Morphology development of isotactic poly(4-methylpentene-1) during melt crystallization

The morphology of melt-crystallized isotactic poly(4-methylpentene-1) samples, prepared by varying crystallization temperature and time, as well as annealing temperature, has been probed by small and wide angle x-ray scattering, and electron microscopy. This was then correlated with the thermal properties investigated by differential scanning calorimetry. Relationships among melting behavior, morphological evidences and X-ray results have been found. Different populations of lamellae, grown with a time-dependent sequence, can be obtained: their relative amount and thermal stability is determined by crystallization and annealing conditions.     

Nonisothermal crystallization of isotactic polypropylene blended with poly(α-pinene). I. Bulk crystallization

The influence of a natural terpene resin, poly(α-pinene) (PαP), on the nonisothermal crystallization process of isotactic polypropylene (iPP) was investigated. The solidification process strongly depends on cooling rate, composition, and miscibility of the system. For the blends containing PαP up to 30 wt %, the overall nonisothermal crystallization rate is depressed with respect to plain iPP. This is probably the result of the diluting effect of the polyterpene because the two components are miscible. The 50/50 blend presents, instead, two amorphous phases: an iPP-rich phase and a PαP-rich phase. For this composition, solidification starts at temperatures higher than those for plain iPP and blends with lower PαP content, given that the diluting effect of PαP in the iPP-rich phase is counterweighted by an increased number of nuclei that originate from the polyterpene-rich phase domains. PαP also influences the morphology of iPP spherulites, which are spherical in plain iPP and become more irregular with increasing PαP content. The number and dimension of iPP spherulites depend on blend composition and miscibility of the components. Moreover, the nonisothermal crystallization kinetics of iPP/PαP blends was analyzed with the Ozawa equation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 358–367, 2001     

Blends of poly(ethylene oxide) samples of different molecular weights: thermal and mechanical properties

Differential scanning calorimetry and mechanical measurements have been performed on binary poly(ethylene oxide) blends of different molecular weight samples. Some thermodynamic and mechanical properties, such as the melting point and the ultimate stress and strain are strongly affected by blend composition. The enthalpy of fusion and the Young's modulus, however, vary only slightly over the entire range of composition. Also the time for dissolution in water, at two different temperatures, has been measured on blends made from the lowest and the highest molecular weight components.The results indicate that by blending two different molecular weight samples, even of the same polymer, it is possible to influence the physical properties of the relative blends, so obtaining improvements of technological importance.