Non-isothermal crystallization behavior of isotactic polypropylene/copper nanocomposites

摘要

The Non-isothermal crystallization behavior of isotactic polypropylene (iPP)/copper nanocomposites with four different mass percentages (0.5, 1.0, 2.0 and 4.0 mass%) of copper nanoparticles (nCu) were study by means of differential scanning calorimeter (DSC) at 2.5, 5, 10 and 20 degrees C min(-1). The nanostructure of PP/nCu nanocomposites was also studied by WAXD, SEM and optical microscopy, while their hierarchical crystalline morphologies (e.g., spherulites, lamellas and unit cell) were studied during the crystallization progress through polarized optical microscopy and in situ X-ray scattering at small and wide angle, observing that the spherulite size was not influenced by the nCu's, although the lamellas size and X-ray diffraction intensity increased with the incorporation of nanoparticles. The PP/nCu nanocomposites presented a mixture morphology with well-dispersed oxidized nanoparticles and some agglomerates, which were larger at higher concentration of particles. The crystallization results obtained by DSC indicated a displacement in the peak crystallization temperature at higher values. These results in combination with the kinetic of crystallization analyzed by the Jeziorny method clearly indicated an acceleration in the crystallization process. Additionally, the crystallization activation energy decreases for all nanoparticle's concentration, indicating a possible nucleating effect. However, the nucleation activity analyzed by the Dobreva and Gutzow's method showed that nCu could not be considered such as conventional heterogeneous nucleating agent of iPP. Conversely, the incorporation of nCu in the iPP matrix increased significantly the thermal conductivity of nanocomposites helping to the thermal dissipation from the melted macromolecules to the nCu's, accelerating the non-isothermal crystallization process.