HCl to TBOT was0.48, the average diameter of the modified nano-TiO2wasthe smallest and the distribution was the narrowest. KH-570modified nano-TiO2andpolyacrylate had good compatibility. With the addition of appropriate amount modifiednano-TiO2, the impact strength, hardness and heat-resistance of the latex films were improved,but the adherence and flexibility was almost unaffected. Secondly, cetyl trimethyl ammonium bromide (CTAB)/acrylic acid (AA)/methylmethacrylate (MMA)/H2O reverse microemulsions were firstly prepared with MMA as oilphase, CTAB and AA as surfactant and co-surfactant, respectively, and appropriate amountwater. In the reverse micelle used as nanoreactor, KH-570modified nano-TiO2sol wasprepared with TBOT and KH-570as precursor and modifier, respectively. The pseudo-ternaryphase diagram was drawn, the important effect factor on the production rate of nano-TiO2solwas studied, and KH-570modified nano-TiO2was characterized by FT-IR, TEM, etc. Theresults showed that when the mass ratio of CTAB to AA was2/3, the bigger reversemicroemulsion area could be obtained. With the increase of m(CTAB)/m(AA) andm(CTAB+AA)/m(MMA), the solubilizing water amount increased, the appropriatem(CTAB)/m(AA) and m(CTAB+AA)/m(MMA) were2/3and5/5, respectively. Thesolubilizing water amount was affected little by temperature. When solubilizing water amountand the mass ratio of KH-570to TBOT were44.5%and0.6, reaction time and temperaturewere20h and25oC, respectively, the production rate of nnao-TiO2attained74.9%. Theaverage diameter of KH-570modified nano-TiO2was about10nm, and their hydrophobicitywas improved obviously. In addition, in the preparation process of nano-TiO2, ethanol was notadded, which was propitious to the stability of the follow-up emulsion polymerization.Thirdly, in KH-570modified nano-TiO2prepared by reverse microemulsion, theappropriate amount water was added dropwise and the nano-TiO2system changed from W/Omicroemulsion to O/W pre-emulsion. Subsequently, polyacrylate/n-TiO2composite emulsionswere synthesized by in-situ emulsion method. The effect of polymerization method, reactiontemperature, KPS amount, TBOT amount, KH-570amount and solubilizing water amount onthe monomer conversion rate, gel ratio, diameter and Zeta potential was studied. The resultsshowed that batch method was more suitable than seeded semi-continuous method andcontinuous method. When reaction temperature was75oC, KPS amount was5%, the massratio of KH-570to TBOT was0.6, TBOT amount was5%and the solubilizing water amountwas44.5%, polyacrylate/n-TiO2composite emulsion had low gel ratio, high reaction stabilityand storage stability.Finally, the structure of polyacrylate/n-TiO2composite emulsions and latex filmsprepared by reverse microemulsion method and in-situ emulsion polymerization method werecharacterized by FT-IR, TG and TEM, the heat resistance, mechanical properties and UVabsorption property of the latex film were studied. In addition, the formation mechanism ofthe composite latex particles was also discussed. The results showed that thepolyacrylate/n-TiO2latex particles appeared apparent core-shell structure, in which nano-TiO2 and polyacrylate were core and shell, respectively, and the particle size was about100~150nm. KH-570modified nano-TiO2had good compatibility and dispersity in polyacrylate. Theheat resistance, hardness and impact strength of the composite latex films were improved withthe addition of nano-TiO2. When TBOT amount was9%, the maximum weight loss ratetemperature of the composite latex film were406.3oC, and the pencil hardness and impactstrength were2H and43kg cm, respectively, and the maximum weight loss rate temperature,pencil hardness and impact strength of the pure polyacrylate latex film were397.4oC,1Hand39kg cm, respectively. In contrast with the pure polyacrylate latex film, the UVabsorption intensity of the composite latex film increased obviously, and with the increase ofTBOT amount, the UV absorption intensity increased accordingly. When TBOT amount was9%, the maximum absorption wavelength and absorbance of the composite latex film were314nm and1.75, and that of pure polyacrylate latex film were298nm and0.40.