An Investigation of Structure-Property Correlations in Polyethylene Terephthalate Films.

摘要

Six characteristic types of polyethylene terephthalate (Mylar) films were studied by x-ray diffraction techniques. The degree of crystallinity, extent of preferred orientation, crystallite sizes, and paracrystalline disorder were evaluated. The tensile properties were measured in directions parallel and normal to the trace of the optic axial plane as well as in the machine and transverse directions of stretch. The influence of crystallite orientation on the mechanical properties is discussed. The exceptionally high strength in the machine direction of type 142T film may be associated with the high degree of orientation achieved by a two-way stretch followed by a post-stretch in the machine direction. The balanced, physical properties in type 1000S film are likewise attributable to the presence of two-way stretches in mutually perpendicular directions. The influence of crystallinity was masked by the anisotropic disorder arising from varying degrees of preferred orientation. The techniques employed are indicated to be applicable to other polymeric materials.