Tear of Polyolefin Films, 1999 Polymers, Laminations & Coatings Conference Proceedings

Andy H. Tsou--Refractive indices in the three principal optical axes of PP and LLDPE films were measured with a prism-coupling device. The three principal axes in PP and LLDPE films coincide with the machine direction (MD), transverse direction (TD), and normal direction (ND). Planar birefringence (PBR) was calculated from measured refractive indices and used to evaluate the planar molecular orientation of both the crystalline and the amorphous phases of these polyolefin films. A moderate increase in PBR was found to raise the tear strengths of both PP and LLDPE films. This moderate increase in PBR can be realized by film casting or blowing. Similarly, the measured refractive indices were used to calculate in-plane birefringence (IBR) of the films studied. The ratio of tear in the transverse direction to that in the machine direction was found to be proportional to the IBR. However, a large increase in planar orientation reduced tear strengths of both PP and LLDPE films. This higher planar orientation brought on by biaxial stretching suppressed the plastic flow capability of the films leading to the lower tear strength.