Abstract:

Objective Among polyester fibers, the black polyester fibers are in great demand. The black polyester fiber produced by conventional printing and dyeing methods is found to have poor color fastness and produce a large amount of printing and dyeing wastewater, but the black polyester produced by dope dyeing can avoid these problems. However, strong mechanical aggregates are formed between the carbon black pigment particles in ethylene glycol-based color paste, and it is difficult to obtain a stable and good glycol-based carbon black pigment suspension and dispersion system. Therefore, it is necessary to modify the carbon black to solve the problem of poor dispersion during the coloring of polyester fiber stock solution.

Method Liquid phase oxidation method was adopted to oxidize carbon black with nitric acid for different time durations (2, 4, 6, 8 h), and the oxidized carbon black was then characterized by X-ray photoelectron spectroscopy, X-ray diffraction, and other instruments to screen out suitable oxidized carbon black. In the presence of dicyclohexylcarbodiimide and 4-dimethylaminopyridine, the 4 h oxidized carbon black was adopted to perform Steglich esterification reaction with ethylene glycol (EG), polyethylene glycol 200 (PEG200), polyethylene glycol 600 (PEG600) and pollyethylene glycol 800 (PEG800) in N,N-dimethylformamide to prepare grafted carbon black, which were named EG-OCB, PEG200-OCB, PEG600-OCB, PEG800-OCB, respectively. according to the graft polymers. The grafted carbon black was analyzed and tested.

Results Through nitric acid oxidation, the particle size of the original carbon black was reduced from 6 686 nm to 156.5-174.9 nm, and the particle size of the carbon black was the smallest with 4 h oxidation. Subsequently, the surface of oxidized carbon black was grafted, and the particle size was further reduced under steric hindrance effect. Compared with the original carbon black, the particle dispersion of oxidized carbon black and grafted carbon black was obvious, and no large aggregates appeared. The oxygen-containing functional groups on the surface of carbon black increased significantly after oxidation. Changing the oxidation time affected the carboxyl content on the surface of carbon black, and the carboxyl content increased with the increase of oxidation time, changing from 0.124 mmol/g to 0.616 mmol/g. It was seen that the diffraction peak of oxidized carbon black did not shift, indicating that nitric acid oxidation of carbon black only occurred on the surface of carbon black without causing serious damage to the carbon black skeleton. The mass loss of grafted carbon black mainly occurred at 40-100 ℃ and 300-450 ℃. The EG, PEG200, PEG600 and PEG800 were successfully grafted onto oxidized carbon black with a 4 h oxidation time duration, with a grafting rate exceeding 33%. The stability test results showed that the heat stability and storage stability of grafted carbon black were above 92% and 93%, respectively. It was found that the deposition of carbon black was not only correlated to the initial particle size, but also to the length of the molecular chain on the surface of carbon black.

Conclusion The average particle size of carbon black decreased significantly after oxidation, and the dispersion effect was the best with 4 h oxidation. The structure of carbon black was not destroyed after oxidation, and the carboxyl content of carbon black increased significantly, from 0.124 mmol/g to 0.537 mmol/g. The surface of oxidized carbon black was successfully grafted with ethylene glycol and polyethylene glycol with different relative molecular weights, and the grafting rate was above 33%. All of them could be stably dispersed in ethylene glycol, and the average particle size was between 132.8 nm and 148.6 nm, among which the average particle size of PEG600-OCB was the smallest. PEG800-OCB has the best storage stability, and the storage stability is above 95%. PEG200-OCB and PEG600-OCB have the best thermal stability, both of which are above 95%. It is dispersed in ethylene glycol to maintain its stability by steric hindrance.

Key words: carbon black nanoparticle, oxidization, dispersity, polyester fiber dope dyeing, esterification grafting, polyethylene glycol, Steglich esterification reaction