Abstract:

Objective The traditional polyester fiber spun-dyed mostly uses in-situ polymerization method to prepare high-performance colored polyester chips, where the carbon black grinding is dispersed in the ethylene glycol, and the carbon black ethylene glycol color paste is applied to the in-situ polymerization of polyester. However, conventional carbon black ethylene glycol color paste have poor storage stability and high transportation cost. In view of this problem, this study uses spray drying method to make self-dispersed nanoscale carbon black, aiming to effectively decrease transportation cost and improve the storage stability of carbon black in ethylene glycol.
Method In this study, nanoscale carbon black paste was prepared into self-dispersed nanoscale carbon black by a spray-drying method. The effects of carbon black, dispersant and dispersion process on self-dispersed nanoscale carbon black were parametrically studied. The effects of mass fraction of dispersant, grinding time and grinding speed on the particle size of self-dispersed nanoscale carbon black were discussed based on the response surface optimization experiment in order to obtain the optimal grinding and dispersion conditions. In addition, transmission electron microscope (TEM), thermogravimetric analysis (TGA) and contact angle meter were employed to study the apparent morphology, heat resistance and hydrophilicity.
Results Parametrical study was carried out to investigate the influence of dispersant and carbon black on the particle size of self-dispersed nanoscale carbon black. When the dispersant SUA-305 and the carbon black AP-104H were selected, the particle size of self-dispersed nanoscale carbon black was found to be the smallest (Fig. 2). The same method was used to study the influence of process conditions on the particle size and PDI (polydispersity index) of self-dispersed nanoscale carbon black. When the mass fraction of dispersant was 30%, the grinding time was 2 h, and the grinding speed was 3 500 r/min, the minimum particle sizes of self-dispersed nanoscale carbon black was 85 nm, and the minimum PDI was 0.163 (Fig. 3). The response surface was used to optimize the experiment, and the particle size was taken as the response value to further optimize the experimental results. The F-value in the model was 23.98 and the P-value was 0.000 2(Tab. 1). The minimum particle size of self-dispersed nanoscale carbon black were found on the three groups of response surfaces, and there were extreme values in the contour map, which were consistent with each other (Fig. 4). In order to determine the feasibility of the test, five groups of validation tests were conducted on the response surface model. The normalized deviation was 2.92%, and the normalized standard deviation was 1.544% (Tab. 2). The optimum process parameters were identified to be as follows: the mass fraction of dispersant is 30%, the grinding time is 2 h, and the grinding speed is 3 500 r/min. The original carbon black has a large particle size of 15.007 μm (Fig. 5). In comparison, the particle size of self-dispersed nanoscale carbon black is 0.085 μm, the contact angle between the original carbon black and ethylene glycol is 147°, and the contact angle between the ethylene glycol of self-dispersed nanoscale carbon black is 7° (Fig. 6). The original carbon black shows multiple agglomerations, and the self-dispersed nanoscale carbon black particles are small and evenly distributed. In Fig. 8, the self-dispersed nanoscale carbon black meets the requirement of decomposition resistant at 280 ℃ (Fig. 7). The self-dispersed nanoscale carbon black ethylene glycol color paste was centrifuged for 19 h at 4 000 r/min, its color paste sedimentation rate is 0.772 %/h, and the estimated storage period is 26.8 months (Fig. 9).
Conclusion This study evaluated the influence of five factors (dispersant, carbon black, dispersant mass fraction, and grinding time, grinding speed) on the particle size of self-dispersed nanoscale carbon black. Response surface methodology was used to optimize the three factors (mass fraction of dispersant, grinding time and grinding speed) in the preparation process of self-dispersed nanoscale carbon black. The variance analysis results of the optimization process show that the regression model is significant, which indicates that the reliability of the response surface model fitting equation is high, and the best process obtained from this model is feasible. Under the technological conditions that the mass fraction of dispersant is 30%, and the grinding time is 2 h, and the grinding speed is 3 500 r/min, the minimum particle size of self-dispersed nanoscale carbon black is 85 nm. The self-dispersed nanoscale carbon black demonstrates good hydrophilicity, good self-dispersion in ethylene glycol solution, and good heat resistance, meeting the preparation requirements of in-situ polymerization polyester fiber chips. The self-dispersed nanoscale carbon black ethylene glycol color paste has good storage stability with an estimated storage period of 26.8 months under the simulated natural sedimentation conditions.

Key words: self-dispersed, nanoscale carbon black, spun-dyed, polyester fiber, response surface optimization