Хибридни еластомерни нанокомпозити: добивање и својства

Abstract

The aim of this PhD work was to obtain complex system based on natural rubber (NR) with outstanding mechanical properties and controlled energy dissipating capacity. First, hybrid nanofillers composed of different ratios of carbon nanotubes (CNT) and sodium montmorillonite (Mt) were prepared by physically pulverizing both materials in powder form. Their dispersion behavior was investigated in several solvents (water, toluene and carbon tetrachloride). UV–Vis spectroscopy showed that the absorbance at 550 nm for the CNT increases with the increasing amount of added Mt, when water is used as a solvent, implying their improved dispersion. This is not so evident for toluene and carbon tetrachloride solutions. TGA analyses showed that the thermal stability of the hybrid nanofillers increases with the increase of the Mt content. Raman spectroscopy confirmed the mutual interaction between CNT and Mt, demonstrated by shift of D and G band with addition of Mt in the nanofiller. Thеn, hybrid natural rubber (NR) nanocomposites, containing 2 phr multiwalled carbon nanotubes (MWCNT) and different quantities (from 0 to 20 phr) of expanded organically modified montmorillonite (EOMt), were prepared in order to produce a NR based material with superior mechanical properties as a first step in obtaining a high-performance damping material suitable for seismic application. Initially a master batch of NR/MWCNT was prepared and then a dilution technique was used for the preparation of NR/EOMt/MWCNT nanocomposites. Raman spectra showed a strong interaction between the rubber matrix and MWCNT and the existence of a simple physical mixture of MWCNT and EOMt. This was reflected on the mechanical properties (both quasi-static and dynamic) which were found to change in the desired way. A remarkable improvement of the lower tensile modulus, tensile strength and storage modulus was achieved with the addition of MWCNT, and then a gradual but permanent improvement of the above mentioned properties, including improved elasticity and elongation at break, with the addition of EOMt. DMA strain sweep measurements showed a pronounced non-linear dependence and a significant increase of the loss factor tan δ (a measure of the dissipation energy) for the nanocomposites with filler concentrations above the mechanical percolation threshold (16 phr). To reveal a hybrid nano-filler synergy, electron spin resonance (ESR) spectra of the MWCNT present in the NR based nanocomposites were investigated and the dependence of the double integral of resonance spectra on the amount of EOMt present in the NR was established. Its decrease with an increasing amount of EOMt confirmed the synergy between these two nano-fillers. Finnaly, complex NR based composites were prepared by addition of conventional fillers to the system containing a hybrid nanofiller (which optimality was assessed in the first step) in order to enhance the energy dissipating capacity of the material. The tensile tests showed that the presence of the hybrid nanofiller enables retention of the high tensile strength of the composites while increasing their elasticity by replacement of carbon black with unmodified silica filler. DMA temperature sweep measurements confirmed nearly the same reinforcing effect for all filler combinations. The cluster–cluster aggregation model was used to assess the apparent filler networking energy. The values obtained suggested that the presence of the hybrid nanofiller strengthens the filler networking. This was also supported by the TEM images. In order to investigate how different fillers influence the strain dependency of the storage modulus or Payne effect, strain sweep measurements in shear mode were performed. The energy dissipating capacity of the material was found to be in the sought range between 10 % and 20 % (at 0.5 Hz and high shear strain). Finally the cluster–cluster aggregation model was used to understand more deeply the Payne effect, which is considered to be one of the mechanisms of energy dissipation in filled rubber.