No abstract

Blends of an amorphous and a semi-crystalline polymer-polystyrene and polypropylene, respectivelywere prepared by melt processing in an extruder at 220°C. These polymers are known to be immiscible and the composite morphologies were characterized by electron microscopy and thermal analysis. Fine micronscale morphologies, ranging from 0.5 to 20 microns were observed. Thermal analysis and dynamic mechanical analysis showed changes in both the polystyrene and polypropylene glass transition temperatures (T g ) over the composition range. The major effect was a sharp increase in polystyrene T g with increasing polypropylene content in the blend. A T g elevation of 5.5°C was observed at 85% polypropylene. The polypropylene T g also increases with increasing polypropylene content, starting at a depressed value in discrete polypropylene domain environments and approaching the bulk polypropylene value after the phase inversion is crossed. Qualitative structural models are proposed based on spatial and mechanical interactions between the components. POLYM. ENG. SCI., 45:1187-1193, 2005. © 2005 Society of Plastics Engineers

The effect of additives on glass transition behavior in melt processed blends of polystyrene (PS) and polypropylene (PP) was studied. Blends of additive-free polystyrene and additive-free polypropylene revealed the known effect of the PS T g increase in blend compositions where PP surrounds PS. Glass transition behavior in these blends was compared to blends prepared from additivefree PP and commercial grade PS, which contained lubricant additives. The thermal transitions of PS and PP were measured using modulated DSC. Although the behavior of low PS concentration blends was similar in both systems, the characteristics of the high PS blends differed substantially. These differences and the contrast in the PP T g behaviors were attributed to the migration of additives from the PS phase across the immiscible interface into the PP phase. Similar T g variations were observed in blends of commercial grade PS and commercial grade PP.

This paper describes the effects of structures on the glass transition of glassy polymers blended with a semi-crystalline polymer. Immiscible blends of PS/PP and PS/HDPE were prepared from commercially available polymers using melt processing and extrusion without additives. The weight fractions of the components were varied from 0 to 1. SEM analysis of the blends showed a range of morphologies over the composition range from small inclusions at low volume concentrations through intertwined co-continuous structures at specific intermediate compositions, and a reversal of this configuration at high volume fractions. The glass transition of the glassy polymer was measured with differential scanning calorimetry using the sensitive and high resolution modulated DSC method. A systematic change in glass transition of glassy polymers is observed as a function of composition in various immiscible polymer blends. Results show that the glass transition of polystyrene increases with a reduction in volume fraction, by approximately 5.4°C in polypropylene and 6.5°C in polyethylene. Probable models which might explain this effect are mentioned.

No abstract