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.

Covalent adaptable networks constructed in biobased cross-linked polymers are used for the thermal-loop process for thermoset materials and composites. In this study, bio-based poly(imine-amide)s (PIAs; biomass content >85%) were synthesized from the lignin-derived monomer vanillin, citrate ester (triethyl citrate), and 1,4-diaminobutane via a condensation reaction. The imide bonds accompanied by a dynamic covalent nature provided PIAs with a satisfactory catalyst-free thermally malleable polymer network. The synthesized PIAs unveil toughness and ductility due to the combined effect of amide and imide structures and become thermally malleable in a few seconds. These PIAs show advanced performance in recyclability (efficient reprocessing) and have excellent foamability (suitable for good sCO 2 compatibility and diffusion), as the foams produced via green sCO 2 batch foaming technology have an expansion ratio of up to 12.1. PIA/multiwalled carbon nanotube (MWCNT) nanocomposites exhibit high electric conductivity (10 −2 to 10 2 S cm −1 in the range of 1−10 wt % MWCNTs), low percolation threshold (0.43%), and excellent EM-shielding properties (above 70 dB at 10 wt % MWCNTs). More promisingly, the electrical conductivity and EM-shielding properties of these PIA/MWCNT nanocomposites are enhanced by forming microcellular structures. This study presents the molecular structure of a green covalent adaptable network with potential foamability and reprocessing ability, which can be used to prepare lightweight nanocomposites with excellent electrical conductivity and EMI-shielding properties.

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terephthalamide/adipic acid (BAHT-AA) was chosen to be used as a comonomer to develop a novel polyamide 6 (PA6) with the trace-content aromatic structure. A series of polyamide 6 copolymers (coPA6) with trace BAHT-AA loading were synthesized to yield the modified copolyamides with multiple interactions of hydrogen bonding and π-π stacking on the PA6 backbone. It was proved that the thermal stability and mechanical properties of coPA6 were significantly enhanced because of the introduction of the trace BAHT-AA segment. More importantly, adding a trace (1, 2, and 4 mole%) of BAHT-AA could effectively increase the network structure and highly decrease the free volume fraction in the polymer system that is proved by the relaxation behavior and melt viscoelastic behavior. The results showed that the integrated performances of coPA6 were better than that of pure PA6, which was highly correlated with the aforementioned multiple interactions. For example, outstanding tensile strength (73.0 vs. 56.8 MPa), and modulus (1167 vs. 929 MPa), and so on. This work provided the traditional PA6 with the modification of outstanding mechanical and thermal performances, thus expanding its application for the plastics and textile industries.

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