Rheological and Architectural Control of Flow-Induced Crystallization

1067554

Milner

Polypropylene (PP), the second-most prevalent synthetic polymer in the world, is used in a vast array of products that are commonplace in daily modern life. In nearly all applications, PP and other semicrystalline polymers are transformed from pellets to a final product in a process that involves melting, flow, and crystallization.

Flow-induced crystallization (FIC) makes the processing practical. Imposing a large and sudden shear flow on a cooling melt greatly speeds up crystallization, and profoundly changes the material properties of the final product.

This commercially important phenomenon is not well understood. Previous studies have been hampered by the lack of three essential ingredients: the right model polymers, rheology to confirm how flows orient and stretch the polymer chains, and a physics-based theory of crystallization in polymers and how flow affects it.

Our proposal combines:1) a unique capability to synthesize PP model combs with controlled architecture; 2) experimental and theoretical expertise in rheology of polymer melts; and 3) a successful theory for nucleation of polymer crystals, which can be extended to address the effects of flow.

Graduate students trained in design of PP additives will be in high demand in the US plastics industry in the coming decade. Students supported by this proposal will benefit from collaboration with industrial scientists from ExxonMobil Corporate Research, and international experts at the University of Sheffield. All three PIs worked in industry before coming to Penn State, enabling them to provide their students a strong industrial perspective. As well, this research area offers many opportunities for undergraduate research in synthesis, rheology, and simulations.

Leading polyolefin manufacturers are working to develop long chain branched PP (LCBPP) for improved melt processability. Similar architectures are hypothesized to be effective in controlling FIC. Discoveries we make regarding control of FIC can likely be translated to industrial practice.

Understanding FIC may be important as well for effective processing of semiconducting and conducting polymers in electronic and photocell applications, where device performance is strongly affected by crystallite size and orientation.