Rheological Properties and Melt Spinning Application of Controlled-Rheology Polypropylenes via Pilot-Scale Reactive Extrusion

Based on pilot-scale twin-screw reactive extrusion, the structural and rheological properties of controlled-rheology polypropylenes (CR-PPs) are investigated, where the effects of peroxide content and extrusion conditions such as screw configuration, extrusion temperature, and screw speed are prioritized. The active chain cleavage reaction by a small peroxide content of less than 600 ppm inside the extruder gradually increases the melt index and narrows the molecular weight distribution of CR-PPs, thereby affording favorable properties that are applicable to the fiber spinning process. The mechanical properties of CR-PPs are slightly degraded owing to the generation of unsaturated chain ends during the reactive extrusion, which suppresses crystal growth. Under all extrusion conditions, the chain scission and thermal degradation of polypropylene samples occur actively in the harsh twin-screw extruder compared with those in the mild twin-screw extruder. Finally, it is confirmed that CR-PPs can be suitably applied to the melt-spinning process for staple fiber production, thereby guaranteeing a more stable spinning process window against draw resonance instability.

Automated summary

This study investigates the structural and rheological properties of controlled-rheology polypropylenes (CR-PPs) using pilot-scale twin-screw reactive extrusion. The effects of peroxide content and extrusion conditions on CR-PPs are prioritized. It is found that a small peroxide content gradually increases the melt index and narrows the molecular weight distribution of CR-PPs, resulting in favorable properties for the fiber spinning process. However, the mechanical properties of CR-PPs are slightly degraded due to unsaturated chain ends generated during the reactive extrusion. The study confirms that CR-PPs can be successfully applied to the melt-spinning process for staple fiber production, ensuring a more stable spinning process window.