Microstructure and crystal modulus of polyamide 4 α-form in the direction parallel to the chain axis

Polyamide 4 (PA4) is a lactam-based aliphatic synthetic polymer with promising properties and admirable biodegradability. In this study, oriented PA4 fibers were fabricated by dry spinning followed by thermal drawing. Elastic modulus (El) of the crystalline regions (crystal modulus) of PA4 fibers in the direction parallel to the chain axis was evaluated from the X-ray diffraction peak shift owing to the tensile stress. The apparent El value of PA4 is 67 GPa for meridional 004 reflection and 119 GPa for 0010 reflection, respectively. The reason for the different El is that the decrease of crystallite size of PA4 by the applied stress brought extra shifts of 004 reflection peak to lower angle based on the Laue factor. In contrast, 0010 reflection peak received less effects from this effect, and the El value of 119 GPa obtained from 0010 reflection was considered to be a reliable value. The observed El value of PA4 is much lower than the calculated values assuming fully extended planar zigzag skeleton for PA4. Thus the low El value is attributed to the highly contraction (−1.9 %) from the fully extended conformation as observed for another polyamides. [Display omitted] •The crystal modulus El of polyamide 4 α-form in the chain direction were obtained as 69 GPa and 119 GPa from 004 and 0010 reflections.•The crystal modulus El of polyamide 4 α-form was corrected as 119 GPa, with Laue factor and structure factor using Hoseman's method.•The relatively low El of polyamide 4 was attributed to the chain contraction.