| Popis: |
Styrene-butadiene (SBR)/clay nanocomposites were synthesized via mechanical mixing using a Brabender mixer and 2-roll mill. The montmorillonite (MMT) used was functionalized with four different surfactants: commercially available octadecyl-amine (C18amine) and laboratory synthesized octadecyldimethyl-betaine (C18DMB), vinylbenzyl-dodecyldimethylammonium chloride (VDAC), and vinylbenzyl-octadecyldimethylammonium chloride (VODAC). The surfactant chain length and functional groups affected the dispersion of clay nanolayers in the matrix and the properties of the nanocomposites. Partially-exfoliated SBR nanocomposite obtained with VODAC-MMT presented the greatest mechanical reinforcement and oxygen barrier: elastic modulus at 25°C was 14 times higher than SBR, and oxygen permeability was reduced by 60% with 15 wt.% silicate. Nielsen model was used to fit the permeability data and to calculate the filler aspect ratio, which was also determined by Transmission Electron Microscopy. The best performance of nanocomposites containing VODAC-MMT is attributed to the presence of the vinyl-benzyl group in the surfactant, which provides higher compatibility with SBR and greater dispersion of the organoclay, increasing the tortuous path for gas diffusion through the rubber. Furthermore, the addition of carbon black to SBR and to SBR/clay nanocomposites was investigated. While carbon black alone (40 phr) offered great improvement in the mechanical properties of the rubber, the synergism of organoclay and carbon black brought similar property enhancements with only half the total filler loading (10 phr each filler). The oxygen permeability of the two-filler system was also lower than for SBR containing only carbon black. Two other types of rubber/clay nanocomposites were synthesized: natural rubber (NR) and bromo-butyl rubber (Br-IIR). Oxygen barrier for both nanocomposites was higher than pure rubber or conventional composite. The types of surfactant used to modify MMT led to different clay morphology in the matrix, affecting the tortuosity for gas diffusion. Significant enhancements in mechanical, thermal, and barrier properties were demonstrated for rubber/clay nanocomposites. In addition, a nanocomposite gel electrolyte consisting of poly(methyl methacrylate) (PMMA)/clay, ethylene carbonate/propylene carbonate as plasticizer, and lithium perchlorate was synthesized for electrochemical studies. Ionic conductivity varied slightly, exhibiting a maximum of 8x10-4 S/cm with 1.5 wt.% clay at 25°C, and stable lithium interfacial resistance was observed over a three-week storage period. |
