Flow Induced Suppression of Crystallization in Immiscible Polymer Blends

Controlling the crystallization behavior of recycled polymer melt blends during manufacturing is crucial for optimizing their mechanical properties and production. Shear and extensional flows, common in recycling processes or manufacturing with recycled materials, can yield flow-induced crystallization in polymer blends by enhancing molecular alignment and nucleation of crystallites. However, we propose a novel phenomenon of the exact opposite behavior- flow-induced suppression of crystallization (FISC). Under specific conditions, scaling arguments indicate that flow can suppress rather than promote crystallization. The suppression is predicted to occur when the concentration of nucleating agents within the polymer droplets dispersed in a matrix is below the critical level required for heterogenous crystallization to occur. This work explores the effect of the flow conditions (shear rate and crystallization temperature) on FISC in a blend of polypropylene droplets dispersed in a polycaprolactone matrix. We control the nucleation density and droplet size by modulating the crystallization temperature and shear rate, respectively. We explore the relationship between the crystallization temperature, which modifies the number of nucleated crystallites per unit area, and the shear rate, which decreases the droplet diameter. We further explore the relationship between FISC and the well studied flow induced crystallization. These findings help broaden the parameter space for processing of recycled polymer blends to achieve a wider range of materials properties.