Low-Density Polyethylene - New insights into an old material under comparative studies using SEC-MALS, AF4-MALS, HT-HPLC and 2D-LC

LDPE can be produced by different types of autoclave or tubular reactors, which can also be cascaded. An important effort is to obtain materials with autoclave-process equivalent properties from tubular technology due to economic reasons. In this way, the molecular understanding of the materials attains a key role. Five LDPE materials were characterized, covering three applications (extrusion coating, blow molding, and film blowing) as well as three reactor technologies (type I autoclave, tubular type, and type II autoclave). SEC-MALS, SEC-IR, AF4-MALS, HPLC, and 2D-LC allowed a detailed characterization of the samples’ molar mass and branching structure while providing a unique opportunity for technique comparison. This allowed for an unprecedented understanding of the differences in molecular structure and the influence of application vs. reactor technology driven differences.
Overall, SEC-IR-MALS was found to provide the most versatile information, making it an excellent choice for an initial characterization. Furthermore, the results indicate that the intended application (and thus property profile) influences LDPE structure much more than reactor technology. All five studied samples exhibit differences in molar mass distribution, short-chain as well as long-chain branching. Yet, the three extrusion coating samples (each derived from a different reactor type) appeared notably similar to each other with regard to each parameter.