Abstract
Optical birefringence (Δ) and tear resistance of tubular polyethylene films extruded under various conditions were measured. The results is as follows:(1) The value of Δ increases as the blow-up ratio decreases or the haul-off speed increases and a linear relationship between Δ and ψ110 is presented. With the aid of this relationship, Δ at ψ110=34°C (corresponding to the perfectly oriented Keller's type II) is evaluated as 9×10-8 by extrapolation, which nearly coincides with the theoretical value, 14.5×10-3.
This suggests that the orientation in most tubular polyethylene film is Keller's type II.
(2) The mesurement of retardation along the direction of thickness of the film indicates the non-uniformity of the crystalline orientation in the plane perpendicular to the machine direction.
(3) From the temperature dependence of the tear resistance of films and the relation between the direction of tear and that of crystalline orientation it may be concluded that the crystalline regions form the layyers parallel to the plane perpendicular to the machine direction and the amorphous regions are sandwitched between them.
