Rheology and morphology of layered polymer melts in shear

Multilayered polymer melt samples with 50 alternating layers of 20 μm average thickness were prepared from polystyrene (PS), reactive styrene copolymers (PS-OX and PS-MA), and amorphous polyamide (aPA). Rheological properties were characterized in steady and dynamic shear modes using a parallel plate rheometer. Optical and scanning electron microscopy were used to obtain images of samples before and after testing. Correlations were identified between break-up of the layers and increase or decrease of viscosity in steady shear testing. Reaction at the interface was shown to stabilize the layers against break-up. Two qualitatively different patterns of rheological behavior in dynamic shear were distinguished. The elastic modulus of the layered sample was typically greater than either corresponding constituent polymer at low frequencies. However, a nonreactive polymer system with low interfacial tension was additive.