Understanding changes in the microstructure of polyolefins during reactive extrusion

Reactive extrusion is a common approach in industry to modify polymer structures and obtain and modify some of their properties. To increase the melt flow rate (MFR) in polypropylene (PP), adding peroxide during extrusion is a very common application. By adding peroxide, the molecular weight of PP is reduced by β-scission [1]. More advanced modification of the polymer structure can be performed by adding a radical initiator like a peroxide an coupling agent [2] or adding another polymer [3] or a combination of both to obtain graft polymers with the target polymer properties. This combination of different substances in conjunction with the radical process leads to variety of products and by-products, which makes the proper characterization of the various products quite challenging.

In this presentation, the characterization of two different polyolefins, LCB-PP and a HDPE-g-PP, obtained by reactive extrusion processes is presented.

To better understand the influence of chain architecture on the melt relaxation dynamics of LCB-PP, a combination of NMR spectroscopy and GPC-V-MALS was employed [2].

HDPE-g-iPP molecules were generated via reactive extrusion without the use of a coupling agent and were identified within the HDPE/iPP matrix using advanced hyphenated fractionation techniques, including cross-fractionation chromatography and two-dimensional HPLC in combination with spectroscopic techniques like IR. The effect of HDPE-g-iPP as a compatibilizer was confirmed by thermal, dynamic mechanical, and morphological analysis, as shifts in crystallization temperatures and glass transition temperatures and diffuse domain interfaces were observed [3].

[1] M. Rätsch, M. Arnold, E. Borsig, H. Bucka, N. Reichelt, Progress in Polymer Science, 2022, 22(7), 1195-1282.

[2] D. Gloger, D. Mileva, A. Albrecht, G. Hubner, R. Androsch, M. Gahleitner, Macromolecules, 2022, 55, 7, 2588-2608.

[3] D. Gloger, G. Hubner, A. Albrecht, L. Sobczak, J.-H. Arndt, D. Tranchida, W. H. Binder, M. Gahleitner, Appl. Polym. Mater., 2024, 6,17, 10824-10841.