New Strategy and Polymer Design to Synthesize Polyamide 66 (PA66) Copolymers with Aromatic Moieties from Recycled PET (rPET)

Recycling of poly(ethylene terephthalate) (PET) is considered to be a promising way to reduce environmental pollution. In this work, the valuable monomer bis(6-aminohexyl) terephthalamide (BAHT) comprising aromatic moieties was synthesized using recycled PET (rPET) waste by an aminolysis process. Five kinds of PA66 copolyamides with different contents of BAHT-AA salt (0–50 mol %, with a partially renewable content of 0–47.1 wt %) were successfully synthesized by the melt polycondensation method. The thermal and mechanical properties, crystallization kinetics, relaxation, and rheological behavior of these copolyamides were systematically investigated. The effect of BAHT-AA content on the resultant PA66 copolyamides properties was studied. The incorporation of BAHT-AA salt greatly improved the thermal and mechanical properties of the PA66 copolyamides compared to PA66/6T. This demonstrates that the monomer derived from the rPET can effectively endow a PA66 system with a well-distributed regulation of aromatic rings on its polymer backbones, with a rapid crystallization rate and high mechanical performance. Furthermore, the rPET-derived polyamides allow higher melt viscosity and exhibit a higher degree of shear-thin behavior, which is caused by the presence of more complex interaction in the polymer system. This discovery could provide a new concept for the PET waste treatment system, thus setting the stage for the recycling technique from rPET to polyamides.