The Effect of Mixing Temperature and Mixing Technique on the MechanicalProperties of Polypropylene - Mesoporous Silica/Hydroxyapatite HybridNanocomposites

This work focuses on the influence of mixing temperature and effectiveness of different mixers on the tensile and flexural properties of polypropylene (PP) and PP/Mesoporous silica-Hydroxyapatite (MCM-41-HA (MH)) hybrid nanocomposites. The other important study is the enhancement of mechanical properties of PP by adding MH nanoparticles. How the mixing efficiency affects the dispersion of nanoparticles was investigated using two different mixing devices, an internal mixer and a twin screw extruder. In the first step, neat PP and hybrid nanocomposites based on PP, containing maleic anhydride grafted polypropylene (PP-g-MA) and MH were prepared in the different mixingtemperatures with using the melt intercalation technique in the internal mixer. Tensile and flexural tests were performed to evaluate the mechanical characteristics (Young’s modulus, tensile strength, flexural strength and strain at rupture) of neat PP and PP/MH hybrid nanocomposites. Results showed that the shear stress and distribution process of nanoparticles have the main effect on the mechanicalproperties of nanocomposites that melt mixed in the internal mixer. Also, the optimum mixing temperature of 180 °C and mixing time of 3 minutes were found and applied to the extruder to achieve better mechanical properties. Results showed that a twin screw extruder is more efficient in breaking down the particles of MH in nano scale building blocks than an internal mixer. Because A higher shear rate of the twin screw extruder and more efficient sol-gel reaction led to better dispersion and higher mechanical properties. From SEM images, it was observed that nanoparticles were distributedreasonably uniformly indicating a good dispersion of nano phase in the PP matrix by using extruder.Moreover, the mesoporous structure and high surface area of MCM-41 particles and also high rigidityand large aspect ratio of HA molecules provided the fine mechanical properties for PP/MHnanocomposites. Approximately 16%, 29%, 43% and 42% increases in tensile strength, tensilemodulus, flexural strength and flexural modulus were observed for samples, respectively.

Keywords:

Processing condition , polypropylene , Mesoporous silica , Hydroxyapatite , Mechanical properties