Phase structure evolution during mixing and processing of poly(lactic acid)/polycaprolactone (PLA/PCL) blends

The morphology of quenched and compression molded samples of poly(lactic acid)/polycaprolactone (PLA/PCL) blend prepared by melt mixing was carefully characterized by the method reflecting eventual nonuniformity of the blend structure and/or broad particle size distribution. Determined number and volume average droplet radii for quenched samples were compared with theory, assuming that flow field in a mixing chamber can be substituted by the shear flow with effective shear rate. An increase in droplet radii during compression molding was compared with theory of the coalescence in quiescent state. Using the concept of effective shear flow to describe mixing leads to a strong disagreement between theory and experiment for the critical droplet radius of its breakup, and for the coalescence efficiency. The theory of coalescence in quiescent state provides fair description of an increase in the number average droplet radius during compression molding, but totally fails at prediction of an increase in the volume average droplet radius.