Relaxation Behavior of Core-Shell Particles in PP/PMMA/PS Ternary Blends: The Effects of Composition, Viscosity Ratio and Temperature

Abstract

The relaxation behavior of PMMA-PS core-shell particles in PP matrix was studied. The effects of composition and viscosity ratio of core and shell forming components on relaxation processes of PP/(PMMA+PS) 80/20 ternary blends were evaluated at three different temperatures (200, 225 and 250°C) and discussed. For the ternary blends containing low-viscosity PMMA (PP/L-PMMA/PS), the shape relaxation time, λ, sharply reduced at first with PS content and then increased after passing through a minimum with further increase in the PS content. The corresponding relaxation strength, λ.H(λ), increased suddenly at first and then monotonically decreased upon further incorporation of PS. The changes of λ and λ.H(λ) with PS content were attributed to a change in the interfacial energy (shell formation) and average viscosity of the dispersed composite droplets upon progressive addition of PS into PP/L-PMMA blend so that the minimum λ corresponding to the maximum λ.H(λ) was observed at shell completion composition with finest core-shell- particles (12 wt% of PS phase). The core-shell particles of all the ternary blends containing L-PMMA exhibited a shape relaxation at 200°C, while at the same temperature for the blends containing high-viscosity PMMA (H-PMMA) no shape relaxation peak was detected when the PS shell content was lower than 62 wt%. This was attributed to restriction effect of non-deformable H-PMMA core droplets, which led to no droplet relaxation. At higher PS contents, appearance of the shape relaxation peak was related to the relaxation of PS shell, suggesting that there is a critical shell thickness above which the relaxation behavior of core-shell droplets is dominated by the low-viscous PS shell. Increase in temperature from 200 to 250°C reduced the PS shell content corresponding to onset of deformation and accelerated the relaxation of composite droplets.