Ethylene α-olefin based linear low density polyethylenes (LLDPE) that exhibit the processability of high pressure, low density polyethylenes (HP-LDPE) are being developed by The Dow Chemical Company as a new polymer family. These High Processability Polymers (HPP) are produced via Constrained Geometry Catalysts (CGC) Technology, which includes the unique single-site catalyst and process technology that has gained recognition through the commercial successes of Polyolefin Plastomers (POP), Enhanced Polyethylenes (EPE) and Polyolefin Elastomers (POE). This HPP family can be split into several product types which exhibit different combinations of extrusion processability and film performance. By understanding the effects of long chain branching, molecular weight distribution and short chain branching distribution, polymer design can be used to match properties with the application performance requirements. This paper will discuss each of the HPP product types, and the versatility of the Constrained Geometry Catalysts Technology to meet the performance requirements of each type.

Coextrusion of flat films and sheets involves the simultaneous extrusion from a single die of multiple layers of polymer melts. Multilayer coextrusion provides an important approach to provide unique product properties through the selection and combination of different polymers within one product. Two families of dies include manifold dies, where the melts meet outside the die, and feedblock dies, where the melts flow in contact within the die cavity. In feedblock type dies, the problems of layer nonuniformity and interfacial instability have received considerable attention in the literature. Recent experimental and computational results have shown that layer nonuniformity (sometimes referred to as encapsulation) is affected by the viscosity and flowrate ratios of the polymer melts, die geometry and normal stress differences. Instability at the interface is also affected by the same quantities, but the elastic contributions are not as clearly understood. This article reviews recent progress in the simulation of flat die coextrusion.