Thermal and rheological properties of poly(ϵ-caprolactone) and polystyrene blends

Abstract

The thermal and rheological properties of blends of poly(ϵ-caprolactone) (PCL) and polystyrene (PS) have been investigated by differential scanning calorimetry (DSC), scanning electron microscopy, and Advanced Rheometric Expansion System. Two different molecular weights of PS 1 (M̄w=1000) and PS 2 (M̄w=69,000) have been used in the PCL–PS blend. In the thermal analysis of the PCL–PS 1 blend by DSC, the Tc of PCL in the blend decreased by about 3–13 degrees with blend composition compared to the Tc of pure PCL. The decrease in Tc of PCL in the blend indicates that the crystallization of PCL in the PCL–PS 1 blend is deactivated by PS 1. The Tm of PCL in the blend decreased by about 2–6 degrees with blend composition compared to the Tm of pure PCL. From the results of Tc and Tm of PCL, it is suggested that the PCL–PS 1 blend is partially miscible. The Tc of PCL in the PCL–PS 2 blend increased by about 2–5 degrees in the PCL-rich compositions. The increase in Tc of PCL can be explained by the nucleating effect of PS 2 on the primary nucleation of PCL in the PCL–PS 2 blend. From the results of the rheological properties of the PCL–PS 2 blend, the storage modulus of the blend at low frequencies has a larger value than that of the simple mixing rule. The elasticity increase from the simple mixing rule is consistent with the emulsion model for a dispersed system.