Orientation studies on drawn polyolefins

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Abstract
The effect of different thermal treatments on the degree and type of orientation produced by cold drawing three polyolefin films: polyethylene, polypropylene, and polybutene‐1, was studied by two complementary techniques: x‐ray diffraction for the measurement of crystal orientation and birefringence for the measurement of the total film orientation. Variations in the texture of these polymer films were characterized by these techniques as well as by density, tensile stress measurements and photomicrographs. The birefringence–strain data showed a decrease in birefringence values at a given strain as the polymer side group size increased. This decrease appears to be associated with a more symmetrical polarizability ellipsoid and hence a decrease in crystal birefringence. The birefringence–strain curves for the same polymer system showed a decrease in birefringence value at a constant strain with increased annealing. X‐ray diffraction data indicate that the a and b axes in both polyethylene and polybutene‐1 film orient by different amounts at a given strain. Polypropylene, on the other hand, shows equal amounts orientation of the a and b axes. The different orientation behavior for these polymer systems is discussed in terms of variation in the ease with which polymer crystals may be deformed.