Correlation of Morphology Evolution with Superior Mechanical Properties in PA6/PS/PP/SEBS Blends Compatibilized by Multi-phase Compatibilizers

In this study, the maleic anhydride (MAH) and styrene (St) dual monomers grafted polypropylene (PP) and poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS), i.e. PP-g-(MAH-co-St) and SEBS-g-(MAH-co-St) are prepared as multi-phase compatibilizers and used to compatibilize the PA6/PS/PP/SEBS (70/10/10/10) model quaternary blends. Both PS and SEBS are encapsulated by the hard shell of PP-g-(MAH-co-St) in the dispersed domains (about 2 μm) of the PA6/PS/PP-g-(MAH-co-St)/SEBS (70/10/10/10) quaternary blend. In contrast, inside the dispersed domains (about 1 μm) of the PA6/PS/PP/SEBS-g-(MAH-co-St) (70/10/10/10) quaternary blend, the soft SEBS-g-(MAH-co-St) encapsulates both the hard PS and PP phases and separates them. With increasing the content of the compatibilizers equally, the morphology of the PA6/PS/(PP+PP-g-(MAH-co-St))/(SEBS+SEBS-g-(MAH-co-St)) (70/10/10/10) quaternary blends evolves from the soft (SEBS+SEBS-g-(MAH-co-St)) encapsulating PS and partially encapsulating PP (about 1 μm), then to PS exclusively encapsulated by the soft SEBS-g-(MAH-co-St) and then separated by PP-g-(MAH-co-St) inside the smaller domains (about 0.6 μm). This morphology evolution has been well predicted by spreading coefficients and explained by the reaction between the matrix PA6 and the compatibilizers. The quaternary blends compatibilized by more compatibilizers exhibit stronger hierarchical interfacial adhesions and smaller dispersed domain, which results in the further improved mechanical properties. Compared to the uncompatibilized blend, the blend with both 10 wt% PP-g-(MAH-co-St) and 10 wt% SEBS-g-(MAH-co-St) has the best mechanical properties with the stress at break, strain at break and impact failure energy improved significantly by 97%, 71% and 261%, respectively. There is a strong correlation between the structure and property in the blends.