| In this thesis, the morphology and rheological behavior of high-density polyethylene (HDPE) /polyamide (PA) blends were investigated using Capillary Rheometer, Advanced Rheometric expanded system (ARES) and Scan Electron Microscope (SEM).The influence of the morphologies of the dispersed phase induced by flowing on the rheological behaviors of steady state for the HDPE/PA66 blends containing very small quantity of PA66 ( ≤7 wt % ) were studied. Little change on the morphology of dispersed phase induced by flow can be found at 240℃ with any shear rate when the PA66 is in solid state. As a result, the rheological behavior of blends can not be affected by adding small amount of PA66. When PA66 melted completely, the dispersed phase shows the spherical droplets in the blends, an obvious viscosity reduction can be observed in flow curves for HDPE/PA66 blends containing 1 wt % or 3 wt % PA66 at 280℃ with any shear rate. The viscosity at 260 ℃, the temperature near the melting point of PA66, and lower apparent shear rate (< 350 s-1 ) for the HDPE/PA66 blend containing only 3 wt % PA66 shows almost the same as that of HDPE; while at high shear rate, the viscosity of the blend is lower than those of HDPE at 260 ℃ or the blend at 280℃. The blend sample obtained at 260 ℃ presented an extraordinary morphology, i.e. appearance of the stretched droplets or fibrils. All of these morphologies suggested that PA-66 with the melt temperature range from 252 ℃ to 268℃ according to the DSC traces, it was a solid filler at 240℃ and had little influence on the HDPE, after blending 3 wt % PA-66 in it. On the other hand, when the blend is extruded from the capillary die under 280 ℃, at this temperature PA-66 melted completely, the molten dispersed component should be stretched by flow. Meanwhile, it was assumed that the stretched droplets broke and relaxed to form droplets again at high temperature. Particularly, even though it is difficult to deform at relative low shear rate because PA-66 is in a semi-molten or semi-solid form at 260℃, it can still deform into fibril-like structure, which would be hard to breakup when it was extruded at 260℃and higher shear rate. It is suggested that the formation of fibrillar morphology of dispersed phase is a key factor for the abnormal reduction of viscosity for the HDPE/PA blend.The morphology evolution and dynamic linear visco-elastisity of HDPE/PA66 blends containing 20 wt % PA6 compatibilized by HDPE-g-MAH were investigated by using SEM and ARES. The morphology of the blend shows the representative sea-island structure. The size of dispersed phase is large and the interface is clear without compatibilizer. The size of dispersed phase particle is small and the distribution of the particle is uniform increasingly with the content increasing of compatibilizer. When the content of compatibilizer increased to the 10 wt %, the average size of dispersed phase reduced sharply, i.e. a order of magnitude reduction, compared with the blends without compatibilizer, there will be unobvious change in the size of dispersed phase when the content of dispersed phase reached 25wt%, the size of dispersed phase will be stable.Using ARES, the linear viscoelastic behavior of the HDPE/PA6 blends containing the PA6 (20wt %) is investigated, the dependence of frequency of dynamic storage modulus G' and Dynamic loss modulus G" reduced gradually at low-frequency region. It will emerge the obvious terminal effects trend when the content of compatibilizer reach 10wt%, viz. the emergence of "the second plateau" at the terminal zone where the frequency trend towards zero. It means that the blends melt elasticity increase due to the special morphology; it corresponds with the results of morphology of the blends, it shows that the dynamic rheology can investigate the evolution of the morphology of blends well. The linear viscoelastic behavior of the blends is related with the morphology of blends closely.
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