Describing the solidification process is very important in polymer processing. In polypropylene (PP), the increase of viscosity, named stiffening or hardening, is determined by a rise in crystallinity. When PP flows in a channel or is stretched on a chill roll, the stress induces an anticipated crystallization and thus can lead to an unexpected solidification. This study explores how flow fields influence the crystallization behavior of PP. A controlled-stress rheometer was used to investigate the effect of short shear stress steps on crystallization kinetics. The results revealed that applying a stress step significantly increased the rate of crystallization compared to a non-stressed sample. This acceleration is attributed to the stress-induced orientation of macromolecules, which promotes nucleation. Furthermore, longer durations of the applied stress led to faster viscosity increases, indicating a higher nucleation density with increased stress exposure. A mastercurve approach validated the consistency of the model describing the stress-crystallization relationship. The calculated parameter relating to nucleation density confirmed a linear increase with stress duration, allowing estimation of the nucleation rate during shear.
Hamdi, A. (2024). Experiments and analysis of stress induced stiffening of a polypropylene. Polyolefins Journal, (), -. doi: 10.22063/poj.2024.3622.1308
MLA
Ahmed Hamdi. "Experiments and analysis of stress induced stiffening of a polypropylene". Polyolefins Journal, , , 2024, -. doi: 10.22063/poj.2024.3622.1308
HARVARD
Hamdi, A. (2024). 'Experiments and analysis of stress induced stiffening of a polypropylene', Polyolefins Journal, (), pp. -. doi: 10.22063/poj.2024.3622.1308
VANCOUVER
Hamdi, A. Experiments and analysis of stress induced stiffening of a polypropylene. Polyolefins Journal, 2024; (): -. doi: 10.22063/poj.2024.3622.1308
)