Investigation of the orientation distribution functions in drawn polyethylene by broad line nuclear magnetic resonance

Measurements have been made of the anisotropy in the nuclear magnetic resonance second moment for the proton resonance of a number of drawn polyethylene films. The results are used to obtain orientation functions for the films, on the basis of a model in which a drawn film is regarded as an aggregate of units which are aligned by the drawing process. The experimental results for low-density polyethylene are compared with the prediction of the affine deformation theory, in which the unique axes of the units undergo the same changes of direction as lines connecting pairs of material points in a body undergoing uniaxial deformation, without change of volume. Reasonable qualitative agreement is obtained. Orientation functions are then obtained directly from the experimental results and used to predict the mechanical anisotropy of the films. Good agreement is obtained with previously reported mechanical data. Finally an attempt is made to obtain the shape of the distribution function at each draw ratio. With the exception of the lowest draw ratio film this is less successful, due to the small number of spherical harmonic functions which can be obtained from the anisotropy of the second moment.