Characterization of impact modified, biaxially oriented poly (vinyl chloride) films

Stretch blow molding bottles produces biaxial deformations which result in anisotropy in the three major directions. With the advent of an increasing use of poly(vinyl chloride) in stretch blown bottles, a characterizational study of this anisotropy and ensuing mechanical behavior was performed. The result of an additional parameter of incorporating impact modifier into the system was also studied.

To produce a wide variety of testing conditions, PVC bottle formulations were stretched with a Long Extensional Tester. Selected parameters could be more easily controlled and manipulated by this approach than by stretched blow molding bottles.

Birefringence was found to be an adequate technique to describe the orientation of unmodified and impact modified (MBS) biaxially stretched PVC film. Trends found in the birefringence data generally coincided with trends found in mechanical properties, particularly the impact properties.

Tensile strength, modulus and impact strength were found to increase as the biaxial stretch ratio was increased. However, a maximum in these properties was found to occur at a 2 x 2 stretch ratio for unmodified PVC film and at a 2.A x 2.4 stretch ratio for film modified with 5 to 15 phr of impact modifier. The elongation was found to increase with the addition of impact modifier in the unstretched film, but decrease with any biaxial stretching.

Biaxial stretching or impact modification alone was found to be effective at increasing the impact strength. However, when these two treatments were combined, the impact modifier was found to have little or no effect on the impact strength above that produced from biaxial stretching.