The yellowing mechanism of polyesteramide based on poly(ethylene terephthalate) and polyamide 6

Abstract The yellowing mechanism in polyesteramide based on poly(ethylene terephthalate) and polyamide 6 (PET‐PA6) has been studied. Amine model compounds were employed to react with acetaldehyde (AA), and 1H‐nuclear magnetic resonance spectrometer ( 1 H‐NMR), fourier transform infrared spectroscopy (FT‐IR), and electrospray ionization mass spectrometry (ESI‐MS) were used to characterize the structure of the yellowing products. 13 C‐NMR, laser confocal micro‐Raman spectrum, and X‐ray photoelectron spectroscopy (XPS) were used to characterize the yellowing products of the reaction of PA6 oligomers and AA. The structures of yellowing substances in the two systems are consistent. The color generation is mainly caused by the reaction of the terminal primary amine group of PA6 with AA, which is the thermal degradation product of PET, to form Schiff bases. These Schiff bases condense further to form a conjugated imine structure, which may be the main chromophore of polyesteramide. Due to the degradation of PA6 segments of the copolymer, it may further degrade to form new primary amino groups and increase yellowness during use.