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Portal del coneixement obert de la UPC http://upcommons.upc.edu/e-prints Aquesta és una còpia de la versió author's final draft d'un article publicat a la revista Polymer Degradation and Stability.

This work presents the preparation and characterization of compression-moulded montmorillonite and carbon nanofibre-polypropylene foams. The influence of these nanofillers on the foaming behaviour was analyzed in terms of the foaming parameters and final cellular structure and morphology of the foams. Both nanofillers induced the formation of a more isometric-like cellular structure in the foams, mainly observed for the MMT-filled nanocomposite foams. Alongside their crystalline characteristics, the nanocomposite foams were also characterized and compared with the unfilled ones regarding their dynamic-mechanical thermal behaviour. The nanocomposite foams showed higher specific storage moduli due to the reinforcement effect of the nanofillers and higher cell density isometric cellular structure. Particularly, the carbon nanofibre foams showed an increasingly higher electrical conductivity with increasing the amount of nanofibres, thus showing promising results as to produce electrically improved lightweight materials for applications such as electrostatic painting.

This article presents the analysis of the processing parameters\ud influence on the foaming behavior and cellular\ud structure of PP-montmorillonite foams. Polypropylene\ud nanocomposites containing 5.0 phr of an organically-\ud modified montmorillonite (MMT) were initially\ud melt-compounded in a twin-screw extruder with azodicarbonamide\ud (ADC) and later foamed using a one-step\ud compression-molding process. The cellular structure\ud and morphology of the foams was assessed using both\ud scanning and transmission electron microscopies. A\ud time-dependant double-effect was observed during\ud foaming: (1) first of all, the melt strength of the polymer,\ud too high for shorter times, not allowing full cell\ud growth, and too low for high foaming times due to\ud thermal oxidation; (2) and polymer degradation, clearly\ud observed for very high foaming times, directly affecting\ud polymer’s melt resistance. Comparatively, PP-MMT\ud foams exhibited a broader foaming time processing\ud window, a more isometric type of cellular structure and\ud decreased open-cell contents, indicating an effective\ud nucleation and cell wall stabilization induced by the\ud exfoliated MMT particles.Peer ReviewedPostprint (published version