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High Temperature Asymmetric Flow Field-Flow Fractionation

Invention by Postnova and Dow Chemical

The most important Asymmetric Flow Field-Flow Fractionation technique for the characterization of polymers at elevated temperatures is High Temperature Asymmetric Flow Field-Flow Fractionation (Asymmetric Flow FFF), which was invented and developed by Postnova Analytics and Dow Chemical in a joint research project.
 

Frist High Temperature FFF

In 2006 the world’s first commercial High Temperature Asymmetric Flow Field-Flow Fractionation was presented. High Temperature Asymmetric Flow Field-Flow Fractionation is a brand-new technology and has not been described in the scientific literature ever before. High Temperature Asymmetric Flow Field-Flow Fractionation technology marks a real break-through in FFF science as it is using - the first time ever - a ceramic membrane composite inside the Asymmetric Flow Field-Flow Fractionation channel. This special membrane enables the user to access completely new applications with Asymmetric Flow Field-Flow Fractionation and to overcome the limitations of the traditionally used polymeric membranes. This membrane technology in High Temperature Asymmetric Flow Field-Flow Fractionation can be used for the characterization of high molar mass polymers at temperatures up to 220°C, such as polyolefin’s (polyethylene, polypropylene).

System setup

A typical High Temperature Asymmetric Flow Field-Flow Fractionation system is comprising of the eluent reservoir, the eluent pump, the FFF module for cross flow control and data acquisition, the injector system, the Field-Flow Fractionation channel and suitable High Temperature Asymmetric Flow Field-Flow Fractionation detectors, which can be Light Scattering, Infrared, RI and Viscometers. The sample injector, the High Temperature Asymmetric Flow Field-Flow Fractionation channel and the High Temperature Asymmetric Flow Field-Flow Fractionation detectors are located inside the heated system. The High Temperature Asymmetric Flow Field-Flow Fractionation is fully automated and controlled by the software, which also allows the data evaluation and molar mass as well as radius calculations.

 

Unique Features of Asymmetric Flow FFF

Ceramic Membrane Channel Cartridge

The channel cartridges used in High Temperature Asymmetric Flow Field-Flow Fractionation are based on a new ceramic composite membrane technology. This membrane is inert, can be used at high temperatures and can be regenerated many times before it needs to be replaced.

Broad Molar Mass Separation Range at high Temperatures

Compared with High Temperature GPC, the separation in High Temperature Asymmetric Flow Field-Flow Fractionation can also be performed for polymers up to molar masses of 109 Da. No size exclusion effect is observed, making High Temperature Asymmetric Flow Field-Flow Fractionation the ideal tool for the separation of large and ultra-large polymers, macromolecules and nanoparticles.

Gentle Separation Conditions

Because of the open channel and the absence of any stationary phase, the separation can be performed under the absence of shear forces and stress to the macromolecule. Typical High Temperature GPC problems, such as filtering/adsorption effects, shear induced chain degradation and late elution effects, can be avoided.

 

Applications of Asymmetric Flow FFF

Because of the extremely gentle separation conditions and the ultra-broad separation range, High Temperature Asymmetric Flow Field-Flow Fractionation (HTFFF) is the most advanced technology for the separation of high and ultra-high molar mass polymers at elevated and high temperatures. High Temperature Asymmetric Flow Field-Flow Fractionation can be used for polymers, macromolecules and nanoparticles in the size range up to 109 Da and up several µm particles size. Unlike High Temperature GPC (Gel Permeation Chromatography), no size exclusion limit is restricting the upper molar mass of the separated polymers. Polyolefin’s are one of the most important groups of polymers which can be analyzed with High Temperature Asymmetric Flow Field-Flow Fractionation, but other macromolecules with higher molar masses can be investigated as well.

High Molecular Weight Low Density Polyethylene

Molar Mass by HTFFF

Molar Mass by HTGPC

Radius of Gyration by HTFFF

Radius of Gyration by HTGPC

 

High Temperature Comparison: FFF and GPC

A comparison of High Temperature Asymmetric Flow Field-Flow Fractionation and High Temperature GPC is done for High Molecular Weight Low Density Polyethylene (LDPE). The data proves that the bimodal distribution shown in the GPC results is only caused by the size exclusion limit of the column. When using High Temperature Asymmetric Flow Field-Flow Fractionation also the high molecular weight range of the Low Density Polyethylene can be accessed. Only by using High Temperature Asymmetric Flow Field-Flow Fractionation the “real” distribution of this sample can be discovered, including the high molar mass fractions, which are missing in the High Temperature GPC data. High Temperature Asymmetric Flow Field-Flow Fractionation has an extended molar mass range up to 109 Da and the size range goes up all the way into the micrometer range.

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