The morphological development of sheared isotactic polypropylene (iPP) containing different amounts of sodium benzoate (SB) has been investigated using wide-and small-angle X-ray scattering techniques. The microbeam of synchrotron radiation allows us to gain, precisely and efficiently, the local morphology at a given position with a good spatial resolution. The morphological distributions such as crystallinity, fractions of R-form and β-form crystals, crystal size, and orientation functions can therefore be well constructed through the shear field or temperature gradient. The distribution of crystallinity is changed from a U-shape without SB to an almost flat with SB, in company with a minimum fraction of R-form crystal and a maximum fraction of β-form crystal. The epitaxial growth of branched lamellae in the presence of SB is confirmed from the orientation functions of two axes using wide-angle diffraction. The effect of SB on the molecular orientation is understood from the orientation function of c-axis and the azimuthal patterns of small-angle scattering. It is found that both the molecular orientation and the lamellar orientation of the R-form crystal are increased with increasing SB. The thickness of crystalline lamellae with respect to flow direction is found to increase with increasing SB in the whole range from shear zone to core center. A slight declination of crystalline lamellae has been observed in the presence of SB.

No abstract

SYNOPSISFire-retardant polypropylene (PP) composites were prepared by combining this polymer with uncoated and surface treated forms of magnesium hydroxide filler and various elastomeric modifiers, with and without maleic anhydride functionalization. Mechanical properties of binary and ternary phase compositions differed significantly and are discussed in terms of their microstructures (determined principally by SEM and FTIR) and the relative interaction of the components. Impact strength, in particular, was strongly influenced by the presence of filler surface treatment and the degree of rubbery phase dispersion. FTIR showed that functionalized ethylene-propylene rubber (F-EPR) reacted with the surface of uncoated magnesium hydroxide leading to extensive rubber encapsulation and an improvement in toughness relative to unmodified EPR, which was present in the matrix only as phase dispersed droplets. However, by blending F-EPR with filler surface treated with magnesium stearate, encapsulation was inhibited and the rubber was preferentially dispersed in the PP matrix. This formulation resulted in both improved filler-matrix interaction and enhanced matrix toughening leading to a further increase in impact strength. The effects of material composition on melt flow behavior and UL94 flammability rating, are also reported.