Change of phase behaviour of SMA PMMA blends during processing at high deformation rates

Processing of a SMA/PMMA blend through a capillary results in a complex change of phase behaviour with deformation rate. Both deformation induced demixing and remixing are observed. This complex phase behaviour as a function of apparent shear rate, is in qualitative agreement with experimental and theoretical results found for a polystyrene/poly vinyl methyl ether (PS/PVME) blend (Fernandez ML, Higgins JS, Horst R, Wolf BA. J. Polym. Sci. Polym. Lett. 1995;36(1)). In addition a different tongue shaped area of partially demixed material is observed in the current work (type b). This sample appearance is proposed to be related to the occurrence of vortices near the entrance of the capillary. This is a phenomenon which only occurs in contraction flow experiments. Pure shear rheological experiments, such as parallel plate or cone and plate, will not show such behaviour. The deformation induced demixing is spinodal phase separation. This is concluded from light microscopy experiments and via reheating experiments, showing that the blend needed only 15-25 s to remix. Preliminary results suggest that in addition to shear, elongation can cause dramatic changes in the blend phase behaviour. Capillary experiments are difficult to interpret because of the combination of shear, elongation, pressure and viscous heating. However, industrial scale blend processing such as injection moulding shows similar complexity. Hence capillary measurements are the best comparable small scale experiment. Future experiments will focus on modifying the capillary geometry, in order to discriminate between the influence of shear and elongation. (C) 1999 Elsevier Science Ltd. All rights reserved.