Pezzuto, Marilena (2011) Polyolefins based hybrid nanocomposites. [Tesi di dottorato] (Inedito)

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Abstract

This thesis aimed at completing the study of the properties of iPP modified with an hydrogenated oligomer resin (Escorez-ESC) and at improving these properties by making nanocomposites with the addition of two clays (modified one 67G and unmodified one HPS) for possible use in the food packaging sector. The study of the structure, morphology and thermal, rheological, mechanical and barrier properties of the binary and ternary systems have been reported as function of composition, kind of constituents and preparation conditions. Moreover for all the systems the study on crystallization in situ under shear and during cooling is reported. From the results obtained the main highlights can be draw: i) the iPP is not intercalated between clay layers. The clay 67G is well dispersed in the matrix (iPP and iPP/ESC blends), whereas HPS forms large agglomerates. ii) The iPP/ESC5%/67G presents similar mechanical properties to iPP and improved barrier properties respect to iPP, it could be a good starting point for investigations in order to use the ternary systems in the food packaging. For these systems the improvement of dispersion of the clay nanoparticles must be achieved by optimizing the preparation conditions and the mixing procedures. iii) The rheological results show that there is a good swelling of the clay HPS and the ESC. HPS should have a better affinity for the oligomer respect to iPP and should be dispersed more in this phase respect to iPP. At this point the modality of blending seems become very important. A masterbach made of Escorez and HPS could present structure intercalated/exfoliated. iv) the in-situ SAXS experiments have revealed that the temperature at which crystal growth rate is at a maxima is strongly dependent on the temperature at which the shear flow was applied. In the melt after shear flow, the polymer chains which were extended will be relaxing towards isotropic state. If crystallisation takes place before the chains are full relaxed, the extended chains acts as row nuclei which has 2 consequences. The first is a high level of common orientation of the crystals and second that crystallisation occurs at a higher temperatures, essential the chains are nucleating agents. As the polymer will crystallise in any event, the questions is really how much is directed by row nuclei and how much by randomly arrange nuclei. This changes the crystallisation temperature and the level of anisotropy. The clay platelet orientation is affected by flow but it does not template the crystallisation, although clearly the crystallisation behaviour depends on the details of the clay and other components.

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