The use of dynamic mechanical thermal analysis technique for determining an uneven distribution of precipitated silica in CPE/NR blends

Precipitated silica is generally used as non-black reinforcing filler for light colored products. Compared with carbon black, the use of silica is subject to many problems, particularly poor silica dispersion and distribution. In silica filled CPE/NR blends, the uneven distribution of silica in each phase of the blend occurs mainly due to strong filler-polymer interaction between silanol groups on the silica surfaces and chlorine atoms on the CPE backbone. In order to investigate the uneven filler distribution in polymer blends, changes in damping behavior could be used to calculate the amount of silica localizing in each phase of the blends. The results reveal that, with small loading of silica, an even silica distribution is observed due to the counter-balancing effects of relatively low viscosity of the NR phase and strong silica-CPE interaction. As silica loading increases, the effect of strong silica-CPE interaction becomes dominant, leading to preferential migration of silica to the CPE phase. The uneven silica distribution at high silica loading is found to be reduced by addition of silane coupling agents. The effect of 3-thiocyanatopropyl triethoxy silane (Si-264) is more pronounced than bis-(3-triethoxysilylpropyl) tetrasulfane (Si-69) due to the superior wettability and, hence, the silanol deactivation efficiency. The determination of uneven silica distribution by dynamic mechanical properties is in good agreement with the phase morphology of blends.