Theory and methods toward an understanding of flow-induced crystallization of isotactic polypropylene

Open Access
Author:
Howard, Michael Patrick
Area of Honors:
Chemical Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Scott Thomas Milner, Thesis Supervisor
  • Ali Borhan, Honors Advisor
Keywords:
  • crystallization
  • polypropylene
  • nucleation
  • shear flow
Abstract:
The flow-induced crystallization (FIC) of polyolefins is an important part of many industrial processes such as injection molding. Injection molding is used to make a variety of commercial products ranging from piping for chemical plants to everyday goods like water bottles and children’s toys. It is well-documented experimentally that FIC can accelerate the rate of crystallization for isotactic polypropylene by a factor of one hundred (changing the crystallization time scale from a matter of hours to seconds), and also greatly affects the material properties of the crystallized product. Yet, the underlying physics of FIC are poorly understood. Some hypothesize that FIC occurs because flow reduces the melt state entropy, and thus eases the transition from melt to crystal. In order to test this hypothesis, it is necessary to understand (1) how crystals form in commercial melts, and (2) how flow might affect the entropy of the melt. Here we present two important steps towards understanding this phenomenon: a model for quiescent crystal nucleation in commercial melts, and a method for simulating dilute polymer solutions in flow. Ultimately, these may be combined with data from melt rheology of entropy reduction due to flow to predict the effects of FIC in commercial processes.