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