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A solvent-dyeing process for aramid fibers is described which is capable of producing fiber and fabrics having excellent depth of shades. The brightness of the fibers and fabrics is quite high when the undyed fibers are bright. When properly selected basic dyes are used, and when heavy shades are developed on the fabrics, good dyed lightfastness values are obtained. Carpet samples of Nomex® dyed via the solvent-dyeing process described are considerably brighter, cleaner, and deeper in shades than commercial carpet samples of Nomex dyed using the producer-recommended dyeing process. Moreover, the dyed lightfastness values (Gray Scale) are considerably higher for these solvent-dyed carpet samples. Thus. ratings as poor as 2 and 1 after, respectively, 20 and 40 hours in the Fade-Ometer were obtained on the commercial carpet samples, whereas certain of the test samples rated 2—3 even after 320 hours.In addition to the improvement in dyeing obtained with the solvent-dyeing process, it was observed that the aramid fibers based on poly-m -phenyleneisophthalamide (MPD-I) and the polyisophthalamide of 4,4'-methylenedianiline (MDA-I) apparently undergo a certain degree of relaxation. For example, on blank dyeing in pyridine the tenacity of the wet-spun MDA-I fiber decreased only slightly, while the initially somewhat low elongation-to-break value increased significantly. For Nomex 10 dpf staple the average elongation-to-break value increased slightly, but the range of this value narrowed considerably. Two rigid, rod-like, wholly aromatic fibers, the DuPont Company's Kevlar® aramid fiber, and the Monsanto Company's experimental X-500 polyamide-hydrazide fiber, do not show the same type relaxation effects exhibited by either MDA-I or MPD-I ( i.e. Nomex). Thus, the tenacity of the Kevlar increased somewhat, and the initial modulus values for both rod-like fibers increased moderately.

Aromatic polyamides of the AB, AA–BB, and ordered copolyamide types plus aromatic hydrazide and amide–hydrazides were prepared via the phosphorylation reaction. The relationship of the molecular weight, as evidenced by the inherent viscosity values obtained, of the several polymers to the structural features and properties of the monomers used and the polymers obtained is discussed in detail. Some salient observations are that poor solubility of the rodlike polymers definitely appears to set limits to obtaining high molecular weight and strongly basic groups, e.g., —CO—NH—NH2, in monomers, prevent the attainment of high molecular weight because such groups coordinate more strongly with the phosphite complex than does the pyridine catalyst in the phosphorylation reaction. Fibers were spun from two aromatic polyamides prepared via the phosphorylation reaction. Excellent tensile properties were achieved for fiber from poly–p–benzamide (PPB) and the polyisophthalamide of 4, 4′‐methylenedianiline despite the relatively low molecular weight of these polymers (?7inh 1.6 and 1.1, respectively). The PPB fiber was spun from both isotropic and anisotropic spinning solutions. Fiber obtained from the anisotropic dope had moderately high tensile strengths (8–12 gpd) and remarkably high initial modulus values (435–745 gpd). These results indicate that polymers made by the phosphorylation route would give fibers with as high tensile properties as polymer made by the diacid chloride‐diamine polycondensation route providing that the inherent viscosities of polymer prepared by the former process could be increased to equal those by the latter process.