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The dynamic shear behavior at 2 O O O 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:l and 17:3; the first series contained 0, the second 5 wt% of the compatibilizing, partially hydrogenated poly(styrene-b-isoprene) di-block copolymer, SEB. From the Casson plot the relative values of apparent yield stress were found to be G I > GZ; 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"(w). 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 (SpE/ps # SPS/PE). or dissymmetry of the interfacial tension coefficient, could provide a possible explanation.

ABSTRACT:The objective of this study is to investigate the effect of low density polyethylene (LDPE) content in linear low density polyethylene (LLDPE) on the crystallinity and strain hardening of LDPE / LLDPE blends. Three different linear low density polyethylenes (LL-1, LL-2 and LL-3) and low density polyethylenes (LD-1, LD-2 and LD-3) were investigated. Eight blends of LL-1 with 10, 20, 30 and 70 wt % of LD-1 and LD-3, respectively, were prepared using a single screw extruder. The elongational behavior of the blends and their constituents were measured at 150°C using an RME rheometer. For the blends of LL-1 with LD-1, the low shear rate viscosity indicated a synergistic effect over the whole range of concentrations, whereas for the blends of LL-1 with LD-3, a different behavior was observed. For the elongational viscosity behavior, no significant differences were observed for the strain hardening of the 10 -30% LDPE blends. Thermal analysis indicated that at concentrations up to 20%, LDPE does not significantly affect the melting and crystallization temperatures of LLDPE blends. In conclusion, the crystallinity and rheological results indicate that 10 -20% LDPE is sufficient to provide improved strain hardening in LLDPE.

Currently, selection of screw configurations as well as the operating conditions for compounding polymer blends with desired morphology in a co-rotating twinscrew extruder is an art based on experience. In this paper a quenching section of a twin-screw extruder is described. The section may replace any segment of the extruder barrel. It allows, on the one hand, a regular operation of the machine, and on the other, a rapid quenching and removal of blend specimens for morphology analysis from any place along the extruder barrel and at any time of the blending. The experimental observation of development during compounding of polymer blends enables verification and improvement of the theoretical model, aimed at predicting and controlling the size and polydispersity of the minor phase. Development of the predictive model for blend morphology will provide a valuable guide to the polymer processing industry. The preliminary data were collected using polystyrene/high density polyethylene (PS/HDPE) blends at low concentration of the dispersed phase, 5 wt% of either PS or HDPE. It was observed that the viscosity ratio, blend composition, screw configuration, temperature, throughput, and screw speed significantly influence the blend morphology.

Polystyrene‐based nanocomposites (PNC) were prepared using three grades of polystyrene (different molecular weights). The resin was melt‐compounded with 0 to 10 wt% of commercial organoclay in a co‐rotating twin‐screw extruder. Owing to thermo‐oxidative degradation the degree of dispersion was poor. The rheological properties of PNC were determined under dynamic and steady state shear as well as under extensional flow conditions. At the higher clay content, dynamic strain sweep demonstrated that the storage and loss moduli decrease continuously with an increase of strain. To characterize this nonlinear viscoelastic behavior, the Fourier‐transform rheology was applied. The low strain frequency sweep showed that the storage and loss moduli increase with organoclay content. The extracted zero‐shear viscosity data were used to calculate the intrinsic viscosity and then the aspect ratio of dispersions. In spite of nonlinear viscoelastic behavior, the time‐temperature superposition was observed in the full range of concentration. The horizontal and vertical shift factors were found to be almost independent of organoclay content and molecular weight of PS. For comparison, PNC was also prepared by the solution method. A high degree of dispersion was obtained, reflected in the aspect ratio: p = 269, to be compared with p = 16 calculated for the melt‐compounded PNC. Polym. Eng. Sci. 44:1061–1076, 2004. © 2004 Society of Plastics Engineers.