Nonisothermal Crystallization and Melting Behaviors of PP/PA6/TiO2 Nanocomposites

Titanium dioxide nanoparticles were functionalized with toluene-2,4-diisocyanate and then polypropylene/polyamide 6 blends containing functionalized titanium dioxide were prepared using a twin-screw extruder. The nonisothermal crystallization and melting behaviors of the as-prepared nanocomposites were investigated using differential scanning calorimetry. The nonisothermal crystallization differential scanning calorimetry data were analyzed by the modified-Avrami (Jeziorny) and combination of Ozawa and Avrami (Mo) methods. It can be found that the Jeziorny method can be used to describe the main crystallization process, and the Mo method can better deal with nonisothermal crystallization kinetics of the polypropylene and polyamide 6 phase in polypropylene/polyamide 6-based nanocomposites. The nonisothermal crystallization analysis shows that the titanium dioxide nanoparticles have two effects on polypropylene/polyamide 6 blends, i.e., it can favor the improvement of crystallization ability and decrease the crystallization rate of the polypropylene and polyamide 6 phase in polypropylene/polyamide 6-based nanocomposites. For one thing, the functionalized titanium dioxide nanoparticles in the polypropylene/polyamide 6-based nanocomposites act as effective nucleation agents and result in higher crystallization temperature (T0) than that of the polypropylene and polyamide 6 in pure polypropylene/polyamide 6 blends, which indicated titanium dioxide nanoparticles favor the improvement of crystallization ability of the polypropylene and polyamide 6 phase. For another, the existence of functionalized titanium dioxide nanoparticles hinders the free movement of polymer chains and results in lower crystallinity than that of the polypropylene and polyamide 6 in pure polypropylene/polyamide 6 blends, which indicated titanium dioxide nanoparticles decrease the crystallization rate of the polypropylene and polyamide 6 phase in polypropylene/polyamide 6-based nanocomposites. The nonisothermal crystallization melting behaviors show that there is single or double melting peak, which varies with different cooling rates for the polyamide 6 phase in polypropylene/polyamide 6-based nanocomposites. Multiple melting peak is mainly caused by the different crystalline structure of the polyamide 6 phase, the melting peak I is mainly caused by γ crystal of the polyamide 6 phase, while the melting peak II corresponds to the thermodynamic stability of α crystal. Besides, the recrystallization of the polyamide 6 phase in the heating process, and the effect of the incorporation of the titanium dioxide nanoparticles may have some contributions to the appeared multiple melting peak of the polyamide 6 phase in the polypropylene/polyamide 6-based nanocomposites.