Rheology, Processing and Properties of Polymer Nanocomposites Based on POSS and Boehmite

Two different types of polyhedral oligomeric silsesquioxane (POSS), octaisobutyl POSS (Oib POSS) and trisilanolphenyl POSS (Tsp POSS), were melt blended with low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) at different processing temperatures on a Brabender plastograph. Scanning electron microscopy (SEM) was used to determine the effect of mixing temperature on the dispersion state of Oib POSS and Tsp POSS nanoparticles in PE matrices. Large agglomerates with sizes of 5-10 ?m were observed in LDPE/Oib POSS blends prepared at 175°C and 200°C, but the size of the agglomerates was reduced to approximately 1?m when the nanoparticles were partially melted during processing at 270°C. The results indicate that the compatibility of LLDPE with Oib POSS is better than with LDPE. SEM images of Tsp POSS nanocomposites show that POSS nanoparticles form agglomerations of sub-micrometer sizes in all the samples. However, the level of agglomerations in LLDPE/Tsp POSS and LDPE/Tsp POSS nanocomposites is decreased with increasing the mixing temperature up to the melting temperature of Tsp POSS. Moreover, frequency sweep tests were carried out to study the rheological behavior of the nanocomposites. A decrease in the complex viscosity was observed by addition of Oib POSS nanoparticles to LDPE and LLDPE matrices. The reduction in the complex viscosity of LDPE was more pronounced at a mixing temperature of 270°C, while the addition of Tsp POSS increased the complex viscosity of PE. Tsp POSS and Oib POSS nanoparticles were incorporated into PP, LLDPE and LDPE by use of a single screw extruder at different POSS contents, and the properties of the nanocomposites were investigated. From the tensile test results it is found that the tensile modulus of PP, LLDPE and LDPE is enhanced by addition of POSS nanoparticles, but this increase is accompanied by a reduction of the tensile strength. The flexural properties of PE are improved in the presence of POSS, whereas the flexural properties of PP depend on the type of POSS. Composites of LLDPE and LDPE with two types of boehmite, BA40 and BA80, with different crystalline size were prepared using a single screw extruder, and their properties were investigated. It is found that the properties of PE/BA composites strongly depend on the type of polyethylene, while there is no significant difference between PE/BA40 and PE/BA80 composites. The complex viscosity of LLDPE is unchanged with addition of BA particles, while it increases in the case of LDPE. Also, the compatibility of BA particles with LLDPE is better than with LDPE. Accordingly, it was found that the tensile properties improve in the case of LLDPE composites, but decreases for LDPE composites, whereas the flexural properties are improved for both types of PE.