Polypropylene(PP)/layered silicate nanocomposites were prepared via simple melt mixing of three components, PP, layered silicates modified with octadecylamine(C18-MMT), and antioxidant, to investigate the role of antioxidant. By X-ray diffraction experiment, PP/C18-MMT composite without antioxidant showed immiscible state because PP and C18-MMT are quite incompatible each other. On the other hand, PP/C18-MMT nanocomposites with antioxidant showed the intercalated states with increased basal spacing of layered silicate. In rheological behavior, the nanocomposite with antioxidant showed higher storage modulus and complex viscosity than pure PP. However, PP/C18-MMT without antioxidant showed lower values owing to the bond breakage of PP molecules and the poor compatibility between PP and C18-MMT. The nanocomposite with 5wt% C18-MMT and 0.5phr antioxidant exhibited about 1.4 times higher tensile modulus and 1.3 times higher dynamic storage modulus than those of PP. These enhanced mechanical properties demonstrate the reinforcing effect of nano-scale dispersed layered silicates in PP matrix. It could be concluded that antioxidants played an important role in enhancing the compatibility between PP and C18-MMT.
The influence of silicates on the crystallographic changes of PP during tensile deformation was investigated by using the technique of real time X-ray scattering. Both PP and PP/C18-MMT nanocomposite showed similar tensile deformation behaviors with yield point, strain softening and load-extension plateau during tensile deformation. However, the nanocomposite had the yield at smaller elongation deformation than PP due to the higher stiffness. The nanocomposite had the weaker ordering of polymer crystals than pure PP in the load-extension plateau region because silicates dispersed in PP matrix inhibited polypropylene crystals from ordering toward the tensile direction.
