Controlling the extent of nano-lamellar crystalline orientation is of great interest in polymer processes because an inexpensive plastic film can be converted into a higher valued film of dramatically improved properties. Where high degrees of uniaxial orientation are required, the polymer is typically oriented in a solid state drawing post-processing operation, where the polymer is stretched in a single direction at temperatures just below the melting point. One commercial example, currently drawing wide interest in the polymer processing field, is known as machine direction orientation (MDO). During this process, pre-existing nano-crystallites are transformed into rigid, anisotropic structures. The presence of these rigid structures significantly enhances the moduli and break strength of the polymer film. A direct connection can be formed between the polymer's analytic characteristics, MDO processing conditions and the final engineering properties of the film.
Within this dissertation are:
Structure-property model applicable to a wide variety of polymers that predicts critical properties of the oriented film.
Process model that estimates the film temperature throughout the orientation process, a necessity for relating the effects of processing conditions to the properties of the film.
Experimental examples of the use of the structure-property model, which provides a detailed description of the structural changes that are occurring during orientation.
This dissertation provides several comprehensive tools for the understanding and the modeling the process-structure-property relationship of oriented polymer films. A universal structure-property model has been developed that predicts the critical properties of a wide range of oriented polymer films. A heat transfer model has also been developed that estimates the film temperature throughout the orientation process. This model can be used in conjunction with the fiber/non-fibrous gel model to understand the effects of orientation conditions and equipment design on the film properties, as well as for the optimization of processing conditions and equipment design. Three independent experiments (LDPE, MDPE and ULDPE) were conducted that utilized the fiber/non-fibrous gel model, along with SAXS, XRD, DSC and mechanical testing, which provided a global understanding of the structure-property relationships that are occurring during orientation. With this knowledge, the structure can be controlled to produce films with specific physical properties.