Preparation And Property Of Polyacrylate/Alumina Or Aluminum Composite Particles By In Situ Polymerization

In order to improve application performances of inorganic powders, such as dispersibility and corrosion resistance, polyacrylate/(alumina or aluminum) composite particles with core-shell structure were prepared by in situ polymerization of acrylate on the surface of alumina (Al₂O₃), flaky aluminum (FA1), and nano-aluminum (Al). Based on the kinetics of emulsion polymerization of methyl methacrylate (MMA) and solution polymerization of trimethylolpropane triacrylate (TMPTA), several methods, such as coupling agent and surface-initiated polymerization, had been used to enhance polymerization to occur on the surface of particles. And the conversion (C), percentage of grafting (PG), and grafting efficiency (GE) in the preparation were systematically studied. In addition, the properties of resulting composite particles were evaluated, and the polyacrylate/FAl composite particles were applied in the painting industry.1. Kinetics of MMA emulsion polymerization and TMPTA solution polymerization. With regard to MMA emulsion polymerization initiated by ammonium persulfate (APS), monomer conversion increased with the increasing polymerizing temperature, APS concentration, MMA concentration, and sodium dodecylsulfate (SDS) concentration. As far as TMPTA solution polymerization initiated by azobisisobutyronitrile (AIBN) was concerned, the experimental polymerization rate ( Rp∝C_AIBN^0.211 and Rp∝C_TMPTA^2.807 ) was basically consistent with thetheoretical result (R_p =KC_AIBN0.25)C _TMPTA³). The conversion of MMA was alittle higher than TMPTA, while the molecular weight of PMMA was lower than PTMPTA.2. Preparation and characterization of PMMA/Al₂O₃ composite particle by in situ emulsion polymerization. Anionic emulsifier, SDS, played an important role in the preparation of PMMA/Al₂O₃ composite particle, and only when SDS concentration was far higher than its critical micelle concentration, could PMMA/Al₂O₃ with high PG be obtained. Concerning the coupling agent, titanium tris(dodecylbenzene-sulfonate) isopropane (NDZ) was more advantageous than 3-methacryloxypropyl-trimethoxysilane (MPS) to the increases of C, PG, and GE, and its optimum experimental dosage accorded with theoretical value of single-molecular-layer adsorption between NDZ and Al₂O₃. TEM and XPS showed that PMMA/Al₂O₃ composite particle had a core-shell structure, and the quantitative relationship between thickness ofpolymeric shell layer and PG was established asδ=ρ(Al₂O₃)·D·PG/ 6·ρ(PMMA).3. Preparation and characterization of PMMA/FAl composite particle by in situ emulsion polymerization. Cationic emulsifier, cetyl trimethyl ammonium bromide (CTAB), was favorable to preparation of PMMA/FAl composite particle with good dispersibility, and the microemulsion system changed from reverse to positive with the increasing CTAB. The preparation of PMMA/FAl composite particle by surface-initiated in situ emulsion polymerization was divided into two steps: adsorption of anionic APS on the surface of positively charged FA1, following by in situ polymerization of MMA. It was found that the adsorption of APS onto FA1 was typical physical process, and the relationship between percentage of adsorption (PA) and C_APS could be described with the Freundlich modeling PA = 8.912C_APS^1.0749 . At the optimum conditions PG could attain 20.5% in the surface-initiated in situ emulsion polymerization. The experimental apparent grafting polymerization rate R_g = KC_FAl^0.521·C_APS^0.429·C_MMA^0.978 was consistent with thetheoretical equation R_g = KC_FAl^1/2·C_APS^1/2·C_MMA, and the apparent activationenergy of grafting polymerization was calculated as 65.1kJ·mol^-1. In addition, PMMA/FAl composite particle was also prepared in the presence of MPS. It was shown that PG was still lower than that in the case of surface-initiated in situ polymerization, although PG increased from 9.5% to 17.2% in the presence of MPS.4. Preparation and characterization of PTMPTA/FAl composite particle by in situ solution polymerization. The polymerization rate was quick at the beginning, and the grafting, homogeneous and total polymerization rates linearly increased with the increasing TMPTA concentration. In the preparation of PTMPTA/FAl, PG and GE could attain 4.3% and 33.5%, respectively, when the percentage of coupling (PC) of MPS was 3.1%. The fact that PG and GE in this case were lower than that of PMMA/FAl may be explained with strong steric hindrance of TMPTA with long carbonic chain and three C=C bonds. Compared to raw FA1, the content of Al, C, and O for PTMPTA/FA1 changed from 30.1%, 40.5%, and 29.4% to 4.2%, 62.4%, and 33.4%, respectively, indicating that PTMPTA had been grafted on the surface of FAl.5. Preparation and characterization of PTMPTA/Al nanocomposite particle by in situ solution polymerization. Due to huge specific surface area of nano-aluminum, the required monomer amount of PTMPTA/Al was more than that of PTMPTA/FAl. The existence of functional monomer (acrylic acid) was useful to the improvement of C, PG, and GE in the preparation of PTMPTA/Al, and the optimum amount was consistent with solution polymerization of pure TMPTA. Compared with that of raw nano-aluminum, activity of PTMPTA/Al nanocomposite particle had been well preserved: activity of nano-aluminum after 60 days decreased about 50%, while activity of PTMPTA/Al kept changeless.6. The application of polyacrylate/FAl composite particle in the painting industry. Compared to that of raw FAl, corrosion resistance and adhesive force of polyacrylate/FAl composite particles, especially of PTMPTA/FAl, had been markedly improved. It was concluded that the modification with multi-functional long-chain acrylate monomer would have extensive application prospect in the aluminum paste painting industry.