The effect of interphases created by Al2O3 nanoparticles in styrene butadiene rubber

Elastomers are key-materials e.g. in tire industry. Nowadays it is common practice to enhance the mechanical performance of elastomers by introducing inorganic nanoparticles into the polymer matrix. Due to the extremely small filler size giant interfaces are created between the surfaces of the nanoparticles and the matrix molecules especially when the fillers are homogeneously distributed throughout the host material. Interfacial interactions can lead to the formation of regions with changed molecular mobility and/or morphology (so-called interphases) in the immediate vicinity of the fillers’ surfaces. A challenging task consists in investigating and understanding the effect produced by interphases on the macroscopic properties of the polymer matrix.
In the frame of the present PhD research project an uncured styrene-butadiene rubber (SBR) was used as a matrix for three types of nanoparticles: native alumina, alumina coated with γ- mercaptopropyltrimethoxysilane (Mercapto) layers and finally alumina-Mercapto nanoparticles with SBR molecules grafted onto. The thermal and mechanical properties of the three families of nanocomposites were investigated using mechanical spectroscopy (rheometry and dynamical mechanic analysis). Electron microscopy was exploited for structural analysis.
Irrespective of the surface treatment of the nanoparticles an unexpected minimum of the glass transition temperature is found at small filler concentrations of about 2 wt.%. At higher filler contents each of the three families of nanocomposites is characterized by its own characteristic evolution of the glass transition temperature as a function of the filler content. Models are suggested to explain the different glass transition behaviors. Furthermore the influence of the surface treatment on the mechanical answer of the nanocomposites especially to low-frequency shear fields is discussed.