Abstract:

Objective The conventional dyeing of polyamide 66 (PA66) has the disadvantage of poor uniformity, color depth and color fastness, and also has other problems such as serious environmental pollution and high energy consumption. Dope dyeing refers to adding colorant during and after the polymerization process to produce colored fibers during fiber spinning. In order to meet the increasingly stringent environmental requirements, the dope dyeing technology has high practical value and good prospects for development. In this research, PA66 salt-based carbon black dispersion was prepared, which was further used as a colorant in dope dyeing of PA66.

Method Self-dispersible carbon black (SPCB) was prepared by combining ultrasonic dispersion with spray drying, which was then dispersed in PA66 salt solution to prepare PA66 salt-based carbon black dispersion, PA66 masterbatch was prepared by in situ polymerization method, and finally PA66 film was further prepared by melt blending method. The factors of PA66 salt-based carbon black dispersion were investigated by estimating its particle size and stability. The SPCB influence on the performance of PA66 film was analyzed.

Results Among the dispersants NNO, Tween 20, SMA and polyvinylpyrrolidone (PVP), it was found PVP is the best dispersant to prepare the PA66 salt-based carbon black dispersion with small particle size and good stability. The influence of mass fraction of carbon black, ultrasonic time and power on the dispersion process was investigated. The optimum preparation process was as follows. The mass fraction of PVP to carbon black was 15%, the mass fraction of carbon black to the system was 10%, the ultrasonic treatment power was 1 260 W, and the time was 80 min. The average particle size of the prepared PA66 salt-based carbon black dispersion was 184.1 nm, the centrifugal stability was 96.20%, and the placement stability was 91.85%. The spray-dried SPCB surface was successfully coated with PVP. Compared with the original carbon black, SPCB showed better self-dispersing properties with a narrow particle size distribution. The average particle size of SPCB was 202 nm, which was about 30 nm larger than that of the carbon black dispersion before spray drying. The pigment particles were evenly dispersed in the PA66 matrix with a particle size of about 200 nm. With the increase of SPCB mass fraction, the color change value of PA66 film gradually became smaller, the color tended to be saturated, and the uniformity was better. At SPCB mass fraction of 0.2%, the K/S value was 9.20, L^* value was 26.82, a^* value was -0.04, and b^* value was -0.55. However, the distribution of pigment particles in the matrix hindered the movement of macromolecular chains, which hindered the crystallization of PA66. The melt temperature of the prepared PA66 film was 259.2 ℃, the crystallization temperature was 230.8 ℃, and the crystallinity was 36.5%.

Conclusion Compared with conventional dyeing, dope dyeing enables PA66 to be prepared with better uniformity, color depth and color fastness, dope dyeing is also a cleaner and greener coloring technology. The most critical issue of dope dyeing is to improve the compatibility and dispersion of pigments in PA66 matrix. The pigments were modified by coating through ultrasonic dispersion and spray drying technique in combination, and PA66 masterbatches were prepared by in situ polymerization after mixing with PA66 salt solution. The results showed that no large particle agglomeration occurred in SPCB in PA66 matrix, and the particle size was 200 nm, which indicated that the experiment improved the compatibility and dispersion of pigments in PA66 matrix very well. The research results show that PA66 salt-based carbon black dispersion is a good colorant for dope dyeing of PA66.

Key words: dope dyeing, self-dispersible carbon black, polyamide 66, polyvinylpyrrolidone, spray drying, in situ polymerization