Ternary blends, based on 70% by weight of polypropylene (PP) with 30% by weight of a dispersed phase, consisting of 15% polyamide-6 (PA6) and 15% of a mixture comprising varying ratios of an unreactive poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) triblock copolymer and a reactive maleic anhydride-grafted SEBS-g-MA, were produced via melt blending in a co-rotating twin-screw extruder. TEM revealed the blend containing only non-reactive SEBS to exhibit individual PA6 and SEBS dispersed phases. However, the progressive replacement of SEBS with reactive SEBS-g-MA increased the degree of interfacial reaction between the SEBS and PA6 phases, thus reducing interfacial tension and providing a driving force for encapsulation of the PA6 by the SEBS. Consequently, the dispersed-phase morphology was observed to transform from two separate phases to acorn-type composite particles, then to individual core-shell particles and finally to agglomerates of the core-shell particles. The resultant blends exhibited significant morphology-induced variations in both thermal and mechanical properties. DSC showed that blends in which the diameter of the PA6 particles was reduced to ≤3 μm by the increasing interfacial reaction exhibited fractionated PA6 crystallisation. In general, mechanical testing showed the blends to exhibit inferior low-strain tensile properties (modulus and yield stress) compared to the matrix PP, but superior ultimate tensile properties (stress and strain at break) and impact strength. These changes are discussed with reference to composite models. 相似文献
Summary: The effectiveness of some thermoplastic elastomers grafted with maleic anhydride (MA) or with glycidyl methacrylate (GMA) as compatibilizer precursors (CPs) for blends of low density polyethylene (LDPE) with polyamide‐6 (PA) has been studied. The CPs were produced by grafting different amounts of MA or GMA onto a styrene‐block‐(ethylene‐co‐1‐butene)‐block‐styrene copolymer (SEBS) (KRATON G 1652), either in the melt or in solution. A commercially available SEBS‐g‐MA copolymer with 1.7 wt.‐% MA (KRATON FG 1901X) was also used. The effect of the MA concentration and of other characteristics of the SEBS‐g‐MA CPs was also studied. The specific interactions between the CPs and the blends components were investigated through characterizations of the binary LDPE/CP and PA/CP blends, in the whole composition range. It was demonstrated that the SEBS‐g‐GMA copolymers display poor compatibilizing effectiveness due to cross‐linking resulting from reactions of the epoxy rings of these CPs with both the amine and the carboxyl end groups of PA. On the contrary, the compatibilizing efficiency of the MA‐grafted elastomers, as revealed by the thermal properties and the morphology of the compatibilized blends, was shown to be excellent. The results of this study confirm that the anhydride functional groups possess considerably higher efficiency, for the reactive compatibilization of LDPE/PA blends, than those of the ethylene‐acrylic acid and ethylene‐glycidyl methacrylate copolymers investigated in previous works.
SEM micrograph of the 75/25 LD08/PA blend (with 2 phr SEBSMA1). 相似文献
A blend of polyamide 6 (PA6) and styrene-ethylene/butylene-styrene (SEBS) with a co-continuous nanolayer network was fabricated by reactive compounding and subsequent injection molding. The nanostructured polymer alloy was found to exhibit an extremely low coefficient of linear thermal expansion (CLTE) in the flow direction, accompanied by a largely suppressed molding shrinkage. To clarify the influence of the microstructure on thermal expansion behavior, a systematic study of morphology evolution, crystalline orientation, and confined crystallization of the PA6/SEBS (60/40) blend was carried out by means of TEM, DMA, DSC and WAXD measurements. It was found that a lower viscosity of SEBS and the capability of in situ compatibility with PA6 enable a morphology evolution from a disordered co-continuous to droplet-continuous and, finally, to a nanolayer network structure. Multi-scale orientations take place during the injection molding process, and the large reduction of CLTE may originate from the high order microstructure in two aspects: (1) the rubber-deformation-induced orientation of PA6 crystalline in which the b-axis with a negative CLTE orients along the flow direction, and (2) the co-continuous orientation of the rubber and plastic nanolayers, of which the thermal expansion favors towards the normal direction. 相似文献
