Composition dependent miscibility in the crystalline state of polyamide 6/polyamide 4,10 blends: From single to double crystalline blends

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 in a wide composition range and characterized by X-ray diffraction (both in-situ and ex-situ SAXS/WAXS), Differential Scanning Calorimetry (DSC), and Polarized Light Optical Microscopy (PLOM) during non-isothermal crystallization. The blends were miscible in the amorphous state, as demonstrated by a single T-g 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. Remarkably, the blends can also be miscible in the crystalline state in a limited composition range. When only 10 or 20% PA6 was 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 was added to PA410, crystallization driven phase segregation occurred 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 the presence of either one or two crystalline phases was obtained 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 were in line with those exhibited by miscible blends following a simple rule of mixtures.

Automated summary

The study focused on the composition-dependent miscibility of polyamide 6 and biobased polyamide 4,10 blends, showing compatibility in the amorphous and melt states, as well as in a limited composition range in the crystalline state. The blends exhibited single or double crystalline phases based on the PA6 content, both displaying good mechanical properties due to excellent compatibility. Temperature-dependent measurements confirmed the presence of unique crystalline phases in the blends.