Stiffness and toughness of polypropylene/glass bead composites

The effects of coupling effect, particle diameter (d), volume fraction (V-b) and size distribution (sigma) of glass beads on the impact strength and tensile modulus of polypropylene (PP)/glass bead composites have been investigated. The toughness and stiffness of the composite can be simultaneously enhanced by using a titanate coupling agent, which gives rise to a moderate interfacial adhesion (characterized by an interaction parameter B similar to 1) between the glass beads and the matxix. With the addition of this coupling agent, the impact strength of the PP/glass bead composite with d = 2.7 mum and sigma = 1.85 increases about 4.5 times as V-b increases from 0 to 0.25, while the tensile modulus remains roughly unchanged. For the composites with larger d and narrower size distribution, the impact strength increases only slightly with increasing V-b. The combined effects of d, V-b and size distribution of the glass beads are described by using a single parameter, the average matrix ligament thickness (T) over bar. Unlike rubber-modified polymers, the impact strength of PP/glass bead composites does not follow a master curve when plotted against (T) over bar.