Shear effect on the phase behavior and morphology in PMMA/SAN-29.5 blend

The effect of simple shear flow on the miscibility and morphology of blends of poly(methyl methacrylate) (PMMA) and a styrene-acrylonitrile random copolymer with 29.5 wt% acrylonitrile (SAN-29.5) has been investigated using shear apparatus and transmission electron microscopy (TEM). The obtained data showed that only shear-induced mixing was observed for all of the composition ratios. The increase of the cloud point (or homogenization temperature) ΔT(qq) = T(qq) - T(0) was investigated as a function of shear rate qq; in addition, the normalized shift in the cloud point ΔT(qq)/T(0) versus qq was also studied and compared with that of simple liquid mixtures and polymer solutions. The results showed that the polymer blends were more sensitive to the shear rate than both simple-liquid mixtures and polymer solutions. The morphology of the PMMA/SAN(= 75/25) blend (the critical composition) indicated that shear-induced phase mixing occurred at a critical shear rate value, below which the two phases were highly oriented and elongated in the flow direction. Three regimes, depending on the applied shear rate values, were detected that were in good agreement with the literature data for polymer solutions. The effect of relaxation times after shear cessation showed a decrease in the orientation of the elongated particles, but it did not completely vanish even for 10 min after the shear cessation.