Paper Number
PO93 

Session
Poster Session

Title
Flow induced crystallization of isotactic polypropylene

Presentation Date and Time
October 14, 2015 (Wednesday) 6:05

Track / Room
Poster Session / Atrium/Harborview

Authors (Click on name to view author profile)

1. Hamad, Fawzi G. (Penn State University, Chemical Engineering)
2. Colby, Ralph H. (Penn State University, Chemical Engineering and Materials Science and Engineering)
3. Milner, Scott T. (Penn State University, Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
Fawzi G. Hamad¹, Ralph H. Colby², and Scott T. Milner^1
1Chemical Engineering, Penn State University, University Park, PA 16802; ²Chemical Engineering and Materials Science and Engineering, Penn State University, University Park, PA 16802

Speaker / Presenter 
Hamad, Fawzi G.

Text of Abstract
Semi-crystalline polymers exhibit flow induced crystallization (FIC), in which brief intervals of strong flow followed by a temperature quench increases the nuclei number density and transforms the morphology. One main requirement for FIC is applying sufficient specific work (W = stress x strain) to form flow-induced nuclei. The objective of this study is to explore the relation between amount of specific work and crystallization kinetics, crystal morphology, and nuclei persistence time during FIC. The crystallization kinetics of isotactic polypropylene is studied in a rotational rheometer. Samples are sheared above Tm and then quenched below Tm while the phase angle (tand) is monitored at a fixed frequency and strain, as a sensitive probe of the onset of solid-like behavior after different shear conditions. The crystallization rate generally increases with increasing applied work, up to a value beyond which the rate remains constant. Samples with lower isotacticity show the fastest crystallization rates after shear (whereas quiescent crystallization rates show the expected opposite trend with tacticity). Using polarized optical microscopy and AFM, we image the changes in morphology of the previously sheared polypropylene sample. Micrographs show that flow promotes the formation of rice grain crystals that are roughly 4 µm long, and 1 µm in diameter. Flow-induced nuclei that promote this morphology have a long persistence time and require prolonged annealing at elevated temperature to erase. This persistence time was determined by monitoring the crystallization temperature of a sheared sample in the DSC after annealing at elevated temperatures until it returns to the quiescent crystallization temperature.