Effects of molecular weight on the drawing and the draw efficiency of nylon-6

Tensile drawing was carried out on nylon-6 films of different viscosity ave rage molecular weights (M-v = 77 and 440 x 10(3)) and crystalline forms (al pha- and gamma-forms). The effects of M-v on the deformation behavior and t he draw efficiency were discussed on the basis of the stress/strain curves recorded upon hot drawing, and wide-angle and small-angle X-ray diffraction , birefringence and tensile properties for the draw ratio (DR) series. The draw stress at a given strain and the fracture stress upon hot drawing were both higher for the higher M-v than for the low M-v, in either the alpha- or the gamma-form sample. For a given M-v, the draw stress was lower for th e gamma-form than one with the alpha-form and the fracture stress was indep endent of the crystal forms, leading the former crystalline form to have a higher drawability than the latter, as previously reported. The M-v and the crystal form of predrawn samples had no effect on the crystalline chain or ientation function (f(c)) measured as a function of DR. In contrast, the dr aw efficiency evaluated from the amorphous chain orientation function (f(a) ) vs. DR and the tensile modulus and strength vs. DR was significantly high er for the higher M-v than for the low M-v. These drawing characteristics w ere discussed in terms of the entanglement effect and the deformability of the two crystal forms. The maximum achieved tensile modulus of 7.7 GPa and a strength of 760 MPa were thus obtained by the straight tensile drawing of the higher M-v sample that was initially a gamma-form. (C) 2000 Elsevier S cience Ltd. All rights reserved.