Tai, Mun Foong (2016) Stabilization study of surface modified magnetite nanoparticles in nitrile butadiene rubber latex / Tai Mun Foong. Masters thesis, University of Malaya.
Abstract
In the present study, magnetite nanoparticles (<50 nm) with high saturation magnetization (80.23 emu/g) was successfully synthesized through co-precipitating technique by co-precipitating iron (II) and iron (III) chloride salts in the presence of 3.00 M ammonium hydroxide at final pH 9.5. It was found that increasing the final pH and total iron salts concentration increased saturation magnetization, but the variation of ammonium hydroxide concentration did not change the saturation magnetization. In contrast, the saturation magnetization decreased from 80.23 emu/g to 64.83 emu/g when the addition rate of ammonium hydroxide was increased from 5 ml/min to 20 ml/min. The reduction of saturation magnetization for these samples was due to decrease in the crystallite size of the particles with increasing addition rate. Additional continuous efforts were made to further improve the dispersion stability of magnetite nanoparticles in aqueous media by modifying the magnetite surface using surface modifiers (e.g., polyethylene glycol, oleic acid) to generate an effective repulsive force in between particles. It was found that the resultant MNPs incorporated with oleic acid demonstrated a maximum stability in maintaining good colloidal dispersion. This MNPs colloidal suspension performance was approximately 7 times higher (21 days) than the uncoated MNPs (3 days). The reason can be mainly attributed to the formation of oleate secondary layer in the bilayer oleic acid coated MNPs that enabled the MNPs to be well dispersed in polar (acrylonitrile) and non-polar (butadiene) parts of the building block of nitrile latex. In addition, the oleic acid coating layer could reduce the oxidation reaction that trigger phase transition as compared with PEG coating. Thermogravimetric analysis (TGA) measurements suggested that there was two kinds of binding between molecules of oleic acid and magnetite. The coating density of PEG and oleic acid on the MNPs particle surface increased with increasing loading amount. iv The mechanical properties of nitrile butadiene rubber latex film were reduced by the addition of oleic acid coated MNPs but it is within the acceptable range. Lastly, the results proved that NBR latex film incorporated with oleic acid coated MNPs has improved magnetic properties and thermal stability. The saturation magnetization of NBR latex film was increased from 0.19 emu/g to 1.85 emu/g. Based on the results, oleic acid coated MNPs is the ideal magnetic additive for metal detectable glove application.
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