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 cop olymer with 29.5 wt% acrylonitrile (SAN-29.5) has been investigated using s hear apparatus and transmission electron microscopy (TEM). The obtained dat a showed that only shear-induced mixing was observed for all of the composi tion ratios. The increase of the cloud point (or homogenization temperature ) Delta T(gamma) = T(gamma) - T(O) was investigated as a function of shear rate gamma; in addition, the normalized shift in the cloud point Delta T(ga mma)/T(O) versus gamma was also studied and compared with that of simple li quid mixtures and polymer solutions. The results showed that the polymer bl ends 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 orient ed and elongated in the flow direction. Three regimes, depending on the app lied 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 part icles, but it did not completely vanish even for 10 min after the shear ces sation.