Anisotropic mechanical properties of drawn nylon 6. II. The γ phase

Abstract

Cold-drawn, uniplanar axially oriented sheets of nylon 6 have been annealed at 195°C, hot-rolled at 130°C, and then chemically treated with iodine (KI₃ aqueous solution) to form the γ crystalline phase (called γ _I ). As with the α phase, the morphology is parallel-lamellar with the molecular chains at right angles to the lamellar plane. The long period is 98.2 ± 0.7 Å. The hydrogen bonds form layers in the crystallite (100) planes which are at about 60° to the sample sheet, whereas in a they formed layers in the (001) planes which lie in the sheet. The extensional compliances S₃₃ (in the draw direction) and S₁₁ (the transverse direction in the sheet) and the shear compliances S₄₄, S₅₅, and S₆₆ have been measured at 20.0 ± 0.3°C by dead-loading creep and torsional methods, in two relative humidity ranges, 0—10% and 61–69% RH. Dependence upon time and humidity have also been determined. In contrast to the α form, the extensional compliances do not show a cross-over of S33 above S₁₁ when the α_a transition or T_g is reduced to near room temperature by increasing the relative humidity from zero to 65%. The results are interpreted by using Takayanagi models for the extensional compliances and interlamellar or crystallite shear for the shear compliances. The overall anisotropy is less in γ_I than in α. This is a consequence of the kink in the molecular chains in γ_I which reduces both the extensional modulus of the crystallites and the intracrystalline shear.