AbstractNylon 3 fibers were produced by wet spinning, and properties and structures of the fibers were investigated. Fiber‐ and film‐forming abilities of nylon 3 dopes in various coagulants, using various solvents, were investigated and it was found that only the nylon 3 spinning dope dissolved in formic acid showed excellent fiber‐ and film‐forming abilities in coagulation baths of ethers, esters, or alcohols. As for mass transportation in these coagulants, solvent (formic acid) was diffused into coagulants, with scarce penetration of the coagulants into protofibers. This was due to the fact that these coagulants had moderate solubility parameter values and moderate proton‐accepting power, which means the existence of some interaction between solvent and coagulants and no interaction between coagulants and polymer. Protofibers thus obtained were already crystallized and stretching them at room temperature was impossible. However, in such media as silicone oil, hot air, and Wood's metal, which were thought to have no interaction with polyamides, nylon 3 fibers were stretchable above their glass transition temperature (170°–180°C), while in such media as hot water, hot glycerin, and hot steam, which were thought to have some interaction with polyamides, nylon 3 fibers could not be stretched. Mechanical properties of nylon 3 fibers were as follow: strength, 2–3 g/d; elongation, 10–20; Young's modulus, 11 × 105–17 × 105psi. High Young's modulus, high transition temperature, and high moisture regain are pointed out as characteristic features of nylon 3 fibers, compared with o
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