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LONG-RANGE PROCESSING CORRELATION AND MORPHOLOGICAL FRACTALITY OF COMPATIBILIZED BLENDS OF PS/ HDPE/ SEBS BLOCK COPOLYMER

The rheological behaviour of PS/HDPE/SEBS blends during twin-screw extruder melt processing was followed by measuring the effective shear rate range for dispersive mixing: the torque (TQ), output (Q) and melt back-pressure (p) in a twin-screw extruder, while the rheological properties of extruded and moulded samples were measured with Dynamic Mechanical Analyser (DMA). The process parameters were decreased with the HDPE content increase. The results show that SEBS can compatibilize the blends by substantially reducing torque and increasing the back-pressure. The fractal-based methods appear to be suitable for describing structures and processes in polymer blend system. In addition, we provide long-range process correlation estimators by the Hurst parameter of a time series, based on the R/S based method. The Hurst roughnesses of melt processing parameters are increased by compatibilization and are the function of composition (Figure 1). Blends formed far from equilibrium (non-compatibilized blends) have higher fractal dimensions compared to blends formed by compatibilization. This is observed empirically as a transition from swallow-tail and dendritic shapes to objects having a more compact density distribution. Fractal indices by “ box-counting” method of original (Figure 2a) and thinned (by the Zhang-Suen method, Figure 2b) SEM images have been well related to the blend composition.The different fractal morphology and its effect on properties suggest that fractal induced morphology change can likely enhance mechanical performance in immiscible polymer blends. However, the compositional variations do not necessarily improve the mechanical properties of blends because the most efficient morphology might not be obtained at any composition if a fixed extruder processing parameters are used.

PS/HDPE/SEBS blends; morphological structure; processing; fractal dimension; Hurst index

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