Dynamics and structure development in biaxially stretched polyethylene terephthalate films and stretch blow molded bottles

The processing of PET films and bottles involves biaxial deformations. This causes development of various complex morphologies in the final product which result in these bottles and films having, anisotropic properties. The stretch blow molding process involves essentially a confined free surface deformation which results in anisotropy of properties in all three major directions.

To study the complex deformations occurring in bottles and to determine various structural properties, dynamic behavior of bottle blowing and resulting structures must be identified and characterized. Initially amorphous and unoriented cast films of PET were stretched in simultaneous biaxial mode to various extension ratios. The resulting films were annealed with all dimensions fixed. These films were characterized with various techniques: density, DSC, wide and small angle x-ray scattering, Abbe refractometer, and tensile testing.

A novel data acquisition system has been devised and constructed to study transient kinematic behavior in stretch blow molding of PET bottles. The data obtained were used with membrane theory to calculate the stresses developed in the deforming parison. Additionally, the bottles produced were structurally characterized using the techniques mentioned above.