Studies were carried out to determine the crystalline elastic modulus E1 along the chain axis for the α‐form of nylon‐6 [poly(ε‐caprolactam)] by X‐ray diffraction. To obtain an inherent E1 value of this polymer the problem was solved that different orders of meridional reflections give different E1 values. Thus the disagreement was found to be due to the increase of the crystallite size by the applied stress. When corrected for this effect, the values from the 040 and 0.14.0 reflections agreed well with each other. The resulting modulus was 183 GN/m2 at 23°C, which was much lower than a theoretically calculated value of 262,8 GN/m2 for the fully extended structure model by Manley and Martin. This seems to be due to the slight shortening at the amide group of the molecular chain because it was confirmed from the intensity changes of the 040 and 0.14.0 reflections of this polymer by the applied stress that the amide part is more extensible than the polymethylene section. Judging from similar considerations the previously reported E1 values for nylon‐66 and nylon‐6,10 are valid.
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Kaji et al. (1978) studied this question.