Plastics, analytics

Taking chromatography to a new level: Fraunhofer LBF develops modern analytics for polyolefin compounds

Press release /

The chromatography team at the Fraunhofer Institute for Structural Durability and System Reliability LBF is constantly developing new methods for generating molecular fingerprints of polyolefin compounds that can also be used in routine analyses. The latest technological achievement is the development of new chromatographic protocols, which become possible on a chromatograph that was developed in collaboration with PolymerChar (Valencia). It is equipped with a newly developed infrared (IR) and UV detector, and covers the full spectrum of vibrational spectroscopy. This opens up entirely new prospects for the future in terms of studying polyolefins, olefin copolymers and their compounds.

Variations in the composition of polypropylene-based reactor blends, identified through chromatography.
Detecting different additive contents in polyethylene using GPC-UV.
Comparing MAH content as a function of the molecular weight of two polyolefin samples modified by reactive extrusion, determined by GPC-IR data.

Manufacturing safety-related components from plastic is becoming increasingly common. When it comes to polyolefins in particular, this trend is driven by the wide variability of property profiles and the attractiveness of their prices compared to traditional materials. The application properties of polyolefins are largely determined by their molecular structure. The most important molecular parameters are chemical composition, molecular weight distribution and corresponding average values. In the case of copolymers, an important characteristic metric is their chemical heterogeneity, which is difficult to determine during routine analyses. Additives have become a major driving force in formulation development. The challenge here is ensuring consistency in terms of the type and content of additives. The chromatography team from Fraunhofer LBF is investigatingmethods to determine all the above parameters.

“Modern chromatographic methods are indispensable tools when it comes to developing polyolefins and ensuring their quality. They allow the polymer chains in the materials specimens to be separated according to size or chemistry, and to then be quantified. That makes them a valuable instrument for analyzing material specimens during incoming goods inspection, for example, in order to detect faulty batches, as well as in the quantitative determination of material changes resulting from use,” explains Dr. Robert Brüll, department manager of Material Analysis at Fraunhofer LBF.


Quickly and accurately identifying batch fluctuations

In routine analytical practice, gel permeation chromatography (GPC) is widely used for the molecular characterization of polyolefins, as well as other polymers. This allows chains in a specimen to be separated by  molecular weight. Usually, only the concentration of the separated molecules is determined. However, information on their composition is not obtained. “Determining the exact chemical composition presents a challenge for the detectors and can only be achieved using a combination of suitable spectroscopic techniques. In terms of polyolefins, there’s currently a technological gap, as due to their semi-crystalline nature, they only dissolve at significantly higher temperatures and therefore require adequately temperature-resistant instrumentation,” says Dr. Brüll.

To meet this need, Fraunhofer LBF collaborated with the company PolymerChar to develop an appropriate chromatograph, which can operate at temperatures of up to 200 °C. It is equipped with a newly developed infrared (IR) and UV detector, covering the entire spectrum of vibrational spectroscopy. This allows polyolefins, olefin copolymers and their compounds to be studied from entirely new perspectives. For example, it is possible to examine propylene-based reactor blends with a level of accuracy that was previously unattainable, and to highlight batch-to-batch variations.


Taking a comprehensive look at formulations

Thanks to additives, tailoring and designing the material properties of formulations is now a flexible and cost-effective process. However, the existing methods require a lot of time and effort and are not suitable for an in depth quality control. Furthermore, additives that are difficult to extract cannot be analyzed in this way. Here, the newly developed IR and UV detectors are opening up innovative possibilities for quickly and accurately analyzing additives. They do so by separating the formulation chromatographically and record the separated fractions spectroscopically, all in a single step. This can greatly expand the scope of additive analysis.

Reactive extrusion

Reactive extrusion is a very flexible and economical way of producing polyolefin compounds with tailor-made property profiles. A well-known example is the modification of polyethylene or polypropylene with maleic anhydride (MAH) to introduce polarity into these essentially unipolar materials. The final properties of the modified polyolefins are influenced by the number of MAH groups and their distribution, in particular. By making it possible to detect these separately while detecting the quantity of the separated polymer chains in parallel, the new chromograph provides decisive information on the quality of the MAH-modified material in just one examination step.