Rheological evaluation of polystyrene/polyethylene blends

The dynamic shear behavior at 200°C of low density polyethylene, LDPE, polystyrene, PS, and their blends was studied. Two series of blends were prepared containing LDPE:PS = 1:2, 2:1 and 17:3; the first series contained 0, the second 5 wt% of the compatibilizing, partially hydro‐genated poly(styrene‐b‐isoprene) di‐block copolymer, SEB. From the Casson plot the relative values of apparent yield stress were found to be G ′ y > G ″ y the addition of SEB decreased both these functions, but the inequality remained valid. After subtracting the yield stress values the frequency relaxation spectrum was computed from the relation G ″ = G ″(ω). The linear viscoelastic functions determined from the spectrum were found to agree with experimental values within a range of error below 5%. The blends were found to be thermorheologically complex with the time‐temperature shift factors depending on both temperature and frequency. A compositional dissymmetry of blend morphology was observed: PS dispersed in LDPE formed spheres, while at corresponding concentration LDPE in PS formed fibers. A difference in surface tension of the two polymers, leading to different spreading coefficients (S PE/PS ≠S PS/PE ), or dissymmetry of the interfacial tension coefficient, could provide a possible explanation.