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Study of the Poly (vinyl acetate)/SiO2 Nanocomposites Produced by in Situ Polymerization

Azamian Jazi, Mehrdad | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48709 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Ramazani Saadat Abadi, Ahmad
  7. Abstract:
  8. The main object of this thesis is synthesizing poly(vinyl acetate)/ colloidal silica nanocomposites via emulsion and in-situ polymerization methods. At the first, nanocomposites were produced in the presence of poly(vinyl alcohol) as the protective colloid, ammonium persulphate as the initiator and sodium bicarbonate as the buffer in an aqueous solution. Then, structural, thermal, rheological, mechanical and surface properties of produced nanocomposites with various colloidal silica content (0.5 %, 1 %, 1.5 %) were evaluated by DLS, FTIR, SEM-EDS, DSC, TGA, dynamic and steady rheological tests, tensile and shear mechanical tests, AFM and static water contact angle. The particle size of commercial colloidal silica was determined about 15-40 nm by Dynamic Light Scattering (DLS) test. Fourier transform infrared spectroscopy (FTIR) revealed the presence of SiO_2 and poly(vinyl acetate) in the prepared nanocomposites. Also, Further investigations were done to obtain information about bound and free carbonyl groups of poly(vinyl acetate) by using this test. Scanning Electron Microscope (SEM) and elemental mapping of Energy Dispersive X-ray Spectroscopy (EDS) were used to study morphology and elemental analysis of products. The results showed that the uniform dispersion of nanoparticles throughout poly(vinyl acetate) matrix. Different regions of thermal activity were investigated by using Differential Scanning Calorimetry (DSC) test. The results showed that the apparent glass transition temperature (Tg) increased very slightly (~1k) compared to pure poly(vinyl acetate). Thermo Gravimetric Analysis (TGA) showed remarkable thermal stability improvement in the presence of colloidal silica nanoparticles. Also, the pyrolysis process which occurs during the thermal degradation of nanocomposites has been studied by using TGA. The effect of the filler on storage and loss modulus and complex viscosity were studied by Rheometric Mechanical Spectrometer (RMS). Storage and loss modulus and complex viscosity increased by introducing colloidal nano silica. Also, the steady shear tests showed that the shear thinning behavior of nanocomposites. Silica nanoparticles were used to improve the bonding capacity of poly(vinyl acetate) known as the wood adhesive. The mechanical properties of nanocomposites were characterized by measuring the tensile and shear strength of synthesized composite adhesives. The results showed that in comparison with the pristine polymer, the tensile and shear strength of nanocomposites with 1 % of silica nanoparticles increased by 55 % and 48 %, respectively. Finally, the impact of hydrophilic nano silica on the poly(vinyl acetate) surface chemistry was investigated with Atomic Force Microscope (AFM) and static water contact angle measurements, which showed decrease of contact angle along with enhancement of the polymer surface free energy
  9. Keywords:
  10. Nanocomposite ; Emulsion Polymerization ; Polyvinylacetate ; In-situ Polymerization ; Nanosilica ; Colloidal Nanosilica

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