Rheological investigation of partially crystallized polymer melts

Modern molecular-based rheological models for polymer melts connect molecular weight distribution, long-chain branching distribution, and rheology. Unfortunately, they are typically limited to completely molten polymers, whereas the arrangement of crystalline and amorphous domains is primarily responsible for the mechanical properties of semi-crystalline polymers. Molecular architecture affects the development of crystallites along with the material's rheology as a semi-crystalline polymer crystallizes.

In this work, we explore the relationships between short-chain branching (SCB), crystallite/amorphous domain arrangement, and rheology of partially crystallized polymers. We apply multi-scale modeling and rheo-Raman measurements to industrial-grade linear low density polyethylenes. SCB variations, usually implicit in the melt rheology, manifest strongly in the structure of the network formed from crystallites and polymer chains participating in both amorphous and crystalline domains. We use the Monte-Carlo copolymer crystallization model to distribute monomers between crystalline and amorphous phases. Then the entanglement-level discrete slip-link model (DSM) uses free, bridging, and dangling chains in the amorphous domain to calculate the rheology of semi-crystalline material.