Internal stresses in glassy polymer materials arise from two different sources; deviation of polymer conformation from its equilibrium state and change of intersegment distances. These stress components may be separately observed by carrying out simultaneous measurements of tensile stress and birefringence relaxations of polymer films, assuming that they are additive. It is pointed out that the change of intersegment distances occurs first, and conformational deformation is gradually induced if a glassy polymer film is elongated.

The heat transfer characteristics of a plastic film were experimentally studied using a two-dimensional plane model apparatus of a double bubble tubular blown film process, which is one of the most important methods of polymer processing to produce a biaxially oriented film. In the model apparatus, a polyethylene film was heated by infrared heaters and cooled by plane air jets. The radiation absorptivity of the film was estimated on the basis of the temperature and irradiation measurements of the film that was cooled by natural convection, i.e., without the air jets. The convective heat transfer coefficient on the film cooled by the air jets was evaluated using the estimated absorptivity of the film.

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