Based on the equilibrium size of PBT minor phase vs. its concentration at 250℃ and 280℃

the effects of viscoelasticity change and coalescence in the melt on the morphology of immiscible PBT/PS blends were investigated. It is shown that the viscoelasticity of blend components

degradation of polymers

and coalescence of minor phase have different influences on the minor phase size. At the initial stage of blending

the dispersed phase size is mainly determined by the viscosity ratio and elasticity ratio of blend components.The dispersed phase size of 280℃ is larger than that of 250℃ due to the much larger elasticity ratio of PBT to PS at 280℃

With increasing mixing time

the viscoelasticity ratio of PBT to PS are changed by the degradation.For lower PBT contents

e.g.5%

the minor phase size at 250℃ is larger than that of 280℃ because of a sharp decrease of elasticity ratio of PBT to PS at 280℃.For higher PBT contents

the coalescence of the minor plays a more important role

which keeps the phase size at 280℃ greater than that of 250℃.