Stiffness and Toughness of Polypropylene/Glass Bead Composites

The effects of coupling effect, particle diameter (d), volume fraction (Vb) and size distribution (σ) 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 -1) between the glass beads and the matrix. With the addition of this coupling agent, the impact strength of the PP/glass bead composite with d = 2.7 μm and σ = 1.85 increases about 4.5 times as Vbincreases 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 Vb. The combined effects of d, Vband size distribution of the glass beads are described by using a single parameter, the average matrix ligament thickness T̄. Unlike rubber-modified polymers, the impact strength of PP/glass bead composites does not follow a master curve when plotted against T̄.