Transitory rheological test as a tool to monitor nano-clay dispersion and distribution in polypropylene-palygorskite composites

The present study focuses on the rheological analysis of melted thermoplastic composites based on a matrix of polypropylene/maleated polypropylene and a nano-reinforcement of palygorskite clay (collected from an open mine in the Yucatan peninsula, Mexico). This clay was purified and modified with a silane coupling agent (3-aminopropyl trimethoxysilane). The composites were processed in a modular extruder fitted with a twin screw, which was configured to promote two different shear stress levels during processing. The composites were characterized in a rotational rheometer fitted with a parallel plate geometry. The maximum value of the overshoot demonstrated that the formulations containing 1% of silanized palygorskite presented the best rheological properties, particularly the formulation processed with lower shear stresses; this rheological response was related to the level of dispersion-distribution of the nano-clay in the molten polypropylene matrix. Similarly, with a clay content above 1%, the rheological properties decreased, due to the formation of clay agglomerates. Transmission electron microscopy micrographs were used to corroborate the degree of dispersion and distribution of nanoparticles.