Coalescence in blends of thermoplastic polyurethane with polyolefins

The coalescence behavior of immiscible blends was determined by annealing t he melt without shear. The kinetics and the mechanism of coalescence were o bserved for blends of thermoplastic polyurethane (TPU) and polyolefins. Two different types of measurements were used to observe coalescence in quiesc ent melt at the processing temperature. On the one hand, the blend granules were annealed in bulk. The resulting particle sizes were determined by lig ht microscopy and by SEM on particles separated from the blend. On the othe r hand, thin samples were annealed on a hot stage. Coalescence was observed in situ by light microscopy or static laser light scattering. It was found that the higher viscosity and elasticity ratios between polyethylene and T PU lead to a more pronounced coarsening of the morphology of 80/20 blends t han in TPU/polypropylene. It has been shown that the process of reshaping c oalescence is one mechanism of coalescence that occurs in quiescent melt. A nother mechanism that was directly observed is a "domino effect" where one coalescence process causes the next one.