The Effect of Miscibility on Rheological and Mechanical Properties of PCL/SAN Blends

Abstract

Abstract Earlier, poly(∊-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) were found to be miscible on molecular level at 8 up to 28 wt.% of acrylonitrile (AN) in SAN copolymer [1]. The combination of PCL and different copolymers of SAN thus offers an opportunity to investigate the effect of miscibility on some key properties of the blends, e.g. rheological or mechanical. In this paper blends containing SAN with 25 wt.% of AN (miscible SAN-25) and 35 wt.% of AN (immiscible SAN-35) were used for this purpose. Blends of PCL with various contents of SANs up to 40 wt.% were prepared by melt mixing in a Brabender laboratory mixer. The miscibility of the mixed PCL/SAN blends was investigated by differential scanning calorimetry (DSC). The blends rheological characteristics were determined on a Rheoflixer capillary rheometer at various temperatures. Rabinowitsch and Bagley corrections and the power-law relation were used. The extrudates were observed under a scanning electron microscope. In addition, mechanical testing was performed on a tensile testing machine. It was found that blends of PCL with a minor amount of miscible SAN-25 provide a better balance of rheological and mechanical properties than those of pure PCL. The immiscible blend shows properties inferior to the miscible one. Immiscible SAN-35 increases viscosity, shear thinning and extrudate swell of PCL more than the miscible type. In contrast to the miscible blends containing SAN-25, which were without any form of unstable flow at shear rates of 10 to 10 000 s−1, melt fracture occurs in the immiscible blends with SAN-35. Positive synergism in tensile strength and elongation at break can be seen for 90/10 PCL/SAN-25 blend processed at 130°C. The addition up to 30 wt.% of SAN-25 miscible with PCL increases elongation at break.