Chemical recycling of waste poly(ethylene terephthalate) fibers into azo disperse dyestuffs

Abstract

In this study, waste poly(ethylene terephthalate) (PET) fibers were chemically recycled into azo disperse dyestuffs. First, waste PET fibers were glycolytically degraded by excess ethylene glycol utilizing zinc acetate dehydrate as a catalyst. The glycolysis product, bis(2-hydroxyethyl) terephthalate (BHET), was purified through recrystallization and hydrolyzed into terephthalic acid (TPA). Thereafter, BHET and TPA were nitrated, reduced and azotized to obtain diazonium salts. Finally, the obtained diazonium salts were coupled with N,N-dimethylaniline to obtain azo disperse dyestuffs (dye A and dye B, respectively). The depolymerized products (BHET and TPA) and azo disperse dyestuffs (dyes A and B) were characterized by FTIR and ¹H NMR spectroscopy. Nylon and polyester filaments were dyed with the synthesized azo dyestuffs with the dye bath pH ranging from 3.6 to 5.8. The performances of the dyestuffs were described by maximum absorption wavelength, K/S, L*, a* and b* values.