Linking process conditions with polymer properties for the LDPE process

Low Density Polyethylene (LDPE) is a polymeric material of great importance on the global marked. Its applications range from commodity purposes such as films, tubes and packaging to the specialty sector including medical products such as implants. One of the characteristics of LDPE is its unique polymeric microstructure exhibiting short- as well as long-chain branching (SCB and LCB) and a broad molecular weight distribution due to the free radical polymerization conditions. The polymeric microstructure of the polymer is mainly dependent on the polymerization process conditions and determines the final product properties and thus also the application area. However, experimental investigations of the free radical polymerization of ethylene are very costly due to the high-pressure (up to 3000 bar) and high-temperature (up to 300°C) conditions. Thus, there is a need for a simulation-based tool to link the process conditions with the resulting LDPE properties. This work presents the successful implementation of a three-step multi-scale modelling approach to reach this aim. A visualization of this approach as well as the benefits of the individual steps is depicted in figure 1. The first step consist of modeling the complex kinetic network of the free radical polymerization of ethylene. Kinetic coefficients can be taken from literature [1] and the numerical solving of the resulting system of differential equations is conducted by the software Predici [2]. This yields average product properties, such as branching densities per 1000 carbon atoms (SCB/1000C and LCB/1000) as well as the molecular weight distribution. Those can be validated against 13C-NMR measurements as well as high-temperature size-exclusion chromatography. Please click Additional Files below to see the full abstract