Directional properties of positive impulse tree propagation in oriented PET and PP barrier films molded in EVA

In this paper, we describe the directional properties of positive impulse tree propagation at an ethylene vinyl acetate copolymer (EVA) base polymer/oriented barrier film (polyethylene terephthalate (PET) and polypropylene (PP)) interface. It was found that, for biaxially oriented PET and PP barrier films, after a positive impulse tree enters a film, the tree develops preferentially in both directions of the machine direction (MD) and transverse direction (TD) drawings of the barrier film. It was also found that, for uniaxially oriented PP barrier films, after the tree enters a film, the tree develops preferentially in the direction of the MD drawing of the barrier film. These results indicate that the preferential direction of positive impulse tree propagation in oriented PET and PP films is closely related to the microstructures of oriented molecular chains in PET and PP barrier films.