Effect of small molecular solvent on phase diagram and tensile strength of polymer blends

Abstract

This work involved the studies of the effects of small molecular solvent on the phase diagrams and tensile strength of polymer blend of styrene-acrylonitrile copolymer (SAN) and poly (methyl methacrylate) (PMMA). For the studies of the effects of solvent on the phase diagrams, SAN/PMMA blends were prepared by solvent casting and melt mixing at the weight percent of SAN: 10, 20, 30, 40, 50, 60, 70, 80, 90. The phase diagrams of SAN/PMMA blends were constructed by plotting the cloud pint temperatures occurred on heating of the blends against blend compositions. It was found that the phase diagrams of the blends cast from five different solvents, which were methylene chloride, acetone, tetrahydrofuran, methyl ethyl ketone and 1, 2-dichloroethane, were different and depended on the type of solvent, the boiling point of solvent and the period of drying time in a vacuum oven. Besides, the phase diagrams of the SAN/PMMA blends from solvent casting occurred at the higher temperatures than that of the blends from melt mixing. For the studies of the effects of solvent on tensile strength, only the SAN/PMMA blends from melt mixing were used. Prior to the tensile testing, the blends were suspended in the vapor of the above five different solvents for 20 min. It was found that tensile strength of the blends suspended in the solvents vapor was not significantly different from that of the blends without solvents (the differences of tensile strength were within +_ 6%). The insignificant change of tensile of the blends should be due to the inability of traces of solvents to plasticize the polymer blends. These were evidenced by the very small change of the glass transition temperatures (Tg) of the blends, which were determined by differential scanning calorimeter (DSC), after suspending in the different vapor of solvents.