Study of the cellular structure heterogeneity and anisotropy of polypropylene and polypropylene nanocomposite foams

Abstract

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

Moulded polypropylene foams produced using chemical or physical blowing agents: structure–properties relationship

“…On the one hand, by filling PP with inorganic compounds such as talc or nanoparticles [10][11][12] and on the other hand by using special PP grades known as high melt strength PPs, on which by promoting a high degree of branching the melt strength is significantly increased [6,11,13]. Finally the less desirable solution because turn the polymer non-recyclable, is crosslinking the PP matrix [1].…”

Multifunctional nanocomposite foams based on polypropylene with carbon nanofillers

“…We have previously shown that the addition of silicate-layered nanoclays, particularly montmorillonite, promotes the formation of polymer foams with more homogeneous cellular structures, resulting in improved mechanical performances due to a combination of the addition of the stiffer particles and a finer foam cellular structure. 11,12 Carbon-based nanofillers, such as carbon nanotubes, carbon nanofibres or graphene, have increasingly been incorporated into polymers in the last years looking not only for mechanical enhancement but mainly for improving their commonly low conduction properties. From these, graphene has attracted a great deal of interest due to its unique combination of properties, 13 which include a very high thermal conductivity and high tensile strength, 14 as well as a particular flat morphology, 15 enabling its use as mechanical reinforcement of polymers at very low concentrations 16,17 and making it suitable for the development of new conductive polymer composites for sectors such as electronics.…”

Recent Developments of Foamed Polymer/Layered Silicates Nanocomposites

“…The MMT nanoparticles thermally stabilize the PP foams during expansion, and this effect is even more pronounced with an increase in ADC content [54]. [44] In EPDM/clay foamed nanocomposites modified by maleic anhydride, an increase in mechanical and dynamic mechanical properties, as well as in non-isothermal crystallization rate, has been observed [55].…”