Composition Dependent Miscibility in the Crystalline State of Polyamide 6 /Polyamide 4,10 Blends: from Single to Double Crystalline Blends

Abstract

In this work, we studied the composition-dependent miscibility of polyamide 6 and biobased polyamide 4,10 (PA6/PA410) blends, as triggered by crystallization driven phase segregation. The blends were prepared by extrusion melt blending in a wide composition range and studied by Differential Scanning Calorimetry (DSC), X-ray diffraction (both in-situ and ex-situ SAXS/WAXS), and Polarized Light Optical Microscopy (PLOM) during non-isothermal crystallization. The blends were found to be miscible in the amorphous state, as demonstrated by a single Tg that follows the Fox equation as a function of composition. The blends were also considered to be miscible in the melt, as no evidence of phase segregation was found by SAXS or phase contrast microscopy in the melt. The miscibility of the blends in the crystalline state is a strong function of composition. When only 10 or 20% PA6 is present in the blends, co-crystallization was evidenced by DSC and WAXS and the blends exhibited a single PA410 rich crystalline phase. On the other hand, as 30% or more PA6 is added to PA410, crystallization driven phase segregation occurs and progressively increased with PA6 content in the blends. Hence double crystalline blends are formed with both PA6 rich and PA410 rich crystalline phases. Clear evidence of either one or two crystalline phases was demonstrated by temperature-dependent measurements employing DSC, PLOM, WAXS and SAXS. Both the single and double crystalline PA6/PA410 blends exhibited good mechanical properties in view of the excellent compatibility displayed by the blends. The mechanical properties are in line with those exhibited by miscible blends following a simple rule of mixtures.