Preparation And Characterization Of Polypropylene/montmorillonite On Complexed Catalyst By In-situ Polymerization

Polypropylene (PP) nanocomposites were prepared by in-situ polymerization. The exfoliation of montmorillonite, crystallization behavior of PP/MMT nanocomposites and the thermal stability of PP/MMT nanocomposites were studied.Factors influencing dispersion extent of MMT layers in PP matrix were investigated. The morphology of nanocomposites obtained was examined using TEM and X-ray diffraction. Results from TEM observation of the composites indicated that MMT fillers have been exfoliated to nano-sized layer structure in PP matrix. We found that high reactivity, low isotactic degree and long reaction time could improve the exfoliation of MMT layers. We also found that some of the MMT layers would come back initialization when the PP/MMT nanocomposites were treated by heat treatment.The crystallization of nanocomposites of isotactic polypropylenes with modified montmorillonite were studied. It was found that the existence of dispersed MMT layers in the nanocomposites inhibited β crystallization initiation when PP matrix was cooling, while resulted incomplete a crystallization of PP, and a little γ crystallization was appeared. The existence of dispersed MMT layers also played an important role in accelerating crystallization of PP, but crystallization degree of PP in the nanocomposites decreased while MMT content increased. The isothermal and nonisothermal crystallization of the nanocomposites were also investigated by DSC method. The isothermal crystallization process was discribed by the Avrami equantion, the Avrami index n was about 3 for PP/MMT nanocomposites. The half crystallization time (t_1/2) of PP/MMT nanocomposites was much short than neat PP. For nonisothermal crystallization, the Avrami index n of nanocomposites prepared via in-situ polymerization was greater than that of nanocomposites prepared via melt compounding.The thermal stability of Polypropylene/montmorillonite nanocomposites, whichwere prepared by melt-mixing and in-situ polymerization process respectively, were studied. TGA analysis showed that the thermal stability of the materials that were prepared by in-situ polymerization were improved remarkably due to the existence of montmorillonite layers whether in air atmosphere or nitrogen atmosphere. But, the thermal stability of the nanocomposites that were prepared by melt-mixing were found different according to the atmosphere, which were declined in nitrogen atmosphere while increased in air atmosphere compared with neat PP.