Solid State Cross-Linked Polypropylene via Reactive Extrusion: A Scalable Approach

Solid-state reactive extrusion provides a promising route for modifying semicrystalline polymers while minimizing degradation associated with conventional melt processing. Here, isotactic polypropylene was modified using benzoyl peroxide at 110 °C, below the polymer melting temperature. Under these conditions, radical reactions occur within the amorphous regions of the semicrystalline matrix while crystalline lamellae remain intact and restrict large-scale chain motion. FTIR and ¹³C CP-MAS NMR analyses indicate that the polypropylene backbone is largely preserved after processing. Differential scanning calorimetry shows increased crystallization temperatures and reduced crystallinity, consistent with restricted chain mobility and network-induced nucleation. Rheological measurements reveal a progressive increase in the storage modulus with increasing peroxide concentration and a transition toward predominantly elastic behavior with the absence of G'/G" crossover, indicating increased molecular connectivity and network formation. Compared with conventional melt-state peroxide modification, the solid-state approach promotes intermolecular connectivity while limiting degradation pathways, providing an energy-efficient and scalable strategy for tailoring polypropylene properties.