Preparation And Characterization Of Cationic Dyes Dyeing Nylon 6

Unmodified nylon is dyeable to a single color only and is almost exclusively dyed with acid dyes that are absorbed with amine groups by strong ionic bonds or electrostatic gravity. Nylon fibers are severely and permanently stained by certain artificial and natural colorants present in common household items. The vast majority of these colorants are acid dyes, all of which have been approved by the Food, Drug and Cosmetic Commission for human consumption, for example:FD&C Red Dye NO. 40. As for acid dye-resistant, the nylon 6 which is affinitive to a basic dyes is demanded.The application of basic dyes which are absorbed by carboxyl groups of the nylon molecules, results in colored nylon having unacceptable wash and light fastness properties. Based on traditional caprolactam hydrolytic polymerization, two types of polycaprolactam (PA6) copolyamide were successfully prepared with 5-sulfoisophthalic acid monosodium salt (5-SSIPA) and poly (ethylene glycol) (PEG) units named as cationic dyeable polyamide (CD-PA6) and easy cationic dyeable polyamide (ECD-PA6). The modified molecules serve a dual role. Firstly, it provide sulfonate groups which can be activated to absorb basic dye under acid conditions without activation of carboxyl groups, thereby providing color of acceptable wash and light fastness. Secondly, they impart acid dye-resistant properties to the nylon by forming salt with amine end groups, thereby rendering these amine groups no longer available to absorb acid dyes.The chemical and crystalline structures of CD-PA6 and ECD-PA6 were characterized by Fourier transform infrared spectroscopy (FT-IR) and wide angle X-ray diffraction (WAXD), and their thermal properties were tested by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG), respectively. In addition, the rheological behavior and cationic dyeable ability of copolyamide were presented in this paper. The influence of chemical modification in polyamide 6 fibers on the dyeing properties was investigated using cationic dye (methylene blue). It shows that the crystallinities and degradation temperature of samples which corresponded to different mass losses of CD-PA 6 and ECD-PA6 declined as a sulfonic group content increased. However, the viscosity of modified PA6 improved with the increase of 5-SSIPA. The incorporation of PEG not only destroyed the regularity of molecular chain arrangement and created more amorphous regions ofECD-PA6 samples, but leads to nylon 6 from α-form to γ-form. In additional, the crystallinities, viscosity and degradation temperature of samples declined as PEG increased but storage modulus improved. According to dyeing experiment, it revealed a distinct improvement of tinctorial affinity and wash fastness to modified fibers compared with those unmodified. In the case of modified polyamide 6, an increased in the mole percentage of 5-SSIPA led to an increase in the amount of cationic dye absorbed onto fibers. Especially, according to the analysis, compared with CD-PA6 at the same quantity of 5-SSIPA, the incorporation of PEG significantly improved the dyeability of ECD-PA6.