Objective Polyester (PET) filament has made remarkable contributions to the development of textiles and is widely applied in various fields because of its high strength, superior durability, and good dimensional stability. At present, the annual production of polyester filament is as high as 43.26 million tons/year, however it is more difficult to degrade under natural conditions, causing environmental concerns. Therefore, it is a critical challenge to improve the degradation properties of PET filament without changing its other performance. Method A novel composite filament was rationally fabricated via poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) modified PET, called PHBV/PET filament. The degradation performance of PHBV/PET filament was investigated by thermal degradation and soil degradation. The influences of temperature and soil filling time on the molecular structure of filaments were studied in depth. Scanning electron microscope, thermogravimetric analyzer (TG), differential scanning calorimeter, and Fourier transform infrared spectroscopy were adopeed to analyze the mechanical properties, crystallinity, structure and surface morphology of the PHBV/PET filaments after degradation. Results The addition of PHBV slightly was found to reduce the strength of the PET fibers with a breaking strength of 1. 69 cN/dtex for 1% PHBV/PET filament. However, the elongation of break was increased significantly, indicating that the introduction of PHBV would not limit the processing applications of the composite yarn (Fig. 1). Apart from its fine mechanical properties, PHBV/PET also exhibited better thermal degradation performance. The 5% mass loss temperature of the 1% PHBV/PET filament was 364 C, lower than 386 t for PET filament. The PHBV cansed the crystallization of the filament more difficult during pyrolysis process, and the filament seemed to be more likely to degrade at low temperatures (Fig. 2). The mass loss of the PHBV/PET filament was only 88.42%, while the mass loss of the non-thermally degraded filament was as high as 94.90% in TG curves (Fig. 4), indicating the PHBV/PET filament macromolecular chains easier to break at high temperatures degradation condition. It was also found that 3% PHBV/PET filament after thermal degradation occurred an apparent absorption peak at 110 t (Fig. 5), implying the high temperatures would promote recrystallization of composite filament and that PHBV can promote the degradation of PET filament. Furthermore, 1% PHBV/PET filament lacked an exothermic peak at 2 959.25 cm after thermal degradation, confirming that 1% PHBV/PET filaments can be degraded (Fig. 6). After 60 d buried in soil environment, grooves distinctly appeared in the surface of the 1% PHBV/PET filament (Fig. 7), suggesting that the 1% PHBV/PET filament was eroded by soil microorganisms, leading a change to the internal structure of the fiber, which caused the breakage and decomposition of the macromolecular chains. The results showed a significant increase in the absorption enthalpy of 1% PHBV/PET filaments (Fig. 8). Conclusion 1% PHBV/PET filament was found to have excellent mechanical properties and can be degraded both thermal and soil embedding. When increasing PHBV content, the side groups and branched chains of PET filaments are more easily moved, and the degradation is much more easily. Therefore, the PHBV/PET filament can be used as a new environment-friendly material to replace part of PET filament in related application fields, contributing to green production of textiles. © 2023 China Textile Engineering Society. All rights reserved.
