Investigation of mixing in the melting regime during polymer compounding

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, February 2000.
Includes bibliographical references (leaves 124-126).
Morphology evolution in the melting regime during compounding of immiscible polymer blends. where most of the size scale reduction occurs. is studied. Starting from an initial solid pellet mixture of two components. the progression to the final two-phase viscoelastic melt involves an intermediate stage where either one or both the components are melting or softening. Our focus is identifying and quantifying the factors that determine morphologies in the melting regime. We identify blend systems that exhibit a transformation in morphology from a minor-component continuous phase with dispersed major component domains to that with the major component being the continuous matrix phase. as a function of mixing time. This phenomenon of phase inversion during compounding is demonstrated to occur even in blends with a higher melting point minor component. A low solid modulus and a low melt viscosity are shown to favor the formation of the continuous phase by the minor component. Polycaprolactone/polyethylene. polystyrene/polyethylene. polycarbonate/ polyethylene, poly(ethylene-co-cyclohexane dimethylene terephthalate)/ polyethylene. and polybutylene/polycaprolactone blends were studied. These model blends were chosen based on the melt viscosity ratio and the relative softening temperatures of the two components. These two parameters were used to develop a two-dimensional framework for summarizing the compounding behavior of blends. For compounding runs with a small amount of the minor component (-1 Owt. % ) at a constant mixer temperature, phase inversion was observed for blend viscosity ratios less than 0.2. irrespective of the relative transition temperatures of the two components. Using a temperature ramping program resulted in the low melting component forming the continuous phase initially. Selective dissolution studies were used to quantify the amount of minor component present in the continuous phase at different mixing times. A polystyrene/polyethylene blend with a
by Ramabhadra Ratnagiri.
Ph.D.