A New Instrument to Monitor the True Stress-True Strain-Birefringence Behavior During Multiaxial Deformation and Annealing of PET Films
With the recent and very fast developments in the polymer processing techniques, which led to very fast and highly productive production lines, the need for fast measurement and monitoring techniques has grown greatly. Knowing that, the off-line or after-the-fact characterization techniques are unable to track the very fast structural changes in the polymeric materials under processing, the demand for on-line fast measurements is increasing. One of the most useful techniques for characterizing the orientation and crystallization of the macromolecules is the birefringence where, optical properties depend on the molecular structure and strong birefringence can be observed if highly polarizable bonds (multiple bonds) are present and if, during processing, they adopt a preferred orientation. We have developed real-time spectral birefringence measurements systems to monitor true stress-true strain-birefringence behavior during multiaxial deformation and annealing of polymer films. The system is able to track the orientation, crystallization and developed stresses in the films in order to facilitate better understanding for the processing-structure relationships in polymeric materials.