The development of molecular orientation during formation of cellulose film from viscose

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Abstract
The distribution of molecular orientation in cellophane and its correlation with processing conditions have been studied by means of optical retardation measurements. With thin sections of cellophane cut with a standard microtome edge views were obtained, and it was possible to measure optical retardation profiles of the sections. This yielded information about the variation of molecular orientation in different layers of the film. In lanes near the edge of the machine‐cast sheet the machine direction orientation was higher than in center lanes. In layers near the surface, machine direction orientation was higher, and transverse direction orientation was lower than in center layers. Studies of shear induced orientation in viscose indicated that this did not persist long enough to contribute to the structure of cellophane. The distribution of molecular orientation in cellophane was explained in terms of the forces acting on the web during and after coagulation and regeneration. These include the viscous drag of the treatment baths, the internal friction as the viscose is drawn outside the extrusion die, the tendency of the film to shrink during its formation and drying, and the tentering action of machine rolls.

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