Specific Work as a Useful Way to Describe Flow of Polyethylene During Injection Molding

The flow-induced polymer chain orientation and subsequent crystallization of polyethylene (PE) is a ubiquitous aspect of processing materials into final articles. Better understanding of how polymer flow affects morphology and crystallization will allow industry to better design materials for downgauging and recycling. While specific work has been shown to be a useful way to describe polymer flow using rheometers in a lab setting, little effort has been put into applying these ideas to commercial scale processing of polyethylene. Here we will describe how specific work can be used to describe the observed polymer orientation, morphology, and crystallization behavior in an injection molded bar. The position dependent flow, both through the thickness and along the length of the molded bar, can be described by modeling the specific work experienced by the material during the entire process.